Holotype, pinned worker, MADAGASCAR, Antsiranana, Parc National de Marojejy, Antranohofa, 26.6 km 31° NNE Andapa, 10.7 km 318° NW Manantenina, 14.44333°S, 49.74333°E, 1325 m, montane rainforest, sifted litter (leaf mould, rotten wood), collection code BLF09080, 18.XI.2003 (B.L. Fisher) (CAS: CASENT0042547). Paratypes, nine pinned workers with same data as holotype (BMNH: CASENT0042817; CAS: CASENT0042703; CASENT0042704; CASENT0042708; CASENT0042813; CASENT0042815; CASENT0042827; CASENT0042835; MCZ: CASENT0042821).

MADAGASCAR: Antsiranana, Rés. Anjanaharibe-Sud, 9.2 km WSW Befingotra, 14.75°S, 49.46667°E, 1280 m, montane rainforest, 5.XI.1994 (B.L. Fisher); Fianarantsoa, Foret d’Ambalagoavy Nord, Ikongo, Ambatombe, 21.8275°S, 47.33889°E, 625 m, 1.XII.2000 (R. Harin’Hala & M.E. Irwin).

Tetramorium alperti differs from the other three species of the group by the following character combination: propodeal spines long to very long (PSLI 29–37); 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.

(N=10). HL 0.56–0.68 (0.64); HW 0.54–0.65 (0.62); SL 0.40–0.47 (0.45); EL 0.13–0.15 (0.14); PH 0.31–0.38 (0.35); PW 0.40–0.50 (0.47); WL 0.70–0.84 (0.79); PSL 0.18–0.23 (0.21); PTL 0.15–0.18 (0.16); PTH 0.23–0.28 (0.26); PTW 0.16–0.19 (0.18); PPL 0.17–0.22 (0.20); PPH 0.23–0.27 (0.25); PPW 0.22–0.28 (0.26); CI 95–97 (96); SI 69–75 (73); OI 22–23 (23); DMI 57–62 (59); LMI 42–46 (44); PSLI 29–37 (33); PeNI 36–40 (38); LPeI 62–68 (64); DPeI 103–115 (108); PpNI 54–57 (55); LPpI 74–84 (80); DPpI 126–132 (128); PPI 139–156 (145).

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 (SI 69–75). Eyes of moderate size (OI 22–23). Mesosomal outline in profile flat to weakly convex, relatively high (LMI 42–46), 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 (PeNI 36–40). 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 (DPpI 126–132), 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 (PPI 139–156). 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.

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.

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 Tetramorium 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, Tetramorium alperti seems to be a leaf litter inhabitant.

Tetramorium alperti cannot be confused with Tetramorium dalek since the latter has no long standing hairs on the waist segments and the first gastral tergite, while these are present in Tetramorium alperti. Differentiation from the other three species of the group, however, is more challenging. The primary diagnostic characters distinguishing Tetramorium 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 Tetramorium enkidu, Tetramorium gilgamesh or Tetramorium naganum since they either lack long and erect hairs or appressed to decumbent pubescence entirely. In addition, Tetramorium alperti also has a thicker petiolar node which is around 1.5 to 1.6 times higher than long (LPeI 62–68), compared to Tetramorium gilgamesh and Tetramorium 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 Tetramorium alperti is Tetramorium 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 1976, 1980; Hita Garcia et al. 2010; Hita Garcia and Fisher 2012a, 2012b). We were able to reveal several consistent patterns of pilosity/pubescence in the Tetramorium naganum species group, and the pattern of Tetramorium alperti is unique to this group, although it resembles the one seen in Tetramorium ryanphelanae Hita Garcia & Fisher from the Tetramorium bessonii species group, and a few species from the Tetramorium schaufussii species complex.

To our knowledge, there is no significant intraspecific variation in the material treated as Tetramorium alperti.

Holotype, MADAGASCAR, Toamasina, Montagne d’Anjanaharibe, 19.5 km 27° NNE Ambinanitelo, 15.1783°S, 49.635°E, 1100 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF08150, 12.–16.III.2003 (B.L. Fisher et al.) (CAS: CASENT0038402). Paratypes, 17 pinned workers with same data as holotype (BMNH: CASENT0038394; CAS: CASENT0038369; CASENT0038372; CASENT0038376; CASENT0038390; CASENT0038408; CASENT0038413; CASENT0038416; CASENT0038425; CASENT0038429; CASENT0038443; CASENT0038445; CASENT0038450; CASENT0038456; CASENT0038465; MCZ: CASENT0038397; CASENT0038424); and seven workers from MADAGASCAR, Toamasina, Montagne d’Anjanaharibe, 18.0 km 21° NNE Ambinanitelo, 15.1883°S, 49.615°E, 470 m, rainforest, sifted litter (leaf mold, rotten wood), collection code BLF08802, 8.–12.III.2003 (B.L. Fisher et al.) (CAS: CASENT0037833; CASENT0037869; CASENT0037903; CASENT0037909; CASENT0037916; CASENT0037933; CASENT0037936).

MADAGASCAR: Antsiranana, 1 km W Andampibe, Cap Masoala, 15.69361°S, 50.18139°E, 125 m, lowland rainforest, 29.XI.1993 (G.D. Alpert); Antsiranana, Res. Anjanaharibe-Sud, 9.2 km WSW Befingotra, 14.75°S, 49.4667°E, 1280 m, 4.–9.XI.1994 (B.L. Fisher); Toamasina, Ambohitsitondroina, 6.9 km NE Ambanizana, 15.5851°S, 50.0095°E, 825 m, rainforest, 2.XII.1993 (B.L. Fisher); Toamasina, Andranobe, 6.3 km S Ambanizana, 15.6813°S, 49.958°E, 25 m, rainforest, 13.–14.XI.1993 (B.L. Fisher); Toamasina, Andranobe, 5.3 km SSE Ambanizana, 15.6713°S, 49.9739°E, 425 m, rainforest, 21.XI.1993 (B.L. Fisher); Toamasina, Montagne d’Anjanaharibe, 18.0 km 21° NNE Ambinanitelo, 15.1883°S, 49.615°E, 470 m, rainforest, 8.–12.III.2003 (B.L. Fisher et al.); Toamasina, Montagne d’Anjanaharibe, 19.5 km 27° NNE Ambinanitelo, 15.1783°S, 49.635°E, 1100 m, montane rainforest, 12.–16.III.2003 (B.L. Fisher et al.); Toamasina, Reserve Betampona, Camp Vohitsivalana, 37.1 km 338° Toamasina, 17.8867°S, 49.2025°E, 520 m, rainforest, 1.–3.XII.2005 (B.L. Fisher et al.); Toamasina, 19 km ESE Maroantsetra, 15.4833°S, 49.9°E, 350 m, rainforest, 22.IV.1989 (P.S. Ward); Toamasina, Montagne d’Akirindro 7.6 km 341° NNW Ambinanitelo, 15.2883°S, 49.5483°E, 600 m, rainforest, 17.–21.III.2003 (B.L. Fisher et al.); Toamasina, Nosy Mangabe, 15.5°S, 49.766667°E, 300 m, rainforest, 18.IV.1989 (P.S. Ward); Toamasina, Ile Sainte Marie, Forêt Ambohidena, 22.8 km 44° Ambodifotatra, 16.8243°S, 49.9642°E, 20 m, littoral rainforest, 21.XI.2005 (B.L. Fisher et al.); Toamasina, F.C. Sandranantitra, 18.0483°S, 49.0917°E, 450 m, rainforest, 21.–24.I.1999 (H.J. Ratsirarson); Toamasina, Parc National de Zahamena, Tetezambatana forest, near junction of Nosivola and Manakambahiny Rivers, 17.743°S, 48.7294°E, 860 m, rainforest, 18.–19.II.2009 (B.L. Fisher et al.); Toamasina, Parc National de Zahamena, Onibe River, 17.7591°S, 48.8547°E, 780 m, rainforest, 21.–23.II.2009 (B.L. Fisher et al.).

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 (PSLI 25–27); first gastral tergite with short, relatively dense, appressed to subdecumbent pubescence and without any standing hairs at all.

(N=12). HL 0.47–0.56 (0.51); HW 0.45–0.54 (0.49); SL 0.31–0.35 (0.33); EL 0.11–0.13 (0.12); PH 0.23–0.30 (0.26); PW 0.34–0.39 (0.36); WL 0.54–0.68 (0.61); PSL 0.12–0.15 (0.13); PTL 0.12–0.14 (0.12); PTH 0.19–0.22 (0.20); PTW 0.13–0.17 (0.15); PPL 0.13–0.16 (0.15); PPH 0.19–0.21 (0.19); PPW 0.18–0.22 (0.20); CI 95–97 (96); SI 63–70 (67); OI 23–24 (24); DMI 54–63 (59); LMI 42–46 (43); PSLI 25–27 (26); PeNI 38–46 (42); LPeI 55–68 (61); DPeI 108–139 (123); PpNI 53–59 (56); LPpI 70–80 (76); DPpI 131–147 (139); PPI 126–138 (133).

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 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 (SI 63–70). Eyes of moderate size (OI 23–24). Mesosomal outline in profile flat to very weakly convex, relatively high (LMI 42–46), and moderately to strongly 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 25–27); propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high, rounded nodiform to weakly rectangular nodiform, with moderately rounded antero- and posterodorsal margins, around 1.5 to 1.8 times higher than long (LPeI 55–68), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height and equally marginate (very rarely posterodorsal margin more rounded and lower than anterodorsal margin), petiolar dorsum flat to very weakly convex; node in dorsal view around 1.1 to 1.4 times wider than long (DPeI 108–139), in dorsal view pronotum between 2.2 to 2.6 times wider than petiolar node (PeNI 38–46). Postpetiole in profile globular, approximately 1.2 to 1.4 times higher than long (LPpI 70–80); in dorsal view around 1.3 to 1.5 times wider than long (DPpI 131–147), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 53–59). 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 126–138). Mandibles distinctly striate; 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 ten 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 longitudinally rugose to reticulate-rugose. Ground sculpture on head absent to weakly punctate. Mesosoma laterally and dorsally mostly irregularly longitudinally rugose. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma weak to absent. Waist segments and gaster completely unsculptured, smooth and shining. Head and mesosoma with numerous, moderately long and fine standing hairs; waist segments and first gastral tergite with short, comparatively dense, appressed to subdecumbent pubescence, sometimes several of these short hairs suberect to erect. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with decumbent to suberect hairs. Head, mesosoma, waist segments, and gaster generally orange-brown to chestnut brown, mandibles, antennae, and legs always lighter, usually yellowish brown.

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 Tetramorium 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.

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, Tetramorium dalek has an elevational range from 20 to 1280 m, and seems to live in leaf litter.

Tetramorium dalek is easily distinguishable within the Tetramorium naganum species group since it is the only species without long, standing hairs on the waist segments and the first gastral tergite, and in addition, it also has generally shorter propodeal spines (PSLI 25–27) than the other four species (PSLI 27–37). But it is possible to mistake Tetramorium dalek with species from other groups. Its general habitus and in particular its lack of standing pilosity on the first gastral tergite could lead to misplacement in the Tetramorium schaufussii complex of the Tetramorium schaufussii species group or the Tetramorium ibycterum complex in the Tetramorium ranarum group. Indeed, a misidentification with one species from the latter complex is likely. Tetramorium ibycterum superficially shares many characters with Tetramorium dalek, and even most morphometric ranges. However, Tetramorium ibycterum has very well developed antennal scrobes with clearly defined margins all around, whereas Tetramorium dalek has weaker antennal scrobes without clearly defined margins all around. In addition, Tetramorium dalek differs from the species of the Tetramorium schaufussii complex in having a broader head (CI 95–97) and higher and stouter mesosoma (LMI 42–46). Consequently, despite morphological similarities to other species groups, we consider Tetramorium dalek best placed in the Tetramorium naganum group.

Holotype, pinned worker, MADAGASCAR, Antsiranana, Forêt Ambanitaza, 26.1 km 347° Antalaha, 14.67933°S, 50.18367°E, 240 m, rainforest, sifted litter (leaf mold, rotten wood), collection code BLF10997, 26.XI.2004 (B.L. Fisher) (CAS: CASENT0056450). Paratypes, ten pinned workers with same data as holotype (BMNH: CASENT0056445; CAS: CASENT0056435; CASENT0056436; CASENT0056437; CASENT0056441; CASENT0056448; CASENT0056449; CASENT0056456; CASENT0056467; MCZ: CASENT0056461).

Antsiranana, Forêt Ambanitaza, 26.1 km 347° Antalaha, 14.6793°S, 50.1837°E, 240 m, rainforest, 26.XI.2004 (B.L. Fisher); Antsiranana, 1 km W Andampibe, Cap Masoala, 15.6936°S, 50.1814°E, 125 m, lowland rainforest, 1.XII.1993 (G.D. Alpert); Antsiranana, Forêt de Binara, 9.4km 235° SW Daraina, 13.2633°S, 49.6°E, 1100 m, montane rainforest, 5.XII.2003 (B.L. Fisher); Antsiranana, Parc National Montagne d’Ambre, 3.6 km 235° SW Joffreville, 12.5344°S, 49.1795°E, 925 m, montane rainforest, 20.–26.I.2001 (B.L. Fisher et al.); Antsiranana, Parc National de Marojejy, Manantenina River, 27.6 km 35° NE Andapa, 9.6 km 327° NNW Manantenina, 14.435°S, 49.76°E, 775 m, 15.–18.XI.2003 (B.L. Fisher et al.); Toamasina, Montagne d’Akirindro, 7.6 km 341° NNW Ambinanitelo, 15.2883°S, 49.5483°E, 600 m, rainforest, 17.–21.III.2003 (B.L. Fisher et al.); Toamasina, 19 km ESE Maroantsetra, 15.4833°S, 49.9°E, 350 m, 22.IV.1989 (P.S. Ward).

Tetramorium enkidu is distinguishable from the other species of the group by the following combination of characters: eyes small to moderate in size (OI 22–24); waist segments with several long erect hairs; propodeal spines long to very long (PSLI 29–36); 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.

(N=12). HL 0.53–0.62 (0.58); HW 0.50–0.60 (0.56); SL 0.33–0.43 (0.39); EL 0.11–0.14 (0.13); PH 0.25–0.34 (0.31); PW 0.36–0.46 (0.43); WL 0.59–0.77 (0.71); PSL 0.16–0.21 (0.19); PTL 0.13–0.16 (0.15); PTH 0.21–0.26 (0.24); PTW 0.14–0.18 (0.17); PPL 0.15–0.21 (0.19); PPH 0.20–0.26 (0.24); PPW 0.21–0.26 (0.24); CI 93–98 (96); SI 64–72 (69); OI 22–24 (23); DMI 58–62 (60); LMI 41–45 (43); PSLI 29–36 (32); PeNI 35–42 (39); LPeI 60–65 (63); DPeI 104–113 (109); PpNI 54–60 (57); LPpI 73–85 (79); DPpI 120–140 (131); PPI 142–155 (147).

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 (SI 64–72). Eyes short to moderate (OI 22–24). 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 (PPI 142–155). 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 completely 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.

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.

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, Tetramorium enkidu appears to live in leaf litter or the ground.

Tetramorium enkidu is easily identifiable within the species group. The presence of several long, erect hairs on the waist segments and much longer propodeal spines (PSLI 29–36) separate Tetramorium enkidu from Tetramorium dalek (PSLI 25–27). The latter species and Tetramorium naganum both lack standing pilosity on the first gastral tergite, which is present in Tetramorium enkidu. Tetramorium naganum also has a thinner petiolar node, which is between 1.7 to 1.9 times higher than long (LPeI 54–58), contrasting with the thicker node of Tetramorium enkidu, which is between 1.5 and 1.7 times higher than long (LPeI 60–65). Also distinguishable from Tetramorium enkidu by a relatively thin petiolar node is Tetramorium gilgamesh (LPeI 50–58). The latter also possesses larger eyes (OI 25–27) than Tetramorium enkidu (OI 22–24), but this can be difficult to see without measuring. The last species of the group, Tetramorium alperti, shares the thicker petiolar node shape with Tetramorium enkidu, as well as most other characters except gastral pilosity. Indeed, as outlined in the description of Tetramorium alperti, both could be easily combined into one species since their separation is based only on differences in gastral pilosity/pubescence. However, we prefer to describe them as distinct because their distribution ranges overlap and both maintain a species-specific pattern of gastral pilosity/pubescence in sympatry.

Holotype, pinned worker, MADAGASCAR, Toamasina, F.C. Sandranantitra, 18.0483°S, 49.0917°E, 450 m, rainforest, sifted litter (leaf mold, rotten wood), collection code HJR101, 18.–21.I.1999 (H.J. Ratsirarson) (CAS: CASENT0247312). Paratypes, four pinned workers with same data as holotype (CAS: CASENT0189097; CASENT0218015); and three pinned workers with same data as holotype except collected from the 21.–24.I.1999 and collection code HJR102 (CAS: CASENT0189096; CASENT0218016).

MADAGASCAR: Antsiranana, 1 km W Andampibe, Cap Masoala, 15.6936°S, 50.1814°E, 125 m, lowland rainforest, 1.XII.1993 (G.D. Alpert); Toamasina, Montagne d’Akirindro 7.6 km 341° NNW Ambinanitelo, 15.2883°S, 49.5483°E, 600 m, rainforest, 17.–21.III.2003 (B.L. Fisher et al.); Toamasina, Andranobe, 5.3 km SSE Ambanizana, 15.6713°S, 49.9739°E, 425 m, rainforest, 21.XI.1993 (B.L. Fisher); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.7727°S, 49.2655°E, 450 m, rainforest, 20.–22.II.2010 (B.L. Fisher et al.); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.7633°S, 49.2669°E, 520 m, rainforest, 22.II.2010 (B.L. Fisher et al.); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.8175°S, 49.295°E, 360 m, rainforest, 25.–27.II.2010 (B.L. Fisher et al.); Toamasina, F.C. Andriantantely, 18.695°S, 48.8133°E, 530 m, rainforest, 7.–10.XII.1998 (H.J. Ratsirarson); Toamasina, Montagne d’Anjanaharibe, 18.0 km 21° NNE Ambinanitelo, 15.1883°S, 49.615°E, 470 m, rainforest, 8.–12.III.2003 (B.L. Fisher et al.); Toamasina, Reserve Betampona, Camp Vohitsivalana, 37.1 km 338° Toamasina, 17.8867°S, 49.2025°E, 520 m, rainforest, 1.–3.XII.2005 (B.L. Fisher et al.); Toamasina, Parc National Mananara-Nord, 7.1 km 261° Antanambe, 16.455°S, 49.7875°E, 225 m, rainforest, 14.XI.2005 (B.L. Fisher et al.); Toamasina, F.C. Sandranantitra, 18.0483°S, 49.0917°E, 450 m, rainforest, 18.–24.I.1999 (H.J. Ratsirarson).

The following character combination distinguishes Tetramorium gilgamesh from the other members of the Tetramorium 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.

(N=12). HL 0.52–0.56 (0.54); HW 0.49–0.55 (0.51); SL 0.36–0.38 (0.37); EL 0.13–0.14 (0.13); PH 0.26–0.30 (0.27); PW 0.36–0.41 (0.38); WL 0.61–0.66 (0.64); PSL 0.14–0.17 (0.15); PTL 0.11–0.14 (0.12); PTH 0.21–0.24 (0.22); PTW 0.13–0.17 (0.14); PPL 0.15–0.18 (0.16); PPH 0.19–0.22 (0.20); PPW 0.20–0.24 (0.22); CI 92–98 (94); SI 68–76 (73); OI 25–27 (26); DMI 58–62 (59); LMI 40–45 (42); PSLI 27–30 (28); PeNI 33–40 (37); LPeI 50–59 (55); DPeI 112–127 (118); PpNI 54–59 (56); LPpI 74–85 (80); DPpI 125–142 (132); PPI 143–169 (153).

Head weakly to distinctly longer than wide (CI 92–98); 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 distinct but relatively shallow, usually with defined margins all around, but ventral margin sometimes poorly defined and merging with surrounding sculpture, median scrobal carina generally not well developed, if present relatively weak and reaching eye level only. Antennal scapes short, not reaching posterior head margin (SI 68–76). Eyes relatively large (OI 25–27). Mesosomal outline in profile weakly convex, relatively high (LMI 40–45), and moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines spinose, long, and acute (PSLI 27–30); 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 1.7 to 2.0 times higher than long (LPeI 50–59), anterior and posterior faces not parallel, node slightly narrowing from base to apex, usually anterodorsal and posterodorsal margins situated at about same height (very rarely anterodorsal margin weakly higher than posterodorsal margin), petiolar dorsum weakly to moderately convex; node in dorsal view around 1.1 to 1.3 times wider than long (DPeI 112–127), in dorsal view pronotum between 2.5 to 3.0 times wider than petiolar node (PeNI 33–40). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 74–85); in dorsal view between 1.2 to 1.4 times wider than long (DPpI 125–142), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 54–59). Postpetiole in profile appearing thicker and lower than petiolar node, postpetiole in dorsal view around 1.4 to 1.7 times wider than petiolar node (PPI 143–169). Mandibles usually unsculptured, smooth, and shining, rarely with traces of longitudinal rugulae; 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 eight to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, some rugae irregular, interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured, smooth and shining; lateral head mostly longitudinally rugose to reticulate-rugose, but with extensive unsculptured areas. Ground sculpture on head absent to weakly punctate. Mesosoma laterally and dorsally irregularly longitudinally rugose, sometimes lateral mesosoma with a few unsculptured areas medially. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma usually 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 to moderately long, abundant, decumbent to suberect pilosity, without short, dense, appressed to subdecumbent pubescence; pilosity appearing disorganized due to varying degrees of inclination and hair length. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to subdecumbent hairs. Head, mesosoma, waist segments, and gaster usually orange to light brown, rarely of darker brown, mandibles, antennae, and legs usually lighter, yellowish brown.

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.

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 Tetramorium gilgamesh seems to be leaf litter.

The identification of Tetramorium gilgamesh within the Tetramorium naganum species group is fairly straightforward. The best diagnostic character is eye size since Tetramorium 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 Tetramorium 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, Tetramorium 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 Tetramorium gilgamesh appears disorganized due to varying degrees of inclination and hair length. The gastral pilosity separates it also from Tetramorium alperti, Tetramorium enkidu, and Tetramorium naganum, which have very different patterns of pilosity/pubescence. Furthermore, Tetramorium alperti and Tetramorium enkidu have thicker petiolar nodes (LPeI 60–68) than Tetramorium gilgamesh (LPeI 50–59). Tetramorium naganum shares the same shape of the petiolar node with Tetramorium 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 Tetramorium gilgamesh.

Holotype, pinned worker, MADAGASCAR, Toamasina, La Mandraka, 18.912778°S, 47.892222°E 1280 m, montane forest, collection code AB41, 8.II.1977 (W.L. & D.E. Brown) (MCZ: MCZ_Holotype_32379) [examined]. Paratypes, 16 pinned workers and one dealate queen with same data as holotype (BMNH: CASENT0102346; CASENT0235212; MCZ: MCZ_Paratype_32379) [examined].

[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 Tetramorium naganum.]

MADAGASCAR: Antsiranana, Rés. Anjanaharibe-Sud, 6.5 km SSW Befingotra, 14.75°S, 49.5°E, 875 m, rainforest, 19.X.1994 (B.L. Fisher); Antsiranana, Rés. Anjanaharibe-Sud, 9.2 km WSW Befingotra, 14.75°S, 49.4667°E, 1280 m, montane rainforest, 5.XI.1994 (B.L. Fisher); Antananarivo, 3 km 41° NE Andranomay, 11.5 km 147° SSE Anjozorobe, 18.4733°S, 47.96°E, 1300 m, 5.–13.XII.2000 (B.L. Fisher et al.); Toamasina, 6.9 km NE Ambanizana, Ambohitsitondroina, 15.5851°S, 50.0095°E, 825 m, rainforest, 2.XII.1993 (B.L. Fisher); Toamasina, Ambanizana, Parc National Masoala, 15.5722°S, 50.0069°E, 1020 m, montane rainforest, 2.–6.III.2003 (D. Andriamalala et al.); Toamasina, Ambatoharanana, Corridor Forestier Analamay-Mantadia, 18.8042°S, 48.4008°E, 968 m, 12.–19.XII.2012 (B.L. Fisher et al.); Toamasina, Analamay, 18.8062°S, 48.3371°E, 1068 m, montane rainforest, 21.III.2004 (B.L. Fisher); Toamasina, Ankerana, 18.4017°S, 48.806°E, 1035 m, montane forest, 24.–29.I.2012 (B.L. Fisher et al.); Toamasina, Montagne d’Anjanaharibe, 19.5 km 27° NNE Ambinanitelo, 15.17833°S, 49.635°E, 1100 m, montane rainforest, 12.–16.III.2003 (B.L. Fisher).

Tetramorium naganum can be easily diagnosed within the Tetramorium 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.

(N=10). HL 0.57–0.72 (0.63); HW 0.59–0.73 (0.65); SL 0.39–0.51 (0.46); EL 0.13–0.16 (0.14); PH 0.29–0.40 (0.33); PW 0.41–0.53 (0.45); WL 0.73–0.92 (0.78); PSL 0.18–0.22 (0.20); PTL 0.13–0.16 (0.14); PTH 0.24–0.28 (0.25); PTW 0.15–0.19 (0.16); PPL 0.18–0.22 (0.19); PPH 0.23–0.27 (0.24); PPW 0.23–0.28 (0.25); CI 94–99 (97); SI 68–77 (73); OI 21–23 (22); DMI 56–62 (58); LMI 40–45 (43); PSLI 28–33 (30); PeNI 34–38 (35); LPeI 54–58 (56); DPeI 107–122 (115); PpNI 52–59 (54); LPpI 77–84 (80); DPpI 125–137 (128); PPI 147–159 (153).

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 (SI 68–77). Eyes short to moderate (OI 21–23). Mesosomal outline in profile weakly convex, relatively high (LMI 40–45), 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 well-rounded 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 (PPI 147–159). 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.

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 Tetramorium alperti and Tetramorium dalek. Tetramorium 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 Tetramorium alperti, it is likely that Tetramorium 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 Tetramorium 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, Tetramorium naganum seems to be a leaf litter inhabitant.

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 Tetramorium alperti and Tetramorium gilgamesh since these possess pilosity in varying degrees of inclination, length, and abundance. The relatively thin and high petiolar node (LPeI 54–58) separates Tetramorium naganum from Tetramorium alperti and Tetramorium enkidu, which have much thicker petiolar nodes (LPeI 60–68). Additionally, Tetramorium naganum has smaller eyes (OI 21–23) than Tetramorium gilgamesh (OI 25–27). The last species of the group, Tetramorium dalek, shares the lack of long, standing pilosity on the first gastral tergite with Tetramorium naganum. Nevertheless, both species are very unlikely to be confused with each other. Tetramorium dalek is generally smaller (HW 0.45–0.54; WL 0.54–68), has shorter propodeal spines (PSLI 25–27), and lacks long, standing hairs on the waist segments, whereas Tetramorium naganum is generally larger (HW 0.55–0.72; WL 0.66–0.92), possesses longer propodeal spines (PSLI 28–33), and always has long, standing hairs on the waist segments.

Holotype, pinned worker, MADAGASCAR, Mahajanga, Parc National de Namoroka, 9.8 km 300° WNW Vilanandro, 16.46667°S, 45.35°E, 140 m, tropical dry forest, sifted litter (leaf mold, rotten wood), collection code BLF06446, 4.–8.XI.2002 (B.L. Fisher et al.) (CAS: CASENT0035677). Paratypes, 27 pinned workers with same data as holotype (BMNH: CASENT0035669; CAS: CASENT0035636; CASENT0035640; CASENT0035642; CASENT0035647; CASENT0035648; CASENT0035649; CASENT0035652; CASENT0035653; CASENT0035654; CASENT0035656; CASENT0035658; CASENT0035660; CASENT0035662; CASENT0035666; CASENT0035667; CASENT0035670; CASENT0035674; CASENT0035675; CASENT0035678; CASENT0035681; CASENT0035686; CASENT0035687; CASENT0035689; CASENT0035694; CASENT0035703; MCZ: CASENT0035646).

MADAGASCAR: Antananarivo, Reserve Speciale d’Ambohitantely, Forêt Ambohitantely, 20.9 km 72°NE Ankazobe, 18.2253°S, 47.2868°E, 1410 m, montane rainforest, 17.–22.IV.2001 (B.L. Fisher et al.); Antsiranana, Forêt d’Anabohazo, 21.6 km 247° WSW Maromandia, 14.3089°S, 47.9143°E, 120 m, tropical dry forest, 11.–16.III.2001 (B.L. Fisher et al.); Fianarantsoa, Ampangabe I Non Protected Area, 21.4 km W Itremo, 20.6111°S, 46.6069°E, 1414 m, savannah woodland, 21.–23.III.2010 (A. Ravelomanana); Fianarantsoa, Ampangabe II Non Protected Area, 21.29 km W Itremo, 20.6114°S, 46.6081°E, 1402 m, savannah woodland, 21.–23.III.2010 (A. Ravelomanana); Fianarantsoa, Ampangabe VI Non Protected Area, 21.16 km W Itremo, 20.6144°S, 46.6104°E, 1379 m, shrubland, 21.–23.III.2010 (A. Ravelomanana); Fianarantsoa, Ampangoabe V Non Protected Area, 21.37 km W Itremo, 20.6136°S, 46.608°E, 1449 m, shrubland, 22.–23.III.2010 (A. Ravelomanana); Fianarantsoa, Ampotoampoto I National Parc, 8.02 km NW Ilakaka, 22.6283°S, 45.1886°E, 917 m, savannah woodland, 26.–28.II.2010 (A. Ravelomanana); Fianarantsoa, Forêt d’Analalava, 29.6 km 280° W Ranohira, 22.5917°S, 45.1283°E, 700 m, 1.–5.II.2003 (B.L. Fisher et al.); Fianarantsoa, Antohatsahomby I Non Protected Area, 22.77 km NW Ambatofinandrahana, 20.5506°S, 46.5856°E, 1550 m, Uapaca woodland, 15.–17.III.2010 (A. Ravelomanana); Fianarantsoa, Forêt d’Atsirakambiaty, 7.6 km 285° WNW Itremo, 20.5933°S, 46.5633°E, 1550 m, montane rainforest, 22.–26.I.2003 (B.L. Fisher et al.); Fianarantsoa, Parc National d’Isalo, 9.1 km 354° N Ranohira, 22.4817°S, 45.4617°E, 725 m, gallery forest, 27.–31.I.2003 (B.L. Fisher et al.); Fianarantsoa, Parc National d’Isalo, Ambovo Springs, 29.3 km 4° N Ranohira, 22.2983°S, 45.3517°E, 990 m, Uapaca woodland, 9.–14.II.2003 (B.L. Fisher et al.); Fianarantsoa, Mampiarika I Non Protected Area, 28.08 km SW Ambositra, 20.7344°S, 47.0835°E, 1480 m, Uapaca woodland, 31.I.–2.II.2010 (A. Ravelomanana); Mahajanga, Forêt Ambohimanga, 26.1 km 314° Mampikony, 15.9627°S, 47.4382°E, 250 m, tropical dry forest, 13.–15.XII.2004 (B.L. Fisher); Mahajanga, Boeny Region, District of Soalala, Analamanitra forest, 14 km SW Mitsinjo, 16.7°S, 45.7°E, 19 m, dense dry forest, 26.II.-4.III.2008 (M. Rin’ha); Mahajanga, Parc National d’Ankarafantsika, Ampijoroa Station Forestiere, 40 km 306° NW Andranofasika, 16.3208°S, 46.8107°E, 130 m, tropical dry forest, 26.III.-1.IV.2001 (B.L. Fisher et al.); Mahajanga, Parc National d’Ankarafantsika, Ampijoroa Station Forestiere, 5.4 km 331° NW Andranofasika, 16.2989°S, 46.813°E, 70 m, tropical dry forest, 26.III.-1.IV.2001 (B.L. Fisher et al.); Mahajanga, Parc National d’Ankarafantsika, Forêt de Tsimaloto, 18.3 km 46° NE de Tsaramandroso, 16.2281°S, 47.1436°E, 135 m, tropical dry forest, 2.IV.-8.IV.2001 (B.L. Fisher et al.); Mahajanga, Parc National de Baie de Baly, 12.4 km 337° NNW Soalala, 16.01°S, 45.265°E, 10 m, tropical dry forest, 26.–30.XI.2002 (B.L. Fisher et al.); Mahajanga, Reserve Forestiere Beanka, 50.2 km E Maintirano, 18.0265°S, 44.0505°E, 250 m, tropical dry forest on tsingy, 19.–26.X.2009 (B.L. Fisher et al.); Mahajanga, Reserve Forestiere Beanka, 52.7 km E Maintirano, 18.0622°S, 44.5259°E, 300 m, tropical dry forest on tsingy, 24.–27.X.2009 (B.L. Fisher et al.); Mahajanga, Reserve Forestiere Beanka, 50.7 km E Maintirano, 17.8802°S, 44.4688°E, 140 m, tropical dry forest on tsingy, 29.X.–1.XI.2009 (B.L. Fisher et al.); Mahajanga, Reserve Forestiere Beanka, 50.2 km E Maintirano, 17.8876°S, 44.4726°E, 153 m, tropical dry forest on tsingy, 31.X.2009 (B.L. Fisher et al.); Mahajanga, Reserve Speciale de Bemarivo, 23.8 km 223° SW Besalampy, 16.925°S, 44.3683°E, 30 m, tropical dry forest, 19.–23.XI.2002 (B.L. Fisher et al.); Mahajanga, Mahavavy River, 6.2 km 145° SE Mitsinjo, 16.0517°S, 45.9083°E, 20 m, gallery forest, 1.–5.XII.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 9.8 km 300° WNW Vilanandro, 16.4667°S, 45.35°E, 140 m, tropical dry forest, 4.–8.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 17.8 km 329° WNW Vilanandro, 16.3767°S, 45.3267°E, 100 m, tropical dry forest, 8.–12.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 16.9 km 317° NW Vilanandro, 16.4067°S, 45.31°E, 100 m, tropical dry forest, 12.–16.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National Tsingy de Bemaraha, 3.4 km 93° E Bekopaka, Tombeau Vazimba, 19.1419°S, 44.828°E, 50 m, tropical dry forest, 6.–10.XI.2001 (B.L. Fisher et al.); Mahajanga, Parc National Tsingy de Bemaraha, 2.5 km 62° ENE Bekopaka, Ankidrodroa River, 19.1322°S, 44.8147°E, 100 m, 11.–15.XI.2001 (B.L. Fisher et al.); Mahajanga, Parc National Tsingy de Bemaraha, 10.6 km ESE 123° Antsalova, 18.7094°S, 44.7182°E, 150 m, tropical dry forest on tsingy, 16.–20.XI.2001 (B.L. Fisher et al.); Toliara, Parc National d’Andohahela, Forêt d’Ambohibory, 1.7 km 61° ENE Tsimelahy, 36.1 km 308° NW Tolagnaro, 24.93°S, 46.6455°E, 300 m, tropical dry forest, 16.–20.I.2002 (B.L. Fisher et al.); Toliara, Andohahela National Park, Tsimelahy, 24.9368°S, 46.6267°E, 180 m, transition forest, 16.–26.II.2003 (M.E. Irwin et al.); Toliara, 18 km NNW Betroka, 23.1633°S, 45.9686°E, 825 m, savannah, 24.XI.-4.XII.1994 (M.A. Ivie & D. A. Pollock); Toliara, Atsimo Andrefana Region, District of Betioky, 30 km E Betioky, Beza Mahafaly Special Reserve, 23.6865°S, 44.591°E, 165 m, gallery dry deciduous forest, 1.–7.I.2002 (M. Rin’ha); Toliara, Beza-Mahafaly, 27 km E Betioky, 23.65°S, 44.6333°E, 135 m, tropical dry forest, 23.IV.1997 (B.L. Fisher); Toliara, Fiherenana, 23.1769°S, 43.9608°E, 100 m, gallery forest, 21.–24.X.2002 (Frontier Project); Toliara, Fiherenana, 23.177°S, 43.9614°E, gallery forest, 18.–19.VII.2003 (Frontier Wilderness Project); Toliara, southern Isoky-Vohimena Forest, 59 km NE Sakaraha, 22.4667°S, 44.85°E, 730 m, tropical dry forest, 21.I.1996 (B.L. Fisher); Toliara, Makay Mts., 21.2098°S, 45.3418°E, 525 m, gallery forest on sandy soil, 27.XI.-2.XII.2010 (B.L. Fisher et al.); Toliara, Makay Mts., 21.2199°S, 45.324°E, 500 m, gallery forest on sandy soil, 24.XI.-12.XII.2010 (B.L. Fisher et al.); Toliara, Makay Mts., 21.31°S, 45.1295°E, 590 m, dry forest on sandy soil, 3.–6.XII.2010 (B.L. Fisher et al.); Toliara, Vohibasia Forest, 59 km NE Sakaraha, 22.4667°S, 44.85°E, 780 m, tropical dry forest, 13.I.1996 (B.L. Fisher); Toliara, Parc National de Zombitse, near road, 22.8405°S, 44.7312°E, 825 m, spiny deciduous forest, 15.X.2001-23.III.2002 (R. Harin’Hala); Toliara, Parc National de Zombitse, near ANGAP office, 22.8865°S, 44.6922°E, 840 m, deciduous spiny forest, 9.XI.2001-26.I.2002 (R. Harin’Hala); Toliara, Parc National de Zombitse, 19.8 km 84° E Sakaraha, 22.8433°S, 44.71°E, 770 m, tropical dry forest, 5.–9.II.2003 (B.L. Fisher et al.).

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 (OI 18–19); 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.

(N=12). HL 0.81–1.00 (0.94); HW 0.80–1.00 (0.94); SL 0.51–0.64 (0.60); EL 0.15–0.19 (0.18); PH 0.42–0.53 (0.48); PW 0.57–0.73 (0.68); WL 0.92–1.15 (1.07); PSL 0.24–0.32 (0.27); PTL 0.20–0.26 (0.23); PTH 0.35–0.42 (0.40); PTW 0.28–0.36 (0.32); PPL 0.23–0.30 (0.27); PPH 0.32–0.41 (0.38); PPW 0.35–0.45 (0.42); CI 98–102 (100); SI 62–65 (64); OI 18–19 (19); DMI 61–66 (64); LMI 43–47 (45); PSLI 26–32 (28); PeNI 45–49 (47); LPeI 56–61 (58); DPeI 135–145 (138); PpNI 59–63 (61); LPpI 70–75 (73); DPpI 150–158 (152); PPI 125–134 (130).

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 (OI 18–19). 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 propodeum 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 reticulate-punctate 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.

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.

As mentioned above, it is surprising that most species in the species group, except the holotype of Tetramorium plesiarum, were previously unknown. This is especially true for Tetramorium bressleri. It is by far the most common and abundant species of the Tetramorium 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 Tetramorium 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.

Tetramorium bressleri is not likely to be confused with Tetramorium gollum, Tetramorium hobbit, or Tetramorium mars, whereas differentiating between Tetramorium bressleri and Tetramorium 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 Tetramorium gollum, nor does it have the blocky petiolar node shape of Tetramorium mars or the massively enlarged petiolar node of Tetramorium hobbit. The separation from Tetramorium 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 Tetramorium 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 Tetramorium bressleri and one very large specimen of Tetramorium 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 Tetramorium plesiarum (OI 21–23) are larger than in Tetramorium bressleri (OI 18–19), 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 Tetramorium bressleri, making the area appear very smooth and shiny, while it is usually longitudinally rugose with reticulate-punctate ground sculpture in Tetramorium plesiarum. The sculpture on the sides of the petiolar node varies too, since it is much more reticulate-punctate and matte in Tetramorium plesiarum than in Tetramorium 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 Tetramorium plesiarum the anterodorsal margin of the node protrudes anteriorly and is a bit more marginate than the more rounded posterodorsal margin, while in Tetramorium bressleri both margins are usually equally marginate and the anterodorsal margin does not protrude anteriorly at all.

Considering how common and abundant Tetramorium bressleri is in western Madagascar, it is interesting that it shows very little intraspecific variation and remains very stable in its morphology.

Holotype, pinned worker, MADAGASCAR, Fianarantsoa, Forêt d’Analalava, 29.6 km 280° W, Ranohira, 22.59167°S, 45.12833°E, 700 m, tropical dry forest, pitfall trap, collection code BLF07381, 1.–5.II.2003 (CAS: CASENT0074849). Paratypes, two pinned workers with same data as holotype (CAS: CASENT0074839, CASENT0074974).

The strongly developed sculpture on the basal half of the first gastral tergite and the extremely swollen gaster clearly distinguish Tetramorium gollum from the other species in the group.

(N=3). HL 0.76–0.90 (0.81); HW 0.74–0.90 (0.80); SL 0.47–0.59 (0.52); EL 0.15–0.18 (0.16); PH 0.48–0.52 (0.50); PW 0.54–0.66 (0.59); WL 0.85–1.03 (0.93); PSL 0.23–0.26 (0.25); PTL 0.20–0.25 (0.23); PTH 0.35–0.42 (0.38); PTW 0.27–0.37 (0.31); PPL 0.24–0.27 (0.25); PPH 0.37–0.43 (0.40); PPW 0.40–0.50 (0.45); CI 97–100 (98); SI 64–66 (65); OI 19–20 (20); DMI 62–64 (63); LMI 50–56 (54); PSLI 29–31 (30); PeNI 50–56 (53); LPeI 57–61 (59); DPeI 130–148 (138); PpNI 75–79 (76); LPpI 63–65 (64); DPpI 167–185 (176); PPI 135–148 (143).

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 (SI 64–66). Eyes relatively small (OI 19–20). 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.

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.

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, Tetramorium gollum probably is one of the more rarely encountered Tetramorium species in Madagascar.

Tetramorium gollum is a very conspicuous species within the Tetramorium 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 Tetramorium jedi in the Tetramorium tortuosum group and Tetramorium sericeiventre in the Tetramorium sericeiventre group. The latter has 12 antennal segments (vs. 11 in Tetramorium gollum) and Tetramorium jedi has, among other characters, a very differently shaped petiolar node (longer than broad in Tetramorium jedi vs. broader than long in Tetramorium gollum). Beyond sculpture and the enlarged gaster, Tetramorium gollum is morphologically very similar to Tetramorium 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 Tetramorium gollum (LPpI 63–65; DPpI 167–185) than in Tetramorium bressleri (LPpI 59–63; DPpI 150–158).

Holotype, pinned worker, MADAGASCAR, Toliara, Parc National de Tsimanampetsotsa, Forêt de Bemanateza, 20.7 km 81° E Efoetse, 23.0 km 131° SE Beheloka, 23.99222°S, 43.88067°E, 90 m, spiny forest/thicket, sifted litter (leaf mold, rotten wood), collection code BLF06254, 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).

MADAGASCAR: Fianarantsoa, Ampandravelo II Non Protected Area, 10.78 km NE Ranohira, 22.5392°S, 45.5155°E, 873 m, shrubland, 20.–22.II.2010 (A. Ravelomanana); Fianarantsoa, Ampotoampoto I National Parc, 8.02 km NW Ilakaka, 22.6283°S, 45.1886°E, 917 m, savannah woodland, 26.–28.II.2010 (A. Ravelomanana); Fianarantsoa, Ampotoampoto III National Parc, 7.91 km NW Ilakaka, 22.6294°S, 45.189°E, 919 m, savannah woodland, 27.–28.II.2010 (A. Ravelomanana); Fianarantsoa, Ampotoampoto IV National Parc, 7.83 km NW Ilakaka, 22.6294°S, 45.1912°E, 923 m, savannah woodland, 27.–28.II.2010 (A. Ravelomanana); Toliara, Parc National d’Andohahela, Forêt de Manantalinjo, 33.6 km 63° ENE Amboasary, 7.6 km 99° E Hazofotsy, 24.8169°S, 46.61°E, 150 m, spiny forest/thicket, 12.–16.I.2002 (B.L. Fisher et al.); Toliara, Forêt de Beroboka, 5.9 km 131° SE Ankidranoka, 22.2331°S, 43.3663°E, 80 m, tropical dry forest, 12.–16.III.2002 (B.L. Fisher et al.); Toliara, Parc National de Kirindy Mite, 16.3 km 127° SE Belo sur Mer, 20.7953°S, 44.147°E, 80 m, tropical dry forest, 6.–10.III.2002 (B.L. Fisher et al.); Toliara, Makay Mts., 21.3411°S, 45.1805°E, 500 m, barren rock with sparse vegetation, burned grass, 28.XI.2010 (B.L. Fisher et al.); Toliara, Parc National de Tsimanampetsotsa, Forêt de Bemanateza, 20.7 km 81° E Efoetse, 23.0 km 131° SE Beheloka, 23.99222°S, 43.88067°E, 90 m, spiny forest/thicket, 22.–26.III.2002 (B.L. Fisher et al.).

Tetramorium hobbit is easily recognisable within the Tetramorium plesiarum species group due to its massively developed petiolar node and very conspicuous reticulate-punctate ground sculpture on head and mesosoma.

(N=12). HL 0.79–0.88 (0.84); HW 0.80–0.88 (0.85); SL 0.52–0.58 (0.55); EL 0.16–0.20 (0.18); PH 0.42–0.53 (0.47); PW 0.63–0.72 (0.69); WL 0.96–1.11 (1.04); PSL 0.16–0.25 (0.20); PTL 0.28–0.31 (0.30); PTH 0.40–0.46 (0.44); PTW 0.38–0.45 (0.41); PPL 0.24–0.30 (0.27); PPH 0.39–0.45 (0.43); PPW 0.45–0.54 (0.51); CI 100–102 (101); SI 64–67 (65); OI 19–22 (21); DMI 63–72 (66); LMI 43–50 (46); PSLI 18–29 (23); PeNI 57–66 (60); LPeI 63–71 (68); DPeI 133–148 (140); PpNI 69–76 (74); LPpI 60–67 (63); DPpI 175–200 (188); PPI 116–126 (122).

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 (OI 19–22). 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.

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.

The distribution of Tetramorium 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, Tetramorium 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.

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, Tetramorium mars seems morphologically closest to Tetramorium 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, Tetramorium mars also has shorter antennal scapes (SI 58–62; DPeI 108–122) and a narrower petiolar node in dorsal view than Tetramorium hobbit (SI 64–67; DPeI 133–148). Tetramorium mars (HW 0.69–0.74; WL 0.83–0.96) is also smaller than Tetramorium hobbit (HW 0.80–0.88; WL 0.96–1.10)

One noticeable intraspecific variation can be observed within Tetramorium 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 (PSLI 18 -20). 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.

Holotype, pinned worker, MADAGASCAR, Toliara, Forêt de Kirindy, 15.5 km 64° ENE Marofandilia, 20.045°S, 44.6622°E, 100 m, tropical dry forest, sifted litter (leaf mold, rotten wood), BLF04605, 28.XI.2001 (B.L. Fisher et al.) (CAS: CASENT0474279). Paratypes, 24 pinned workers with same data as holotype (BMNH: CASENT0474298; CAS: CASENT0474278; CASENT0474281; CASENT0474287; CASENT0474289; CASENT0474292; CASENT0474294; CASENT0474304; CASENT0474310; CASENT0474312; CASENT0474322; CASENT0474328; CASENT0474331; CASENT0474335; CASENT0474338; CASENT0474345; CASENT0474347; CASENT0474349; CASENT0474354; CASENT0474357; CASENT0474366; CASENT0474371; MHNG: CASENT0474312; MCZ: CASENT0474286; CASENT0474307).

MADAGASCAR: Mahajanga, Parc National d’Ankarafantsika, Forêt de Tsimaloto, 18.3 km 46° NE de Tsaramandroso, 16.2281°S, 47.1436°E, 135 m, tropical dry forest, 2.–8.IV.2001 (B.L. Fisher et al.); Mahajanga, Parc National d’Ankarafantsika, Ampijoroa Station Forestiere, 5.4 km 331° NW Andranofasika, 16.2989°S, 46.813°E, 70 m, tropical dry forest, 26.III.-1.IV.2001 (B.L. Fisher et al.); Mahajanga, Parc National de Baie de Baly, 12.4 km 337° NNW Soalala, 16.01°S, 45.265°E, 10 m, tropical dry forest, 26.–30.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National Tsingy de Bemaraha, 10.6 km ESE 123° Antsalova, 18.7094°S, 44.7182°E, 150 m, tropical dry forest on tsingy, 16.–20.XI.2001 (B.L. Fisher et al.); Toliara, Tulear, Bereboka, 60 km NE Morondava, 18.–23.V.1983 (J.S. Noyes & M.C. Day); Toliara, Atsimo Andrefana Region, District of Betioky, 30 km E Betioky, Beza Mahafaly Special Reserve, 23.6865°S, 44.591°E, 165 m, gallery dry deciduous forest, 29.IV.-19.V.2002 (M. Rin’ha); Toliara, Res. Beza-Mahafaly, Parcel 1, 23.65833°S, 44.62889°E, 160 m, tropical dry forest, 13.II.1993 (G.D. Alpert); Toliara, Res. Beza-Mahafaly, Parcel 1, 23.65°S, 44.63333°E, 130 m, tropical dry forest, 13.XI.1993 (P.S. Ward); Toliara, Beza-Mahafaly, 27 km E Betioky, 23.65°S, 44.6333°E, 135 m, tropical dry forest, 23.IV.1997 (B.L. Fisher); Toliara, Kirindy Forest, 20.07458°S, 44.67611°E, 100m, tropical dry forest, 20.XII.1993 (G.D. Alpert); Toliara, Forêt de Kirindy, 15.5 km 64° ENE Marofandilia, 20.045°S, 44.6622°E, 100 m, tropical dry forest, 28.XI.-3.XII.2001 (B.L. Fisher et al.); Toliara, Parc National de Kirindy Mite, 16.3 km 127° SE Belo sur Mer, 20.7953°S, 44.147°E, 80 m, tropical dry forest, 6.–10.XII.2001 (B.L. Fisher et al.); Toliara, Forêt de Mite, 20.7 km 29° WNW Tongobory, 23.5242°S, 44.1213°E, 75 m, gallery forest, 27.II.–3.III.2002 (B.L. Fisher et al.); Toliara, 48 km ENE Morondava, 20.06667°S, 44.65°E, 30 m, tropical dry forest, 4.–7.I.1991 (D.M. Olson).

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.

(N=12). HL 0.71–0.77 (0.74); HW 0.69–0.74 (0.72); SL 0.42–0.46 (0.44); EL 0.15–0.17 (0.16); PH 0.35–0.44 (0.38); PW 0.50–0.58 (0.54); WL 0.83–0.96 (0.88); PSL 0.21–0.24 (0.22); PTL 0.22–0.27 (0.24); PTH 0.32–0.37 (0.34); PTW 0.26–0.33 (0.29); PPL 0.22–0.26 (0.24); PPH 0.28–0.33 (0.31); PPW 0.36–0.42 (0.38); CI 96–99 (98); SI 58–62 (60); OI 21–22 (22); DMI 60–64 (62); LMI 42–46 (44); PSLI 28–32 (30); PeNI 51–56 (53); LPeI 69–76 (73); DPeI 108–123 (117); PpNI 68–72 (70); LPpI 75–80 (78); DPpI 156–165 (160); PPI 129–137 (134).

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 relatively small to moderate (OI 21–22). 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 cross-meshes, 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.

This new species is named after the ancient Roman god of war, “Mars”. The species epithet is an arbitrary combination of letters, thus invariable.

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, Tetramorium mars was not found in Andohahela in the southeast of Madagascar, even though Tetramorium bressleri, Tetramorium hobbit, and Tetramorium plesiarum occur there. This is surprising since the four species of the group except Tetramorium gollum share more or less the same distribution range.

Within the species group Tetramorium 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 Tetramorium mars (LPeI 69–76; DPeI 108–123) clearly from Tetramorium gollum (LPeI 57–60; DPeI 130–148). Despite the fact that Tetramorium mars shares some similarities with Tetramorium bressleri and Tetramorium plesiarum, the latter also have relatively higher, thinner, and wider petiolar nodes (LPeI 56–63; DPeI 130–144) which distinguish them from Tetramorium mars. In addition, Tetramorium mars has much better developed sculpture on the dorsum of the petiolar node than Tetramorium bressleri or Tetramorium plesiarum. The species most similar morphologically to Tetramorium mars is Tetramorium hobbit. Both share a more blocky nodiform petiolar node, but which is still much larger in Tetramorium hobbit. Indeed, this massively developed node, in combination with very conspicuous punctate ground sculpture on head and mesosoma, separates Tetramorium hobbit from Tetramorium mars, which has a much smaller petiolar node and only weakly developed ground sculpture on head and mesosoma. Further characters that distinguish Tetramorium 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, Tetramorium mars displays very little intraspecific or geographic variation.

Holotype, pinned worker, MADAGASCAR, Causse de Kelifely, 17.30306°S, 45.73444°E, forest humus and litter, dry forest, 20.–30.XI.1974 (A. Peyrieras) (MCZ: MCZ_Holotype_32372) [examined].

[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.]

MADAGASCAR: Mahajanga, Reserve Forestiere Beanka, 50.7 km E Maintirano, 17.8802°S, 44.4688°E, 140 m, tropical dry forest on tsingy, 29.X.–1.XI.2009 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 9.8 km 300° WNW Vilanandro, 16.4667°S, 45.35°E, 140 m, tropical dry forest, 4.–8.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 17.8 km 329° WNW Vilanandro, 16.3767°S, 45.3267°E, 100 m, tropical dry forest, 8.–12.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 16.9 km 317° NW Vilanandro, 16.4067°S, 45.31°E, 100 m, tropical dry forest, 12.–16.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National Tsingy de Bemaraha, 10.6 km ESE 123° Antsalova, 18.7094°S, 44.7182°E, 150 m, tropical dry forest on tsingy, 16.–20.XI.2001 (B.L. Fisher et al.); Toliara, Parc National d’Andohahela, Forêt de Manantalinjo, 33.6 km 63° ENE Amboasary, 7.6 km 99° E Hazofotsy, 24.8169°S, 46.61°E, 150 m, spiny forest/thicket, 12.–16.I.2002 (B.L. Fisher et al.); Toliara, Parc National d’Andohahela, Forêt d’Ambohibory, 1.7 km 61° ENE Tsimelahy, 36.1 km 308° NW Tolagnaro, 24.93°S, 46.6455°E, 300 m, tropical dry forest, 16.–20.I.2002 (B.L. Fisher et al.); Toliara, Andohahela National Park, Tsimelahy–Parcel II, 24.9368°S, 46.6267°E, 180 m, transition forest, 5.–15.II.2003 (M.E. Irwin et al.); Toliara, Makay Mts., 21.2184°S, 45.3106°E, 510 m, gallery forest on sandy soil, 24.–27.XI.2010 (B.L. Fisher et al.); Toliara, Makay Mts., 21.2176°S, 45.3392°E, 500 m, gallery forest on sandy soil, 28.XI.2010 (B.L. Fisher et al.); Toliara, Makay Mts., 21.3136°S, 45.1478°E, 525 m, gallery forest on sandy soil, 6.XII.2010 (B.L. Fisher et al.); Toliara, Vohibasia Forest, 59 km NE Sakaraha, 22.4667°S, 44.85°E, 780 m, tropical dry forest, 13.I.1996 (B.L. Fisher); Toliara, Parc National de Zombitse, 19.8 km 84° E Sakaraha, 22.8433°S, 44.71°E, 770 m, tropical dry forest, 5.–9.II.2003 (B.L. Fisher et al.).

The following character set separates Tetramorium 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.

(N=12). HL 0.66–0.75 (0.73); HW 0.67–0.76 (0.72); SL 0.45–0.49 (0.47); EL 0.15–0.17 (0.15); PH 0.33–0.44 (0.36); PW 0.50–0.57 (0.53); WL 0.81–0.92 (0.85); PSL 0.16–0.21 (0.18); PTL 0.18–0.22 (0.19); PTH 0.31–0.35 (0.33); PTW 0.23–0.29 (0.26); PPL 0.22–0.26 (0.24); PPH 0.29–0.33 (0.31); PPW 0.32–0.40 (0.35); CI 97–102 (99); SI 64–69 (66); OI 21–23 (22); DMI 60–65 (63); LMI 41–47 (43); PSLI 23–28 (25); PeNI 45–51 (49); LPeI 56–63 (59); DPeI 131–137 (133); PpNI 63–70 (66); LPpI 73–79 (76); DPpI 140–157 (149); PPI 129–143 (136).

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 cross-meshes, 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.

Despite being known only from seven localities and fewer than 20 specimens, Tetramorium 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 Tetramorium plesiarum is much less common than the sympatric Tetramorium bressleri, which shares much of the distribution range, but is known from many more localities and hundreds of specimens. The rarity of Tetramorium 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 Tetramorium plesiarum was mostly collected by pitfall trapping and litter sifting suggesting a ground-active lifestyle.

Tetramorium plesiarum lacks strong specialisations, such as the strongly sculptured and enlarged gaster of Tetramorium gollum, or the massively developed petiolar node of Tetramorium hobbit. Furthermore, Tetramorium mars has a lower and wider petiolar node (LPeI 69–76; DPeI 108–123) compared to Tetramorium 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 Tetramorium plesiarum is morphologically most similar to Tetramorium 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 Tetramorium bressleri (HW 0.80–1.00; WL 0.92–1.15) is much larger than Tetramorium 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 Tetramorium plesiarum and very few small specimens of Tetramorium 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 Tetramorium plesiarum (OI 21–23) are larger than in Tetramorium bressleri (OI 18–19). The mesopleuron and lateral propodeum of Tetramorium bressleri is usually mostly unsculptured and relatively smooth and shining, whereas this area is longitudinally rugose with reticulate-punctate ground sculpture in Tetramorium 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 Tetramorium plesiarum than in Tetramorium 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 Tetramorium plesiarum than in Tetramorium 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 Tetramorium 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 Tetramorium bressleri, in which both margins are usually equally marginate and the anterodorsal margin does not protrude anteriorly at all.