41 specimens: NHMUK015991449, 1♀, Cinq Cases, 16.03.1974; NHMUK015991450, 2♀, Malabar, 14.02.1975; NHMUK015991451 1♀, Picard, 28.02.1975; NHMUK015991452, 3♀, 1 juvenile, Cinq Cases B. F., 20.03.1974; NHMUK015991453, 2♀, Picard, 23.02.1974; NHMUK015991454, 2♀, Cinq Cases, 24.03.1974; NHMUK015991458, 3♀, Malabar, 08.06.1974; NHMUK015991455, 1♀, 1 juvenile, Aldabra, 30.01.1975; NHMUK015991456, 21♀, Picard, Summer 1975, leg. V. W. Spaull; NHMUK015991457, 2♀, 1 juvenile, Ochna litter, Cinq Cases B. F., 23.03.1974.

The 38 specimens from the Aldabra Atoll (from Cinq Cases, Malabar, and Picard) for which sex can reliably be determined are all females, such that the population is parthenogenetic. They are likely conspecific with L. tristani as described from the Chagos Archipelago (Popovici et al. 2024), sharing the distinctly reduced spinous process on the tibia of leg pair 12, often taking the form of a rounded bump (Fig. 1C). The stability of this character is however uncertain as specimens from localities in the Aldabra Atoll exhibit conspicuous variation in the shape of the process (Fig. 1D, Table 1). Additional similarities between these two populations include the morphology of the forcipular coxosternite (Fig. 1A, B), the number of antennal articles, and the number and shape of the spurs on the female gonopods (Fig. 1E). Variability in the characters of antennal article number, number, and distribution of coxal pores and shape of the distal spinous process on the tibia of leg pair 12 are listed in Table 1 and compared with putatively conspecific individuals from the Chagos Archipelago, excluding anamorphic stages.

Figure 1. 

Lamyctes tristani (Pocock, 1893) A, B, D NHMUK015991452 A forcipular segment, ventral view B anterior margin of forcipular coxosternite, ventral view C NHMUK015991458, distal end of tibia of leg pair 12, lateral view D distal end of tibia of leg pair 12, lateral view E NHMUK015991456, Female gonopods, ventral view.

35 specimens: NHMUK015991425, 4 specimens, Black Path, Picard, Summer 1975, leg. V. W. Spaull; NHMUK015991429, 1 specimen, Aldabra, 10.11.1973; NHMUK015991430, 6 specimens, Point Hodoul, Grande Terre, 22.03.1974; NHMUK015991431, 2 specimens, Ile. Malabar, 08.06.1974; NHMUK015991432, 18 specimens, Casuarina and Sideroxylon litter, Anse Cedres, 12.02.1974; NHMUK015991433, 4 specimens, Esprit, 14.12.1974.

Cryptops cf. japonicus collected in Aldabra is an unexpected occurrence for a species otherwise restricted to localities in southern Japan, the Korean peninsula, Manchuria (Takakuwa 1936) and Taiwan (Chao 2008). Despite the description of the morphologically similar C. doriae Pocock, 1891 from nearby localities in the Seychelles (Lewis 2007a), consistent diagnostic morphological characters separate these two populations. Most prominently, specimens from Aldabra only have one pretarsal accessory spur on legs 1–20, > 1/2 the length of the pretarsus (Fig. 2E), in contrast to C. doriae from the Seychelles which has been described with two generally subequal, conspicuous, accessory spurs that are much shorter relative to the pretarsus, on the same leg pair range (Lewis 2007a). The examined specimens agree with the description provided by Chao (2008) based on specimens collected in Taiwan, in which he notes the low number of coxopleural pores (9) in the immature (“larva”) stages, which overlaps with the condition of Aldabra specimens (Fig. 2C), the presence of 4 setae along the anterior margin of the forcipular coxosternite (Fig. 2A), and the ovoid shape of the calyx of the venom gland (Fig. 2B).

Figure 2. 

Cryptops cf. japonicus Takakuwa, 1934 A, B, D NHMUK015991433 A anterior margin of forcipular coxosternite, ventral view B Calyx of venom gland, lateral view C NHMUK015991430, coxopleuron of ultimate leg-bearing segment, lateral view D femur, tibia, and tarsus 1 of ultimate leg telopodite, lateral view E. NHMUK015991429, pretarsus of leg pair 8, lateral view.

All specimens from Aldabra Atoll range from 3–10 mm and exhibit several traits characteristic of juvenile specimens including reduced number of pores on the coxopleuron, indistinct paramedian sutures on tergites, and a reduced number of tibial and tarsal saw teeth (Fig. 2D). Following clearing, no spermatozoa or oocytes could be observed in the posterior trunk of specimens. Without additional sampling to confirm the condition of adult specimens it is not possible to comment on the presence or absence of sexually mature adults in the present sample. Introduced populations of C. doriae have been described bearing similar neotenic characteristics (reduced body size, number of coxal pores, number of saw teeth), even in sexually mature adults (Lewis 2007b), potentially explaining the morphology of the Aldabra specimens in light of possible introduction to the atoll. Nevertheless, in the absence of additional material and molecular data, our assignment to Cryptops japonicus is only tentative. The status and relationships of different populations identified as C. doriae and related taxa remains to be clarified.

NHMUK015991434, 1 specimen, Sideroxylon litter, Anses Coco & Porche, Aldabra, 03.12.1974, V. W. Spaull. leg.

Cryptops mauritianus has been described by Verhoeff (1939) from Mauritius. Subsequent taxonomic revision of Mauritian Cryptops species (Lewis 2002) completed the summary original description and provided additional illustrations of material from near the type locality. In the singular Aldabra specimen examined, the presence of minute accessory spurs on the pretarsus of leg pairs 1–20 (Fig. 3G) clearly delimits it from all other Cryptops species known from localities in the Western Indian Ocean (Lewis 2011). Subsequent re-description by Lewis (2002) provided data on an immature (“adolescens”) specimen which matches the condition of the material presently examined (body length 8 mm), allowing us to confidently refer it to C. mauritianus.

Figure 3. 

Cryptops mauritianus Verhoeff, 1939. NHMUK015991434 A anterior margin of forcipular coxosternite, ventral view B calyx of venom gland. Left forcipule (top), right forcipule (bottom) C coxopleuron of ultimate leg-bearing segment, lateral view D Ultimate leg telopodite, lateral view E tibia and tarsal articles of ultimate leg, lateral view F tibial comb (top), tarsal comb of left ultimate leg (middle), tarsal comb of right ultimate leg (bottom) G pretarsus of leg pair 18, lateral view.

12 specimens: NHMUK015991424, 3 specimens, Black Path, Picard, Aldabra, Summer 1975; NHMUK015991426, 3 specimens, Calophyllum litter, Takamaka, Grande Terre, 14.01.1975; NHMUK015991427, 2 specimens, Sideroxylon litter, Au Parc, Aldabra, 14.02.1975. V. W. Spaull leg; NHMUK015991428, 1 specimen, Picard, Aldabra, 28.02.1975; NHMUK015991445, 1 specimen, Sideroxylon litter, Ile. Michel, Aldabra, 28.03.1975; NHMUK015991446, 2 specimens, Casuarina litter, Picard, Aldabra, 08.05.1974.

Taxonomic revision of Cryptops species belonging to the “hortensis group” identified C. decoratus Lawrence, 1960, C. melanotypus Chamberlin, 1941, and C. nigropictus Takakuwa, 1936 as a potential species complex, raising doubts on the taxonomic validity of many morphologically similar species (Lewis 2011). A reliable diagnostic trait mentioned by Lewis (2011) is the presence of a single long pretarsal accessory spur in C. nigropictus (Fig. 4K), differentiating it from C. decoratus and C. melanotypus which bear two small pretarsal accessory spurs on leg pairs 1–20. The Aldabra specimens key out to C. nigropictus in the key provided within the same article and agree with its revised description. Although originally described from East Asia, various nominal taxa recorded from East Africa and islands of the Indian Ocean (including Mauritius and Rodrigues) have been placed in synonymy with C. nigropictus (Lewis 2011).

Figure 4. 

Cryptops nigropictus Takakuwa, 1936 A, F, K, I, B NHMUK015991426 H, J NHMUK015991446 G NHMUK015991424 C “Cryptops daszaki” holotype, Île aux Aigrettes, 19.10.1995 D, E paratype, Île aux Aigrettes, 18.10.1995 A, B, C, D, E anterior margin of forcipular coxosternite, ventral view F calyx of venom gland, lateral view G, H coxopleuron of ultimate leg-bearing segment, lateral view I, J tibia and tarsus of ultimate leg telopodite, lateral view K pretarsus of leg pair 8, lateral view.

Cryptops daszaki Lewis, 2002 was described from several localities in Mauritius. Lewis (2002) remarked on the small body size (4.5–7.5 mm) of sexually mature specimens and their apparent juvenile characteristics (low number of coxal pores, reduced setation). The specimens collected from Aldabra with a similar body length to specimens assigned by Lewis to C. daszaki overlap in morphology with respect to the usual lack of subcuticular dark pigment, the number of setae on the anterior margin of the forcipular coxosternite (2 or 3 on each side in C. daszaki, 3 or 4 on each side in C. nigropictus; Fig. 4C versus Fig. 4A, B, D, respectively), the relative length of the single pretarsal accessory spur on legs 1–20 (> 1/2 the length of the pretarsus) and the number of coxal pores (5 or 6 in C. daszaki, 4–9 in C. nigropictus) but show greater variation than C. daszaki in the number of saw teeth on the tibia (3–5) and tarsus (2 or 3). The number of tibial and tarsal saw teeth is known to be intraspecifically variable in Cryptops (Iorio and Geoffroy 2003; Lewis 2009) and scales allometrically with body size, as exemplified by the largest C. nigropictus specimen in our sample (12 mm, NHMUK015991426; Fig. 4I).

The only other diagnostic trait given by Lewis (2011) separating C. daszaki and C. nigropictus is the position of the setae near the anterior margin of the forcipular coxosternite, being described as “marginal” in C. daszaki and “submarginal” in C. nigropictus. Re-examination of the type specimens of C. daszaki revealed that these setae occupy a submarginal position (Fig. 4C), which may be misinterpreted as marginal depending on the orientation of the specimens. As both of the two putative diagnostic traits separating C. daszaki and C. nigropictus are fully encompassed by intraspecific variation within C. nigropictus and the latter species has been recorded from nearby localities (Lewis 2002), we consider C. daszaki a likely junior subjective synonym of C. nigropictus, from which it cannot be reliably distinguished by morphology alone. Similarly, the presence of subcuticular dark pigment cannot be reliably used to separate putative Cryptops species in Western Indian Ocean and Eastern African localities. This character is variable within our sample, with all specimens with the exception of NHMUK015991428 lacking dark subcuticular pigment. Dark pigmentation is also variable in the type specimens of Cryptops niloticus Lewis, 1967 (present in male allotype but absent in female holotype and in juvenile paratype), a species previously recorded from the Western Indian Ocean (Lewis 2002) but subsequently synonymised with C. nigropictus (Lewis 2011).

52 specimens: NHMUK015991435, 33 juveniles; Casuarina litter, Picard, Aldabra, 18.04.1974, leg. V. W. Spaull; NHMUK015991436, 1 specimen, Casuarina, Picard, Aldabra, 04.02.1974; NHMUK015991437, 1 specimen, Ochna soil, Picard, Aldabra, 15.02.1974; NHMUK015991438; 2 specimens, mixed scrub, Picard, 24.12.1974; NHMUK015991439, 1 specimen, Thespesia litter, Cinq Cases, Aldabra, 15.11.1973; NHMUK015991441, 5 specimens, Black Path, Picard, 1975; NHMUK015991442, 1 specimen, Picard, 03.12.1973; NHMUK015991443, 1 specimen, Picard, 18.01.1974; NHMUK015991440, 4 specimens, Picard, 18.11.1974; NHMUK015991444, 1 specimen, Pitfall trap 5, 08.12.1974; NHMUK015991447, 1 specimen, South Island, Aldabra, 13–20.03.1968, leg. B. Cogan & A. Hutson; NHMUK015991448, 1 specimen, Ile. Michel, 02.1968, leg. B. Cogan & A. Hutson.

Specimens of S. morsitans Linnaeus, 1758 collected from mainland Africa, originally identified as Scolopendra amazonica Bücherl, 1946 overlap with the specimens from the Aldabra Atoll in several characters (Table 2) (Lewis 1966, 1967, 1968, 1969), but generally have a greater number of glabrous basal antennal articles, a character in which specimens from the Aldabra Atoll more closely match Indian specimens of S. morsitans previously assigned to S. amazonica (Jangi 1955, 1959). In the absence of newly collected material from which molecular data can be collected to evaluate possible interspecific delimitation between different population of S. morsitans, we assign material collected in the Aldabra Atoll to S. morsitans, following the conclusions on interspecific variation within this taxon reached by Würmli (1975). Subsequent phylogenetic analyses of molecular data for S. morsitans identified multiple lineages within this taxon (Joshi and Karanth 2011; Siriwut et al. 2016), potentially indicating the existence of a cryptic species complex as suggested by recent taxonomic review (Lewis 2010a). Until the global taxonomy of S. morsitans is interrogated using molecular data to establish if this is the case, we classify the examined material as S. morsitans.

Additionally, specimens were compared to the original description of the morphologically similar and geographically proximate Scolopendra antananarivoensis Kronmüller, 2010. Material from the Aldabra Atoll did not exhibit the characters given as diagnostic for S. antananarivoensis, lacking a longitudinal median depression on sternite 21 and not having a distinctly more elongate coxopleural process (Kronmüller 2010).

NHMUK015991467, 1 juvenile, Casuarina litter, Picard, Aldabra, 10.12.1974, leg. V. W. Spaull.

The sexually immature specimen found in the present sample displays all diagnostic characters that support its assignment to Ribautia, comprising an elongate cephalic shield, lack of lappets on the first maxillae, the two halves of the second maxillary coxosternite being united by a sclerotised isthmus and the pleural sutures of the forcipular coxosternite being parallel to its lateral edge distally. A potentially novel ontogenetic observation is the incomplete separation of the two halves of the second maxillary coxosternite by an isthmus (Fig. 5B), as is a characteristic of Ribautia. Taking into account the very small size (length 7 mm) and sexual immaturity of the specimen, this may be a character state that becomes more conspicuous in older individuals.

Figure 5. 

Ribautia cf. paucipes Attems, 1952. NHMUK015991467 A head and forcipular segment, ventral view B anterior margin of second maxillary coxosternite, ventral view C calyx of venom gland, lateral view D ultimate leg-bearing and postpedal segments, ventral view.

Beside the very low number of leg-bearing segments (37), which is shared with R. cf. paucipes reported from the Seychelles (Bonato and Minelli 2010), the developmental stage of the present specimen does not allow for satisfactory evaluation of potential morphological differences between Ribautia specimens described from Western Indian Ocean localities and type material of Ribautia paucipes described from the environs of Lake Kivu in Central Africa. Notably, the Aldabra specimen lacks evident denticles on the anterior margin of the forcipular coxosternite and the interior margin of the forcipular trochanteroprefemur, although these are clearly illustrated in the original description of R. paucipes (Attems 1952: fig. 203). The specimen also lacks conspicuous coxal organs or coxal pores, a character state not noted in R. cf. paucipes recorded from the Seychelles. Ontogenetic variation in the number of coxal pores has been well-documented for other geophilid centipedes (Horneland and Meidell 2009; Gregory and Barber 2010; Brena 2014; Stojanović et al. 2020), increasing with body size at each postembryonic stage, and being absent in comparably sized adolescens stages of some species (Gregory and Barber 2010). Additionally, the second maxillary pretarsus of the present specimen is markedly shorter and less acuminate than illustrated for R. paucipes from continental Africa. As the ontogenetic variation of the morphology of the second maxillae in Ribautia is not presently known and in other characters the specimen strongly resembles individuals described from the Seychelles, we maintain its presently assigned identity.

The monotypic genus Mixophilus was erected by Silvestri (1929) to place a new species of geophilomorph sampled from riparian sites in Madras (Chennai), Southern India. The original description of Mixophilus indicus includes illustrations of the head, forcipular apparatus and ultimate leg-bearing segment as well as detailed ecological observations concerning its preferred microhabitats in the type locality. Subsequent physiological investigations revealed a modified tracheal system, comprising possible adaptations to immersion for long periods of time (Rajulu 1970). An affinity to Henia and Chaetechelyne (Dignathodontidae) was suggested, however, within the same section Silvestri (1929) pointed to differences between Mixophilus and both of these genera in “the structure of the labrum” (tripartite in M. indicus but unipartite in Dignathodontidae), “the distribution of sternal pores” (transverse band in M. indicus, medial sub-circular/elliptical field in Dignathodontidae), in the last leg-bearing segment (telopodite composed of 7 articles in M. indicus but 6 in Henia), and in the elongation of the forcipular pretergite (longer in M. indicus than in Chaetechelyne). The structure of the labrum described and illustrated for M. indicus, comprising three conspicuous pieces, suggests a close affinity to other members of Geophilidae s. str. An estuarine habitat preference and multiple morphological characters show a near complete overlap between the diagnoses of Tuoba and Mixophilus (Table 3). Complete chitin lines in M. indicus may indicate intraspecific or interspecific variability which has been recorded in Tuoba (Jones 1998) or artifacts of examination under light microscopy. In light of this re-evaluation of its original description, we propose reassignment of M. indicus to Tuoba considering the available data on its morphology, with Tuoba indica comb. nov. as the valid name for specimens on which its original description was based. Consequently, we propose that Mixophilus is the junior subjective synonym of Tuoba syn. nov. Similarities between Tuoba indica comb. nov. and T. sydneyensis exist in elongation of the ultimate legs and reduction of the second maxillary pretarsus, however these characters are shared by several species of Tuoba. The incomplete original description provided by Silvestri does not allow for definitive assignment of Tuoba indica comb. nov. to another species of Tuoba until the type material can be adequately re-described.

Similarly, the genus Hovanyx was erected for the species Hovanyx waterloti, described in Lawrence’s (1960) catalogue of Malagasy centipedes. An affinity to Dignathodontidae was again proposed based on similarities in the structure of the labrum, originally described for H. waterloti as composed of a single piece and bearing a small number of rudimentary, anteriorly oriented tubercles (“Labre […] à dents pas très distinctes, quatre courtes dents triangulaires dirigées vers l’avant, de chaque côté.”). The diagnosis of Hovanyx singled out the absence of coxal organs (“[…] diffère de tous les autres membres de la sous-famille des Dignathodontinæ par l’absence de pores aux pattes terminales.”) as the main distinguishing trait separating it from all other dignathodontid genera. However, both the original description and accompanying illustrations suggest a closer affinity to Geophilidae s. str., as multiple other morphological characters (shape of head, forcipular coxosternite, metasternal pore fields) are characteristic of the Geophilidae rather than the Dignathodontidae, and subsequent taxonomic revision of both families placed Hovanyx under Geophilidae (Bonato 2011). Furthermore, the incomplete original description overlaps almost entirely with that of T. sydneyensis, a wide-ranging geophilid encountered in littoral sites in the Seychelles (Bonato and Minelli 2010) and the Aldabra Atoll (present records) close to the type locality of H. waterloti. Shared characters include range of leg bearing segment number (41–43), morphology of the labrum, condition of chitin lines on the forcipular coxosternite (incomplete) (Table 3). The only putative differences between H. waterloti and T. sydneyensis are the unipartite labrum and absence of coxal organs in the former (Table 3). These may however be unreliable characters because of inadequate documentation, as published illustrations of Tuoba specimens and the material here illustrated show great variability in the orientation and shape of the labral pieces, which depending on the degree of sclerotization seen in the specimen and shape and number of denticles on the side pieces, may resemble the labrum of Dignathodontidae under light microscopy. The absence of coxal organs has not been previously reported in any species of Tuoba, however this character shows extensive ontogenetic plasticity within Geophilidae (Horneland and Meidell 2009; Gregory and Barber 2010; Tuf and Dányi 2015; Peretti and Bonato 2016; Stojanović et al. 2020) and the small size of the holotype and only known specimen as well as variations in clearing and position of the coxopleuron may render the pit inconspicuous.

19 specimens: NHMUK015991475, 1 specimen, South Island, Aldabra, 13–20.03.1968, leg. B. Cogan & A. Hutson; NHMUK015991476, 1 juvenile, Cinq Cases/Point Hodoul Arga, 27.03.1974, leg. V. W. Spaull; NHMUK015991477, 1♀, inside fallen dead coconut tree, Picard, Aldabra, 23.02.1974, leg. V. W. Spaull; NHMUK015991478, 3♀, 1♂, 1 juvenile, Cinq Cases, Aldabra, 10–17.03.1974, leg. V. W. Spaull; NHMUK015991479, 1♀, Cyperus ligularis soil and litter, Dune Patates, Aldabra, 05.06.1974, leg. V. W. Spaull; NHMUK015991480, 1♂, 1 incomplete, Mystroxylon and Dracaena litter, Gionnet, 03.12.1974, leg. V. W. Spaull; NHMUK015991481, 1♀, 1♂, Casuarina litter, Picard, Aldabra, 08.05.1974, leg. V. W. Spaull; NHMUK015991482, 1♂, Pemphis litter, Dune D’Messe, Grande Terre, 29.01.1975, leg. V. W. Spaull; NHMUK015991483, 2♂, 1♀, Casuarina, Picard, 27.12.1974, leg. V. W. Spaull.; NHMUK015991484, 2♀, Suriana litter near Point Hodoul, Grande Terre, 22.03.1974, leg. V. W. Spaull; 1 juvenile, Cocos litter, Esprit, Aldabra, 14.12.1974, leg. V. W. Spaull.

Tuoba sydneyensis has previously been reported from the Seychelles (Bonato and Minelli 2010). Material presently described from the Aldabra Atoll, as well as specimens collected on Serpent Island (Mauritius) and other islands of the Seychelles (Bonato and Minelli 2010) can be assigned as conspecific on the basis of the low number of leg-bearing segments (41–45), elongation of the antennal articles (Fig. 6A) and in the shape of the ultimate leg-bearing segment metasternite (Jones 1998).

Figure 6. 

Tuoba sydneyensis (Pocock, 1891a). NHMUK015991484 A head and antennae, dorsal view B cephalic shield, dorsal view C antennal article XIV, dorsal view.

Figure 7. 

Tuoba sydneyensis (Pocock, 1891a) B, C NHMUK015991478 A NHMUK015991484 B clypeus and labrum, ventral view C labrum, ventral view.

The only other species of Tuoba hitherto reported from the East African coast are Tuoba poseidonis Verhoeff, 1901 (Zapparoli 1990) and Tuoba sudanensis Lewis, 1963. The small number of diagnostic characters separating these two species casts doubt on the validity of T. sudanensis or on the Somali record of T. poseidonis. Examination of additional material from the East African coast would be necessary to elucidate the diversity of Tuoba in Northern and Eastern Africa.

Both species can be reliably differentiated from T. sydneyensis in the Western Indian Ocean by the larger number of leg-bearing segments (51–53 in T. sudanensis compared to 41–45 in T. sydneyensis), greater elongation of the telopodal lappets of the first maxillae (30% of the length of the telopodite as illustrated for T. sudanensis; compared to minute in T. sydneyensis (Fig. 8B)), shape of the carpophagus structure (with a distinct median “hump” in T. sudanensis; lacking any “hump” medially in T. sydneyensis), point of the midbody transition (sternites 20–22 in T. poseidonis and T. sudanensis; sternites 14–15 in T. sydneyensis) and the shape of the ultimate leg-bearing segment metasternite (1.6 × wider than long as illustrated for male T. sudanensis; 1.9 × wider than long in male T. sydneyensis, Fig. 10A). The combination of diagnostic characters presented clearly unify the Western Indian Ocean populations of Tuoba under one morphospecies, closely matching the description of T. sydneyensis, which is distinct from Tuoba species recorded in continental Eastern and Northern Africa.

Figure 8. 

Tuoba sydneyensis (Pocock, 1891a). NHMUK015991484 A Mandible, lateral view B First and second maxillae, ventral view C second maxillary article III and pretarsus, ventral view D forcipular segment, ventral view E right forcipule, ventral view.

Verhoeff (1939) described Geophilus (Bothrogeophilus) lemuricus from La Ponce, Mauritius and remarked that it is closely related to (“[…] nahe verwandt […]”) Geophilus carpophagus Leach, 1815. Although incomplete, the description provides several characters that allow reliable assignment to T. sydneyensis, with which it agrees in number of leg-bearing segments (47 in G. lemuricus, 41–45 in T. sydneyensis from the Western Indian Ocean), the apical claw of the second maxillae being reduced in size and not overtaking surrounding setae in length (“[...], überragt nicht die Nachbarborsten.”) (Fig. 8B, C), and in the arrangement of the coxal organs on the coxopleuron of the last leg-bearing segment, which are arranged into a rosette opening in a pouch near the edge of the metasternite (“[...] neben dem Endbeinsternit mündet eine Tasche und in diese eine Rosette von Drüsen”) (Figs 9A, 10A). We consider G. lemuricus to be a junior subjective synonym of T. sydneyensis, which has been subsequently collected from Mauritius (NHMUK015991411).

Figure 9. 

Tuoba sydneyensis (Pocock, 1891a) A NHMUK015991484, female ultimate leg-bearing and postpedal segments, ventral view B NHMUK015991478, juvenile ultimate leg-bearing and postpedal segments, ventral view.

Figure 10. 

Tuoba sydneyensis (Pocock, 1891a), NHMUK01591483 A male ultimate leg-bearing and postpedal segments, ventral view B male gonopods, ventral view C penis, ventral view.

11 specimens: NHMUK015991461, 1♂, Pandanus tectorius soil and litter, Cinq Cases, 24.03.1974, leg. V. W. Spaull; NHMUK015991462, 1♀, 2 km N of Cinq Cases, 11.03.1974, leg. V. W. Spaull; NHMUK015991463, 6 juveniles, Sideroxylon litter, Cinq Cases, 10–17.03.1974, leg. V. W. Spaull; NHMUK015991464, 1♀, Pandanus tectorius soil and litter, Cinq Cases/Point Hodoul, 27.03.1974, leg. V. W. Spaull; NHMUK015991465, 1♂, Gionnet, Aldabra, 03.12.1974, leg. V. W. Spaull; NHMUK015991466, 1♂, Casuarina, Aldabra, 04.02.1974, leg. V. W. Spaull.

Previously recorded from multiple localities near the East African Coast and the Western Indian Ocean (Ribaut 1914; Bonato and Minelli 2010; Popovici et al. 2024), making natural dispersal a likely explanation for the presence of M. angusticeps in Aldabra. Presently examined specimens are morphologically indistinguishable from conspecifics recorded from the Seychelles and the Chagos Islands. Although not previously noted, the forcipular cerri were found to be absent in examined specimens (Fig. 11B). In combination with other diagnostic characters (47 leg-bearing segments, conspicuous medial reduction in clypeal reticulation, large distal trochanteroprefemoral denticle and sternal sulcus not furcate), this allows for easy separation from other syntopic Mecistocephalus spp. within its range.

Figure 11. 

A Mecistocephalus lohmanderi Verhoeff, 1939, NHMUK015991460, forcipular segment, dorsal view B Mecistocephalus angusticeps (Ribaut, 1914), NHMUK015991466, forcipular segment, dorsal view.

2 specimens: NHMUK015991459, 1♀, Black Path, Picard, Aldabra, Summer 1975, leg. V. W. Spaull; NHMUK015991460, 1♂, Casuarina litter, Picard, 10.12.1974, leg. V. W. Spaull.

Originally described from Mauritius (Verhoeff, 1939), M. lohmanderi has been found on other Western Indian Ocean Islands (Bonato and Minelli 2010; Popovici et al. 2024). Similarly to M. angusticeps (Fig. 11B), examined specimens lack forcipular cerri (Fig. 11A). Presently examined specimens are most similar to M. lohmanderi specimens collected from the Diego Garcia atoll (Popovici et al. 2024). Adults (female 34 mm body length, male 34 mm body length) in the Aldabra sample lack dark subcutaneous pigment patches and maintain the characteristic clypeal setation pattern described in M. lohmanderi from other localities (Bonato and Minelli 2010; Popovici et al. 2024). Similarly, specimens assigned to M. insularis described from Socotra (Lewis and Wranik 1990) match all diagnostic characters outlined for M. lohmanderi, and can be referred to this taxon, thus extending its range to island localities in the Northwestern Indian Ocean.

Records of large adult specimens (70–91 mm) assigned to Mecistocephalus insularis from the Arabian Peninsula (Lewis 1996) are fully consistent with the revised description of Mecistocephalus glabridorsalis Attems, 1900 from the Seychelles (Bonato and Minelli 2010) and are almost certainly misidentified M. glabridorsalis. In particular, the clypeal morphology illustrated for specimens from Saudi Arabia shares the presence of a small non-areolate insula anterior to the plagulae with specimens from the Seychelles and the arrangement of setae in a transverse line on the areolate part of the clypeus. This morphology has hitherto only been recorded in M. glabridorsalis and M. punctifrons Newport, 1843 (Bonato and Minelli 2004), casting further doubt on the true identity and distribution of M. insularis. Insufficient data on morphological variability in M. lohmanderi and the uncertain status of M. insularis records from past literature prevent further inferences on the taxonomic validity and relationships between these species.

6 specimens: NHMUK015991469, 1♂, 40 mm, 73 leg-bearing segments, Picard, Aldabra, 08.10.1974; NHMUK015991470, 1♂, 35 mm, 75 leg-bearing segments, Picard, 09.04.1974; NHMUK015991471, 1♀, 24 mm, 81 leg-bearing segments, Grande Terre, Aldabra, 03.1974, leg. J. Wilson; NHMUK015991472, 1 juvenile, 13 mm, 81 leg-bearing segments, Grande Terre, Aldabra, 05.1974, leg. J. Wilson; NHMUK015991473, 1♂, 37 mm, 75 leg-bearing segments, Pandanus litter, Aldabra, 22.03.1974; NHMUK015991474, 1♀, 51 mm, Takamaka (Anse Takamaka), 23–27.02.1968, leg. B. Cogan & A. Hutson.

Diagnosis. Medium to large size Orphnaeus species, with 73–81 leg-bearing segments and variable but generally present longitudinal bands of dark pigment flanking the central vessel. Mandible with three or four pectinate lamellae. First maxillae with both telopodal and coxosternal lappets present and uniarticulate telopodite. Second maxillary pretarsus spatulate, fringed by acuminate hyaline projections. Posterior trunk metasternites with paired pore fields at the posterior end. Pore fields on posterior metasternites, procoxae and metacoxae bordered by dense groups of setae-like projections. Female gonopods uniarticulate, medially overlapping, with angled, rounded external margin.

Head and antennae. Cephalic plate with broadly rounded anterior margin and straight posterior margin, overlapping the forcipular tergite. Head approximately as broad as long (NHMUK015991473) to 1.2 × broader than long (NHMUK015991474). Antennae approximately 2.5 × longer than head, weakly tapering distally (Fig. 12A). In older specimens, the tapering of antennae and dorsoventral compression of proximal antennal articles are more clearly visible (Fig. 12C). Antennal article XIV 1.9 × longer than the penultimate, with two clusters of sensilla basiconica arranged in lateral pits. Small, spear-like sensilla present at apical end.

Figure 12. 

Orphnaeus dekanius Verhoeff, 1938 A, B, D NHMUK015991470 A, C NHMUK015991474. Head and antennae, dorsal view B antennal article XIV, dorsal view D forcipular segment, ventral view.

Mandibles. Of typical aspect for the genus (Fig. 13C, D). Four conspicuous pectinate lamellae evident, arranged concentrically around distal edge. Proximal to the outermost lamella, isolated projections resembling those on the lamellae are present. Two minute sensilla present laterally.

Figure 13. 

Orphnaeus dekanius Verhoeff, 1938. NHMUK015991470 A clypeus and labrum, ventral view B labrum, ventral view C, D Mandible, lateral and dorsal views.

Labrum and clypeus. Labrum of typical oryid aspect, with short hairlike hyaline projections on middle part (Fig. 13B). Lateral parts incompletely separated from middle part and clypeus by evident sutures. Clypeus with two pairs of postantennal sensilla, a median field of sensilla spanning its mediolateral axis and one pair of prelabral sensilla posterior to these (Fig. 13A). Polygonal reticulation evident.

Maxillae. First maxillae with apically rounded, short coxal projections, bearing 8–11 sensilla (Fig. 14A). Telopodite broadly rounded, uniarticulated, of similar size to the coxal projection, bearing 7–12 sensilla. Both telopodal and coxosternal pairs of lappets present, with distinct spinous reticulation (Fig. 14C). Coxosternal pair of lappets completely obscured by second maxillary telopodite in ventral view. Second maxillary coxosternite with shallow, concave, rounded anterior margin bordered by a row of trichoid sensilla and two groups of trichoid sensilla proximally (Fig. 14A). Metameric pore conspicuous, surrounded by sclerotised rim. Telopodal articles stout. Pretarsus with spine-like projections around entire exterior margin and two pores opening on its dorsal surface (Fig. 14D, E).

Figure 14. 

Orphnaeus dekanius Verhoeff, 1938 NHMUK015991470 A first and second maxillae, ventral view B first maxillary right telopodal lappet, ventral view C first maxillary left telopodal and coxosternal lappets, dorsal view D, E left and right second maxillary pretarsi, ventral view.

Forcipular segment. Forcipular tergite 3.2 × broader than long. Exposed surface of forcipular coxosternite 2.2 × broader than long (Fig. 12D). Chitin lines absent. Anterior margin rounded, deeply concave. Pleural sutures strongly converging posteriorly. Trochanteroprefemur ~ 1.5 × broader than long, with evidently rounded external face. Tarsungulum stout, large, entirely covered by anterior edge of cephalic plate, with smooth inner concavity. Opening of venom gland channel immediately proximal to tip of tarsungulum. All forcipular articles without denticles.

Trunk. Last five or six trunk metasternites with two posteriorly located pore fields (Fig. 15D), anteriorly bordered by dense clusters of hairs (Fig. 15A). All other trunk metasternites with four pore fields, two anterior and two posterior, of equal size on metasternites 2–46, the anterior gradually decreasing in size until disappearing on metasternites 74–76. One single row of paratergites present beginning from the second leg-bearing segment, becoming very conspicuous on the eighth leg-bearing segment. General setation of sclerites sparse.

Figure 15. 

Orphnaeus dekanius Verhoeff, 1938 A, D NHMUK015991474 B, C NHMUK015991470 A metasternites of leg-bearing segments 79 – 80, ventral view B walking leg, pair 74, lateral view C Walking leg pair 74 pretarsus, lateral view D Leg-bearing segments 79 – 81, ventral view.

Ultimate leg-bearing and postpedal segments. Ultimate leg-bearing segment metasternite variably trapeziform, 2.3 × broader than long (Fig. 16A, B). Posterior edge with dense field of hairs and occasionally small clusters of pores. Coxopleuron stout, without coxal organs. Telopodite of ultimate leg-pair only moderately inflated in both males (Fig. 16B) and females (Fig. 16A), with dense fields of hairs present on the ventral side of all articles. Pretarsus absent (Fig. 16C). Metatarsus with small hair-like projections at its apical edge.

Figure 16. 

Orphnaeus dekanius Verhoeff, 1938 A, C, D NHMUK015991471 B, E NHMUK015991470 A, B ultimate leg-bearing and postpedal segments, ventral view C ultimate leg pair metatarsus, lateral view D female gonopods, ventral view E male gonopods, ventral view.

Female gonopods usually uni-articulated (Figs 15D, 16D), occasionally with an anterior notch or asymmetrical articulation. Lateral edge smooth, rounded, forming strongly acute angle with posterior edge of first genital sternite. Male gonopods biarticulated, bearing 16 setae (Fig. 16E).

Orphnaeus dekanius was originally described from Trivandrum (Thiruvanathapuram), India (Verhoeff 1938), and maintained as a valid species under Orphnaeus until its reassignment to Nycternyssa, justified by the description of the female gonopods as “uni-articulate”. A detailed re-evaluation of the status of Nycternyssa is provided below.

Subsequent to its original description, there is no evidence that other specimens had been assigned to either O. dekanius or N. dekania prior to recent records from the Chagos Archipelago (Popovici et al. 2024). Based on morphology alone, the present specimens are considered conspecific with those collected in the Chagos Archipelago and match the original description of O. dekanius. The most salient diagnostic trait allowing for reliable differentiation of O. dekanius from O. brevilabiatus is the presence of dense clusters of minute setae bordering the posterior pore fields of the former (Fig. 15A). Although this character was illustrated by Verhoeff in the original description of O. dekanius (Verhoeff 1938: tafel 8, fig. 61), no mention was made of it in the text of the description. It is unambiguously shared by all specimens studied here from near the type locality of O. dekanius (specimens from Sri Lanka listed above under “Specimen data”), and from other localities in the Western Indian Ocean, and is consistent in both sexes in specimens. Setae are sparse in the smallest studied Aldabra specimen (13 mm) but are clustered by a body length of 24 mm. As these clusters of setae are completely absent in specimens identified as O. brevilabiatus from near its type locality in Myanmar (Fig. 17) and other localities in mainland and maritime Southeast Asia, we maintain the validity of O. dekanius and O. brevilabiatus even in light of the variability of female gonopodal articulation in the latter (Fig. 18A–C). The incomplete description of Orphnaeus meruinus Attems, 1909 does not allow for reliable separation from O. dekanius, given the inconsistencies in how diagnostic characters for these two taxa are coded in past literature. One salient difference from all O. dekanius specimens in our sample is the greatly inflated ultimate leg telopodite in males assigned to O. meruinus collected in Oman (Lewis and Gallagher 1993), a character that separates these species even when accounting for body size.

Figure 17. 

Orphnaeus brevilabiatus (Newport, 1845). NHMUK015991423 A leg bearing segments 77 – 79, ventral view B metasternite of leg-bearing segment 78, ventral view.

Figure 18. 

Female gonopods of Orphnaeus Meinert, 1870 species A, B, C Orphnaeus brevilabiatus (Newport, 1845). (A = NHMUK015991423 (Myanmar), B = NHMUK015991421 (Thailand), C = NHMUK015991420 (Singapore)) D, E, F, G, H Orphnaeus dekanius Verhoeff, 1938. (D = NHMUK015991415 (Sri Lanka), E = NHMUK015991413 (Sri Lanka), F = NHMUK015991417 (Singapore), G = NHMUK015991418 (Singapore), H = NHMUK015991416 (Sri Lanka)). Scale bars: 0.1 mm.

NHMUK015991468, 1♂, Aldabra, 21.03.1974., V. W. Spaull leg.

Head and antennae. Antennae conspicuously claviform in shape, medially weakly geniculate, with articles IX–XIV widened (Figs 19A, 20A, C). Articles IX and XIII with clusters of type c sensilla (sensu Pereira 2017) on the distal edge of the dorsal side (Fig. 19C, D). Article XIV with two lateral clusters of sensilla basiconica and a small number of spear-shaped sensilla at its apex (Fig. 19B). Head approximately as wide as forcipular tergite, 1.14 × broader than long. Curved sulcus near posterior margin. Chaetotaxy of head as in Fig. 20B.

Figure 19. 

Ityphilus cf. taeniaformis (Lawrence, 1960). NHMUK015991468 A right antenna, dorsal view B antennal article XIV, ventral view C clusters of type c sensilla on antennal article XIII (top) and IX (bottom), dorsal view.

Figure 20. 

Ityphilus cf. taeniaformis (Lawrence, 1960) NHMUK015991468 A head and antennae, dorsal view B cephalic shield, dorsal view C right antenna, ventral view.

Mandibles. Dentate lamella with seven denticles, only six conspicuous in lateral view. Pectinate lamella with approximately 22 hyaline projections (Fig. 21A).

Figure 21. 

Ityphilus cf. taeniaformis (Lawrence, 1960). NHMUK015991468 A mandible, lateral view B first and second maxillae, ventral view C anterior margin of second maxillary coxosternite, ventral view D second maxillary pretarsus left (top), right (bottom), ventral view.

Labrum and clypeus. Clypeus with a pair of postantennal setae, a cluster of seven medial setae and one prelabral seta. Lateral pieces of labrum narrow, conspicuously sclerotised, lacking any fringes or projections. Medial piece contiguous with clypeus, poorly sclerotised, membranous and lacking conspicuous hairs or projections.

Maxillae. First maxillae with evident, triangular coxal projections, each bearing one sensillum. Telopodites bearing one sensillum each, conspicuously larger than coxal projections and partly covering them (Fig. 21B). Lappets absent. Second maxillary coxosternite with evident but incomplete medial suture, extending for half of its length (Fig. 21C). Each side of the suture bearing one sensillum. Telopodite stout, terminating in large pretarsus. Second maxillary pretarsus spatulate, lateral edges densely fringed (Fig. 21D, E).

Forcipular segment. Exposed face of forcipular coxosternite 2.2 × broader than long (Fig. 22A). Chitin lines present, reaching the condyles. Forcipular trochanteroprefemur 1.25 × longer than broad. Calyx of venom gland elongated, ovoid in shape (Fig. 22C). All forcipular articles without denticles (Fig. 22B). Internal margin of tarsungulum smooth. Extended, forcipules do not reach the anterior margin of the head.

Figure 22. 

Ityphilus cf. taeniaformis (Lawrence, 1960). NHMUK015991468 A forcipular segment, ventral view B left forcipule, ventral view C calyx of venom gland, ventral view D leg-bearing segment 9, ventral view.

Trunk. 75 leg-bearing segments. Pore fields located on raised areas in the middle of all metasternites excluding those of leg-bearing segments 1, 74, and 75. Shape of pore field oval, medially constricted and anteriorly bordered by a line of setae (Fig. 22D). Colour of pore field bluish grey, conspicuously pigmented relative to surrounding cuticle. Despite the faded colour of the ethanol-preserved specimen, pigmentation of the pore field is conspicuous and the trunk is generally greenish grey in appearance.

Ultimate leg-bearing and postpedal segments. Intercalary pleurites separated from ultimate pretergite by evident sutures. Ultimate metasternite trapezoidal, 1.3 × longer than broad. Coxopleura each with two distinct coxal organs, partially covered by the ultimate metasternite (Fig. 23A). Entire ventral side of ultimate leg-bearing segment covered in setae. Ultimate leg telopodite composed of seven articles, all distinctly thickened. Pretarsus absent (Fig. 23B). Metatarsus with a small spine subapically. Intermediate sternite indistinct. First genital sternite with straight posterior margin. Gonopods uni-articulate, flanking penis (Fig. 23C).

Figure 23. 

Ityphilus cf. taeniaformis (Lawrence, 1960). NHMUK015991468 A ultimate leg-bearing and postpedal segments, ventral view B tip of right ultimate leg telopodite, ventral view C male gonopods, ventral view.

The taxonomy of Ityphilus remains largely unresolved, especially outside of South America, where different authors have disagreed on its relation to Ballophilus, alternatively considering it a different genus (Attems 1929) or a synonym of Ballophilus (Verhoeff 1939). Recent revision of the genus (Bonato et al. 2007) has maintained the distinction between Ityphilus and Ballophilus, but remarked on the close relationship between the two, and on cases in which the presence of complete or nearly complete chitin lines is doubtful, such as in Ityphilus boteltobogensis (Wang, 1955), despite this character being predominantly used to distinguish the two genera. Similarly, several Ballophilus species are described as bearing a cuticular thickening in the usual position of the chitin line (Demange 1963; Pereira et al. 1997), further confounding the utility of this character in taxonomy within the Ballophilidae. The presence of a median sulcus in the second maxillary coxosternite has been shown to be unreliable in separating Ballophilus and Ityphilus. This character has been described in both Ballophilus (Ribaut 1914; Pereira et al. 1997) and Ityphilus (Pereira et al. 2000), in some cases as incomplete (Brölemann 1909) (Fig. 21B, C), and is not included in the most recent diagnosis of the latter genus (Bonato et al. 2007).

Verhoeff (1939) described two Ballophilus species from Mauritius, B. lawrencei Verhoeff, 1939 and B. mauritianus Verhoeff, 1939. Both are known from single specimens but, according to their original description, compare closely with Ballophilus allauadi Ribaut, 1914 described from Eastern Africa. The Aldabra specimen differs from these species in the presence of pore fields on all but the first and last two leg-bearing segment metasternites (contrasting with the absence of the pore field on the first and the last four metasternites). Additionally, the distal end of the antenna of B. lawrencei is illustrated as markedly less clavate than observed for the Aldabra specimen. Despite this, the Ityphilus specimen collected in Aldabra overlaps in the shape of the metasternal pore field, its position on a raised area and in the relative elongation of the ultimate leg-bearing segment telopodite and the number of leg-bearing segments with B. lawrencei. As all Mauritian Ballophilus species are known solely from their holotypes, it is not possible to comment on intraspecific variability that may account for the overlap in these traits.

Ballophilus maldivensis Pocock, 1906, described from the Maldives, similarly resembles the Aldabra specimen in the shape of the metasternal pore fields and their pigmentation. The incomplete original description did not allow for comparison of any other putative diagnostic characters beside the number of leg-bearing segments (67 in the female holotype), which is lower than that of the Aldabra specimen (75 in a male). Re-examination of the holotype (Fig. 24), the sole known specimen, revealed several features that further distance it from the Aldabra specimen and bring it closer to the currently accepted diagnosis of Ballophilus. Ballophilus maldivensis lacks chitin lines or any cuticular thickenings near their position (Fig. 24A, B). Other important differences from I. cf. taeniaformis from Aldabra include the absence of the metasternal pore field from the last four leg-bearing segments and a more strongly enlarged ultimate leg telopodite (Fig. 24D).

Figure 24. 

Ballophilus maldivensis Pocock, 1906. BMNH #200555 A head and forcipular segment, ventral view B magnified view of forcipular coxosternite showing lateral pleurite and condyle, right side, ventral view C metasternite of leg-bearing segment 7, ventral view D ultimate leg-bearing and postpedal segments, ventral view.

Lawrence (1960) described three species assigned to Ballophilus from Madagascar, of which Ballophilus taeniaformis Lawrence, 1960 overlaps in nearly all diagnostic traits with the Aldabra material examined, differing only in the number of teeth on the dentate lamella of the mandible (7 in the Aldabra specimen compared to eight or nine in B. taeniaformis). Lawrence made no comment on the presence or absence of the chitin line on the forcipular coxosternite for the species he assigned to Ballophilus. As noted above, this character has been used to differentiate between the genera Ballophilus and Ityphilus, although its variability as discussed above and the lack of consensus on the status of Ityphilus at the time of Lawrence’s original description of B. taeniaformis prompt us to refer the examined specimen from Aldabra to Ityphilus.

In nearly all characters examined, the singular specimen from Aldabra agrees with the description of Ityphilus melanostigma (Attems 1900) and the subsequent redescription of this species from specimens collected in the Seychelles (Bonato and Minelli 2010). However, the greatly reduced number of leg-bearing segments (75) relative to the presently known range within I. melanostigma (95–101) suggest specific distinction, as extensive variation in leg-bearing segment number is not generally known from other species of Ityphilus. Other putative differences to the original description of I. melanostigma include the greater relative enlargement of the ultimate leg pair telopodites in the Aldabra specimen, relative to Ityphilus specimens illustrated from the Seychelles (Bonato and Minelli 2010).