The hyper-diverse ant genus Tetramorium Mayr (Hymenoptera, Formicidae) in the Malagasy region taxonomic revision of the T. naganum, T. plesiarum, T. schaufussii, and T. severini species groups

Abstract The taxonomy of the Tetramorium naganum, T. plesiarum, T. schaufussii, and T. severini species groups are revised for the Malagasy region. A total of 31 species are treated, of which 22 are newly described and nine redescribed. This increases the richness of the hyper-diverse genus Tetramorium in the Malagasy region to 106 species, which makes it the most species-rich genus in the region. Twenty-nine of the treated species are endemic to Madagascar, one is endemic to the Comoros, and one species is found predominantly in Madagascar but also on the island of Reunion. The T. naganum species group contains five species, which are mainly distributed in the rainforests and montane rainforests of eastern and northern Madagascar: T. alperti sp. n., T. dalek sp. n., T. enkidu sp. n., T. gilgamesh sp. n., and T. naganum Bolton, 1979. The T. plesiarum species group holds five species: T. bressleri sp. n., T. hobbit sp. n., T. gollum sp. n., T. mars sp. n., and T. plesiarum Bolton, 1979. All five are arid-adapted species occurring in the southwest and west of Madagascar. The second-most species-rich group in the region is the T. schaufussii species group with 20 species, most of which inhabit rainforests or montane rainforests of eastern and northern Madagascar. This group includes two species complexes each containing ten species: the T. cognatum complex with the species T. aspis sp. n., T. camelliae sp. n., T. cognatum Bolton, 1979, T. freya sp. n., T. gladius sp. n., T. karthala sp. n., T. myrmidon sp. n., T. proximum Bolton, 1979, T. rumo sp. n., and T. tenuinode sp. n.; and the T. schaufussii complex with the species T. merina sp. n., T. monticola sp. n., T. nassonowii Forel, 1892 stat. n., T. obiwan sp. n., T. pseudogladius sp. n., T. rala sp. n., T. schaufussii Forel, 1891, T. sikorae Forel, 1892 (= T. latior (Santschi, 1926)), T. scutum sp. n., T. xanthogaster Santschi, 1911. The last group treated in this study is the T. severini species group, which contains only the species T. severini (Emery, 1895). This very conspicuous species is widely distributed in the rainforests and montane rainforests of eastern and northern Madagascar. All four groups are fully revised with group diagnoses, illustrated species-level identification keys, and detailed descriptions for all species that include multifocused montage images and distribution maps.


Introduction
The hyper-diverse genus Tetramorium Mayr is widely distributed throughout all biogeographic regions, and with currently 520 described species (Bolton 2014) one of the most species-rich ant genera. Tetramorium is most diverse in the subtropics and tropics of the Old World, especially the Afrotropics and Madagascar, but is species-poor in the New World. Most regional faunas were revised by Bolton (1976Bolton ( , 1977Bolton ( , 1979Bolton ( , 1980, who provided a good taxonomic foundation on which later works could build (e.g. Csösz et al. 2007;Csösz and Schulz 2010;Hita Garcia et al. 2010;Hita Garcia and Fisher 2011;Bharti and Kumar 2012;Sharaf et al. 2012). The Malagasy Tetramorium fauna was also first revised by Bolton (1979), who treated eight species groups containing 36 species, of which 29 were endemic to Madagascar. The synonymisation of Triglyphothrix Forel (Bolton 1985) under Tetramorium added an additional species group with one tramp species; two additional tramp species were reported much later (Blard et al. 2003;Roberts and McGlynn 2004), for a total of 39 species known prior to 2011.
Recently, we started a large-scale taxonomic revision of the genus Tetramorium for the Malagasy region based initially on more than 160 morphospecies with more than 40,000 mounted specimens (Hita Garcia and Fisher 2011). We proposed 14 species groups as a foundation and provided a preliminary identification key to the Malagasy groups. In the same study we also revised the taxonomy of the T. bicarinatum, T. obesum, T. sericeiventre, and T. tosii species groups. One species was newly described while another was synonymised, leaving the species count for the region at 39. Based on that work, the T. bessonii, T. bonibony, T. dysalum, T. kelleri, T. marginatum, T. tortuosum, T. tsingy, and T. tosii species groups were revised shortly afterward (Hita Fisher 2012a, 2012b). The latter two studies dealt with 58 species, of which 45 were described as new, and increased the species count for the Malagasy region to 84. We also proposed additional species groups for a total of 18 for the region (not 19 as noted in Hita Garcia and Fisher 2012b).
In this study we revise the taxonomy of four more Malagasy species groups: T. naganum, T. plesiarum, T. schaufussii, and T. severini species groups. All are fully revised with group diagnoses, illustrated species-level identification keys, multifocused montage images for all species, descriptions of 22 new species, redescriptions of nine previously known species, and distribution maps for all species. The species treated here increase the total species count for the genus Tetramorium in the Malagasy region to 106, which means that at present this genus holds the highest described species richness in the region. Furthermore, this study increases the number of recently revised Malagasy Tetramorium species groups to 16 (Hita Garcia and Fisher 2011, 2012a, 2012b, leaving only two species groups untreated: the species-rich T. ranarum group and the less diverse but abundant T. simillimum group. These groups will be revised in an upcoming study. to be of high diagnostic value (Hita Garcia et al. 2010). Measurements of the whole petiole, peduncle plus node, would mask important differences between species. In contrast, we measured the whole postpetiole because it was rounded in most species and without a distinct peduncle-like structure. As a consequence, some information might be lost in the few species with a moderately or strongly anteroposteriorly compressed postpetiole. Even so, the postpetiole measurements as defined still permit better comparisons for most species.

Tetramorium naganum species group
Diagnosis. Eleven-segmented antennae; anterior clypeal margin medially impressed; frontal carinae always well developed, diverging posteriorly and usually approaching or reaching corners of posterior head margin; antennal scrobe present, weakly to very well developed; mesosoma moderately to strongly marginate from sides to dorsum; propodeal spines medium-sized to long, elongate-triangular to spinose; propodeal lobes triangular and short; petiolar node in profile high rounded nodiform to rectangular nodiform with moderately to well-rounded margins, in profile 1.5 to two times higher than long (LPeI 50-68), in dorsal view between 1.0 and 1.4 times wider than long (DPeI 103-139), anterior and posterior faces parallel, anterodorsal and posterodorsal margins usually at about same height (sometimes anterodorsal margin higher); postpetiole in profile always more or less globular; mandibles variably sculptured, but mostly unsculptured; cephalic dorsum and dorsal mesosoma with distinct longitudinally rugose sculpture; waist segments and gaster always unsculptured, smooth, and shiny; dorsal surfaces of head, mesosoma, and usually waist segments with few to abundant long, standing hairs; pilosity/pubescence on first gastral tergite variable, but with tendencies to more inclined pilosity and dense pubescence; sting appendage spatulate.
Comments. This small and compact group is restricted in its distribution to eastern and northern Madagascar. All five species are found only in rainforests or montane rainforests and seem to live mainly in leaf litter.
Within the 13 species groups with 11-segmented antennae, the T. naganum group shares the complete lack of sculpture on both waist segments with the majority of groups, but differs from the T. kelleri, T. ranarum, T. tortuosum, and parts of the T. dysalum groups. These groups contain only species in which either one or both waist segments are clearly sculptured. In addition, the very well developed sculpture on head and mesosoma distinguishes the T. naganum group from the groups with reduced sculpture: the T. bessonii, T. marginatum, and T. tsingy groups. Also, T. severini, the only member of the T. severini group, has a longer and lower mesosoma  with less margination from the sides to the dorsum, while the species of the T. naganum group have a higher , stouter, and more angled mesosoma. The T. plesiarum group is characterised by the presence of relatively deep and well-developed antennal scrobes with margins all around and a strongly developed median scrobal carina, a character always absent in the T. naganum group. The latter also cannot be mistaken for the T. bonibony group, in which some species possess a very conspicuous bump or protuberance on the pronotal dorsum while the remainder of the species have triangular or cuneiform petiolar nodes. The differentiation between the T. naganum group and the T. dysalum group can be more difficult however. The T. dysalum group is relatively heterogeneous and there are a few species that are morphologically close to some species in the T. naganum group. Nevertheless, the best method to discriminate between these two groups is to compare gastral pubescence and/or pilosity. In all species of the T. dysalum group appressed pubescence on the first gastral is scarce and inconspicuous, and pilosity consists of numerous long suberect to erect hairs. By contrast, pubescence and pilosity are very variable in the T. naganum group, but never with very reduced pubescence and long, standing pilosity as in the T. dysalum group.
The separation from the T. schaufussii group is likely the most difficult, and T. naganum was a member of that group until recently (Hita Garcia and Fisher 2012a). The five species of the T. naganum group have much stronger developed frontal carinae, a generally broader head (CI 92-99), a higher mesosoma , and usually longer propodeal spines . In the T. schaufussii group most species (but not all) have weaker frontal carinae, a usually thinner head (CI 85-95), a lower mesosoma , and usually much shorter propodeal spines . These values overlap in a few species. In fact, most members of the T. schaufussii group have relatively short spines with a PSLI below 20, a few species have slightly longer spines , and only a few specimens of T. gladius and T. rumo have a higher PSLI of 26-28.
The five species of the group are morphologically very close to each other, and their delimitations are mainly based on different patterns of pilosity/pubescence on the waist segments and the first gastral tergite. Tetramorium dalek is easily separable from the other four species on the basis of the absence of standing hairs on the waist segments and shorter propodeal spines, but T. alperti, T. enkidu, T. gilgamesh, and T. naganum are morphologically very similar. Indeed, they are often difficult to discriminate and there are only very few reliable diagnostic characters, mainly gastral pilosity/pubescence. It is possible that two, three, or all four are conspecific and the abovementioned differences are just intraspecific variation. Nevertheless, we prefer to treat them as four distinct species since gastral pilosity/pubescence is usually very species-specific within the genus Tetramorium and other myrmicine genera and the material listed here can be moderately well distinguished by the diagnostics given in the key and the descriptions. However, we cannot rule out that gastral pilosity/ pubescence is highly variable in this group, and if so, our hypotheses may not reflect real species boundaries.
Diagnosis. Tetramorium alperti differs from the other three species of the group by the following character combination: propodeal spines long to very long ; waist segments with several long erect hairs; first gastral tergite with moderately long, scattered, appressed to decumbent pubescence in combination with several much longer, erect standing hairs.
Worker measurements ( Worker description. Head longer than wide (CI 95-97); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, diverging posteriorly and approaching or ending at posterior head margin; antennal scrobe present, but weak, shallow, and without defined posterior or ventral margins. Antennal scapes short, not reaching posterior head margin . Eyes of moderate size . Mesosomal outline in profile flat to weakly convex, relatively high , and moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines long to very long, spinose, acute, and often thick (PSLI 29-37); propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high, rounded nodiform with moderately rounded antero-and posterodorsal margins, around 1.5 to 1.6 times higher than long (LPeI 62-68), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height and equally marginate, petiolar dorsum weakly convex; node in dorsal view around 1.0 to 1.1 times wider than long (DPeI 103-115), in dorsal view pronotum between 2.4 to 2.8 times wider than petiolar node . Postpetiole in profile globular to subglobular, approximately 1.2 to 1.3 times higher than long (LPpI 74-84); in dorsal view around 1.2 to 1.3 times wider than long , pronotum between 1.7 to 1.8 times wider than postpetiole (PpNI 54-57). Postpetiole in profile appearing less voluminous than petiolar node, postpetiole in dorsal view between 1.3 to 1.6 times wider than petiolar node . Mandibles usually mostly unsculptured and smooth with some weakly striate parts, generally very shiny; clypeus longitudinally rugose/rugulose, with three to five rugae/rugulae, median ruga always well developed and distinct, lateral rugae/rugulae sometimes weaker and interrupted; cephalic dorsum between frontal carinae with seven to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured; lateral head reticulate-rugose to longitudinally rugose. Ground sculpture on head absent to weakly punctate. Dorsum of mesosoma mostly irregularly longitudinally rugose; lateral mesosoma variably sculptured, lateral pronotum and anepisternum mostly unsculptured, smooth and shining with very little sculpture, usually only traces of rugulae present, katepisternum, metapleuron, and lateral propodeum noticeably irregularly longitudinally rugose. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma weak to absent. Waist segments and gaster completely unsculptured, smooth and shining. Whole body with numerous, long, and fine standing hairs; first gastral tergite with moderately long, relatively scattered, appressed to decumbent pubescence in combination with several much longer, fine, and erect hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with decumbent to suberect hairs. Head, mesosoma, waist segments, and gaster orange-brown to chestnut brown, mandibles, antennae, and legs always lighter, usually yellowish brown.
Etymology. The name of the new species is a patronym dedicated to Gary D. Alpert from Cambridge, Massachusetts, U.S.A., to honour his numerous ant collecting activities in Madagascar.
Distribution and biology. This new species is only known from three localities (Fig. 61). Two are located in the northeast of Madagascar (Anjanaharibe-Sud and Marorejy) while the third is found much further south (Ambalagoavy). Anjanaharibe-Sud and Marorejy are montane forests ranging from 1280 to 1325 m elevation, whereas Ambalagoavy is located at 525 m. This distributional and elevational pattern suggests that T. alperti might have been distributed throughout most of the eastern Madagascar humid forests, but is now only found in a few montane forests and one lower rainforest site. Based on the available collection data, T. alperti seems to be a leaf litter inhabitant.
Discussion. Tetramorium alperti cannot be confused with T. dalek since the latter has no long standing hairs on the waist segments and the first gastral tergite, while these are present in T. alperti. Differentiation from the other three species of the group, however, is more challenging. The primary diagnostic characters distinguishing T. alperti are the pilosity/pubescence pattern on the first gastral tergite and the shape of the petiolar node in profile. Tetramorium alperti possesses moderately long, relatively scattered, appressed to decumbent pubescence in combination with several much longer and erect hairs. This pattern on the first gastral tergite is not found in T. enkidu, T. gilgamesh or T. naganum since they either lack long and erect hairs or appressed to decumbent pubescence entirely. In addition, T. alperti also has a thicker petiolar node which is around 1.5 to 1.6 times higher than long (LPeI 62-68), compared to T. gilgamesh and T. naganum, in which the petiolar nodes are around 1.7 to 2.0 times higher than long (LPeI 50-59). The species probably most easily confused with T. alperti is T. enkidu since both share the same general habitus and the same morphometric range, and the only difference is the pattern of pilosity/ pubescence on the first gastral tergite outlined above. Possibly they are conspecific and the differences in gastral pilosity/pubescence represent intraspecific variation, however, there are some good arguments to separate them as two distinct species. First, both species are found in sympatry in Marojejy, and they are easily identified by the differences in pilosity/pubescence mentioned above without any intermediate forms. Second, patterns of pilosity/pubescence are usually very species-specific within the genus Tetramorium (e.g. Bolton 1976Bolton , 1980Hita Garcia et al. 2010;Fisher 2012a, 2012b). We were able to reveal several consistent patterns of pilosity/pubescence in the T. naganum species group, and the pattern of T. alperti is unique to this group, although it resembles the one seen in T. ryanphelanae Hita Garcia & Fisher from the T. bessonii species group, and a few species from the T. schaufussii species complex.

Tetramorium dalek
Diagnosis. Tetramorium dalek is easily distinguishable by the following combination of characters: waist segments without long standing hairs, instead with short, appressed to subdecumbent pubescence only, sometimes with one or two short erect to suberect hairs; propodeal spines moderately long to long ; first gastral tergite with short, relatively dense, appressed to subdecumbent pubescence and without any standing hairs at all.
Etymology. The name of the new species is taken from the popular British TV show "Dr. Who" and refers to a fictional, extra-terrestrial race of evil mutants. During different stages of the revision we considered placing the material listed here as T. dalek in at least three to four different groups, which caused a significant amount of nuisance, especially to the first author. Naming this species after an evil, extra-terrestrial, and often annoying race was a logical consequence. The species epithet is an arbitrary combination of letters, thus invariant.
Distribution and biology. The new species is found in the lowland and montane rainforests of eastern Madagascar from the southernmost localities Sandranantitra, Betampona, and Zahamena, north to Anjanaharibe-Sud (Fig. 61). In addition, T. dalek has an elevational range from 20 to 1280 m, and seems to live in leaf litter.

Tetramorium enkidu
Diagnosis. Tetramorium enkidu is distinguishable from the other species of the group by the following combination of characters: eyes small to moderate in size ; waist segments with several long erect hairs; propodeal spines long to very long ; in profile petiolar node relatively thick, between 1.5 and 1.7 times higher than long (LPeI 60-65); first gastral tergite with moderately short, abundant, subdecumbent to suberect pilosity, and without short, dense, appressed to decumbent pubescence.
Worker measurements (N=12 Worker description. Head weakly to distinctly longer than wide (CI 93-98); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, diverging posteriorly, and usually approaching or ending at posterior head margin; antennal scrobe present, but weak, shallow, and without defined posterior or ventral margins. Antennal scapes very short, not reaching posterior head margin . Eyes short to moderate . Mesosomal outline in profile weakly convex, relatively high (LMI 41-45), and moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines spinose, long to very long, and acute (PSLI 29-36); propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high, rounded nodiform, with well-rounded antero-and posterodorsal margins, around 1.5 to 1.7 times higher than long (LPeI 60-65), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height and equally marginate, petiolar dorsum always distinctly convex; node in dorsal view slightly wider than long (DPeI 104-113), in dorsal view pronotum between 2.4 to 2.8 times wider than petiolar node (PeNI 36-42). Postpetiole in profile globular, approximately 1.2 to 1.4 times higher than long (LPpI 73-85); in dorsal view between 1.2 to 1.4 times wider than long (DPpI 120-140), pronotum around 1.7 to 1.8 times wider than postpetiole (PpNI 54-60). Postpetiole in profile appearing slightly lower and thicker than petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node . Mandibles usually unsculptured, smooth, and shining, sometimes weakly partially striate (especially basally), rarely fully covered in fine striations; clypeus longitudinally rugose/rugulose, with three to six rugae/rugulae, median ruga always well developed and distinct, lateral rugae/rugulae usually weaker and/or interrupted; cephalic dorsum between frontal carinae with seven to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often irregular, interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head weak to absent. Mesosoma laterally and dorsally irregularly longitudinally rugose, rarely lateral mesosoma with few unsculptured areas. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma very weak to absent. Waist segments and gaster com- pletely unsculptured, smooth and shining. Head, mesosoma, and waist segments with numerous, long, and fine standing hairs; first gastral tergite with moderately short, abundant, subdecumbent to suberect pilosity, and without short, dense, appressed to decumbent pubescence; pilosity appearing disorganized due to varying degrees of inclination. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Head, mesosoma, waist segments, and gaster light to dark brown, mandibles, antennae, and legs always of lighter brown.
Etymology. The new species is named after the fictional character "Enkidu" who is a central figure in the ancient Mesopotamian poem "Epic of Gilgamesh", one of the oldest written stories in human history. The species epithet is an arbitrary combination of letters, thus invariant.
Distribution and biology. The new species is restricted to the northern part of Madagascar. Its distribution ranges from Montagne d'Akirindro, the area around Maroantsetra, and Cap Masoala north through Ambanitaza, and Marojejy to Binara and Montagne d'Ambre (Fig. 61). The localities are rainforests or montane rainforests situated at altitudes from 125 to 1100. In addition, T. enkidu appears to live in leaf litter or the ground.

Tetramorium gilgamesh
Diagnosis. The following character combination distinguishes T. gilgamesh from the other members of the T. naganum group: relatively large eyes (OI 25-27); propodeal spines long (PSLI 27-30); petiolar node relatively high and thin, around 1.7 to 2.0 times higher than long (LPeI 50-59); waist segments with several long erect hairs; first gastral tergite with short to moderately long, abundant, decumbent to suberect pilosity, and without short, dense, appressed to subdecumbent pubescence; pilosity appearing disorganized due to varying degrees of inclination and hair length.
Etymology. The new species is named after the fictional character "Gilgamesh", the main figure in the ancient Mesopotamian poem "Epic of Gilgamesh", one of the earliest surviving works of literature. The species epithet is an arbitrary combination of letters, thus invariant.

Distribution and biology.
Tetramorium gilgamesh is distributed in eastern Madagascar (Fig. 61). Its distribution ranges from the southernmost known locality Andriantantely north to Montagne d'Anjanaharibe and Montagne d'Akirindro, and northeast to Andranobe and Andampibe on the Masoala Peninsula. All localities are lowland rainforests situated at elevations of 125 to 600 m. The preferred microhabitat of T. gilgamesh seems to be leaf litter.
Discussion. The identification of T. gilgamesh within the T. naganum species group is fairly straightforward. The best diagnostic character is eye size since T. gilgamesh has the largest eyes of the group with an OI 25-27 (vs. OI 21-24 in the other four species). Beyond this, it cannot be mistaken for T. dalek since the waist segments and a first gastral tergite of the latter species are covered with short, comparatively dense, appressed to subdecumbent pubescence without standing pilosity. By contrast, T. gilgamesh has long, erect hairs on the waist segments and the first gastral tergite is covered with short to moderately long, abundant, decumbent to suberect pilosity, but without short, dense, appressed to subdecumbent pubescence. Additionally, the pilosity on the first gastral tergite of T. gilgamesh appears disorganized due to varying degrees of inclination and hair length. The gastral pilosity separates it also from T. alperti, T. enkidu, and T. naganum, which have very different patterns of pilosity/pubescence. Furthermore, T. alperti and T. enkidu have thicker petiolar nodes (LPeI 60-68) than T. gilgamesh (LPeI 50-59). Tetramorium naganum shares the same shape of the petiolar node with T. gilgamesh, and both are also found in sympatry throughout most of their distribution ranges. However, differences in eye size and gastral pilosity distinguish between both species fairly well.
On the basis of the available material it seems that intraspecific variation is generally low in T. gilgamesh. 2C,4B,9,61 Tetramorium naganum Bolton, 1979 [Note: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own georeferencing of the rainforest locality La Mandraka and should be considered an approximation and not the exact location of the type locality of T. naganum.]
Diagnosis. Tetramorium naganum can be easily diagnosed within the T. naganum group on the basis of the following character combination: eyes small to moderate in size (OI 21-23); propodeal spines relatively long (PSLI 28-33); petiolar node in profile relatively thin, between 1.7 to 1.9 times higher than long (LPeI 54-58); waist segments with long, standing hairs; first gastral tergite with short, comparatively dense, appressed to decumbent pubescence, and without any long standing hairs.
Worker measurements (N=10 Worker description. Head weakly to distinctly longer than wide (CI 94-99); posterior head margin moderately concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, diverging posteriorly, and usually approaching or ending at posterior head margin; antennal scrobe present, but weak, shallow, and without defined posterior or ventral margins. Antennal scapes short, not reaching posterior head margin . Eyes short to moderate (OI 21-23). Mesosomal outline in profile weakly convex, relatively high , and moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines spinose, long, and acute (PSLI 28-33); propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high, rounded nodiform, with wellrounded antero-and posterodorsal margins, between 1.7 to 1.9 times higher than long (LPeI 54-58), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height (very rarely anterodorsal margin higher than posterodorsal margin) and equally marginate, petiolar dorsum always convex; node in dorsal view around 1.1 to 1.2 times wider than long (DPeI 107-122), in dorsal view pronotum between 2.7 to 3.0 times wider than petiolar node (PeNI 34-38). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 77-84); in dorsal view between 1.2 to 1.4 times wider than long (DPpI 125-137), pronotum around 1.7 to 1.9 times wider than postpetiole (PpNI 52-59). Postpetiole in profile thicker and lower than petiolar node, postpetiole in dorsal view around 1.5 to 1.6 times wider than petiolar node . Mandibles variably sculptured, ranging from fully unsculptured, smooth, and shining through partially striate to fully striate; clypeus longitudinally rugose/rugulose, with two to six rugae/ rugulae, median ruga always well developed and distinct, lateral rugae/rugulae usually weaker and/or interrupted; cephalic dorsum between frontal carinae with six to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin but very often irregular, interrupted or with cross-meshes, especially posteriorly; scrobal area usually mostly unsculptured, rarely longitudinally rugose to reticulate-rugose; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head absent to weakly punctate. Mesosoma laterally and dorsally irregularly longitudinally rugose, rarely lateral mesosoma with a few unsculptured areas medially. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma very weak to absent. Waist segments and gaster completely unsculptured, smooth and shining. Head, mesosoma, and waist segments with numerous, long, and fine standing hairs; first gastral tergite with short, comparatively dense, appressed to subdecumbent pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with decumbent to suberect hairs. Head, mesosoma, waist segments, and gaster usually orange to light brown, rarely of darker brown, mandibles, antennae, and legs always lighter, usually light yellowish brown.
Distribution and biology. Tetramorium naganum is found in rainforests or montane rainforests in eastern and north-eastern Madagascar (Fig. 61). The distribution range is disjunctive, very much as in T. alperti and T. dalek. T. naganum is either found in the region around La Mandraka, Analamay, Andranomay, and Andasibe-Mantadia, and Ankerana, or much further north between Anjanaharibe-Sud and the Masoala Peninsula (Ambanizana), with Montagne d'Anjanaharibe being in-between. The reasons behind this discontinuous distribution are not clear yet, but as for T. alperti, it is likely that T. naganum was previously much more common in eastern Malagasy humid forests, and present-day populations represent only relict populations. The altitudinal range of the species with 825-1300 m supports this. However, since T. naganum is not particularly abundant or common where it occurs, it may just be a relatively rare faunal element in eastern Madagascar. If so, further sampling might yield additional material in the future, especially in the geographic areas between the two main populations mentioned above. Like most species in this group, T. naganum seems to be a leaf litter inhabitant.
Discussion. Tetramorium naganum is the only species of the group that was known prior to our revision, and can be seen as the core species of the group. The lack of pilosity on the first gastral tergite isolates it fairly well from T. alperti and T. gilgamesh since these possess pilosity in varying degrees of inclination, length, and abundance. The relatively thin and high petiolar node (LPeI 54-58) separates T. naganum from T. alperti and T. enkidu, which have much thicker petiolar nodes (LPeI 60-68). Additionally, T. naganum has smaller eyes (OI 21-23) than T. gilgamesh . The last species of the group, T. dalek, shares the lack of long, standing pilosity on the first gastral tergite with T. naganum. Nevertheless, both species are very unlikely to be confused with each other. Tetramorium dalek is generally smaller , has shorter propodeal spines , and lacks long, standing hairs on the waist segments, whereas T. naganum is generally larger (HW 0.55-0.72; WL 0.66-0.92), possesses longer propodeal spines , and always has long, standing hairs on the waist segments.

Tetramorium plesiarum species group
Diagnosis. Eleven-segmented antennae; anterior clypeal margin medially impressed; frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around (except in T. gollum); median scrobal carina very well developed and distinctly surpassing posterior eye level, usually ending between posterior eye margin and posterior scrobe margin, often approaching the latter; anterior face of mesosoma weakly developed; mesosomal outline in profile moderately to strongly convex, moderately marginate from lateral to dorsal mesosoma; mesosoma relatively high (LMI 41-56); propodeal spines usually medium-sized to long, elongate-triangular to spinose (PSLI 23-32), rarely short ; propodeal lobes usually short, triangular to elongate-triangular, and acute; petiolar node in profile nodiform to high nodiform, in profile between 1.3 to 1.8 times higher than long, (LPeI 56-76), anterior and posterior faces generally parallel, anterodorsal and posterodorsal margins situated at about same height; node in dorsal view typically distinctly wider than long, between 1.1 to 1.5 times (DPeI 108-148); postpetiole much broader than long and transverse, between 1.4 to 2 times broader than long (DPpI 141-200); sculpture on mandibles variably developed; cephalic sculpture distinct, between frontal carinae predominantly longitudinally rugose; mesosoma with well-developed longitudinally rugose sculpture; waist segments weakly to moderately sculptured, never completely unsculptured; first gastral tergite usually with weak ground sculpture at base or completely unsculptured, in T. gollum basal half of tergite strongly reticulate-rugose; whole body with abundant, usually dense, long, and standing hairs; sting appendage spatulate.
Comments. The T. plesiarum group is a compact assemblage of five species that resemble one another very closely. All are morphologically very conspicuous elements within the Malagasy Tetramorium fauna, and represent arid-adapted species found mostly in the drier western and southern parts of Madagascar. Surprisingly, T. plesiarum, which is much less common than T. bressleri, T. hobbit, and T. mars, is the only member of the species group that was known prior to this revision, and only from the holotype. The other four species, T. bressleri, T. gollum, T. hobbit, and T. mars, are newly described here. All five species share a more or less similar habitus with very well developed antennal scrobes, more or less convex mesosomal profiles, usually mediumsized to long propodeal spines, higher than long and broader than long petiolar nodes, and abundant, long, and often dense pilosity. The species delimitations presented here are mainly based on differences in the shape of the petiolar node and sculpture on different parts of the body. One intriguing feature of the group is the morphological cline observable in the shape of the petiolar node (see Fig. 10), which ranges from massively enlarged and blocky (T. hobbit) through smaller, but still relatively blocky (T. mars), to much higher and thinner (T. bressleri, T. gollum, T. plesiarum).
Tetramorium plesiarum was initially placed in the T. ranarum species group by Bolton (1979) mainly on the basis of petiolar node shape and pilosity. However, in Hita Garcia and Fisher (2012a) we proposed a T. plesiarum species group based on the very conspicuous antennal scrobes present in all species of the group, a character absent in most other Malagasy Tetramorium. We still think that the T. plesiarum species group presents a well distinguishable grouping, although the conspicuous antennal scrobes unfortunately do not separate it from all other Malagasy groups. Several species within the T. ranarum group (e.g. T. zenatum, T. ibycterum, and two additional, yet-undescribed species) also have distinct antennal scrobes, although in these species the margins around the scrobes are much less distinctive and the scrobes themselves shallower than in the T. plesiarum group. However, the species of the T. ranarum group with a scrobe 1) either lack any long, suberect to erect pilosity on the first gastral tergite (T. ibycterum and another undescribed species here listed as T. fhg-bilb), or 2) they have long, subdecumbent pilosity (e.g. one yet-undescribed species listed here as T. fhg-vazi), or 3) if they possess long, standing pilosity, the petiolar node is much longer than broad (T. zenatum). Therefore they cannot be confused with any species of the T. plesiarum group.
Identification key to species of the T. plesiarum species group (workers)

1
Gaster conspicuously enlarged, appearing swollen; basal half of first gastral tergite strongly sculptured (   ; in profile anterodorsal margin of petiolar node not protruding anteriorly; mesopleuron and lateral propodeum with very little rugose/rugulose sculpture, mostly unsculptured, smooth, and shining; sides of petiolar node with weak but distinct reticulate-punctate ground sculpture, appearing only slightly matte and mostly smooth and shining (       (B.L. Fisher et al.).
Diagnosis. Tetramorium bressleri can be recognised by the following combination of characters: larger species (HW 0.80-1.00; WL 0.92-1.15); eyes relatively small ; petiolar node high nodiform, not blocky and massively enlarged, anterodorsal and posterodorsal margins at about the same height and equally marginate, anterodorsal margin not protruding anteriorly nor very sharply angled; petiolar node in profile relatively high and thin, between 1.6 to 1.8 times higher than long (LPeI 56-61), in dorsal view between 1.3 to 1.5 times wider than long (DPeI 135-145); gaster never extremely enlarged and swollen; head and mesosoma without strongly developed and conspicuous reticulate-punctate ground sculpture; usually sculpture on the mesopleuron and lateral propodeum mostly absent; basal half of first gastral tergite not strongly reticulate-rugose, only base of tergite weakly sculptured; pilosity on first gastral tergite mostly erect.
Worker measurements (N=12). HL 0.81-1.00 (0.94); HW 0.80-1.00 ( Worker description. Head more or less as long as broad (CI 98-102); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around; median scrobal carina very well developed and distinctly surpassing posterior eye level, usually ending halfway between posterior eye margin and posterior scrobe margin. Antennal scapes short, not reaching posterior head margin (SI 62-65). Eyes relatively small . Mesosomal outline in profile weakly to moderately convex, rounded and high (LMI 43-47), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines elongate-triangular to spinose, long, and acute (PSLI 26-32), propodeal lobes short, triangular, and acute, always much shorter than propodeal spines. Petiolar node in profile high, rectangular nodiform with well defined antero-and posterodorsal margins, between 1.6 to 1.8 times higher than long (LPeI 56-61), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height, petiolar dorsum flat to weakly convex, anterodorsal margin not protruding anteriorly; node in dorsal view between 1.3 to 1.5 times wider than long (DPeI 135-145), in dorsal view pronotum between 2.0 to 2.2 times wider than petiolar node (PeNI 45-49). Postpetiole in profile subglobular and weakly anteroposteriorly compressed, approximately 1.3 to 1.4 times higher than long (LPpI 70-75); in dorsal view around 1.5 to 1.6 times wider than long (DPpI 150-158), pronotum between 1.6 to 1.7 times wider than postpetiole (PpNI 59-63). Postpetiole in profile appearing slightly less voluminous than petiolar node, postpetiole in dorsal view between 1.2 to 1.4 times wider than petiolar node (PPI 125-134). Mandibles variably sculptured, either unsculptured, smooth, and shining, or partly or fully finely rugulose; clypeus longitudinally rugose/rugulose, with five to eight distinct rugae, median ruga always distinct, lateral rugae often weaker and sometimes interrupted; cephalic dorsum between frontal carinae with ten to thirteen longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, rarely interrupted or with cross-meshes; scrobal area mostly unsculptured, smooth and shiny; lateral head mainly longitudinally rugose. Ground sculpture on head usually weak to absent. Dorsum of mesosoma mostly longitudinally rugose without any distinct ground sculpture, spaces between rugae smooth and shining; lateral pronotum irregularly longitudinally rugose, often with weak to moderate punctate ground sculpture, mesopleuron and lateral pro-podeum usually with very little sculpture, few irregular rugae/rugulae and no ground sculpture. Forecoxae often with weak ground sculpture, but generally very smooth and shining. Petiolar node laterally with conspicuous but relatively weak reticulatepunctate ground sculpture only, appearing weakly matte but still relatively smooth and shiny; dorsum of node medially almost unsculptured, smooth, and shiny, surrounding areas rugulose, ground sculpture on petiolar dorsum neglectable. Postpetiole laterally and dorsally weakly to moderately rugose/rugulose and with conspicuous, moderate reticulate-punctate ground sculpture, appearing relatively matte; base of first gastral tergite usually weakly punctate and/or costulate and/or shagreened, remainder of tergite unsculptured, smooth, and shining. Whole body with abundant, long, and fine standing hairs; first gastral tergite with abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Body usually of uniform brown, appendages often lighter.
Etymology. The name of the new species is a patronym dedicated to Dr. Barry Lee Bressler, retired physicist, former adjunct professor of physics at Virginia Polytechnic Institute and State University, and amateur naturalist, in recognition of his interest in myrmecology and his support of ant taxonomy.
Distribution and biology. As mentioned above, it is surprising that most species in the species group, except the holotype of T. plesiarum, were previously unknown. This is especially true for T. bressleri. It is by far the most common and abundant species of the T. plesiarum group. The material available was sampled in many localities and includes more than 500 mounted specimens with many more in alcohol. The distribution ranges of all group members strongly overlap, but the range of T. bressleri is by far the largest; this species is known from many more localities than the other four (Fig.  62). The southernmost localities are Andohahela, Beza Mahafaly, and Fiherenana, and from there the distribution ranges north through much of western Madagascar up to the northernmost known locality Anabohazo. The eastern limit of the range goes in an almost straight line north from Andohahela through Mampiarika, Ambohitantely, and Ambohimanga to Anabohazo. The new species prefers arid habitats such as tropical dry forests, tropical dry forests on tsingy, gallery forests, spiny deciduous forests, savannah woodland, Uapaca woodland, and spiny thickets. The elevational range of the species is a relatively broad one, ranging from 10 to 1550 m, but most of the material was collected at low elevations (ca. 420 m on average). Tetramorium bressleri was mainly sampled by pitfall trapping and litter sifting, suggesting a ground-active life style.
Discussion. Tetramorium bressleri is not likely to be confused with T. gollum, T. hobbit, or T. mars, whereas differentiating between T. bressleri and T. plesiarum can be challenging at first glance. Tetramorium bressleri lacks the enlarged gaster and strong reticulate-rugose sculpture on the basal half of the first gastral tergite seen in T. gollum, nor does it have the blocky petiolar node shape of T. mars or the massively enlarged petiolar node of T. hobbit. The separation from T. plesiarum requires more attention and caution. The main and obvious difference is body size. Tetramorium bressleri is usually a much larger species (HW 0.80-1.00; WL 0.92-1.15) than T. plesiarum (HW 0.80-1.00; WL 0.92-1.15). There is some overlap, but this is mainly due to a few very small specimens of T. bressleri and one very large specimen of T. plesiarum. Otherwise, both species fall neatly into their respective size ranges. However, body size alone should not be used as a primary diagnostic character, and in this case, we provide more evidence for their heterospecificity. The eyes of T. plesiarum (OI 21-23) are larger than in T. bressleri , although this is often difficult to assess without measuring. In addition, both can be separated by the sculpture on the mesopleuron and lateral propodeum; this sculpture is usually mostly absent in T. bressleri, making the area appear very smooth and shiny, while it is usually longitudinally rugose with reticulate-punctate ground sculpture in T. plesiarum. The sculpture on the sides of the petiolar node varies too, since it is much more reticulate-punctate and matte in T. plesiarum than in T. bressleri, in which the weak reticulate-punctate ground sculpture looks faintly matte but still relatively smooth and shiny. The shape of the petiolar node in profile is an additional useful character. In T. plesiarum the anterodorsal margin of the node protrudes anteriorly and is a bit more marginate than the more rounded posterodorsal margin, while in T. bressleri both margins are usually equally marginate and the anterodorsal margin does not protrude anteriorly at all.
Considering how common and abundant T. bressleri is in western Madagascar, it is interesting that it shows very little intraspecific variation and remains very stable in its morphology. Diagnosis. The strongly developed sculpture on the basal half of the first gastral tergite and the extremely swollen gaster clearly distinguish T. gollum from the other species in the group. Worker description. Head weakly longer than wide to as long as wide (CI 97-100); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, curving down shortly before posterior head margin, forming dorsal margin of very well-developed antennal scrobes; scrobes moderately shallow; posterior and ventral margins not fully defined, merging with very strong cephalic sculpture. Antennal scapes short, not reaching posterior head margin . Eyes relatively small . Mesosomal outline in profile conspicuously convex, rounded, and very high (LMI 50-56), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines long (PSLI 29-31), elongate-triangular to spinose, and acute; propodeal lobes short, triangular to elongate-triangular, and acute. Petiolar node in profile high, rectangular nodiform with well-defined antero-and posterodorsal margins, between 1.6 to 1.8 times higher than long (LPeI 57-61), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height, petiolar dorsum flat to weakly convex; node in dorsal view around 1.3 to 1.5 times wider than long (DPeI 130-148), in dorsal view pronotum between 1.8 to 2.0 times wider than petiolar node (PeNI 50-56). Postpetiole in profile anteroposteriorly compressed, approximately 1.5 to 1.6 times higher than long (LPpI 63-65); in dorsal view around 1.7 to 1.9 times wider than long (DPpI 167-185), pronotum only around 1.3 times wider than postpetiole (PpNI 75-79). Postpetiole in profile appearing approximately as voluminous as petiolar node but relatively thinner, postpetiole in dorsal view approximately 1.3 to 1.5 times wider than petiolar node (PPI 135-148). Gaster extremely enlarged and swollen. Mandibles unsculptured, smooth, and shining; clypeus longitudinally rugose, with five to six distinct rugae, median ruga better developed than remainder, rugae without cross-meshes; sculpture on cephalic dorsum between frontal carinae variable: either mainly longitudinally rugose with higher proportion of reticulate-rugose areas towards posterior head margin, or irregularly reticulate-rugose with a higher proportion of longitudinally rugose sculpture restricted anteriorly close to posterior clypeal margin; scrobal area partly unsculptured; lateral head longitudinally rugose to reticulate-rugose. Mesosoma laterally reticulate-rugose to irregularly longitudinally rugose with a few shining areas on mesopleuron and propodeum, dorsally reticulate-rugose to irregularly longitudinally rugose. Forecoxae unsculptured, smooth, and shining. Petiolar node laterally with weak, longitudinally rugose sculpture mostly restricted towards dorsum, dorsum of node mostly unsculptured, smooth, and shiny; sculpture on postpetiole better developed, laterally and dorsally reticulate-rugose. Basal half of first gastral tergite and most of first sternite with very conspicuous and strongly developed reticulate-rugose sculpture superimposed on a reticulate-punctate ground sculpture; remainder of gaster unsculptured, smooth, and shining. Ground sculpture on head, mesosoma, and waist segments weak to moderate, except procoxae with weak but distinct rugulose ground sculpture. Whole body with abundant, long, and fine standing hairs; first gastral tergite with a mix of more abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Head, mesosoma, and waist segments light to dark brown, mandibles, antennae, and legs light brown to yellow, and gaster much darker brown than remainder of body.

Tetramorium gollum
Etymology. The new species is named after the fictional character "Gollum" from J.R.R. Tolkien's novels "The Hobbit" and "The Lord of the Rings". The species epithet is an arbitrary combination of letters, thus invariable.
Distribution and ecology. The new species is only known from the type locality, the Forêt d'Analalava, which is a tropical dry forest located at an elevation of 700 m (Fig. 62). The biology of the species is unknown, but foraging might be undertaken on the ground since the only three known specimens were collected from a pitfall trap. Indicated by this lack of material, T. gollum probably is one of the more rarely encountered Tetramorium species in Madagascar.
Discussion. Tetramorium gollum is a very conspicuous species within the T. plesiarum group and the whole Malagasy Tetramorium fauna. The extremely swollen gaster with strongly developed sculpture on the basal half of the tergite is easily recognisable within the species group. The only other Malagasy species with such conspicuous sculpture clearly extending to half of the tergite or more are T. jedi in the T. tortuosum group and T. sericeiventre in the T. sericeiventre group. The latter has 12 antennal segments (vs. 11 in T. gollum) and T. jedi has, among other characters, a very differently shaped petiolar node (longer than broad in T. jedi vs. broader than long in T. gollum). Beyond sculpture and the enlarged gaster, T. gollum is morphologically very similar to T. bressleri, for example the petiolar node shape is identical in both suggesting a close relationship. However, they both also differ in the shape of the postpetiole, which is much higher and broader in T. gollum (LPpI 63-65; DPpI 167-185) than in T. bressleri (LPpI 59-63; DPpI 150-158)  22.-26.III.2002 (B.L. Fisher et al.) (CAS: CASENT0019207). Paratypes, 2 pinned workers with same data as holotype (CAS: CASENT0019210; CASENT0019227); 2 pinned workers with same data as holotype except collected from pitfall trap and collection code BLF06258 (CAS: CASENT0078055; MHNG: CASENT0078059); 5 pinned workers with same data as holotype except collected from ground nest and collection code BLF06270 (CAS: CASENT0445004; CASENT0445005); and 2 pinned workers with same data as holotype except sampled from ground and collection code BLF06337 (MCZ: CASENT0445502; CASENT0445520).  Fisher et al.).
Diagnosis. Tetramorium hobbit is easily recognisable within the T. plesiarum species group due to its massively developed petiolar node and very conspicuous reticulate-punctate ground sculpture on head and mesosoma. Worker description. Head as long as wide to weakly longer than wide (CI 100-102); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around; median scrobal carina very well developed and distinctly surpassing posterior eye level, usually approaching posterior scrobe margin. Antennal scapes short, not reaching posterior head margin (SI 64-67). Eyes relatively small to moderate . Mesosomal outline in profile conspicuously convex, rounded and often very high (LMI 43-50), moderately marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines either short and elongate-triangular or long and spinose (PSLI 18-29; material from Andohahela and Tsimanampetsotsa with PSLI of 28-29; material from other localities PSLI 18-20), spines always with broad base and acute tip; propodeal lobes well developed, elongate-triangular, and acute, always shorter than propodeal spines. Petiolar node massively developed, very large, in profile high, rectangular, blocky nodiform with well defined antero-and posterodorsal margins, between 1.4 to 1.6 times higher than long (LPeI 63-71), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height, petiolar dorsum flat to weakly convex; node in dorsal view around 1.3 to 1.5 times wider than long (DPeI 133-148), in dorsal view pronotum around 1.5 to 1.7 times wider than petiolar node (PeNI 57-66). Postpetiole in profile subglobular to anteroposteriorly compressed, approximately 1.5 to 1.7 times higher than long (LPpI 60-67); in dorsal view around 1.7 to 1.9 times wider than long (DPpI 175-200), pronotum around 1.3 to 1.4 times wider than postpetiole (PpNI 69-76). Petiole in profile much more voluminous than postpetiole, in dorsal view postpetiole only about 1.1 to 1.3 times wider than petiolar node (PPI 116-126). Mandibles usually finely longitudinally rugulose, fairly smooth and shiny, sometimes unsculptured; clypeus longitudinally rugose, usually with five to seven very distinct and strong rugae, median ruga better developed than remainder, rugae usually without cross-meshes; cephalic dorsum between frontal carinae with 11 to 13 longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured, only with ground sculpture; lateral head mainly reticulate-rugose. Mesosoma laterally reticulate-rugose to irregularly longitudinally rugose, dorsally mostly longitudinally rugose. Forecoxae unsculptured, smooth, and shining, often with weak traces of ground sculpture. In profile, basal half of petiolar node mostly unsculptured, upper half distinctly reticulate-rugose, dorsum of node distinctly reticulate-rugose; sculpture on postpetiole much weaker, laterally and dorsally only weakly rugulose. Gaster usually unsculptured, smooth and shining, sometimes with weak punctate ground sculpture at base of tergite. Ground sculpture on head, mesosoma, and petiolar node very conspicuous, usually strongly reticulate-punctate; ground sculpture on postpetiole and gaster usually much weaker but present, though sometimes absent. Whole body with very abundant, long, and fine standing hairs; first gastral tergite with abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Body reddish to dark brown, head and gaster usually darker than rest of body.
Etymology. This very hairy new species is named after the fictional people from J.R.R. Tolkien's novels "The Hobbit" and "The Lord of the Rings". The species epithet is an arbitrary combination of letters, thus invariant.
Distribution and biology. The distribution of T. hobbit is approximately restricted to the southern third of the island of Madagascar (Fig. 62). In the south, the distribution range encompasses the type locality Tsimanampetsotsa in the west and Andohahela in the east, while the Makay Mountains and Isalo mark the northernmost known localities. Interestingly, the population in Andohahela seems to be slightly isolated from the other, more western localities. However, we consider this to be more of a sampling artifact. Like the remainder of the species group, T. hobbit prefers arid habitats, such as tropical dry forests, spiny forests and thickets, savannah woodland, and barren rocks with little vegetation. It is found at elevations of 80 to 923 m. Tetramorium hobbit is likely a ground-active species since it was mainly collected from leaf litter extractions and pitfall traps.
Discussion. Tetramorium hobbit is very unlikely misidentified with the other four species of the group. The massively enlarged petiolar node, in combination with the distinct reticulate-punctate ground sculpture on head and mesosoma, are not seen in any other group member. However, of all group members, T. mars seems morphologically closest to T. hobbit, especially on the basis of the blockier petiolar node shape seen in profile that both species share. However, in addition to the smaller petiolar node and the lack of reticulate-punctate ground sculpture on head and mesosoma, T. mars also has shorter antennal scapes (SI 58-62; DPeI 108-122) and a narrower petiolar node in dorsal view than T. hobbit (SI 64-67; DPeI 133-148). Tetramorium mars (HW 0.69-0.74; WL 0.83-0.96) is also smaller than T. hobbit (HW 0.80-0.88; WL 0.96-1.10) One noticeable intraspecific variation can be observed within T. hobbit. There are two distinct groups with differently developed propodeal spines. The populations from the type localities Tsimanampetsotsa and Andohahela always have relatively long spines (PSLI of 28-29), which contrast with the much shorter spines seen in the material from in Beroboka, Kirindy, Isalo, and the Makay Mountains . This difference is very pronounced and constant in all of the examined material. However, since there is no other obvious morphological difference between the short-spined and the long-spined populations, we treat them as conspecific in this study. Diagnosis. Tetramorium mars is distinguishable from the other group members by the following combination of characters: antennal scapes very short (SI 58-62); petiolar node never enlarged and massive; node in profile high, rectangular, blocky nodiform with well-defined antero-and posterodorsal margins; anterodorsal margin not protruding anteriorly nor very sharply angled; petiolar node in profile relatively low, between 1.3 to 1.5 times higher than long (LPeI 69-76), in dorsal view only 1.1 to 1.2 times wider than long (DPeI 108-123); gaster never enlarged or swollen; ground sculpture on head and mesosoma weak to absent; first gastral tergite without strong reticulate-rugose sculpture, usually completely unsculptured, but if sculpture present, then relatively weak and restricted to base of tergite; pilosity on first gastral tergite mostly erect.

Tetramorium mars
Worker measurements ( Worker description. Head longer than wide (CI 96-98); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around; median scrobal carina very well developed and distinctly surpassing posterior eye level. Antennal scapes very short, not reaching posterior head margin (SI 58-62). Eyes rela-tively small to moderate . Mesosomal outline in profile moderately convex, rounded and high (LMI 42-46), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines long, elongate-triangular to spinose (PSLI 28-32), spines always with broad base and acute tip; propodeal lobes well developed, elongate-triangular, and acute, always much shorter than propodeal spines. Petiolar node in profile high, rectangular, blocky nodiform with well-defined antero-and posterodorsal margins, between 1.3 to 1.5 times higher than long (LPeI 68-76), anterior and posterior faces approximately parallel, antero-and posterodorsal margins situated at about same height, petiolar dorsum weakly convex; node in dorsal view around 1.1 to 1.2 times wider than long (DPeI 108-123), in dorsal view pronotum between 1.8 to 2.0 times wider than petiolar node (PeNI 51-56). Postpetiole in profile subglobular, approximately 1.3 times higher than long (LPpI 75-80); in dorsal view around 1.5 to 1.7 times wider than long (DPpI 156-165), pronotum around 1.4 to 1.5 times wider than postpetiole (PpNI 68-72). Postpetiole in profile appearing much less voluminous than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 129-137). Mandibles unsculptured, smooth, and shining; clypeus longitudinally rugose/rugulose, with five to seven distinct rugae/rugulae, median ruga better developed than remainder, all rugae without cross-meshes; cephalic dorsum between frontal carinae with eight to twelve longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted or with crossmeshes, especially posteriorly; scrobal area mostly unsculptured; lateral head mainly longitudinally rugose. Ground sculpture on head generally weak to absent, sometimes a few areas weakly punctate. Mesosoma laterally irregularly longitudinally rugose with a few shining areas on mesopleuron and propodeum, mesosomal dorsum longitudinally rugose. Forecoxae unsculptured, smooth, and shining. Ground sculpture on mesosoma absent. In profile, basal half of petiolar node mostly unsculptured, upper half distinctly reticulate-rugose, whole dorsum of node distinctly reticulate-rugose; sculpture on postpetiole much more weakly developed, laterally and dorsally weakly irregularly rugulose. Ground sculpture on waist segments variable, usually weak or absent, often petiole and/ or postpetiole conspicuously reticulate-punctate. Gaster usually unsculptured, smooth, and shining, sometimes base of first gastral tergite weakly punctate. Whole body with very abundant, long, and fine standing hairs; first gastral tergite with abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Usually body uniformly light to reddish brown, sometimes darker.
Etymology. This new species is named after the ancient Roman god of war, "Mars". The species epithet is an arbitrary combination of letters, thus invariable.
Distribution and biology. Tetramorium mars has a broad distribution in western Madagascar (Fig. 62). It ranges from the southernmost known localities, Beza-Mahafaly and Forêt de Mite, through Kirindy Mite and Tsingy de Bemaraha to the northernmost localities, Baie de Baly and Ankarafantsika. All known localities are tropical dry or gallery forests at low elevations from 10 to 165 m. The new species was mainly sampled by litter extraction or pitfall trapping, which suggests a ground active lifestyle. Interestingly, T. mars was not found in Andohahela in the southeast of Madagascar, even though T. bressleri, T. hobbit, and T. plesiarum occur there. This is surprising since the four species of the group except T. gollum share more or less the same distribution range.
Discussion. Within the species group T. mars is not likely to be confused with the other five species. The lack of strong and conspicuous sculpture on the basal half of the first gastral tergite, an enlarged gaster, and the lower and less broad petiolar node separate T. mars (LPeI 69-76; DPeI 108-123) clearly from T. gollum (LPeI 57-60; DPeI 130-148). Despite the fact that T. mars shares some similarities with T. bressleri and T. plesiarum, the latter also have relatively higher, thinner, and wider petiolar nodes (LPeI 56-63; DPeI 130-144) which distinguish them from T. mars. In addition, T. mars has much better developed sculpture on the dorsum of the petiolar node than T. bressleri or T. plesiarum. The species most similar morphologically to T. mars is T. hobbit. Both share a more blocky nodiform petiolar node, but which is still much larger in T. hobbit. Indeed, this massively developed node, in combination with very conspicuous punctate ground sculpture on head and mesosoma, separates T. hobbit from T. mars, which has a much smaller petiolar node and only weakly developed ground sculpture on head and mesosoma. Further characters that distinguish T. mars are the comparatively short antennal scapes (SI 58-62 vs. SI 64-67) and smaller body size (HW 0.69-0.74 vs. HW 0.80-0.88).
Despite its relatively broad distribution range, T. mars displays very little intraspecific or geographic variation. [Note: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own geo-referencing of the Kelifely limestone plateau and should be considered an approximation but not the exact position of the type locality. Diagnosis. The following character set separates T. plesiarum from the remainder of the species group: smaller species (HW 0.80-1.00; WL 0.92-1.15); eyes of moderate size (OI 21-23); petiolar node high nodiform, not massively enlarged, anterodorsal margin protruding anteriorly and slightly more marginate than posterodorsal margin; petiolar node in profile relatively high and thin, between 1.6 to 1.8 times higher than long (LPeI 56-63), in dorsal view between 1.3 to 1.4 times wider than long (DPeI 131-137); gaster never extremely enlarged and swollen; head without strongly developed and conspicuous reticulate-punctate ground sculpture; mesopleuron and lateral propodeum with moderate punctate ground sculpture; first gastral tergite without strong reticulate-rugose sculpture, usually completely unsculptured, but if sculpture present, then relatively weak and restricted to base of tergite; pilosity on first gastral tergite mostly erect. Worker description. Head more or less as long as broad (CI 97-102); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around; median scrobal carina very well developed and distinctly surpassing posterior eye level, usually ending halfway between posterior eye margin and posterior scrobe margin, often approaching posterior scrobe margin. Antennal scapes short, not reaching posterior head margin (SI 64-69). Eyes small to moderate (OI 21-23). Mesosomal outline in profile weakly to moderately convex, rounded and high (LMI 41-47), moderately marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines elongate-triangular to spinose, moderately long to long, and acute (PSLI 23-28), spines always with broad base and acute tip; propodeal lobes well developed, triangular to elongate-triangular, and acute, always much shorter than propodeal spines. Petiolar node in profile high nodiform, between 1.6 to 1.8 times higher than long (LPeI 56-63), anterodorsal margin situated higher and more angled than posterodorsal, more rounded margin, petiolar dorsum weakly to moderately tapering backwards posteriorly, anterodorsal margin slightly protruding anteriorly, anterior and posterior faces approximately parallel; node in dorsal view between 1.3 to 1.4 times wider than long (DPeI 131-137), pronotum between 1.9 to 2.2 times wider than petiolar node (PeNI 45-51). Postpetiole in profile subglobular, approximately 1.3 to 1.4 times higher than long (LPpI 73-79); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 140-157), in dorsal view pronotum between 1.4 to 1.6 times wider than postpetiole (PpNI 63-70). Postpetiole in profile appearing slightly less voluminous than petiolar node, postpetiole in dorsal view about 1.3 to 1.4 times wider than petiolar node (PPI 129-143). Mandibles unsculptured, smooth, and shining; clypeus longitudinally rugose, with three to five distinct rugae, median ruga better developed than remainder, rugae without cross-meshes; cephalic dorsum between frontal carinae with ten to twelve longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted or with crossmeshes, especially posteriorly; scrobal area mostly unsculptured, relatively smooth and shiny; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head usually present but weak. Mesosoma laterally irregularly longitudinally rugose, usually with moderate punctate ground sculpture on mesopleuron and propodeum, dorsal mesosoma longitudinally rugose without any distinct ground sculpture, spaces between rugae smooth and shining. Forecoxae unsculptured, smooth, and shining. Sides of petiolar node and postpetiole with conspicuous, moderate reticulate-punctate ground sculpture, both nodes appearing relatively matte; petiolar node and postpetiole dorsally weakly rugulose/rugose, but mostly unsculptured, and appearing smooth and shining. Gaster usually unsculptured, smooth and shining, sometimes base of first gastral tergite with traces of punctate ground sculpture. Whole body with very abundant, dense, moderately long, and fine standing hairs; first gastral tergite with abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Body of uniform brown, appendages often lighter.

Tetramorium plesiarum
Distribution and biology. Despite being known only from seven localities and fewer than 20 specimens, T. plesiarum has a comparatively large distribution range ( Fig. 62). However, the populations appear to be relatively disjunctive. The species is known from Andohahela in the southeast of Madagascar and from six additional, more or less scattered localities in the western part of the island ranging from Zombitse and Vohibatsia north through the Makay Mountains, Tsingy de Bemaraha, and Beanka to the Kelifely plateau and Namoroka. The small number of specimens suggests that T. plesiarum is much less common than the sympatric T. bressleri, which shares much of the distribution range, but is known from many more localities and hundreds of specimens. The rarity of T. plesiarum might well explain the disjunctive distribution. Unfortunately, there is no "fresh" material available from the type locality since the holotype remains the only known specimen from the Kelifely plateau. All localities are tropical dry forests, tropical dry forests on tsingy, or gallery forests ranging from 100 to 780 m elevation. Like the other group members T. plesiarum was mostly collected by pitfall trapping and litter sifting suggesting a ground-active lifestyle.
Discussion. Tetramorium plesiarum lacks strong specialisations, such as the strongly sculptured and enlarged gaster of T. gollum, or the massively developed petiolar node of T. hobbit. Furthermore, T. mars has a lower and wider petiolar node (LPeI 69-76; DPeI 108-123) compared to T. plesiarum (LPeI 56-63; DPeI 131-137). The latter also has much less sculpture on the dorsum of the petiolar node. Within the species group T. plesiarum is morphologically most similar to T. bressleri, and as mentioned in the description of the latter, we have treated them as conspecific through most of the revision The most noticeable difference is certainly body size since T. bressleri (HW 0.80-1.00; WL 0.92-1.15) is much larger than T. plesiarum (HW 0.80-1.00; WL 0.92-1.15). As noted above, there is some slight overlap caused by one large specimen of T. plesiarum and very few small specimens of T. bressleri, but in the main they fit their respective size ranges. Not considering body size, they also differ in eye size and sculpture on mesosoma and waist segments. The eyes of T. plesiarum (OI 21-23) are larger than in T. bressleri . The mesopleuron and lateral propodeum of T. bressleri is usually mostly unsculptured and relatively smooth and shining, whereas this area is longitudinally rugose with reticulate-punctate ground sculpture in T. plesiarum. Almost the same pattern is seen in the sculpture on the lateral petiolar node as it is significantly more reticulate-punctate and matte in T. plesiarum than in T. bressleri, in which the weak reticulate-punctate ground sculpture appears faintly matte but still relatively smooth and shiny. The sculpture on the sides of the petiolar node varies, too, since it is much more reticulate-punctate and matte in T. plesiarum than in T. bressleri, in which the weak reticulate-punctate ground sculpture looks faintly matte but still relatively smooth and shiny. The shape of the petiolar node in profile is an additional useful character. Finally, in T. plesiarum the anterodorsal margin of the petiolar node protrudes anteriorly and is slightly more marginate than the more rounded posterodorsal margin, contrasting with the shape observed in T. bressleri, in which both margins are usually equally marginate and the anterodorsal margin does not protrude anteriorly at all.

Tetramorium schaufussii species group
Diagnosis. Eleven-segmented antennae; anterior clypeal margin medially impressed; frontal carinae variably developed, always present and surpassing eye level, usually weak to moderate and posteriorly merging into the surrounding sculpture, in a few species very well developed, noticeably raised and approaching posterior head margin; antennal scrobes usually weak, shallow, and without clearly defined posterior and ventral margins; anterior face of mesosoma weakly developed; mesosomal outline in profile relatively flat, usually comparatively low and elongated (LMI 35-42), usually moderately marginate from lateral to dorsal mesosoma; propodeal spines usually short to moderately long, triangular to elongate-triangular, long and spinose in a few species (PSLI 7-28); propodeal lobes usually triangular and short; petiolar node in profile rounded nodiform to high rounded nodiform with well-rounded margins, rarely high cuneiform or squamiform, node in profile between 1.2 to 3.0 times higher than long (LPeI 33-81), in dorsal view usually wider than long (DPeI 111-238), rarely longer than wide (DPeI 87-98), anterior and posterior faces parallel in most species; postpetiole in profile globular to subglobular, 1.2 to 1.7 times higher than long (LPeI 60-83), in dorsal view between 1.2 to 1.7 times wider than long (DPpI 120-168); mandibles always unsculptured, smooth, and shining; cephalic sculpture distinct, between frontal carinae predominantly longitudinally rugose; mesosoma usually with well-developed longitudinally rugose/rugulose sculpture, in some species sculpture mainly irregularly rugose/rugulose, rarely irregularly rugose/rugulose to reticulate-rugose; waist segments and gaster unsculptured, smooth, and shiny; standing pilosity always present on head, but variable on remainder of body, first gastral tergite often without standing pilosity at all, appressed pubescence on first gastral tergite variably developed, varying from very short and scarce to long and dense; sting appendage spatulate.
Comments. With 20 recognised species the T. schaufussii species group is second in terms of species-richness in the Malagasy region, following the T. tortuosum group with 22 (Hita Garcia and Fisher 2012b). This group is of special importance for Madagascar since many of its members are very widespread, common, and/or abundant. Almost all species prefer rainforests or montane rainforests, and with few exceptions, live in the forest leaf litter stratum.
The T. schaufussii species group is a very distinctive group among the thirteen groups with eleven-segmented antennae, and most of its members are unlikely to be mistaken for any other group. In general, most T. schaufussii group species are small to medium-sized ants, have a comparatively low and elongated mesosoma, and short to very short propodeal spines. Even though these characters are not unique to this group its members are usually easily recognisable. One interesting feature of the T. schaufussii group is that the mandibles of all species are completely unsculptured, smooth, and shining. This character alone already separates the T. schaufussii group from the T. bessonii, T. bonibony, T. kelleri, T. tortuosum, and T. weitzeckeri groups, in which all species have noticeably sculptured mandibles. In most other groups this character, however, is variable. Some species of the T. dysalum group have unsculptured mandibles, but these have either much longer propodeal spines or a much higher mesosoma. Another important group character is the lack of sculpture on the waist segments. The T. schaufussii group shares this character with a number of other groups, but it does distinguish the group from the T. kelleri, T. ranarum, and T. tortuosum groups, as well as from parts of the T. bonibony and T. dysalum groups. All these groups have at least one waist segment with distinct sculpture, but most of their species have conspicuous sculpture on both. Furthermore, in the T. schaufussii group the antennal scrobe is either weakly developed or absent distinguishing it immediately from the T. plesiarum group and a few species of the T. ibycterum complex of the T. ranarum group with moderately to very deep scrobes with clearly defined margins all around.
Moreover, all species of the T. schaufussii species group have relatively well developed cephalic and mesosomal sculpture. The sculpture on the cephalic dorsum between the frontal carinae is always well developed, whereas sculpture on the mesosomal dorsum can be weak in some species (but remains distinctly present). This separates the group from the T. bessonii, T. marginatum, T. tsingy groups, which usually have strongly reduced sculpture on the head and mesosoma. The members of the T. marginatum group that possess more sculpture have strongly cuneiform and/or triangular petiolar nodes, and are thus not confusable with the T. schaufussii group. The groups being morphologically most similar to the T. schaufussii group are the T. naganum and T. severini groups, as they share the usually high nodiform petiolar node and completely unsculptured waist segments. The only previously known species of both groups, T. naganum and T. severini, were initially recognised as members of the T. schaufussii group by Bolton (1979), but recently split by Hita Garcia and Fisher (2011, 2012a, 2012b. The separation from the T. severini group is relatively straightforward. The latter species is very large, very darkly coloured, and has very long to extremely long and curved propodeal spines that easily distinguish its members from the T. schaufussii group. The distinction between the T. schaufussii and the T. naganum group is less clear. The members of the T. naganum group usually have much more strongly developed frontal carinae, a generally broader head (CI 92-99), a higher mesosoma (LMI 40-46), and usually longer propodeal spines (PSLI 25-37). Some of these values overlap with a few species of T. schaufussii group, but they separate the bulk of species comparatively well. Bolton (1979) divided the group into two complexes on the basis of the absence (T. cognatum complex) or presence (T. schaufussii complex) of long, standing pilosity on the first gastral tergite. We follow this division and have placed all the new species into these two complexes even though at present we have no more evidence that these complexes represent monophyletic, mutually exclusive clades or lineages within the species group. Indeed, the only separating character is gastral pilosity, and future studies on the group that ideally include molecular data will likely yield different groupings. However, with 20 species the group is relatively species-rich and the clear-cut division into these two complexes facilitates the taxonomic organisation of the species group.

Key to species complexes of the Tetramorium schaufussii species group
1 First gastral tergite with appressed pubescence of varying length and without any standing hairs (Fig. 20A

Tetramorium cognatum species complex
Comments. This species complex contains a compact assemblage of ten species that are separated from the T. schaufussii species complex by their lack of any long, standing pilosity on the first gastral tergite, a character present in all members of the T. schaufussii complex. The ten species of the T. cognatum complex might be further divided into three smaller groupings: the first of these contains the five small to moderately large species with weak to very weak frontal carinae (T. aspis, T. camelliae, T. cognatum, T. karthala, and T. rumo); the second includes the four larger species with very well developed frontal carinae (T. gladius, T. myrmidon, T. proximum, and T. tenuinode); the third sub-grouping contains only T. freya, which is the only species of the complex lacking standing pilosity on the mesosoma, but it also possesses reduced frontal carinae and a larger body size. Four species of the complex have very restricted distribution ranges and are endemics to smaller areas or localities in Madagascar or the Comoros (Figs 63, 64): T. aspis (Andringitra and Ivohibe), T. camelliae (Ranomafana), T. karthala (Grand Comore), and T. myrmidon (Ambohijanahary), while T. freya was found only in a few littoral localities ranging from Nosy Be to the northernmost tip of Madagascar. The remaining species (T. cognatum, T. gladius, T. proximum, T. rumo, and T. tenuinode) have much wider distribution ranges, especially T. cognatum and T. proximum, which are found in almost all rainforests and montane rainforests from which material is available. Interestingly, almost all species appear be restricted to or prefer rainforests or montane rainforests, even the widely distributed T. cognatum, T. proximum, and T. tenuinode. However, T. cognatum was occasionally collected in drier habitats and T. freya occurs also in littoral and dry forests.

Identification key to species of the T. cognatum species complex (workers)
1 Mesosoma without any long, standing hairs ( Fig. 21A)  Petiolar node never strongly squamiform as above, in profile 1.6 to 2.7 (usually 1.6 to 2.2) times higher than long (LPeI 37-62) and in dorsal view between 1.1 to 1.7 times wider than long DPeI 111-171) ( Antennal scapes shorter (SI 66-70); petiolar node higher, around 1.8 to 2.2 times higher than long (LPeI 45-54); postpetiole in dorsal view around 1.5 to 1.7 times broader than petiolar node (PPI 148-167) (Fig. 26A Eyes smaller (OI 25-27); propodeal lobes always only weakly shorter than propodeal spines, and spines and lobes strongly inclined towards each other; dorsal mesosoma with six or more pairs of long, standing hairs on pronotum and mesonotum, and propodeum usually with one or two pairs anteriorly (         Diagnosis. The following character combination clearly diagnoses T. aspis within the T. cognatum species complex: relatively large eyes (OI 25-27); frontal carinae weakly developed; propodeal spines short, triangular to elongate-triangular, and acute (PSLI 18-21), propodeal lobes always only weakly shorter than propodeal spines, and spines and lobes strongly inclined towards each other; petiolar node in profile high rounded nodiform, weakly squamiform and relatively thin, in profile around 2.0 to 2.2 times higher than long (LPeI 46-51), and in dorsal view around 1.4 to 1.6 times wider than long (DPeI 146-161); mesosoma with six or more pairs of long, standing hairs on pronotum and mesonotum, propodeum usually with one or two pairs located anteriorly. Worker description. Head much longer than wide (CI 85-88); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly developed, only faintly raised, slightly diverging posteriorly, merging with surrounding sculpture halfway between posterior eye margin and posterior head margin. Antennal scrobes weak to absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 68-72). Eyes relatively large . Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 35-37), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove usually present, but very weakly developed. Propodeal spines short, triangular to elongate-triangular, and acute (PSLI 18-21), propodeal lobes triangular to elongate-triangular, always slightly shorter than propodeal spines, in profile spines and lobes strongly inclined towards each other. Petiolar node in profile high rounded nodiform, weakly squamiform and relatively thin, around 2.0 to 2.2 times higher than long (LPeI 46-51), anterior and posterior faces approximately parallel, anterodorsal margin usually situated slightly higher and more angulate than posterodorsal margin, petiolar dorsum relatively flat to weakly convex; node in dorsal view around 1.5 to 1.6 times wider than long (DPeI 146-161), in dorsal view pronotum around 2.3 to 2.5 times wider than petiolar node (PeNI 40-44). Postpetiole in profile globular, between 1.2 to 1.4 times higher than long (LPpI 70-81); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 126-135), pronotum around 1.8 to 2.0 times wider than postpetiole (PpNI 51-56). Postpetiole in profile appearing more voluminous than petiolar node, postpetiole in dorsal view around 1.2 to 1.4 times wider than petiolar node (PPI 121-137). Mandibles completely unsculptured, smooth, and shiny; clypeus weakly irregularly longitudinally rugulose, median ruga never fully developed, usually reduced to few traces, one or two mostly unbroken lateral rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with seven to nine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, often irregularly shaped, interrupted or with cross-meshes; scrobal area mostly unsculptured; lateral head reticulate-rugose to longitudinally rugose, often with larger areas with reduced sculpture. Ground sculpture on head weakly to moderately reticulate-punctate, especially laterally. Dorsum and sides of mesosoma mostly irregularly longitudinally rugose/rugulose, sides of mesosoma often with some reticulate-rugose areas. Ground sculpture on dorsal mesosoma mostly absent, lateral mesosoma usually weakly to moderately reticulate-punctate. Forecoxae usually unsculptured, smooth and shining. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with six or more pairs on pronotum and mesonotum, propodeum usually with one or two pairs anteriorly; waist segments and first gastral tergite without any standing hairs at all; first gastral tergite with short, moderately dense, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments and gaster usually of uniform brown to dark brown, appendages yellowish to light brown; sometimes waist segments and gaster lighter than head and mesosoma but still darker than appendages.
Etymology. The name of the new species is Old Greek and means "shield," referring to the weakly squamiform condition of the petiolar node. The species epithet is a nominative noun, and thus invariant.
Distribution and biology. So far T. aspis is known only from a few localities in the southeast of Madagascar around Ivohibe and Andringitra, where it was collected in rainforests or montane rainforests at elevations ranging from 785 to 1680 m (Fig.  63). Tetramorium aspis was mainly sampled from leaf litter or general collecting on the ground, which suggests that it might be a ground-active species.
Discussion. The new species is clearly distinguishable within the T. cognatum species complex. Tetramorium aspis with its large eyes (OI 25-27) and presence of six or more pairs of long, standing hairs on the mesosoma is unlikely to be confused with the small-eyed T. gladius , or T. freya, which lacks standing pilosity on the mesosomal dorsum. Furthermore, the weakly developed frontal carinae separate it from the species with strong frontal carinae T. myrmidon, T. proximum, and T. tenuinode. The latter three are also mostly larger species (HW 0.58-0.81; WL 0.76-1.07) compared to T. aspis (HW 0.51-0.55; WL 0.72-0.81). The remaining four species are morphologically closer to T. aspis. Of these, T. camelliae differs significantly from T. aspis on the basis of petiolar node development. In the latter the node is only weakly squamiform, in profile around 2.0 to 2.2 times higher than long (LPeI 46-51), and in dorsal view between 1.4 to 1.6 times wider than long (DPeI 146-161). This shape contrasts with the node of T. camelliae, which is around 2.8 to 3.0 times higher than long (LPeI 33-36) and around 2.3 to 2.4 times wider than long (DPeI 228-238). The best character for separating T. aspis from the remaining three species is the development and arrangement of propodeal spines and lobes. In T. aspis the spines are short, triangular to elongate-triangular, and acute (PSLI 18-21), the lobes relatively long, only weakly shorter than the spines, and the spines and lobes are strongly inclined towards each other. This arrangement is not seen in T. cognatum, T. karthala or T. rumo (it is present in T. camelliae though) since they either have short to moderate spines (T. karthala + T. rumo: PSLI 20-26), much longer than the lobes, or the spines are very short (T. cognatum: PSLI 12-16) and approximately same length as lobes or even shorter. Beyond this conspicuous character, T. aspis also has longer antennal scapes (SI 68-72), a broader petiolar node (DPeI 146-161), and a narrower postpetiole (DPpI 126-135) than T. cognatum (SI 61-67; DPeI 129-142; DPpI 137-153). Tetramorium karthala, which is only found on the Comoros, has only two to four pairs of long, standing hairs on the pronotum and mesonotum while T. aspis has least least six pairs. The last species, T. rumo, has very short antennal scapes (SI 60-66), a thinly cuneiform and moderately squamiform petiolar node, and is usually very bright yellow to light brown.
Intriguingly, T. scutum from the T. sikorae complex, which is endemic to the same geographic area, bears a strong superficial resemblance to T. aspis. However, they are in different species complexes based on their differences in pilosity on the first gastral tergite (present in T. scutum but absent in T. aspis). Apart from this key character they also differ slightly in eye size and propodeal spine length.
To our best knowledge, there is no apparent intraspecific variation in T. aspis.  (B.L. Fisher et al.).
Diagnosis. The strongly squamiform and transverse petiolar node, which in profile is around 2.7 to 3.0 times higher than long (LPeI 33-36), and in dorsal view around 2.3 to 2.4 times wider than long (DPeI 228-238), isolates T. camelliae from the other members of the T. cognatum species complex.
Worker measurements ( Worker description. Head much longer than wide (CI 89-91); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae moderately developed, diverging posteriorly, merging with surrounding sculpture halfway between posterior eye margin and posterior head margin. Antennal scrobes weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 66-70). Eyes relatively large . Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36-37), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, but weakly developed. Propodeal spines short, triangular to elongate-triangular, and acute , propodeal lobes triangular to elongate-triangular and of approximately same length as propodeal spines, in profile spines and lobes strongly inclined towards each other. Petiolar node in profile strongly squamiform, around 2.7 to 3.0 times higher than long (LPeI 33-36), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height, petiolar dorsum relatively flat to weakly convex; node in dorsal view transverse and 2.3 to 2.4 times wider than long (DPeI 228-238), in dorsal view pronotum between 2.1 to 2.5 times wider than petiolar node (PeNI 40-48). Postpetiole in profile subglobular, between 1.2 to 1.4 times higher than long (LPpI 69-80); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 133-141), pronotum between 1.7 to 2.0 times wider than postpetiole (PpNI 50-59). Postpetiole in profile much more voluminous than petiolar node, postpetiole in dorsal view around 1.2 to 1.4 times wider than petiolar node (PPI 120-134). Mandibles completely unsculptured, smooth, and shiny; clypeus irregularly longitudinally rugulose, median ruga never fully developed, usually reduced to few traces posteriorly or medially, one or two mostly unbroken lateral rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugose/rugulose with seven to eight rugae/rugulae, rugae usually running unbroken from posterior clypeal margin to posterior head margin, sometimes interrupted or with cross-meshes; scrobal area partly unsculptured, but mostly merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral head. Dorsum and sides of mesosoma longitudinally rugose/ rugulose. Forecoxae unsculptured, smooth and shining. Ground sculpture on head and mesosoma weak to absent. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with seven to eight pairs restricted to pronotum and mesonotum; propodeum, waist segments and first gastral tergite without any standing hairs; first gastral tergite with short, moderately dense, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments, and gaster uniform brown to dark brown, appendages yellowish to light brown.
Etymology. The new species is dedicated to the first author's lovely life partner, Tracy Lynn Camellia Audisio from San Francisco, California, U.S.A.
Distribution and biology. Tetramorium camelliae is a rare species only known from Ranomafana National Park (Fig. 63) where it was collected twice in montane rainforest at elevations ranging from 1100 to 1173. The little available data indicates that T. camelliae lives in leaf litter.
Discussion. Tetramorium camelliae is easily distinguishable from the other members of the T. cognatum species complex. The main diagnostic character is the petiolar node shape, which is strongly squamiform in T. camelliae (LPeI 33-36; DPeI 228-238) but not in the remainder of the species complex (LPeI 37-62; DPeI 111-171). Generally, its smaller body size, weaker frontal carinae, and gastral pubescence ally T. camelliae morphologically with T. aspis, T. cognatum, T. karthala and T. rumo. [Note: the GPS data of the type locality was not provided either by the locality label or the original description. The data presented above is based on our own georeferencing of the Périnet=Andasibe area and should be considered an approximation and not the exact position of the type locality.  332° Toamasina, 17.924°S, 49.19967°E, 390 m, rainforest, 28.XI.2005 (B.L. Fisher et al.); Toamasina,Bevolota,17.  Diagnosis. Tetramorium cognatum can be easily separated from the other members of the T. cognatum species group by the following character combination: eyes very large (OI 27-29); antennal scapes very short (SI 61-67); frontal carinae weakly developed; propodeal spines reduced to very short, triangular teeth (PSLI 12-16), spines and lobes usually of approximately same length, often spines weakly shorter than lobes, very rarely spines weakly longer than lobes, never strongly directed towards each other; petiolar node high nodiform, in profile around 1.8 to 2.0 times higher than long (LPeI 49-55), in dorsal view around 1.3 to 1.4 times wider than long (DPeI 129-142); dorsal mesosoma normally with four to six (sometimes reduced to two to three) pairs of long, standing hairs occurring from anterior pronotum to metanotal groove, but absent from propodeum.

Tetramorium cognatum
Worker measurements ( Worker description. Head much longer than wide (CI 87-91); in full-face view posterior head margin usually very weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly developed, only faintly raised, slightly diverging posteriorly, and relatively long, often ending shortly before posterior head margin. Antennal scrobes very weakly developed, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 61-67). Eyes very large . Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36-40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove usually present, but relatively weak. Propodeal spines reduced to very short, triangular teeth (PSLI 12-16), propodeal lobes short and triangular, spines and lobes usually of approximately same length, often spines weakly shorter than lobes, very rarely spines weakly longer than lobes. Petiolar node in profile rounded high nodiform, around 1.8 to 2.0 times higher than long (LPeI 49-55), anterior and posterior faces approximately parallel, anterodorsal margin usually sharper than more rounded posterodorsal margin, both margins often situated at about same height, often anterodorsal margin slightly higher, petiolar dorsum usually weakly convex; node in dorsal view around 1.3 to 2 times wider than long (DPeI 129-142), in dorsal view pronotum between 2.3 to 2.7 times wider than petiolar node (PeNI 38-44). Postpetiole in profile globular, rarely subglobular, between 1.3 to 1.5 times higher than long (LPpI 66-75); in dorsal view around 1.3 to 1.5 times wider than long (DPpI 137-153), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 53-59). Postpetiole in profile usually appearing shorter and less voluminous than petiolar node, postpetiole in dorsal view between 1.3 to 1.5 times wider than petiolar node (PPI 131-147). Mandibles completely unsculptured, smooth, and shiny; clypeus usually irregularly longitudinally rugulose, median ruga often unbroken and well developed, often partly reduced, and often fully absent; lateral rugulae ranging from one to three on each side, often irregularly shaped, broken, or reduced to traces; cephalic dorsum between frontal carinae longitudinally rugulose with six to ten fine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, mostly irregularly shaped, interrupted, meandering or with cross-meshes, and sometimes becoming much weaker posteriorly; scrobal area mostly unsculptured, merging with surrounding sculpture; lateral head reticulate-rugose to longitudinally rugose, often with larger areas of reduced sculpture; ground sculpture on head weakly to moderately punctate, sometimes completely absent. Dorsum of mesosoma irregularly longitudinally rugulose, sometimes weakly so; lateral mesosoma usually mostly irregularly longitudinally rugulose, lateral pronotum often much weaker-sculptured, almost smooth, and sometimes reticulate-rugulose; ground sculpture on mesosoma usually weakly to moderately punctate, sometimes completely absent. Forecoxae usually unsculptured, smooth and shining, sometimes with traces of ground sculpture dorsally. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, standing hairs, dorsal mesosoma normally with four to six (sometimes reduced to two to three) pairs occurring from anterior pronotum to metanotal groove, but absent from propodeum; waist segments and first gastral tergite without any long, standing hairs at all; first gastral tergite with moderately long, dense, appressed to decumbent pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to subdecumbent hairs. Body colouration variable, ranging from uniformly bright yellow to very dark brown, if colour brown to dark brown, appendages usually lighter.
Distribution and biology. This species is one of the most common Tetramorium encountered in the rainforests and montane rainforests of Madagascar (Fig. 63). Its distribution range encompasses almost all sampled forests in eastern and northern Madagascar, as well as the isolated humid forests in central and western parts of the island (e.g. Ambohijanahary, Isalo). Surprisingly, T. cognatum also seems to do fairly well outside humid forests since it is also found in a few disturbed gallery forests, in Uapaca woodland and tropical dry forests, and very rarely in spiny forest/thicket and savannah/grassland. Additional sampling in arid habitats might show that T. cognatum is even more widely distributed than currently understood. The species was mostly collected from leaf litter and the ground.
Discussion. Tetramorium cognatum is an important species within this species complex. As outlined above, it is very widely distributed and common, and co-occurs in sympatry with almost all other members of the complex. It is easily distinguishable from the usually larger T. freya, which also lacks pilosity on the dorsal mesosoma, and T. gladius, the species with the smallest eyes in the complex . Furthermore, T. cognatum possesses relatively weakly developed frontal carinae, separating it from T. myrmidon, T. proximum, and T. tenuinode. This character allies T. cognatum with T. aspis, T. camelliae, T. karthala, and T. rumo, to which it is generally closer in morphology. Of these species close to T. cognatum, T. karthala (endemic to Grand Comore) has longer antennal scapes (SI 70-74) and propodeal spines (PSLI 20-22) than T. cognatum (SI 61-67; PSLI 12-16). Tetramorium camelliae, only found in Ranomafana, and T. rumo have squamiform or thinly cuneiform petiolar nodes, which in profile are between 2.3 to 3.0 times higher than long (LPeI 33-43) while the node of T. cognatum is only 1.8 to 2.0 times higher than long (LPeI 49-55). Tetramorium aspis, which is only found in the area around Andringitra and Ivohibe, has longer propodeal spines (PSLI 18-21) than T. cognatum. More importantly however, the propodeal spines and lobes of T. cognatum are not strongly inclined towards each other as they are in T. aspis. Considering its local abundance, relative flexibility in habitat requirements, and widespread distribution, T. cognatum shows startlingly little intraspecific variation. From the southern spiny forest Lavanono and the montane rainforests in Andohahela to the northernmost known localities at Montagne d'Ambre/Sakaramy, T. cognatum is always easily recognisable. However, some noticeable variation in sculpture and body colouration still exists. Colouration ranges from very light yellow through all shades of yellowish orange or brown to very dark brown, almost black. The southeastern and northern populations are mostly light yellow to light brown while most material from the central-eastern populations is mainly brown to very dark brown. There is also some variation in the degree to which sculpture is developed on the clypeus and the sides of the head and mesosoma as outlined in the description above. Diagnosis. The following character combination distinguishes T. freya from the other species of the T. cognatum species complex: frontal carinae weakly developed, merging with surrounding sculpture halfway between posterior eye margin and posterior head margin; petiolar node high nodiform with well rounded margins, in profile around 1.6 to 1.7 times higher than long (LPeI 58-62), in dorsal view 1.2 to 1.3 times wider than long (DPeI 124-131); lack of any long, standing pilosity on dorsal mesosoma. Worker description. Head much longer than wide (CI 90-92); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly to moderately developed, merging with surrounding sculpture halfway between posterior eye margin and posterior head margin. Anten-nal scrobes weak to absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 68-71). Eyes relatively large (OI 25). Mesosomal outline in profile weakly to moderately convex, moderately high and stout (LMI 40-42), weakly to moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, but weakly developed. Propodeal spines short, triangular to elongate-triangular, and acute , propodeal lobes triangular and short, always much shorter than propodeal spines. Petiolar node in profile high nodiform with well-rounded margins, around 1.6 to 1.7 times higher than long (LPeI 58-62), anterior and posterior faces approximately parallel and rounding smoothly onto dorsum, anterodorsal and posterodorsal margins situated at about same height, petiolar dorsum relatively noticeably convex; node in dorsal view 1.2 to 1.3 times wider than long (DPeI 124-131), in dorsal view pronotum between 2.0 to 2.4 times wider than petiolar node (PeNI 42-50). Postpetiole in profile globular to subglobular, between 1.3 to 1.4 times higher than long (LPpI 72-77); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 127-144), pronotum between 1.4 to 1.8 times wider than postpetiole (PpNI 59-70). Postpetiole in profile appearing approximately as voluminous as petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 133-140). Mandibles completely unsculptured, smooth, and shiny; clypeus in parts irregularly longitudinally rugulose, median ruga never fully developed, usually reduced to a few traces, one or two irregular and broken lateral rugulae present on each side; cephalic dorsum between frontal carinae weakly irregularly longitudinally rugulose, rugulae weak, often interrupted or with cross-meshes and becoming much weaker posteriorly; scrobal area mostly irregularly longitudinally rugulose and merging with surrounding irregularly longitudinally rugose to reticulate-rugose sculpture present on lateral head. Head with very conspicuous punctate ground sculpture. Mesosoma laterally and dorsally with traces of irregular rugulae or reticulate-rugose sculpture overlaying a distinct punctate ground sculpture. Forecoxae in parts weakly longitudinally rugulose and partly unsculptured, smooth, and shining. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of hairs. Mesosoma, waist segments, and first gastral tergite without any standing hairs at all; first gastral tergite with very short, moderately dense, and appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments, and gaster uniform brown, appendages yellowish to light brown.

Tetramorium freya
Etymology. The name of the new species was inspired and derived from the name of the Old Norse goddess Freyja (which means "Lady" in Old Norse) who was considered the goddess of love, beauty, fertility, war, and death. As a name taken from Norse mythology, it is treated as an arbitrary combination of letters, thus invariant.
Distribution and biology. Tetramorium freya is a rare species only known from a few localities at the northernmost tip of Madagascar and from the island of Nosy Be (Fig. 63). The species was collected in rainforests, dry forests, and coastal dunes at elevations from 10 to 1000 m. Also, T. freya was mostly sampled from Malaise traps or from vegetation and only once from leaf litter; considering there are only five known specimens, it seems likely that T. freya nests and forages in vegetation. Additional sampling in lower vegetation might yield more material of this otherwise very rare species.
Discussion. The identification of T. freya is easy and straightforward since it is the only species of the species complex without any long, standing pilosity on the mesosomal dorsum. Beyond mesosomal pilosity, T. freya also has weakly developed frontal carinae and sculpture on the head and mesosoma, which separate it from T. gladius, T. myrmidon, T. proximum, and T. tenuinode. In addition, T. freya possesses a stouter and higher mesosoma (LMI 40-42) and a lower and thicker petiolar node (LPeI 58-62, around 1.6 to 1.7 times higher than long) compared to T. aspis, T. camelliae, T. cognatum, T. karthala, and T. rumo (LMI 35-40; LPeI 33-55, around 1.8 to 3.0 times higher than long).
Based on the limited number of specimens available for this study, there seems to be no significant intraspecific variation in T. freya. Paratypes, one pinned worker with same data as holotype (CAS: CASENT0406981); four pinned worker with same data as holotype but collected ex rotten stick on ground and collection codes BLF02407 and BLF02408 (CAS: CASENT0406964; CASENT0406971); fifteen pinned workers with same data as holotype but collected ex rotten log and collection codes BLF02429, BLF02498, and BLF02500 (CAS: CASENT0406966; CASENT0406967; CASENT0406968; CASENT0406969; CASENT0406974; CASENT0406975; MCZ: CASENT0406976); one pinned worker with same data as holotype but collected ex rotten tree stump and collection code BLF02486 (BMNH: CASENT0406965). Worker description. Head longer than wide (CI 92-95); in full-face view posterior head margin weakly to moderately concave. Anterior clypeal margin with distinct median impression. Frontal carinae moderately to well developed, diverging posteriorly, either merging with surrounding sculpture halfway between posterior eye margin and posterior head margin or only becoming weaker after posterior eye level but still approaching posterior head margin. Antennal scrobes very weak, shallow, and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 71-74). Eyes relatively small . Mesosomal outline in profile flat to weakly convex, moderately low and long (LMI 36-38), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove mostly reduced and absent, if present weakly developed. Propodeal spines moderately long to long, elongate-triangular to spinose, and usually acute (PSLI 21-28), propodeal lobes short and triangular, always much shorter than propodeal spines. Petiolar node in profile nodiform to high rounded nodiform, around 1.7 to 2.1 times higher than long (LPeI 48-58), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins usually situated at about same height and weakly rounded, petiolar dorsum weakly to moderately convex; node in dorsal view between 1.1 to 1.3 times wider than long (DPeI 113-133), in dorsal view pronotum between 2.8 to 3.2 times wider than petiolar node (PeNI 31-36). Postpetiole in profile globular, around 1.2 to 1.4 times higher than long (LPpI 70-82); in dorsal view around 1.2 to 1.3 times wider than long (DPpI 120-133), pronotum around 1.8 to 2.0 times wider than postpetiole (PpNI 49-56). Postpetiole in profile usually appearing more voluminous than petiolar node, postpetiole in dorsal view around 1.5 to 1.6 times wider than petiolar node (PPI 148-159). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugose/rugulose with three to seven median ruga always fully developed and distinct, and one to three mostly unbroken lateral rugae/rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugose with seven to nine rugae, rugae running mostly unbroken from posterior clypeal margin to posterior head margin, sometimes interrupted or with cross-meshes; scrobal area partly unsculptured, but mostly merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral head. Dorsum and sides of mesosoma mostly irregularly longitudinally rugose. Forecoxae unsculptured, smooth, and shining. Ground sculpture on head and mesosoma usually weak to absent. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; dorsum of mesosoma with six to eight pairs on pronotum and mesonotum, anterior propodeum with one pair; waist segments and first gastral tergite without any standing hairs; first gastral tergite with very short, scarce, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed, rarely decumbent hairs. Head, mesosoma, waist segments, and gaster uniform reddish, orange-brown, appendages always lighter, yellowish to light brown.

Tetramorium gladius
Etymology. The name of the new species is the ancient Latin general word for sword, although it mostly refers to the short swords used by foot soldiers of the Roman legion. The name was chosen based on the shape of the propodeal spines in most specimens of T. gladius, which resemble this type of sword. The species epithet is a nominative noun, and thus invariant.
Distribution and biology. Tetramorium gladius has a relatively wide but patchy distribution in central, central-eastern, and northern Madagascar (Fig. 63). The southernmost localities are Ambohitantely and Andranomay and the northernmost is Binara with Ambatovaky, Ambanizana, and Anjanaharibe-Sud in-between. All localities are rainforests and montane rainforests at elevations ranging from 425 to 1490 m. Tetramorium gladius seems to be only moderately common and living in the leaf litter.
Discussion. The relatively small eyes of T. gladius (OI 19-20) differentiate it immediately from the remainder of the T. cognatum species complex, in which all species have much larger eyes (OI 24-31). Apart from this, T. gladius appears to be morphologically close to T. myrmidon, T. proximum, and T. tenuinode since they all share a larger body size and very well developed frontal carinae and sculpture.

Tetramorium karthala
Diagnosis. Tetramorium karthala is diagnosable within the T. cognatum complex on the basis of the following character combination: very large eyes (OI 29-30); short antennal scapes (SI 70-74); frontal carinae weakly to moderately developed; propodeal spines short to moderate, elongate-triangular to spinose, and usually acute (PSLI 20-22), propodeal lobes always much shorter than spines and lobes never strongly inclined towards each other; petiolar node rounded high nodiform, in profile around 1.8 to 2.0 times higher than long (LPeI 50-54), in dorsal view around 1.5 to 1.6 times wider than long (DPeI 148-158); mesosoma with two to four pairs of long, standing hairs on pronotum and mesonotum.
Worker measurements ( Worker description. Head much longer than wide (CI 86-87); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly to moderately developed, only weakly raised, and ending between posterior head margin and posterior head margin. Antennal scrobes very weakly developed to almost absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 70-74). Eyes very large (OI 29-30). Mesosomal outline in profile flat to weakly convex, moderately low and long (LMI 37-39), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present and distinctly developed. Propodeal spines short to moderately long, elongate-triangular to spinose, and usually acute (PSLI 20-22), propodeal lobes short and triangular, always much shorter than propodeal spines, spines and lobes never strongly inclined towards each other. Petiolar node in profile rounded high nodiform, around 1.8 to 2.0 times higher than long (LPeI 50-54), usually anterior and posterior faces more or less parallel, anterodorsal and posterodorsal margins both well-rounded and usually situated at about same height, petiolar dorsum moderately convex; node in dorsal view around 1.5 to 1.6 times wider than long (DPeI 148-158), in dorsal view pronotum between 2.0 to 2.2 times wider than petiolar node (PeNI 45-49). Postpetiole in profile subglobular, between 1.4 to 1.6 times higher than long (LPpI 65-68); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 138-158), pronotum around 1.6 to 1.8 times wider than postpetiole (PpNI 55-61). Postpetiole in profile usually appearing of more or less same volume as petiolar node, postpetiole in dorsal view around 1.1 to 1.3 times wider than petiolar node (PPI 112-131). Mandibles completely unsculptured, smooth, and shiny; clypeus usually irregularly longitudinally rugulose with three to five, often broken, rugulae, sometimes rugulae reduced to one or two, median ruga/rugula often developed, but usually broken, rarely completely absent; cephalic dorsum between frontal carinae longitudinally rugose/rugulose with seven to nine rugae/rugulae, rugae usually running from posterior clypeal margin to posterior head margin, often interrupted, rarely with cross-meshes; scrobal area mostly unsculptured with ground sculpture only, lateral head reticulate-rugose to longitudinally rugose. Dorsum and sides of mesosoma mostly irregularly longitudinally rugose/rugulose. Forecoxae dorsally with few traces of rugulae, otherwise mostly unsculptured, smooth, and shining. Ground sculpture on head and mesosoma very distinct, usually reticulate-punctate with few areas very finely reticulate-rugulose. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with numerous pairs of standing, long, fine hairs; mesosoma usually with two to four pairs: one long pair on anterior pronotum and one long pair on anterior mesonotum, sometimes two shorter pairs present, one on posterior pronotum and one on posterior mesonotum; propodeum, waist segments and first gastral tergite without any standing hairs; first gastral tergite with short, moderately dense, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Head, mesosoma, waist segments and gaster uniform light brown, appendages often lighter, more yellowish brown.
Etymology. The new species is named after the type locality, Karthala Forest on Mount Karthala volcano on the island of Grand Comore. The species epithet is a noun in apposition, and thus invariable.
Distribution and biology. This new species is only known from the type locality, which is a montane rainforest on the Comorian island Grande Comore (Fig. 63). At present, it is the only described Tetramorium species endemic to any Comorian island. All other Tetramorium species (except one undescribed species from the T. ranarum species group from Anjouan) found on the Comoros Islands are either introduced tramp species or species shared between Africa, the Comoros and Madagascar, or between the Comoros and Madagascar. Intriguingly, the type locality appears to have a quite unique fauna. Just recently Fischer and Fisher (2013) described a new Pheidole species (Pheidole vulcan Fischer & Fisher) from this locality, which is also endemic to the island of Grande Comore. Tetramorium karthala is at elevations between 1000 to 1125 m where it was mainly collected from leaf litter, under moss, or within rotten logs.
Discussion. Tetramorium karthala is easily identifiable in the Malagasy region since it is the only species of the T. cognatum species complex and the whole T. schaufussii species group found on the Comores. Even without considering geography the new species can be well distinguished from the remainder of its species complex. In general, it is morphologically close to T. aspis, T. camelliae, T. cognatum, and T. rumo, whereas it differs more strongly from the rest of the complex. Since T. karthala has several pairs of long, standing hairs on the dorsum of the mesosoma and much larger eyes (OI 29-30), it is unlikely to be mistaken for T. freya, which has no standing pilosity on the mesosomal dorsum, or for T. gladius, which has the smallest eyes in the complex . Also, T. karthala cannot be confused with T. myrmidon, T. proximum, or T. tenuinode as the latter three have very well developed, noticeably raised, and long frontal carinae compared to the much weaker frontal carinae seen in T. karthala.
The separation from the other five species, which appear closer to T. karthala, is also straightforward. Tetramorium camelliae has a strongly squamiform petiolar node which is around 2.8 to 3.0 times higher than long (LPeI 33-36) and around 2.3 to 2.4 times wider than long (DPeI 228-238), while T. karthala has a high nodiform petiolar node which is around 1.8 to 2.0 times higher than long (LPeI 50-54) and around 1.5 to 1.6 times wider than long (DPeI 148-158). The smallest species of the complex, T. rumo (HW 0.43-0.49; WL 0.56-0.67), differs from T. karthala (HW 0.51-0.55; WL 0.72-0.79) not only in body size but also in the shape of the petiolar node. The node of T. rumo is thinly cuneiform and moderately squamiform, in profile 2.3 to 2.7 times higher than long (LPeI 37-43) while, as noted above, the node of T. karthala is high nodiform and thicker, only 1.8 to 2.0 times higher than long (LPeI 50-54). Furthermore, in T. aspis the propodeal spines and lobes are strongly inclined towards each other, whereas the spines and lobes of T. karthala are not. The latter species also has two to four pairs of long, standing hairs on the dorsal pronotum and mesonotum while T. aspis has at least six on the pronotum and mesonotum and usually one or two on the anterior propodeum. The last species in the complex, T. cognatum, appears morphologically very close to T. karthala, but has noticeably shorter antennal scapes (SI 61-67) and propodeal spines (PSLI 12-16) than T. karthala .
To our knowledge, there is no significant intraspecific variation in T. karthala. Diagnosis. Tetramorium myrmidon can be easily distinguished from the other members of the group by the following combination of characters: eyes relatively large (OI 24-25); antennal scapes short (SI 74-76); frontal carinae well developed, noticeably raised, ending shortly before posterior head margin; petiolar node high rounded nodiform, in profile around 1.7 times higher than long (LPeI 58-60), in dorsal view around 1.2 to 1.3 times wider than long (DPeI 121-129); in dorsal view postpetiole around 1.3 to 1.5 times broader than petiolar node (PPI 133-141); dorsum of mesosoma with two pairs of long, standing hairs on pronotum and mesonotum.

Tetramorium myrmidon
Worker measurements ( Worker description. Head much longer than wide (CI 88-91); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae well developed, noticeably raised, diverging posteriorly, merging with surrounding sculpture shortly before posterior head margin. Antennal scrobes very weakly developed, almost absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 74-76). Eyes relatively large (OI 24-25). Mesosomal outline in profile flat to weakly convex, moderately low and long (LMI 38-40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, but weakly developed. Propodeal spines short to moderate, elongate-triangular, and acute (PSLI 18-20), propodeal lobes triangular and short, always much shorter than propodeal spines. Petiolar node in profile high nodiform with well rounded margins, around 1.7 times higher than long (LPeI 58-60), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height, anterodorsal margin slightly more angulate than posterodorsal, more rounded margin, petiolar dorsum relatively flat to weakly convex; node in dorsal view 1.2 to 1.3 times wider than long (DPeI 121-129), in dorsal view pronotum between 2.5 to 2.6 times wider than petiolar node (PeNI 39-40). Postpetiole in profile globular, between 1.3 to 1.4 times higher than long (LPpI 73-77); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 129-136), pronotum around 1.8 to 1.9 times wider than postpetiole (PpNI 52-55). Postpetiole in profile appearing more voluminous than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 133-141). Mandibles completely unsculptured, smooth, and shiny; clypeus irregularly longitudinally rugulose with three to seven rugulae, median ruga usually fully developed, one to three mostly unbroken lateral rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with seven to nine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, often interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured with ground sculpture only, lateral head reticulate-rugose to longitudinally rugulose. Ground sculpture on head well developed and distinct, mostly reticulate-punctate. Dorsum and sides of mesosoma irregularly longitudinally rugulose to reticulate-rugulose. Forecoxae dorsally weakly rugulose, but mostly unsculptured, smooth, and shining. Ground sculpture on mesosoma weakly to moderately punctate. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of standing, long, fine hairs; dorsum of mesosoma with two pairs only, one on anterior pronotum and one on anterior mesonotum; propodeum, waist segments, and first gastral tergite without any standing hairs; first gastral tergite with very short, scarce, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments, and gaster uniformly brown to dark brown, appendages yellowish to light brown.
Etymology. The name of the new species is inspired by the ancient Greek "myrmidons", which were skilled warriors and known as the legendary "ant-people" who inhabited the Greek island of Aegina. The species epithet is a noun in apposition, and thus invariant.
Distribution and biology. The new species is so far only known from Ambohijanahary, which is an isolated montane rainforest located in the midwest of Madagascar (Fig. 64), where it was collected only twice. With only six known specimens it represents an extremely rare species. Tetramorium myrmidon was collected from leaf litter at elevations of 1050 to 1100 m.
Discussion. Based on its larger body size and very well developed frontal carinae, T. myrmidon differs strongly from the smaller species T. aspis, T. camelliae, T. cognatum, T. karthala and T. rumo, all with more weakly developed frontal carinae, while being presumably morphologically closer to T. gladius, T. proximum and T. tenuinode. Of these, T. gladius possesses very small eyes , while the eyes of T. myrmidon are much larger . Tetramorium tenuinode has shorter antennal scapes (SI 66-70) and a thinner petiolar node, in profile 1.8 to 2.2 times higher than long (LPeI 45-54), in contrast to T. myrmidon with its longer scapes (SI 74-76) and lower and thicker petiolar node, which is in profile around 1.7 times higher than long (LPeI 58-60). The widespread T. proximum, however, appears to be the species morphologically closest to T. myrmidon and most of their morphometric ranges and characters overlap. Nonetheless, we consider both sufficiently demarcated from each other since they are found to co-occur in sympatry in Ambohijanahary. The specimens of T. proximum from this locality differ from T. myrmidon by having five to six pairs of long, standing hairs on the mesosoma and a generally thinner and higher petiolar node. Finally, T. myrmidon is unlikely to be confused with the last species of the complex, T. freya, since the latter lacks long, standing pilosity on the mesosomal dorsum (present in T. myrmidon).
Diagnosis. Tetramorium proximum can be distinguished from the other members of the species complex on the basis of the following character combination: eyes relatively large (OI 24-28); antennal scapes short (SI 74-76); frontal carinae strongly developed, noticeably raised, and reaching or ending shortly before posterior head margin; propodeal spines short to medium-sized, elongate-triangular, and usually acute ; petiolar node high rounded nodiform, in profile around 1.7 to 1.9 times higher than long (LPeI 52-60), and in dorsal view around 1.3 to 1.5 times wider than long (DPpI 135-153); mesosoma with four to nine pairs of long, fine, standing hairs, usually five or six ranging from anterior pronotum to metanotal groove. Worker description. Head much longer than wide (CI 89-94); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, noticeably raised, diverging posteriorly, and either reaching or ending shortly before posterior head margin. Antennal scrobes present and distinct but weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 74-76). Eyes relatively large (24-28). Mesosomal outline in profile flat to weakly convex, relatively low and long (LMI 37-40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weakly to moderately developed. Propodeal spines short to medium-sized, elongate-triangular, and usually acute (PSLI 17-21), propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high nodiform with well-rounded antero-and posterodorsal margins and strongly convex dorsum, around 1.7 to 1.9 times higher than long (LPeI 52-60), anterior and posterior faces approximately parallel, antero-and posterodorsal margins situated at about same height; petiolar node in dorsal view around 1.1 to 1.3 times wider than long (DPeI 111-130), in dorsal view pronotum around 2.4 to 2.7 times wider than petiolar node (PeNI 37-42). Postpetiole in profile subglobular and weakly anteroposteriorly compressed, around 1.4 to 1.5 times higher than long (LPpI 65-74); in dorsal view around 1.3 to 1.5 times wider than long (DPpI 135-153), pro-notum around 1.7 to 1.9 times wider than postpetiole (PpNI 52-61). Postpetiole in profile appearing approximately of same volume as petiolar node, and both nodes of approximately similar height; postpetiole in dorsal view between 1.3 to 1.6 times wider than petiolar node (PPI 135-160). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugose with usually three to five rugae, median ruga usually distinct and fully developed, sometimes partly reduced or broken, one or two weaker rugae present on each side; cephalic dorsum between frontal carinae longitudinally rugose with six to nine rugae, rugae running from posterior clypeal margin to posterior head margin, but often interrupted, splitting up or with cross-meshes; scrobal area mostly unsculptured; lateral head reticulate-rugose to longitudinally rugose. Ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma mostly reticulate-rugose with smaller proportions of irregularly longitudinally rugose sculpture medially; lateral mesosoma mostly irregularly longitudinally rugose. Forecoxae mostly unsculptured, smooth, and shining, sometimes with traces of ground sculpture. Ground sculpture on mesosoma usually weak to absent. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with four to nine pairs of long, fine, standing hairs, usually with five or six ranging from anterior pronotum to metanotal groove, rarely propodeum with one pair anteriorly; waist segments and first gastral tergite without any standing hairs; appressed pubescence on first gastral tergite highly variable: ranging from short to very short and relatively scarce to relatively long and dense. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with appressed, rarely decumbent, hairs. Head, mesosoma, waist segments, and gaster light brown to reddish brown, rarely of darker brown; mandibles, antennae, and legs lighter, usually light yellowish brown.
Distribution and biology. Tetramorium proximum has a very broad distribution in Madagascar, and is indeed found in most sampled rainforests or montane rainforests at elevations from 25 to 1680 m (Fig. 64). The southernmost locality is Andohahela in the southeast; from there the species ranges with few interruptions up to Montagne d'Ambre at the northern tip of Madagascar. In addition to the eastern and northern forest belt, T. proximum is also found in the few isolated humid forests located further west, such as Analavelona, Isalo, and Ambohijanahary. Tetramorium proximum appears to live in leaf litter.
Discussion. Tetramorium proximum is a very distinct species within the species complex. Due to its large body size (HW 0.65-0.81; WL 0.92-1.07) and strongly developed frontal carinae it cannot be mistaken for the five smaller species T. aspis, T. camelliae,T. cognatum,T. karthala,, all of which have weakly to moderately developed frontal carinae. Nor can T. proximum with its larger eyes (OI 24-28) and its long, standing pilosity on the dorsal mesosoma be confused with the smaller-eyed T. gladius  or T. freya, which lacks any standing pilosity on the mesosoma. The remaining two species, T. myrmidon and T. tenuinode, are both morphologically close and relatively similar to T. proximum. The separation of these three requires more attention.
Tetramorium tenuinode, despite sharing a superficially similar habitus, differs from T. proximum in a number of characters, and co-occurs with the latter species throughout most of its distribution range while both species maintain their speciesspecific differences. The main diagnostic character is the pilosity on the dorsal mesosoma, which consists of two pairs of long, standing hairs (one on anterior pronotum and one on anterior mesonotum) in T. tenuinode, while in T. proximum there are usually five to six pairs (rarely four or more than six) from anterior pronotum to posterior mesonotum. Furthermore, T. proximum has significantly longer antennal scapes (SI 74-77) than T. tenuinode , and is normally a darker colour. Also, T. tenuinode generally has a thinner petiolar node in lateral view that is around 1.8 to 2.2 times higher than long (LPeI 45-54), while the node of T. proximum is around 1.7 to 1.9 times higher than long (LPeI 52-60). There is some overlap in these morphometric ranges, but there is a strong general trend towards a much thinner node in T. tenuinode, which together with the other characters mentioned above works very well in distinguishing both species. The remaining species, T. myrmidon, might be confused with T. proximum since they share most morphological characters and their morphometric ranges overlap. Nevertheless, T. myrmidon is only found in Ambohijanahary where it co-occurs with T. proximum, and there they are both easily separable based on mesosomal pilosity (two pairs in T. myrmidon vs. five or six in T. proximum) and petiolar node height.
Tetramorium proximum is a relatively variable species with respect to certain characters. The greatest variation can be seen in gastral pubescence, which is always strongly appressed, but can vary from very short and scarce to relatively long and dense. Often this variation can be observed within the same locality or series, sometimes all specimens from one locality have short pubescence while populations from other localities have long pubescence. However, it seems that there is also a geographical component to this variation. The material from the southeast has predominantly long and dense pubescence, and the form with short pubescence is relatively rare, but still present. The material from central eastern Madagascar is a well-balanced mix of short and long pubescence. Interestingly, the material from the northeast, north, and the isolated forests in the west possesses almost exclusively short and scarce pubescence. Another, even though less variable character, is the shape of the petiolar node, which is high nodiform with a rounded dorsum, but can vary in height or thickness from population to population. Furthermore, some populations have fewer or more pairs of long, standing hairs on the mesosomal dorsum. The most common count is five to six pairs ranging throughout most of the distribution range, but in some localities one can see only four pairs while in others six to seven, and in a few series seven to eight pairs are common. The variation observed in T. proximum is not surprising, however, due to its wide distribution and commonness. Compared to other widely distributed and common Malagasy or Afrotropical Tetramorium species, this species actually shows much less variation.  Enakara, 24.56667°S, 46.81667°E, 420-430 m, rainforest, 15.-22.XI.1992 (B.L. Fisher); Toliara, Rés. Andohahela, 13 km NW Enakara, 24.55°S, 46.8°E, 1250m, montane rainforest, 30.XI.1992; Toliara, Rés. Andohahela, 6 km SSW Eminiminy, 24.73333°S, 46.8°E, 330 m, rainforest, 4.II.1993 (P.S. Ward); Toliara, Parc National Andohahela, Col de Tanatana, 33.3 km NW Tolagnaro, 24.7585°S, 46.85367°E, 275 m, rainforest, 28.XI.2006 (B.L. Fisher et al.); Toliara, Andohahela, 24.77639°S, 46.70528°E, 320 m, 9.XII.2007 (A. Ballerio); Toliara, Forêt Ivohibe, 55.0 km N Tolagnaro, 24.569°S, 47.204°E, 200 m, rainforest, 2.-4.XII.2006 (B.L. Fisher et al.).
Diagnosis. Tetramorium rumo can be well recognised within the T. cognatum species complex on the basis of the following character combination: very large eyes (OI 28-31); antennal scapes very short (SI 60-66); propodeal spines moderately long, elongate-triangular to spinose, and usually acute ; propodeal spines and lobes not strongly inclined towards each other; petiolar node thinly cuneiform and moderately squamiform, in profile around 2.3 to 2.7 times higher than long (LPeI 37-43), in dorsal view between 1.5 to 1.7 times wider than long (DPeI 156-171); mesosoma either with at least seven pairs of long, standing hairs on pronotum and mesonotum and propodeum sometimes with one pair anteriorly, or with just two pairs of long, standing hairs, one on anterior pronotum and one on anterior mesonotum.
Worker measurements ( Worker description. Head much longer than wide (CI 88-91); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae very weakly developed, only feebly raised, usually ending shortly after posterior eye margin or merging with cephalic sculpture halfway between posterior eye margin and posterior head margin. Antennal scrobes very weak to absent, very shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 60-66). Eyes very large (OI 28-31). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36-38), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove very weak to absent. Propodeal spines moderately long, elongate-triangular to spinose, and usually acute , propodeal lobes triangular and short, always much shorter than propodeal spines, in profile spines and lobes not strongly inclined towards each other. Petiolar node thinly cuneiform and moderately squamiform, in profile around 2.3 to 2.7 times higher than long (LPeI 37-43), anterior and posterior faces not parallel, anterodorsal margin usually situated higher and more strongly angled than posterodorsal margin, petiolar dorsum relatively flat to weakly convex and tapering backwards posteriorly; node in dorsal view between 1.5 to 1.7 times wider than long (DPeI 156-171), in dorsal view pronotum around 2.6 to 2.8 times wider than petiolar node (PeNI 35-39). Postpetiole in profile globular, between 1.3 to 1.5 times higher than long (LPpI 68-75); in dorsal view around 1.4 to 1.5 times wider than long (DPpI 138-152), pronotum around 1.8 to 1.9 times wider than postpetiole (PpNI 51-56). Postpetiole in profile appearing shorter and thicker than petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node (PPI 141-152). Mandibles completely unsculptured, smooth, and shiny; clypeus weakly irregularly longitudinally rugulose, median rugula usually present but rarely fully developed, one or two mostly broken lateral rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with eight to eleven fine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, often irregularly shaped, interrupted or with cross-meshes; scrobal area mostly unsculptured; lateral head mainly longitudinally rugulose to reticulaterugulose, but larger areas often only weakly sculptured and appearing fairly smooth and shiny. Ground sculpture on head variable, ranging from weakly developed or absent to moderately punctate. Dorsum of mesosoma mostly longitudinally rugulose; lateral mesosoma mostly unsculptured with smaller, irregularly longitudinally rugulose or reticulate-rugulose areas. Ground sculpture on mesosoma very weak to absent. Forecoxae usually unsculptured, smooth, and shining. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; pilosity on dorsal mesosoma variable: southern populations with at least seven pairs on pronotum and mesonotum, propodeum sometimes with one pair anteriorly, and northern populations with only two pairs, one on anterior pronotum and one on anterior mesonotum; waist segments and first gastral tergite without any standing hairs; first gastral tergite with short, dense, appressed (rarely decumbent) pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Body usually uniformly whitish yellow to light brown, very rarely darker.
Etymology. The new species is named after the fictional character "Rumo" from Walter Moers' fantasy novel "Rumo and His Miraculous Adventures". Tetramorium rumo is a very bright species, almost white, with distinct propodeal spines reminiscent of "Rumo", who is a white wolperting with short but acute horns. The species epithet is an arbitrary combination of letter, thus invariable.
Distribution and biology. The new species is another rainforest inhabitant mainly found in eastern Madagascar (Fig. 64). However, the distribution range is somewhat unusual since T. rumo is found in the southeast from Andohahela to Ranomafana, and then much further north from Perinet to Betampona. The reasons for this patchy distribution are unclear. Tetramorium rumo was mainly sampled in rainforests, rarely montane rainforests or littoral rainforests, at elevations ranging from 20 to 1250 m. In addition, T. rumo appears to live in leaf litter.
Discussion. Tetramorium rumo is very unlikely to be confused with the much larger species T. freya, T. gladius, T. myrmidon, T. proximum, and T. tenuinode. All the latter species, except T. freya, also have very well developed frontal carinae, which contrast with the reduced and very weak frontal carinae seen in T. rumo. Tetramorium freya has weaker frontal carinae than the other four species, but in contrast to T. rumo this species does not have any standing pilosity on the mesosomal dorsum. Furthermore, T. gladius has very small eyes (OI 19-20) compared to T. rumo, which has very large eyes (OI 28-31). The remaining four species of the T. cognatum complex are morphologically much closer to T. rumo than the five species mentioned above. However, T. camelliae is easily separable from T. rumo on the basis of the petiolar node shape, which is strongly squamiform and transverse in the former (LPeI 33-36; DPeI 228-238), contrasting with the highly nodiform to thinly cuneiform node of the latter (LPeI 37-43; DPeI 156-171). Tetramorium aspis and T. karthala both have longer antennal scapes (SI 68-74), shorter propodeal spines , thicker and lower petiolar nodes in profile (LPeI 46-54), and less transverse nodes in dorsal view (DPeI 146-161) compared to T. rumo . In addition, T. aspis has propodeal spines and lobes strongly inclined towards each other, an arrangement absent in T. rumo, and T. karthala is only found on the Comorian island of Grand Comore while T. rumo is distributed in Madagascar. The last species of the T. cognatum complex, T. cognatum itself, is probably the closest relative of T. rumo within the complex, and without careful examination they could be confused in some cases. However, both differ clearly in propodeal spine length and petiolar node shape. Tetramorium rumo has relatively long and spinose propodeal spines  which contrast with the much more reduced, short, and triangular teeth of T. cognatum . Also, the thinly cuneiform petiolar node of T. rumo, which is 2.3 to 2.7 times higher than long (LPeI 37-43) and around 1.6 to 1.7 times wider than long (DPeI 156-171), discriminates it from T. cognatum, in which the node is 1.8 to 2.0 times higher than long (LPeI 49-55) and around 1.3 to 1.4 times wider than long (DPeI 129-142).
Nonetheless, the species most similar to T. rumo is likely T. rala from the T. schaufussi complex. Both species share a very similar habitus. Compared to all other species of the T. schaufussi species group, they are smaller in size, have relatively longer propodeal spines, a high nodiform to thinly cuneiform petiolar node, lack standing pilosity on the waist segments, and possess very bright body colouration. We have placed them in different species complexes on the basis of the presence (T. rala) or absence (T. rumo) of standing pilosity on the first gastral tergite, but otherwise these two species could be easily confused. However, despite the very strong similarities, substantial differences separate these species from each other. Most obviously, the petiolar node of T. rumo is thinner and stronger anteroposteriorly compressed, in profile around 2.3 to 2.7 times higher than long (LPeI 37-43), and in dorsal view between 1.5 to 1.7 times wider than long (DPeI 156-171). By contrast, T. rala has a node in profile is 2.0 to 2.2 times higher than long (LPeI 45-50), and in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145). Also, T. rumo has larger eyes (OI 28-31) than T. rala . In addition, their distribution ranges strongly overlap in central-eastern Madagascar and both species maintain their species identities without intermediate forms.

Tetramorium tenuinode
Diagnosis. The following character set clearly distinguishes T. tenuinode from the remainder of the T. cognatum species complex: eyes relatively large (OI 25-27); antennal scapes very short (SI 66-70); frontal carinae well developed, noticeably raised, and approaching or ending at posterior head margin; petiolar node high rounded nodiform, in profile around 1.8 to 2.2 times higher than long (LPeI 45-54), in dorsal view around 1.3 to 1.4 times wider than long (DPeI 125-143); mesosoma with only two pairs of long, standing hairs, one on anterior pronotum and one on anterior mesonotum. Worker description. Head longer than wide (CI 91-93); in full-face view posterior head margin weakly to moderately concave. Anterior clypeal margin with distinct median impression. Frontal carinae well developed, noticeably raised, diverging posteriorly, approaching or ending at posterior head margin. Antennal scrobes weakly developed, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 66-70). Eyes relatively large . Mesosomal outline in profile flat to weakly convex, moderately low and long (LMI 38-40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove very weak to absent. Propodeal spines short to moderately long, usually elongate-triangular, and acute (PSLI 17-24), propodeal lobes short and triangular, always much shorter than propodeal spines. Petiolar node in profile high rounded nodiform and relatively thin, around 1.8 to 2.2 times higher than long (LPeI 45-54), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins usually situated at about same height and moderately rounded, petiolar dorsum distinctly convex; petiolar node in dorsal view around 1.2 to 1.4 times wider than long (DPeI 125-143), in dorsal view pronotum between 2.4 to 2.8 times wider than petiolar node (PeNI 36-42). Postpetiole in profile subglobular and weakly anteroposteriorly compressed, around 1.4 to 1.7 times higher than long (LPpI 60-72); in dorsal view between 1.4 to 1.7 times wider than long (DPpI 143-168), pronotum around 1.6 to 1.7 times wider than postpetiole (PpNI 57-64). Postpetiole in profile appearing more voluminous than petiolar node, postpetiole in dorsal view around 1.5 to 1.7 times wider than petiolar node (PPI 148-167). Mandibles completely unsculptured, smooth, and shiny; clypeus irregularly longitudinally rugose/rugulose with two to seven rugae/rugulae, median ruga rarely fully developed, usually broken, most other rugulae usually broken, sometimes merging with each other; cephalic dorsum between frontal carinae longitudinally rugose, usually with six to seven, rarely eight or nine rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted, splitting up or with cross-meshes, especially posteriorly; scrobal area partly unsculptured, but mostly merging with surrounding longitudinally rugose to reticulate-rugose sculpture present on lateral head. Ground sculpture on head weakly to moderately punctate. Dorsum and sides of mesosoma reticulate-rugose/rugulose to irregularly longitudinally rugose/rugulose, lateral pronotum sometimes only weakly sculptured and relatively smooth and shining. Forecoxae mostly unsculptured, smooth and shining, sometimes with traces of ground sculpture. Ground sculpture on mesosoma usually weak to absent. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; dorsum of mesosoma with two pairs only, one on anterior pronotum and one on anterior mesonotum; propodeum, waist segments and first gastral tergite without any standing hairs at all; first gastral tergite with very short, scarce, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with appressed, rarely decumbent, hairs. Head, mesosoma, waist segments and gaster usually uniformly chestnut brown to very dark brown, sometimes of lighter reddish brown; appendages usually of slightly lighter brown than remainder of body.
Etymology. The name of the new species is a combination of the Latin adjective "tenuis", meaning thin, and the Latin noun "nodus", meaning node.
Distribution and biology. Tetramorium tenuinode is widely distributed in eastern Madagascar (Fig. 64). It is found with few interruptions in an almost straight line from Grand Lavasoa and Andohahela in the southeast to Ambanitaza in the northeast. The new species clearly prefers rainforests and montane rainforests at elevations from 25 to 1200 m, even though it was also collected several times from guava forest and urban gardens. In addition, T. tenuinode appears to be a leaf litter inhabitant since almost all of the material was collected from this microhabitat.
Discussion. This new species is easily identifiable within its species complex. The presence of well developed, raised, and long frontal carinae separates T. tenuinode from the species T. aspis, T. camelliae, T. cognatum, T. karthala, and T. rumo. These five species are generally also much smaller (WL 0.56-0.81) than T. tenuinode (WL 0.76-0.94). Also, T. tenuinode possesses much larger eyes (OI 25-27) than T. gladius  and much shorter antennal scapes (SI 66-70) than T. myrmidon and T. proximum . Lastly, the presence of two pairs of long, standing hairs on the dorsal mesosoma distinguishes T. tenuinode from T. freya, which lacks any standing hairs on the dorsal mesosoma. The latter species also displays weaker sculpture on the head and mesosoma than T. tenuinode. It should be noted, however, that T. tenuinode is morphologically still very close to T. proximum, and on very superficial observation it is possible to confuse both. At the initial stage of the revision we considered T. tenuinode conspecific with T. proximum, a very variable species. However, after the detailed examination of more than five hundred pinned workers, it became apparent that the material consisted of these two fairly distinct species. Indeed, even though T. proximum is more broadly distributed than T. tenuinode, both co-occur in sympatry throughout most of their respective distribution ranges, and both are always very well distinguishable. The most obvious character to separate both species is pilosity on the dorsal mesosoma. In T. tenuinode this consists of two pairs of long, standing hairs only, one on anterior pronotum and one on anterior mesonotum, which contrasts with the usually five to six (rarely four or more than six) pairs found from anterior pronotum to posterior mesonotum in T. proximum. In addition to mesosomal pilosity and the shorter antennal scapes mentioned above, T. tenuinode usually also has a thinner petiolar node in profile, which is around 1.8 to 2.2 times higher than long (LPeI 45-54), while the node of T. proximum is around 1.7 to 1.9 times higher than long (LPeI 52-60). The identification key presented above might suggest that T. tenuinode can be easily confused with T. myrmidon, but this is not the case since the two species differ in a number of characters. Among others, T. tenuinode has a broader head (CI 91-93), shorter antennal scapes (SI 66-70), and a higher petiolar node (LPeI 45-54) than T. myrmidon .
In contrast to the more variable T. proximum, T. tenuinode has little observed intraspecific variation. Some populations vary very slightly in propodeal spine length, thickness of the petiolar node, or body colouration.

Tetramorium schaufussii species complex
Comments. This complex contains ten species, which are characterised and distinguishable from the T. cognatum species complex by their presence of standing pilosity on the first gastral tergite. All species are endemic to Madagascar, except T. schaufussii, which is also known from Reunion. Also, they inhabit rainforests or montane rainforests and are only occasionally found in other habitats. The taxonomy of this species complex is challenging. Some species like T. nassonowii, T. pseudogladius, T. rala or T. scutum are relatively easily recognisable due to species-specific character states, but this is not true for the rest of the complex. Tetramorium schaufussii and T. xanthogaster are especially widespread species with high degrees of intraspecific variation, which causes a number of problems for the delimitation of species boundaries for most member of the complex. Intriguingly, only two species of this complex have very limited distribution ranges: T. scutum is only known from Ivohibe and T. pseudogladius from Zahamena. The remainder are all much more widespread.

Identification key to species of the T. schaufussii species complex (workers)
1 Petiolar node relatively long and low, in profile around 1.2 to 1.4 times higher than long (LPeI 72-81) and in dorsal view between 1.0 to 1.2 times longer than wide (DPeI 87-98) (Fig. 40A) [Madagascar] ................. T. nassonowii -Petiolar node shorter and higher than above, in profile around 1.5 to 2.2 times higher than long (LPeI 45-67) and in dorsal view between 1.1 to 1.5 times wider than long (DPeI 109-154) (Fig. 40B, C)  Eyes relatively small (OI 20) (Fig. 41A) [Madagascar]. ......T. pseudogladius -Eyes usually much larger than above (OI 25-28, rarely OI 22-24) (Fig. 41A Smaller species (HW 0.46-0.49; WL 0.58-0.64); propodeal spines relatively long (PSLI 21-25); petiolar node thinly cuneiform, in profile 2.0 to 2.2 times higher than long (LPeI 45-50); waist segments without long, standing pilosity; body colour whitish yellow to light brown (Fig. 43A) [Madagascar] .......T. rala -Character combination never as above, larger species (HW 0.53-0.84; WL 0.70-1.20) with relatively short propodeal spines/teeth, which are always shorter than above (PSLI 8-18); petiolar node variably shaped but always lower than above, in profile around 1.5 to 1.9 times higher than long (LPeI 52-67); waist segments with or without long, standing pilosity; body colour variable (Fig. 43A Dorsum of promesonotum always with more than four pairs of long, standing hairs; waist segments always with standing pilosity (Fig. 45B, C, D) ........... 7 7 Bicoloured species, head and/or mesosoma very dark brown to black and strongly contrasting with yellow to light brown waist segments and gaster (rarely also mesosoma) (Fig. 46A Head relatively shorter and thicker (CI 92-95); clypeus usually with either median area unsculptured or traces of median ruga present but weakly developed and irregularly shaped (Fig. 47C, D), very rarely with a well-developed longitudinal ruga (Fig. 47E)  Frontal carinae relatively better developed; cephalic dorsum between frontal carinae with nine to thirteen relatively regularly shaped, mostly unbroken rugae; propodeal spines short to medium-sized (PSLI 18-22) (Fig. 48A Frontal carinae relatively more weakly developed; cephalic dorsum between frontal carinae with six to ten relatively irregularly shaped, often meandering or broken rugulae; propodeal spines reduced to short to very short teeth/ denticles (PSLI 8-16) (Fig. 48C, D)           Diagnosis. The following character combination separates T. merina from the remaining species of the T. schaufussii complex: larger species (HW 0.69-0.79; WL 1.01-1.10); head longer than wide (CI 92-95); eyes relatively large (OI 26-28); frontal carinae usually weakly developed, only slightly raised, often not better developed than cephalic rugulae, and usually fading out halfway between posterior eye margin and posterior head margin; propodeal spines reduced to very short triangular teeth/ denticles (PSLI 8-11), propodeal lobes short and triangular, always appearing more voluminous than propodeal teeth, and spines and lobes not strongly inclined towards each other; petiolar node rounded nodiform to rounded high nodiform, in profile around 1.6 to 1.8 times higher than long (LPeI 57-64), in dorsal view around 1.2 times wider than long (DPeI 117-124); dorsum of promesonotum with at least ten pairs of long, fine, standing hairs, propodeum without standing pilosity, and both waist segments with few long pairs each; body uniformly light to dark brown, gaster often darker, appendages usually lighter. Worker description. Head longer than wide (CI 92-95); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae usually weakly developed, only slightly raised, often not better developed than cephalic rugulae, and usually fading out halfway between posterior eye margin and posterior head margin. Antennal scrobes present but weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 72-75). Eyes relatively large . Mesosomal outline in profile flat to weakly convex, comparatively low and elongate (LMI 36-38), weakly marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove very weakly developed to absent. Propodeal spines reduced to very short, triangular, and acute or blunt teeth/denticles (PSLI 8-11), propodeal lobes short, triangular, and acute or blunt, always appearing more voluminous than propodeal teeth, spines and lobes not strongly inclined towards each other. Petiolar node in profile nodiform to high nodiform with well-rounded antero-and posterodorsal margins, around 1.6 to 1.8 times higher than long (LPeI 57-64), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height, petiolar dorsum weakly to moderately convex; petiolar node in dorsal view around 1.2 times wider than long (DPeI 117-124), in dorsal view pronotum between 2.3 to 2.7 times wider than petiolar node (PeNI 36-43). Postpetiole in profile globular, approximately 1.3 to 1.4 times higher than long (LPpI 71-80); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 128-136), pronotum between 1.8 to 2.0 times wider than postpetiole (PpNI 50-56). Postpetiole in profile appearing slightly lower or of same height but thicker than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 125-142). Mandibles unsculptured, smooth, and shiny; clypeus weakly longitudinally rugulose with two to five lateral rugulae, median area usually completely unsculptured or only weakly sculptured, median ruga usually absent, at most traces present, lateral rugulae often interrupted or irregularly shaped, but at least one lateral rugula well developed on each side; cephalic dorsum between frontal carinae irregularly longitudinally rugulose with eight to ten rugulae; rugulae running from posterior clypeal margin to posterior head margin, often meandering, broken or with cross-meshes; scrobal area mostly unsculptured and laterally merging with surrounding reticulate-rugose sculpture present on lateral head; ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma reticulate-rugose, especially anteriorly, to irregularly longitudinally rugose, lateral mesosoma mostly irregularly longitudinally rugose; ground sculpture on mesosoma weak to absent. Forecoxae mainly unsculptured, smooth, and shining. Waist segments and gaster unsculptured, smooth, and shining. Dorsum of head with numerous pairs of long, fine, standing hairs; dorsum of mesosoma with at least eleven or twelve pairs of long, standing hairs ranging from anterior pronotum to posterior mesonotum, propodeum without long, standing pilosity; petiole usually with two pairs and postpetiole with three to four pairs; first gastral tergite with short, scarce, appressed pubescence in combination with abundant, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Body uniformly light brown to dark brown, gaster often of darker brown, appendages usually lighter.
Etymology. The new species is named for the Merina people of Madagascar, in honor of their culture and language. The distribution range of T. merina fits the boundaries of the traditional Merina kingdom very well. The species epithet is an arbitrary combination of letters, thus invariant.
Distribution and biology. Tetramorium merina is only known from the Central Highlands of Madagascar (Fig. 65). Its distribution ranges from the two southernmost localities Atsirakambiaty and Ankazomivady through Manjakatompo north to Andranomay, Ambohitantely and Sohisika. All localities are montane rainforests situated at elevations of 1410 to 1700 m, where T. merina appears to live in leaf litter.
Discussion. Tetramorium merina is only moderately distinct within the T. schaufussii complex, and can be confused with several other species. The possession of large eyes (OI 26-28) separates T. merina from T. pseudogladius (OI 20), and the petiolar node, which in dorsal view is around 1.2 times wider than long (DPeI 117-124) distinguishes it from T. nassonowii since the petiolar node of the latter in dorsal view is between 1.0 to 1.2 times longer than wide (DPeI 87-98). Tetramorium merina with its very short propodeal teeth (PSLI 8-11) is also not likely to be mistaken for T. scutum, which possesses much longer propodeal spines  and relatively well-developed propodeal lobes. Also, in T. scutum the propodeal spines and lobes are strongly inclined towards each other, a condition absent in T. merina. Tetramorium rala, which is also the smallest species of the complex (HW 0.46-0.49; WL 0.58-0.64), has relatively long propodeal spines , and the body is very bright yellowish to light brown, and thus not confusable with T. merina. In addition, the latter has numerous pairs of long, fine, standing hairs on each waist segment distinguishing it from T. sikorae, which lacks any standing pilosity on the waist segments.
The species closest to T. merina are T. monticola, T. obiwan, T. schaufussii, and T. xanthogaster, and the differentiation between these is sometimes challenging. Tetramorium merina is a relatively large species (HW 0.69-0.79; WL 1.01-1.10) and could be confused with T. obiwan, which is in the same size range or even larger (HW 0.71-0.84; WL 1.00-1.20), or T. xanthogaster, which is usually smaller but reaches its upper size limit in the range of T. merina ). However, T. obiwan has longer antennal scapes (SI 77-82), better-developed frontal carinae, and usually no standing pilosity on the waist segments contrasting with the shorter antennal scapes (SI 72-75), much weaker frontal carinae and the presence of several pairs of standing pilosity on the waist segments of T. merina. Furthermore, T. xanthogaster, despite being a very variable species throughout its range, can be easily separated from T. merina in the central Highlands where they are usually found occurring in sympatry. In this region T. xanthogaster is always strongly bicoloured with head and mesosoma very dark brown to black, strongly contrasting with the yellow to light brown waist segments and gaster. Also, T. xanthogaster usually has long, fine, standing pilosity on the propodeal dorsum while T. merina lacks any standing pilosity on the propodeum. Few other diagnostic characters separate both species, but the fact that they co-occur in sympatry in several localities without any intermediate forms is a good indication of their heterospecificity. Tetramorium monticola, which is found in the northeast and north of Madagascar, does not co-occur with T. merina, and both are relatively easy to differentiate. In T. monticola the frontal carinae are relatively better developed, the cephalic dorsum between them has nine to thirteen relatively regularly shaped, mostly unbroken rugae, and the propodeum is armed with short to medium-sized spines  while T. merina has much weaker frontal carinae with eight to ten, often broken and irregular rugulae, and the propodeum is only armed with small teeth/ denticles .
The most difficult species to separate from T. merina is certainly T. schaufussii. As is the case with T. xanthogaster, T. merina is also found regularly in sympatry with T. schaufussii, and again, they are separable based on a few characters. Tetramorium merina is larger in size (HW 0.69-0.79; WL 1.01-1.10), has a broader head , and longer (though not significantly so) antennal scapes (SI 72-75) than T. schaufussii . These differences seem difficult to assess without measuring, except for body size, which however, can vary from one population to another and therefore should only be used with caution. Nevertheless, where the two species are found in sympatry (often they are found within the same litter sample) they can be easily discriminated based on body size. In contrast to T. schaufussii and T. xanthogaster, which are both very variable species, T. merina is very stable in its morphological appearance. Type material. Holotype, pinned worker, MADAGASCAR, Antsiranana, Betaolana Forest, along Bekona River, 14.52996°S, 49.44039°E, 880 m, rainforest, ex rotten log, collection code BLF22473, 4.III.2009 (B.L. Fisher et al.) (CAS: CASENT0152401). Paratypes, 1 pinned worker with same data as holotype (CAS: CASENT0152402); three pinned workers with same data as holotype except collection codes BLF22465, BLF22486, and BLF22504 (CAS: CASENT0151864; CASENT0151868; CASENT0152427); and four pinned workers with same data as holotype except collection date 5.III.2009 and collection codes BLF22612, BLF22644, and BLF22667 (BMNH: CASENT0151589; CAS: CASENT0151590; CASENT0151949; MCZ: CASENT0152285).
Worker description. Head longer than wide (CI 92-94); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae usually well developed, moderately raised on anterior half, strongly diverging posteriorly, and usually approaching or ending at posterior head margin. Antennal scrobes usually weakly developed, shallow and without clear and distinct posterior and ventral margins, sometimes scrobe better developed, slightly deeper and with weak posterior, and rarely even ventral margin. Antennal scapes very short, not reaching posterior head margin . Eyes relatively large . Mesosomal outline in profile flat to weakly convex, comparatively low and elongate , weakly marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weakly to moderately developed, sometimes slightly impressed, but mostly moderately deep. Propodeal spines of moderate length, elongate-triangular to spinose, and usually acute (PSLI 8-11), propodeal lobes short, triangular, and usually blunt, always much smaller than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high nodiform to high cuneiform, around 1.7 to 2.0 times higher than long (LPeI 50-60), anterior and posterior faces approximately parallel, anterodorsal margin always higher and more angled than posterodorsal margin, petiolar dorsum usually weakly convex and tapering backwards posteriorly; petiolar node in dorsal view around 1.2 to 1.3 times wider than long (DPeI 124-133), in dorsal view pronotum between 2.4 to 2.7 times wider than petiolar node (PeNI 37-42). Postpetiole in profile globular, approximately 1.3 to 1.4 times higher than long (LPpI 71-78); in dorsal view around 1.3 to 1.5 times wider than long (DPpI 131-153), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 54-60). Postpetiole in profile appearing always lower and having less volume than petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node . Mandibles unsculptured, smooth, and shiny; clypeus usually longitudinally rugulose with two to six rugulae, median area usually either completely unsculptured without median rugula or only weakly sculptured with traces of median rugula, very rarely median rugula fully developed, lateral rugulae usually well developed and unbroken, sometimes irregularly shaped or broken; cephalic dorsum between frontal carinae longitudinally rugose with nine to thirteen rugae; rugae running from posterior clypeal margin to posterior head margin, generally very regularly shaped and only rarely broken or with cross-meshes; scrobal area partly unsculptured and laterally merging with surrounding longitudinally rugulose to reticulate-rugose sculpture present on lateral head; ground sculpture on head usually moderately punctate. Dorsum of mesosoma usually longitudinally rugose, sometimes irregularly so; lateral mesosoma irregularly longitudinally rugose to reticulate-rugose, sometimes lateral pronotum with less sculpture; ground sculpture on mesosoma weak to absent. Forecoxae always unsculptured, smooth and shining. Waist segments and gaster unsculptured, smooth, and shining. Dorsum of head with numerous pairs of long, fine, standing hairs; dorsum of promesonotum with at least ten pairs of long, standing hairs ranging from anterior pronotum to posterior mesonotum, propodeum usually without long, standing pilosity, sometimes with one or two shorter pairs of hairs; petiole usually with at least two pairs and postpetiole with at least three to four pairs; first gastral tergite with short, scarce to abundant, decumbent to appressed pubescence in combination with abundant, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with decumbent to suberect hairs. Body uniformly dark yellow to orange light brown, gaster sometimes of darker brown, appendages usually slightly lighter.
Etymology. The name of the new species is a Latin noun and means "inhabitant of the mountains" referring to the fact that T. monticola is predominantly found in higher elevation montane forests. The species epithet is a nominative noun, and thus invariant.
Distribution and biology. Tetramorium monticola is distributed in the northeast and north of Madagascar (Fig. 65). The distribution range is outlined by Manongarivo in the west, the northernmost locality Makirovana, and the easternmost Ambanizana on the Masoala Peninsula. Most of the material available was collected in that triangle, but T. monticola is also known from Zahamena and Sandranantitra, which are located much further south. All localities are rainforests or montane rainforests situated at elevation ranging from 415 to 2000 m. Also, it seems that T. monticola lives in leaf litter.
Discussion. Tetramorium monticola is well recognisable within the T. schaufussii complex. It differs from T. pseudogladius (OI 20) by its much larger eye size (OI 24-28), and from T. scutum by having propodeal spines and lobes not strongly inclined towards each other. Also, T. monticola (DPeI 124-133; LPeI 50-60) is very unlikely to be confused with T. nassonowii, which has a much longer and lower petiolar node (DPeI 87-98; LPeI 72-81). In addition, T. monticola is a relatively hairy species with long pilosity all over the body, which separates it from the few species with partly reduced pilosity, such as T. rala, T. sikorae, and T. obiwan, which all usually lack standing pilosity on the propodeum and waist segments, except in T. obiwan, where the petiole or postpetiole occasionally have a few long hairs. Nevertheless, T. monticola cannot be mistaken for T. obiwan. The latter is of larger body size (HW 0.71-0.84; WL 1.00-1.20), has longer antennal scapes (SI 77-82), and has a petiolar node with the antero-and posterodorsal margins situated at about the same height and well rounded. Tetramorium monticola is much smaller than that (HW 0.51-0.67; WL 0.67-0.88), has shorter antennal scapes (SI 67-74), and its petiolar node has the anterodorsal margin always higher and a little bit more angled than the posterodorsal margin with the petiolar dorsum tapering backwards.
The remaining three species, T. merina, T. schaufussii, and T. xanthogaster, are morphologically closer to T. monticola, and their separation requires more attention. Tetramorium schaufussii can be easily mistaken for T. monticola in northern Madagascar where both are sympatric, but T. schaufussii differs from T. monticola (and the other two) by having a much longer and thinner head in full-face view . The other two species, T. merina and T. xanthogaster, usually have shorter, and in the case of T. merina much shorter, propodeal spines (PSLI 8-16) than T. monticola . However, since the spine length is somewhat variable in the latter species, this character cannot be the sole distinguishing feature. In addition, T. monticola also differs from the other two by having relatively better developed frontal carinae and the cephalic dorsum between them with nine to thirteen relatively regularly shaped, mostly unbroken rugae. Tetramorium merina and T. xanthogaster have relatively weaker developed, and often shorter, frontal carinae and a cephalic dorsum with six to ten relatively irregularly shaped, often meandering or broken rugulae. [Note 1: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own geo-referencing of the Foret d' Andrangoloaca and should be considered as an approximation and not the exact position of the type locality.]
Diagnosis. Tetramorium nassonowii is clearly recognisable within the T. schaufussii complex on the basis of its petiolar node shape, which is relatively long and low, in profile around 1.2 to 1.4 times higher than long (LPeI 72-81) and in dorsal view between 1.0 to 1.2 times longer than wide (DPeI 87-98).
Worker measurements ( Worker description. Head clearly longer than wide (CI 90-92); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly to moderately developed, moderately raised, diverging posteriorly, and usually fading out halfway between posterior eye margin and posterior head margin or approaching posterior head margin. Antennal scrobes present but weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin . Eyes moderate to large . Mesosomal outline in profile flat to weakly convex, comparatively low and long , weakly to moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weakly developed or absent. Propodeal spines reduced to very short teeth (PSLI 7-11), propodeal lobes short, triangular, and blunt or acute, usually longer than propodeal spines, rarely as long as propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node rounded nodiform, in profile around 1.2 to 1.4 times higher than long (LPeI 72-81), anterior and posterior faces not parallel, anterodorsal and posterodorsal margins situated at about same height, petiolar dorsum distinctly convex; node in dorsal view weakly longer than wide (DPeI 92-96), in dorsal view pronotum between 2.5 to 2.8 times wider than petiolar node (PeNI 36-40). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 75-82); in dorsal view around 1.2 to 1.3 times wider than long (DPpI 122-134), pronotum between 1.8 to 2.0 times wider than postpetiole (PpNI 50-55). Postpetiole in profile appearing more or less of same volume as petiolar node, postpetiole in dorsal view around 1.3 to 1.5 times wider than petiolar node . Mandibles unsculptured, smooth, and shiny; clypeus weakly longitudinally rugulose with three to seven rugulae, rugulae often interrupted or irregularly shaped, median area often weakly sculptured, median ruga usually absent or mostly reduced, very rarely fully developed; cephalic dorsum between frontal carinae irregularly longitudinally rugose/rugulose with six to nine rugae/rugulae; rugae/ rugulae running from posterior clypeal margin to posterior head margin, often meandering, broken or with cross-meshes; scrobal area mostly unsculptured and laterally merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral head; ground sculpture on head weak to absent. Dorsum of mesosoma irregularly longitudinally rugose to reticulate-rugose, lateral mesosoma mostly irregularly longitudinally rugose; ground sculpture on mesosoma weak to absent. Forecoxae mainly unsculptured, smooth and shining. Waist segments and gaster unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; dorsum of mesosoma with at least six or seven pairs of long, standing hairs ranging from anterior pronotum to posterior mesonotum, propodeum without long, standing pilosity; petiole with one pair and postpetiole with one or two pairs; first gastral tergite with short, scarce, appressed pubescence in combination with scattered, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Body uniformly light brown to dark brown colour, appendages often lighter.
Distribution and biology. Tetramorium nassonowii is distributed in the montane rainforests and rainforest belt of eastern Madagascar (Fig. 65) at altitudes ranging from 425 to 1700 m, although it is predominantly found in montane rainforests situated higher than 1000 m. Also, based on the available collection data, it seems that T. nassonowii inhabits leaf litter or the ground.
Discussion. In this study we propose to raise T. nassonowii, which was first described by Forel (1892), to species rank. In the original description Forel (1892) compared T. nassonowii with T. schaufussii, and found them to be different in petiolar node shape and propodeal spine length. Much later, in his revision of the Malagasy Tetramorium, Bolton (1979) synonymised T. nassonowii under T. schaufussii, likely because the limited material available for both species suggested their conspecificity. Indeed, the only genuine specimens of T. nassonowii available to Forel and Bolton were the two syntypes from MHNG. Based on the examination of a few thousand specimens from the whole T. schaufussii complex, we believe the material listed as T. schaufussii by Bolton (1979) to consist of the species T. merina, T. nassonowii, T. obiwan, and T. schaufussi. Tetramorium nassonowii is especially distinctive within the complex due to its large body size and characteristic petiolar node shape. As noted in the diagnosis, the lower and longer petiolar node shape of T. nassonowii, which in profile is around 1.2 to 1.4 times higher than long (LPeI 72-81) and in dorsal view between 1.0 to 1.2 times longer than wide (DPeI 87-98), clearly distinguishes it from the remainder of the T. schaufussii species complex. The other species all have a higher and broader petiolar node, in profile around 1.5 to 2.2 times higher than long (LPeI 45-67) and in dorsal view between 1.1 to 1.5 times wider than long (DPeI 109-154).
Diagnosis. The following character combination distinguishes T. obiwan from the other species of the T. schaufussii complex: relatively larger species (HW 0.71-0.84; WL 1.00-1.20); frontal carinae moderately to very well developed, diverging posteriorly, becoming weaker halfway between posterior eye margin and posterior head margin, and ending at or shortly before posterior head margin; antennal scapes short to moderate (SI 77-82); eyes relatively large ; propodeal spines short, triangular to elongate-triangular, and acute (PSLI 10-16), propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines, spines and lobes never strongly inclined towards each other; petiolar node high rounded nodiform, in profile around 1.6 to 1.9 times higher than long (LPeI 54-64), and in dorsal view around 1.1 to 1.3 times wider than long (DPeI 109-129); waist segments usually without any standing hairs, sometimes one pair of long, standing hairs present on petiole and/or postpetiole.
Worker measurements ( Worker description. Head clearly longer than wide (89-92); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae moderately to very well developed, diverging posteriorly, becoming weaker halfway between posterior eye margin and posterior head margin, and ending at or shortly before posterior head margin. Antennal scrobes very weak to absent, shallow, and without any posterior and ventral margins. Antennal scapes short to moderate, not reaching posterior head margin . Eyes relatively large . Mesosomal outline in profile relatively flat to weakly convex, comparatively low and elongate (LMI 36-38), weakly to moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove either weakly developed or absent. Propodeal spines short, triangular to elongate-triangular, and acute (PSLI 10-16), propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high rounded nodiform, around 1.6 to 1.9 times higher than long (LPeI 54-64), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and well rounded, petiolar dorsum weakly to moderately convex; node in dorsal view around 1.1 to 1.3 times wider than long (DPeI 109-129); in dorsal view pronotum around 2.6 to 2.9 times wider than petiolar node (PeNI 35-39). Postpetiole in profile globular, around 1.3 to 1.4 times higher than long (LPpI 70-77); in dorsal view around 1.2 to 1.4 times wider than long (DPpI 124-135); in dorsal view pronotum around 1.9 to 2.0 times wider than postpetiole (PpNI 50-53). Postpetiole in profile appearing more or less of same volume as petiolar node, postpetiole in dorsal view between 1.3 to 1.5 times wider than petiolar node . Mandibles unsculptured, smooth, and shiny; clypeus weakly longitudinally rugulose with three to five, rarely more, rugulae, rugulae often interrupted or irregularly shaped, median area usually weakly sculptured without median rugula, median rugula sometimes partly and rarely fully developed; cephalic dorsum between frontal carinae longitudinally rugose/ rugulose with seven to ten rugae/rugulae; rugae/rugulae running from posterior clypeal margin to posterior head margin, often interrupted, or with cross-meshes; scrobal area mostly unsculptured and laterally merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral head, sometimes head posterolaterally with very little sculpture, very smooth, and shining. Dorsum of mesosoma irregularly longitudinally rugose to reticulate-rugose, anterior pronotum especially reticulate-rugose; lateral mesosoma mostly irregularly longitudinally rugose with few unsculptured areas on lateral pronotum and/or katepisternum. Forecoxae mainly unsculptured, smooth, and shining. Waist segments and gaster unsculptured, smooth, and shining. Ground sculpture everywhere on body weak to absent. Dorsum of head with numerous pairs of long, fine, standing hairs; dorsum of mesosoma with seven to ten pairs, hairs present from anterior pronotum to posterior mesonotum, propodeum without standing pilosity; usually waist segments without any standing hairs, sometimes one pair of long, standing hairs present on petiole and/or postpetiole; first gastral tergite with very short, scarce, appressed pubescence in combination with few scarce, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with appressed, rarely decumbent hairs. Head, mesosoma, waist segments and gaster uniformly light reddish, orange-brown to dark brown contrasting with lighter yellowish to light brown mandibles, antennae, and legs.
Etymology. The name of the new species is inspired by a fictional character from George Lucas' "Star Wars" Universe: the wise Jedi master Obi-Wan Kenobi. The species epithet is an arbitrary combination of letters, thus invariant.
Distribution and biology. Tetramorium obiwan is widely but relatively patchily distributed throughout the rainforests and montane rainforests of eastern Madagascar (Fig. 65). Its known distribution encompasses nine localities, ranging from Andohahela in the southeast to Anjanaharibe-Sud in the northeast. A likely explanation for this patchy distribution record may be that T. obiwan lives in the vegetation and is consequently less often sampled by ground or leaf litter methods. The available collection data supports this, as T. obiwan was mainly collected by beating low vegetation or Malaise traps, and rarely from pitfall traps or leaf litter. If true, then T. obiwan is possibly much more widespread than currently known, and more collecting in lower vegetation will likely provide additional material of this species. Furthermore, T. obiwan seems to prefer higher elevations. It can be found from 675 to 1300 m, but most collections were from the upper altitudinal range limit.
Discussion. Tetramorium obiwan is a fairly conspicuous member of the T. schaufussii complex, thus easily separable from the other species. As mentioned in the diag- nosis above, its larger body size (HW 0.71-0.84; WL 1.00-1.20), strongly developed frontal carinae, relatively long antennal scapes (SI 77-82), relatively large eyes , lack of median clypeal ruga, and (usually) lack of long, standing pilosity on the waist segments will separate it from the other species of the complex. Except for the relatively long antennal scapes, none of the characters listed is unique to T. obiwan, but the combination renders its identification very straightforward. Still, in a few cases it is possible to mistake T. obiwan at first glance for T. merina or T. nassonowii, which are also larger species. Nevertheless, T. merina has noticeably much weaker frontal carinae than T. obiwan. Tetramorium nassonowii is likely the species closest to T. obiwan but they differ significantly in the shape of the petiolar node. The node of T. obiwan is higher and broader, in profile around 1.6 to 1.9 times higher than long (LPeI 54-64), and in dorsal view around 1.1 to 1.3 times wider than long (DPeI 109-129), whereas the node of T. nassonowii is relatively long and low, in profile around 1.2 to 1.4 times higher than long (LPeI 72-81), and in dorsal view between 1.0 to 1.2 times longer than wide (DPeI 87-98). Despite being that distinctive in its own species complex, T. obiwan is comparatively similar to T. proximum from the T. cognatum species complex in that they are both large, reddish-brown species with relatively well-developed frontal carinae and a high rounded nodiform petiolar node. Nevertheless, the presence of long, standing pilosity on the first gastral tergite easily distinguishes T. obiwan from T. proximum that lacks any standing pilosity on the first gastral tergite.
Intraspecific variation in T. obiwan seems relatively low, especially considering that the species is fairly widely distributed. Worker description. Head longer than wide (CI 91); in full-face view posterior head margin weakly to moderately concave. Anterior clypeal margin with distinct median im-pression. Frontal carinae well developed, diverging posteriorly, approaching posterolateral corners of head. Antennal scrobes very weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes of moderate length, not reaching posterior head margin (SI 80). Eyes relatively small (OI 20). Mesosomal outline in profile relatively flat, moderately low and long (LMI 38), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove mostly reduced. Propodeal spines moderately long, elongate-triangular to spinose, acute (PSLI 22), propodeal lobes short and triangular, much shorter than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high rounded nodiform, around 1.9 times higher than long (LPeI 52), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and weakly rounded, petiolar dorsum weakly convex; node in dorsal view around 1.3 times wider than long (DPeI 132); in dorsal view pronotum around 2.8 to 2.9 times wider than petiolar node (PeNI 35). Postpetiole in profile globular, around 1.3 times higher than long (LPpI 75); in dorsal view around 1.3 times wider than long (DPpI 129); in dorsal view pronotum around 1.9 to 2.0 times wider than postpetiole (PpNI 51). Postpetiole in profile appearing more or less of same volume as petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node (PPI 146). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugulose with three similarly weak but unbroken rugulae; cephalic dorsum between frontal carinae longitudinally rugose with six or seven rugae, rugae running mostly unbroken from posterior clypeal margin to posterior head margin, a few rugae interrupted or with cross-meshes; scrobal area partly unsculptured, but mostly merging with surrounding reticulate-rugose to longitudinally rugose sculpture present on lateral head; ground sculpture on head weakly to moderately punctate. Dorsum and sides of mesosoma mostly irregularly longitudinally rugose; forecoxae mostly unsculptured, smooth, and shining; ground sculpture on mesosoma very weak to absent. Both waist segments and gaster completely unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; dorsum of mesosoma with six pairs restricted to pronotum and mesonotum, propodeum without standing pilosity; waist segments and first gastral tergite without any standing hairs; first gastral tergite with very short, scarce, appressed pubescence in combination with a few scarce, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Head, mesosoma, waist segments and gaster uniformly reddish, orange-brown contrasting with lighter yellowish to light brown mandibles, antennae, and legs.

Tetramorium pseudogladius
Etymology. The name of the new species is a combination of the ancient Greek word "pseudes", which means "false" or "lying", and the species name of T. gladius from the T. cognatum complex. This combined name takes account for the fact that both species are almost identical in morphology. The species epithet is treated as a nominative noun, and is thus invariant.
Distribution and biology. At present, T. pseudogladius is known only from the type locality, Parc National de Zahamena (Fig. 65) where it was collected in lowland rainforest at an altitude of 860 m. In addition, the new species was sampled from leaf litter. Discussion. Like T. gladius in the T. cognatum complex, T. pseudogladius is also immediately recognisable on the basis of its much smaller eyes (OI 20). The other species of the T. schaufussii complex all have much larger eyes . In addition, T. pseudogladius lacks the long, standing pilosity on the waist segments present in most other members of the species complex, and has relatively long antennal scapes (SI 80).
Generally, T. pseudogladius looks very similar to T. gladius in the T. cognatum species complex and they also share most of their morphometric range. Indeed, if not for the few long, standing hairs on its first gastral tergite, the holotype of T. pseudogladius could be easily confused with T. gladius. They also differ in antennal scape length, however, which is longer in T. pseudogladius (SI 80) than in T. gladius . Until more material from the type locality becomes available, we consider these differences as diagnostic to delimit the species boundary between these two species.  17.2825°S, 49.43°E, 10 m, littoral rainforest, 4.IV.1997.

Tetramorium rala
Diagnosis. The following character combination distinguishes T. rala from the remainder of the T. schaufussii species complex: relatively small species (HW 0.46-0.49; WL 0.58-0.64); eyes relatively large (OI 26-28); antennal scapes very short (SI 61-68); frontal carinae usually very weakly developed, only feebly raised, usually ending shortly after posterior eye margin or merging with cephalic sculpture halfway between posterior eye margin and posterior head margin; propodeal spines medium-sized to long, elongate-triangular to spinose, and acute (PSLI 21-25), propodeal lobes short, triangular, and acute or blunt, but always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other; petiolar node in profile high rounded nodiform to thinly cuneiform, in profile 2.0 to 2.2 times higher than long (LPeI 45-50), in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145); mesosoma with three to four pairs on dorsal promesonotum, propodeum and waist segments without any standing pilosity; body uniformly whitish yellow to light brown. Worker description. Head clearly longer than wide (CI 90-94); posterior head margin weakly concave, almost straight. Anterior clypeal margin with distinct median impression. Frontal carinae usually very weakly developed, only feebly raised, usually ending shortly after posterior eye margin or merging with cephalic sculpture halfway between posterior eye margin and posterior head margin. Antennal scrobes very weak to absent, very shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 61-68). Eyes relatively large (OI 26-28). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36-39), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove very weak to absent. Propodeal spines medium-sized, elongate-triangular to spinose, and acute (PSLI 21-25), propodeal lobes short, triangular, and acute or blunt, but always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high rounded nodiform to thinly cuneiform, around 2.0 to 2.2 times higher than long (LPeI 45-50), anterior and posterior faces not parallel, anterodorsal margin usually situated higher and more strongly angled than posterodorsal margin, petiolar dorsum relatively flat to weakly convex and tapering backwards posteriorly; node in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145), in dorsal view pronotum between 2.3 to 2.7 times wider than petiolar node (PeNI 37-43). Postpetiole in profile globular to subglobular, approximately 1.3 to 1.5 times higher than long (LPpI 67-75); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 141-157), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 52-59). Postpetiole in profile lower, thicker, and more rounded than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 129-142). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugulose with three to five rugulae, median rugula always present and usually fully developed, one or two mostly entire, rarely broken, lateral rugulae present on each side; cephalic dorsum between frontal carinae irregularly longitudinally rugulose with seven to ten fine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, but mostly irregularly shaped, interrupted or with crossmeshes; scrobal area mostly unsculptured; lateral head mainly longitudinally rugulose to reticulate-rugulose, but larger areas often only weakly sculptured and appearing fairly smooth and shiny; ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma ranging from weakly longitudinally rugulose with larger areas with almost completely reduced sculpture to longitudinally rugose with well developed rugae; lateral mesosoma weakly to moderately irregularly longitudinally rugulose or reticulate-rugulose, often with larger areas of almost completely reduced sculpture; ground sculpture on mesosoma usually weak to absent, sometimes moderately punctate. Forecoxae , both waist segments, and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with three to four pairs on promesonotum; propodeum and waist segments without any standing pilosity; first gastral tergite with short, moderately dense, appressed (rarely decumbent) pubescence combined with several scattered, long, fine erect to suberect hairs; anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Body uniformly whitish yellow to light brown.
Etymology. The new species is named after the fictional character "Rala" from Walter Moers' fantasy novel "Rumo and His Miraculous Adventures". The species epithet is an arbitrary combination of letter, thus invariable.
Distribution and biology. The distribution range of T. rala is relatively disjunctive (Fig. 65). Its main distribution seems to be in the northeast in the area around the Bay of Antongil and the Masoala Peninsula north to Marojejy and Makirovana. Further south of this main cluster of localities T. rala is only known from three additional places: Ambatovaky, Tampolo, and Manombo. One explanation for this patchy distribution would be a preferense for lowland rainforests. Tetramorium rala lives in rainforests and littoral forests at lower elevations ranging from 10 to 550 m where it is found in leaf litter. Very few intact lowland rainforests remain south of its main distribution in the northeast of Madagascar. Discussion. Tetramorium rala is a very distinctive member of the T. schaufussii complex due to its smaller size, relatively long propodeal spines, high nodiform to thinly cuneiform petiolar node, lack of standing pilosity on the waist segments, and very bright body colouration. Consequently, it is very unlikely to be confused with any other species. Most species are much larger in body size, have shorter propodeal spines, and/or possess standing pilosity on the waist segments. Only some smaller specimens of T. schaufussii could at first glance be mistaken with T. rala, but these two species are effortlessly separable. Tetramorium schaufussii has much shorter propodeal spines (PSLI 11-18), a lower petiolar node, which in profile is only 1.6 to 1.9 times higher than long (LPeI 52-63), and long, standing pilosity on the waist segments. By contrast, in T. rala the propodeal spines are much longer (PSLI 21-25), the petiolar node is higher, in profile around 2.0 to 2.2 higher than long (LPeI 45-50), and the waist segments lack standing pilosity.
However, even though T. rala is easily identifiable within the T. schaufussii complex, it is morphologically very close to T. rumo from the T. cognatum complex since they share a very similar gestalt. Both species are smaller in size, have relatively longer propodeal spines (compared to most other species of the species group), a high nodiform to thinly cuneiform petiolar node, lack standing pilosity on the waist segments, and possess very bright body colouration. The main separating character, which also places them in separate species complexes, is the lack of standing pilosity on the first gastral tergite in T. rumo versus the presence of standing pilosity on the first gastral tergite in T. rala. Both species are morphologically closer to each other than to any other species of the T. schaufussii species group, but there are highly diagnostic differences to support their heterospecificity. The petiolar node of T. rumo is thinner and stronger anteroposteriorly compressed, in profile around 2.3 to 2.7 times higher than long (LPeI 37-43), and in dorsal view between 1.5 to 1.7 times wider than long (DPeI 156-171), whereas T. rala has a node which in profile is 2.0 to 2.2 times higher than long (LPeI 45-50), and in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145). In addition, T. rumo also has larger eyes (OI 28-31) than T. rala . Further evidence of their heterospecifity can be deduced from their distribution ranges, which overlap in central-eastern Madagascar, but both species maintain their species-specific characteristic without intermediate forms. In Manombo both species were also found living in sympatry in close proximity. terodorsal margin slightly higher, petiolar dorsum generally weakly convex, sometimes flat; node in dorsal view between 1.1 to 1.4 times wider than long (DPeI 112-136), in dorsal view pronotum between 2.4 to 2.8 times wider than petiolar node (PeNI 35-41). Postpetiole in profile globular, around 1.2 to 1.4 times higher than long (LPpI 69-83); in dorsal view between 1.2 to 1.5 times wider than long (DPpI 125-150), pronotum between 1.6 to 1.9 times wider than postpetiole (PpNI 53-61). Postpetiole in profile appearing more or less of similar volume as petiolar node, postpetiole in dorsal view around 1.3 to 1.5 times wider than petiolar node (PPI 131-153). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugulose/rugose with three to six usually regularly shaped and unbroken rugulae/rugae, median ruga usually fully developed and distinct, very rarely broken, one or two lateral rugulae/rugae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose/ rugose with seven to ten rugae/rugulae, rugae/rugulae usually running from posterior clypeal margin to posterior head margin, often irregularly shaped, interrupted, or with cross-meshes; scrobal area partly unsculptured and merging with surrounding sculpture; lateral head reticulate-rugose to longitudinally rugose, often posteriorly mostly unsculptured. Ground sculpture on head usually well developed, moderately reticulatepunctate, especially on cephalic dorsum and scrobal area, sometimes ground sculpture much weaker, almost absent. Dorsum of mesosoma usually irregularly longitudinally rugose to reticulate-rugose, sometimes almost completely reticulate-rugose with few longitudinally rugose elements; lateral mesosoma mostly irregularly longitudinally rugose to reticulate-rugose, often lateral pronotum weaker sculptured to almost unsculptured. Ground sculpture on mesosoma variably developed, usually weakly to moderately punctate, sometimes very weak or absent. Forecoxae either unsculptured, smooth, and shining or with longitudinally rugulose or reticulate-rugose sculpture on upper half. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with six or more pairs on promesonotum, propodeum without standing pilosity; petiole usually with one or two and postpetiole with two to three pairs of long, standing hairs; first gastral tergite with short, moderately dense, appressed pubescence in combination with several scattered to numerous, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Head, mesosoma, waist segments, and gaster uniformly light yellowish brown to very dark brown, almost black contrasting with lighter yellowish to light brown mandibles, antennae, and legs.

Tetramorium schaufussii
Distribution and biology. Tetramorium schaufussii is broadly distributed throughout most of the humid forest zones from the southeast to the north of Madagascar (Fig. 66). Surprisingly, T. schaufussii is also known from one very old collection event from the island of Reunion, but apart from that no modern collection exists from that island. Despite that we list Reunion as record for T. schaufussii we consider that record as problematic and highly questionable. In Madagascar T. schaufussii is almost always found in rainforests or montane rainforests at elevations from 210 to 1875 m, even though most of the material was collected at elevations higher than 1000 m. In addition, T. schaufussii seems to be an inhabitant of the leaf litter stratum.
Discussion. Tetramorium schaufussi is the most widespread, common, and abundant species of the T. schaufussi complex. Also, T. schaufussii co-occurs with all other members of the complex throughout its range. It can be well separated from most species, but its separation from a few morphologically close forms is more challenging. Due to its larger eyes (OI 24-28) T. schaufussii is very unlikely to be mistaken for T. pseudogladius (OI 20). Additionally, its petiolar node shape, which is always broader than long (DPeI 112-136), distinguishes it from T. nassonowii, which has a longer than broad node (DPeI 87-98). The species T. scutum, despite being morphologically relatively similar, has longer propodeal spines  and the spines and propodeal lobes are strongly inclined towards each other. Tetramorium schaufussii always has shorter spines (PSLI 11-18) and the spines and lobes are never strongly inclined towards each other. Tetramorium rala and T. sikorae lack long, standing pilosity on the waist segments, separating them easily from T. schaufussii, but is should be noted that without consideration of the pilosity on the waist segments, T. sikorae is generally very similar to T. schaufussii. The difference, however, is very constant and both are usually found in sympatry, leading us to the decision to retain them as two species. Furthermore, most of the material of T. obiwan also lacks pilosity on the waist segments, distinguishing it from T. schaufussii, and, if pilosity is present, it is reduced to one pair on the petiole or postpetiole. Additionally, T. obiwan possesses longer antennal scapes (SI 77-82) and is much larger (HW 0.71-0.84; WL 1.00-1.20) than T. schaufussii (SI 66-73; HW 0.51-0.68; WL 0.70-0.93). In Tetramorium body size is usually not useful and often even misleading due to high intraspecific variation in many species (Hita Garcia et al. 2010;Hita Garcia and Fisher 2012a), but in the case of these two species we can confidently separate them by size.
The three species T. merina, T. monticola, and T. xanthogaster are often difficult to separate from T. schaufussii. The most important discriminating difference between these three and T. schaufussii is the shape of the head. In T. schaufussii the head is usually much longer and thinner (CI 86-90 vs. CI 91-95 in the other three species). Additionally, in T. schaufussii the clypeus almost always has a very distinct and unbroken median longitudinal ruga, whereas T. merina, T. monticola, and T. xanthogaster normally have the median area fully unsculptured without any median ruga/rugula at all, or the median ruga/rugula is present, but then it is usually interrupted, very irregularly shaped, or only present as traces. This character has to be treated with caution however, as there are a few specimens in T. merina, T. monticola, and T. xanthogaster, in which the median ruga/rugula is present. The delimitations of T. merina and T. schaufussii can be difficult, but in areas where they co-occur in the Central Highlands of Madagascar they can be easily separated by body size. In that area T. merina is always much larger in size and has shorter propodeal spines (PSLI 7-11) than T. schaufussii .
It must be pointed out that T. schaufussii is highly variable, likely the most variable species of the T. schaufussii complex and the whole species group. There are several important characters varying significantly throughout the distribution range that need to be addressed here. The frontal carinae are moderately well developed in most of the material, but in one series from Mt. Anjanaharibe they are reduced and much weaker. As do several other species of the group, T. schaufussii possesses a comparatively variable petiolar node shape. It is generally high rounded nodiform with the anterodorsal and posterodorsal margins situated at about the same height and both equally rounded or an-gled. However, the node is often lower and thicker, and this variation can be seen within the same series or population. Sometimes the node also has a slightly higher and more angled anterodorsal margin in comparison to the posterodorsal margin, even though only weakly so. In addition, even though mostly stable, the propodeal spines do occasionally vary. They are usually short to very short (PSLI 11-15), but some specimens from Andranomay, Binara, and Marojejy have longer spines . Also highly variable is colouration that also contains a geographic component. Most of the material from the southeast to the central east is much darker in colour, usually dark brown to almost black. The material from the north is very variable in colour ranging from very bright yellow (Mt. Anjanaharibe) to almost black (Marojejy), but usually constant on a local scale. Parallel to the colouration, there is also geographic variation observable in the sculpture on the forecoxae. Most of the darker material has the upper part of the forecoxae distinctly sculptured, whereas in most of the brighter material the forecoxae are completely unsculptured. However, this is not always the case, and thus not used for diagnostics.
The series from Mt. Anjanaharibe mentioned above also requires some comments. The specimens are much brighter in color, smaller in size, and have much weaker frontal carinae than the rest of the T. schaufussii material. These are not unlikely to turn out to be a distinct species, but for the moment we keep it as a smaller, brighter geographical variation of T. schaufussii. Diagnosis. Tetramorium scutum can be separated from the remainder of the species complex by the following character combination: moderate to large eyes (OI 24-25); short antennal scapes (SI 71-74); frontal carinae moderately to well developed, slightly diverging posteriorly, ending at or shortly before posterior head margin; propodeal spines moderate to long , propodeal lobes elongate-triangular, always weakly shorter than propodeal spines, in profile spines and lobes strongly inclined towards each other; petiolar node in profile around 2.0 to 2.1 times higher than long (LPeI 48-50) and in dorsal view around 1.4 to 1.5 times wider than long (DPeI 144-154); dorsum of mesosoma with six or more pairs of long, standing hairs from anterior pronotum to posterior mesonotum, propodeum without any standing pilosity; waist segments with long, standing pilosity.

Tetramorium scutum
Worker measurements ( Worker description. Head longer than wide (CI 90-92); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae moderately to well developed, slightly diverging posteriorly, ending at or shortly before posterior head margin. Antennal scrobes weak to absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 71-74). Eyes moderate to relatively large . Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 38-39), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weak or absent. Propodeal spines moderate to long, elongate-triangular to spinose, and acute (PSLI 22-24); propodeal lobes elongate-triangular, always weakly shorter than propodeal spines, in profile spines and lobes strongly inclined towards each other. Petiolar node in profile high rounded nodiform to weakly squamiform, around 2.0 to 2.1 times higher than long (LPeI 48-50), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height, petiolar dorsum relatively flat; node in dorsal view between 1.4 to 1.6 times wider than long (DPeI 144-154), in dorsal view pronotum between 2.2 to 2.5 times wider than petiolar node (PeNI 41-44). Postpetiole in profile subglobular, around 1.3 to 1.4 times higher than long (LPpI 70-74); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 134-140), pronotum between 1.6 to 1.8 times wider than postpetiole (PpNI 57-62). Postpetiole in profile appearing slightly more voluminous than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 133-142). Mandibles completely unsculptured, smooth, and shiny; clypeus weakly, irregularly, longitudinally rugulose with median area mostly unsculptured, smooth, and shiny, sometimes median rugula present, but then weakly developed and/or interrupted, one or two weak, irregular and broken rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with six to nine rugae/rugulae, rugae/rugulae usually running from posterior clypeal margin to posterior head margin, often irregularly shaped, interrupted or with cross-meshes; scrobal area partly unsculptured and merging with surrounding sculpture; lateral head anteriorly reticulate-rugose to longitudinally rugose and posteriorly mostly unsculptured. Ground sculpture on head weakly to moderately reticulatepunctate, especially laterally. Dorsum of mesosoma irregularly longitudinally rugose; lateral mesosoma mostly irregularly longitudinally rugose with some reticulate-rugose elements. Ground sculpture on mesosoma weak to absent. Forecoxae unsculptured, smooth, and shining. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with six or more pairs from anterior pronotum to posterior mesonotum, propodeum without standing pilosity; petiole with one and postpetiole with one or two pairs of long, standing hairs; first gastral tergite with short, moderately dense, appressed pubescence in combination with several scattered, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments and gaster uniformly brown to dark brown contrasting with yellowish to light brown mandibles, antennae, and legs.
Etymology. The name of the new species is Latin and means "shield", referring to the weakly squamiform condition of the petiolar node. The species epithet is a nominative noun, and thus invariant.
Distribution and biology. This new species is only known from the area around Ivohibe (Fig. 66) where it was collected from a few montane rainforest localities situated at elevations of 1200 to 1575 m. All specimens were sampled from leaf litter.
Discussion. Tetramorium scutum is relatively easy to distinguish within the species complex since it is the only species in which the moderately long spines (PSLI  and the comparatively long propodeal lobes are strongly inclined towards each other. In all the other group members the spines are either much shorter or if they are of approximately similar length as in T. scutum, then the lobes are much smaller and spines and lobes are never strongly inclined towards each other. Interestingly, the species most similar to T. scutum are T. aspis and T. camelliae from the T. cognatum complex, and we suspect that they are also more closely related to each other than to the rest of the group. These three species all have strongly inclined spines and lobes and are also found in the same small area in the southeast of Madagascar. The new species is only known from a relatively small area and consequently shows very little intraspecific variation.  Santschi, 1926:243. [Synonymy with T. sikorae by Bolton 1979here confirmed] six to ten rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, but mostly irregularly shaped, meandering, interrupted or with cross-meshes; scrobal area mostly unsculptured; lateral head reticulate-rugulose to longitudinally rugulose, posteriorly often partly unsculptured; ground sculpture on head weakly to moderately punctate. Dorsum and sides of mesosoma irregularly longitudinally rugulose to reticulate-rugulose, sometimes in parts only very weakly sculptured and relatively smooth; ground sculpture on mesosoma weak to absent. Forecoxae, both waist segments, and gaster fully unsculptured, smooth, and shining. Dorsum of head with numerous pairs of long, fine, standing hairs; dorsal promesonotum usually with two pairs, rarely three or four; propodeum and waist segments without long, standing pilosity; first gastral tergite with short, moderately dense, appressed pubescence in combination with several scattered, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Head, mesosoma, waist segments and gaster uniformly orange brown contrasting with yellowish to light brown mandibles, antennae, and legs. Distribution and biology. Tetramorium sikorae is widely distributed in Madagascar from Andrambovato in Fianarantsoa in the southeast to Binara in the north, and is also found in the isolated montane forest Ambohijanahary in western Madagascar (Fig. 66). Its main distribution is centered in central-eastern Madagascar in the area from Torotorofotsy and Andasibe-Mantadia north to Betampona and Zahamena. Tetramorium sikorae clearly prefers montane rainforests, rarely lowland rainforests, and the elevational range of 240 m to 1100 m must be taken with caution since it is predominantly found at the higher range limit. Also, T. sikorae seems to be a leaf litter inhabitant.
Discussion. Tetramorium sikorae is easily identifiable within the T. schaufussii species complex. The character that best separates it from most species is the lack of long, standing pilosity on the waist segments since such pilosity is present in T. merina, T. monticola, T. nassonowii, T. pseudogladius, T. schaufussii, T. scutum, and T. xanthogaster. Only T. rala and T. obiwan share the lack of pilosity on the waist segments, and sometimes pilosity is present in the latter species. However, T. sikorae is unlikely to be confused with T. obiwan for several reasons. First, the latter species is much larger in body size (HW 0.71-0.84; WL 1.00-1.20) than T. sikorae (HW 0.53-0.61; WL 0.70-0.82). Second, T. obiwan has longer antennal scapes (SI 77 -82) than T. sikorae . Third, both species appear to live in different microhabitats with T. obiwan in the lower vegetation and T. sikorae in leaf litter. Beyond the differing pilosity on the waist segments, T. sikorae is morphologically very close to T. schaufussii. Since the presence or absence of this pilosity seems fairly stable at species levelwe retain these as separate species. Tetramorium sikorae is also relatively similar to T. cognatum in the T. cognatum complex, but apart from the gastral pilosity diagnostic for the species complexes, both species also differ in antennal scape length.
Worker description. Head clearly longer than wide (CI 92-94); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly developed, only faintly raised, usually becoming much weaker around eye level and fading out halfway between posterior eye margin and posterior head margin. Antennal scrobes very weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin . Eyes moderate to relatively large . Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36-39), weakly to moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weakly developed or absent. Propodeal spines/teeth very short to short, varying from triangular and blunt to elongate-triangular and acute (PSLI 10-16), propodeal lobes short, triangular, and blunt, always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high nodiform, nodiform or weakly cuneiform, always with relatively well rounded anteroand posterodorsal margins, around 1.5 to 1.7 times higher than long (LPeI 59-67), anterior and posterior faces often approximately parallel and often not, anterodorsal and posterodorsal margins usually at about same height, sometimes anterodorsal margin situated slightly higher than posterodorsal, petiolar dorsum weakly to moderately convex; petiolar node in dorsal view around 1.2 to 1.3 times wider than long (DPeI 119-133), in dorsal view pronotum between 2.2 to 2.7 times wider than petiolar node (PeNI 37-46). Postpetiole in profile globular to subglobular, approximately 1.3 to 1.5 times higher than long (LPpI 68-80); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 125-140), pronotum between 1.8 to 2.1 times wider than postpetiole (PpNI 48-56). Postpetiole in profile appearing more or less as voluminous as petiolar node, postpetiole in dorsal view around 1.2 to 1.3 times wider than petiolar node (PPI 117-129). Mandibles unsculptured, smooth, and shining; generally sculpture on clypeus very much reduced, median area usually unsculptured with one or two weak, irregular, and broken rugulae laterally, very rarely median rugula present but then weak and broken; cephalic dorsum between frontal carinae irregularly longitudinally rugulose with six to eight widely separated rugulae, rugulae running from posterior clypeal margin to posterior head margin, but irregularly shaped, often broken or with cross-meshes, and becoming weaker or fading out towards posterior head margin; scrobal area partly unsculptured, but mostly merging laterally with surrounding reticulate-rugose to longitudinally rugose sculpture present around eyes, most of lateral head predominantly unsculptured, smooth, and shiny; ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma weakly to moderately longitudinally rugulose, sometimes irregularly so, often rugulae very weak and parts of dorsal mesosoma smooth; lateral mesosoma anteriorly often only weakly sculptured and shiny, katepisternum and lateral propodeum usually irregularly longitudinally rugulose to reticulate-rugose, sometimes almost completely unsculptured, smooth, and shiny; ground sculpture on mesosoma usually only weakly developed, mostly absent. Forecoxae unsculptured, smooth, and shining. Waist segments and gaster unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; dorsum of promesonotum always with more than ten pairs of long, standing hairs, propodeum usually with one or two pairs, sometimes with up to five, rarely without any standing pilosity; waist segments each with several pairs; first gastral tergite with short, scarce to moderately abundant, appressed to decumbent pubescence in combination with scattered, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to subdecumbent hairs. Body colour variable, usually bicoloured with head and mesosoma of dark brown to blackish colour contrasting with yellowish or light brown appendages, waist segments, and gaster; very rarely only head of dark brown contrasting with yellowish remainder of body, sometimes body uniformly coloured, ranging from yellow to dark brown.
Distribution and biology. Tetramorium xanthogaster has a relatively patchy distribution range (Fig. 66). The southernmost locality is Analavelona in the southwest. The next known localities are located in the Central Highlands much further north and east (Ambohitantely, Ankokoy, and Marotandrano). The remaining localities are situated in the northern part of Madagascar (Andranobe, Marojejy, Binara, Montagne d'Ambre, and Manongarivo). Many of these localities are widely separated from each other. Furthermore, it seems that T. xanthogaster prefers montane rainforests since most collections are from elevations around or above 1000 m, whereas it was only occasionally collected from lower elevations. An explanation for the currently patchy distribution records could be that T. xanthogaster nests and/or forages in the vegetation since almost all of the available material was collected either from beating low vegetation or Malaise traps. Consequently, we expect that more collecting in the lower vegetation stratum will likely yield more material of this species.
Discussion. Despite its pronounced variability in colouration and petiolar node shape, the determination of T. xanthogaster is fairly straightforward. The species was described by Santschi (1911) and later redescribed by Bolton (1979) as a bicoloured species with dark head and mesosoma contrasting with the yellowish to light brown remainder of the body. Indeed, the material from the southwest and the Central Highlands is consistently strongly bicoloured, and even though one should not overly rely too heavily on body colouration, no other species of the T. schaufussii species group is similarly bicoloured. However, material from the northern localities shows remarkable diversity in colouration. The populations from Andranobe, Marojejy, and Binara are of a fairly bright, yellowish brown. By contrast, the material from Manongarivo and Montagne d'Ambre is in parts bicoloured like the southern populations, partly bicoloured with only the head or mesosoma darker than the rest of the body, or just uniformly light brown to dark brown. But even misregarding colouration, T. xanthogaster cannot be misidentified with another member of the complex. Due to the presence of long, standing pilosity on its waist segments it cannot be mistaken for T. obiwan (partly), T. pseudogladius, T. sikorae, or T. rala, and the broader than long petiolar node (DPeI 119-133) distinguishes it from T. nassonowii . In addition, the petiolar node of T. xanthogaster in profile is around 1.5 to 1.7 times higher than long (LPeI 59-67), which separates it from T. rala and T. scutum that have nodes which are 2.0 to 2.2 times higher than long (LPeI 45-50). The petiolar nodes of the latter two are also thinly cuneiform to weakly squamiform while the node of T. xanthogaster is variably shaped, but lower and less angled. Tetramorium obiwan possesses well-developed frontal carinae and cephalic sculpture, as well as relatively long antennal scapes (SI 77-82), whereas T. xanthogaster has much weaker frontal carinae and cephalic sculpture and shorter antennal scapes (SI 70-75). The remaining three species, T. merina, T. monticola, and T. schaufussii, are more difficult to separate from T. xanthogaster. Tetramorium merina is only found in the central Highlands and co-occurs there with T. xanthogaster. In this region T. xanthogaster is always strongly bicoloured with head and mesosoma very dark brown to black, which contrasts with the yellow to light brown waist segments and gaster. In addition, T. merina lacks any standing pilosity on the propodeum while T. xanthogaster usually has long, fine, standing pilosity on the propodeal dorsum. As mentioned above, there are not too many other diagnostic characters to separate these species, but the fact that they co-occur in sympatry in several localities without any intermediate forms supports their heterospecificity. Tetramorium monticola is also sympatric with T. xanthogaster, this time in the northern part of Madagascar, where the colouration of the latter species is not reliable. However, in T. monticola the frontal carinae are more strongly developed and the cephalic dorsum between the frontal carinae has nine to thirteen relatively regularly shaped, mostly unbroken rugae while the frontal carinae of T. xanthogaster are weakly developed and the cephalic dorsum has only six to eight widely separated, often irregularly shaped rugulae. Also, the propodeal spines of the latter are shorter (PSLI 10-16) than in T. monticola . The last and most common and abundant species of the complex, T. schaufussii, is also usually found in sympatry with T. xanthogaster, but both species can be well separated by head shape. The head of T. schaufussii is much longer and thinner (CI 86-90) than in T. xanthogaster . Additional differentiating characters are the long, standing pilosity on the propodeal dorsum (usually present in T. xanthogaster but absent in T. schaufussii) and the median clypeal ruga (present in T. schaufussii but absent in T. xanthogaster).
It has to be noted that T. xanthogaster is relatively variable in the shape of the petiolar node, which can be high nodiform, nodiform, cuneiform, or in intermediate stages. The node shape varies strongly even within material from the same collection event. Another noteworthy variation can be seen in the material from Analavelona. In contrast to the rest of the material from all other localities it seems that the sculpture on the cephalic dorsum and the mesosomal dorsum is much better developed, and does not differ significantly from other species like T. schaufussii. However, the frontal carinae are still weaker than in the latter.

Tetramorium severini species group
Diagnosis. Eleven-segmented antennae; anterior clypeal margin with distinct median impression; frontal carinae strongly developed and long, usually ending shortly before posterior head margin; antennal scrobes present, but weak and without well-developed posterior and ventral margins; anterior face of mesosoma weakly developed; mesosomal outline in profile flat and relatively elongated, only very weakly marginate from lateral to dorsal mesosoma, sides usually rounding onto dorsum; mesosoma relatively low (LMI 35-37); propodeal spines long to very long, spinose and acute (PSLI 38-43); propodeal lobes triangular and short; petiolar node in profile high rounded nodiform, in profile around 1.5 to 1.7 times higher than long (LPeI 57-69), node in dorsal view around 1.1 to 1.2 times wider than long (DPeI 104-121), anterior and posterior faces approximately parallel; postpetiole in profile globular to subglobular; mandibles unsculptured, smooth, and shining; cephalic dorsum with distinct longitudinally rugose sculpture; mesosoma laterally, distinctly, irregularly, and longitudinally rugose to reticulate-rugose, sculpture on mesosomal dorsum relatively weak, usually consisting of feeble, irregular longitudinal rugulae; waist segments and gaster unsculptured, smooth, and shiny; head with numerous standing, long hairs, mesosoma with one or two long hairs, waist segments and first gastral tergite without any standing pilosity; first gastral tergite with very short and appressed pubescence; sting appendage spatulate.
Comments. This group only holds the species T. severini, which is a common faunal element in most rainforests in eastern Madagascar. Previous to Hita Garcia and Fisher (2011), T. severini was placed in the T. schaufussii group by Bolton (1979). Despite strong similarities in the shape of the mesosoma and waist segments, we still consider T. severini distinct enough from all members of the T. schaufussii group to justify its placement in its own species group. All species of the T. schaufussii group are comparatively small species with very short to moderately long propodeal spines, whereas T. severini is one of the largest species found in Madagascar outside the T. tortuosum, T. kelleri, and T. tosii species groups, and possesses very long propodeal spines. Admittedly few more factors argue for the separation, and future reexaminations may come to a different conclusion. However, at present, we believe the similarities between T. severini and the T. schaufussii group are convergent in nature, an idea also supported by unpublished mtDNA data (FHG & BLF, unpublished data).
Furthermore, the T. severini group can be easily distinguished from all other Malagasy Tetramorium species and groups by its 11-segmented antennae, long and slender mesosoma (LMI 35-37) without distinct margination between lateral and dorsal mesosoma, very long propodeal spines (PSLI 38-43), rounded high nodiform petiolar node, and completely unsculptured waist segments. size, very dark colour, very long propodeal spines, reduced sculpture on the mesosoma, and complete lack of sculpture on the waist segments render it immediately recognisable. Considering its wide distribution and large number of specimens examined, T. severini displays very little intraspecific variation.       . Geographic distribution maps for the species of the T. schaufussii species complex II and the T. severini species group. Star symbols represent type localities while circles represent non-type localities. Note that T. schaufussii is also recorded from the island of Reunion, but we omit it from the map due to questionable locality data.