Tetramorium karthala

This new species is only known from the type locality, which is a montane rainforest on the Comorian island Grande Comore. At present, it is the only described Tetramorium species endemic to any Comorian island. All other Tetramorium species (except one undescribed species from the T. ranarum species group from Anjouan) found on the Comoros Islands are either introduced tramp species or species shared between Africa, the Comoros and Madagascar, or between the Comoros and Madagascar. Intriguingly, the type locality appears to have a quite unique fauna. Just recently Fischer and Fisher (2013) described a new Pheidole species (Pheidole vulcan) from this locality, which is also endemic to the island of Grande Comore. Tetramorium karthala is at elevations between 1000 to 1125 m where it was mainly collected from leaf litter, under moss, or within rotten logs.

Identification
A member of the Tetramorium cognatum species complex of the Tetramorium schaufussii species group. Hita Garcia and Fisher (2014) - Tetramorium karthala is diagnosable within the T. cognatum complex on the basis of the following character combination: very large eyes (OI 29–30); short antennal scapes (SI 70–74); frontal carinae weakly to moderately developed; propodeal spines short to moderate, elongate-triangular to spinose, and usually acute (PSLI 20–22), propodeal lobes always much shorter than spines and lobes never strongly inclined towards each other; petiolar node rounded high nodiform, in profile around 1.8 to 2.0 times higher than long (LPeI 50–54), in dorsal view around 1.5 to 1.6 times wider than long (DPeI 148–158); mesosoma with two to four pairs of long, standing hairs on pronotum and mesonotum.

Tetramorium karthala is easily identifiable in the Malagasy region since it is the only species of the T. cognatum species complex and the whole T. schaufussii species group found on the Comores. Even without considering geography the new species can be well distinguished from the remainder of its species complex. In general, it is morphologically close to Tetramorium aspis, Tetramorium camelliae, Tetramorium cognatum, and Tetramorium rumo, whereas it differs more strongly from the rest of the complex. Since T. karthala has several pairs of long, standing hairs on the dorsum of the mesosoma and much larger eyes (OI 29–30), it is unlikely to be mistaken for Tetramorium freya, which has no standing pilosity on the mesosomal dorsum, or for Tetramorium gladius, which has the smallest eyes in the complex (OI 19–20). Also, T. karthala cannot be confused with Tetramorium myrmidon, Tetramorium proximum, or Tetramorium tenuinode as the latter three have very well developed, noticeably raised, and long frontal carinae compared to the much weaker frontal carinae seen in T. karthala.

The separation from the other five species, which appear closer to T. karthala, is also straightforward. Tetramorium camelliae has a strongly squamiform petiolar node which is around 2.8 to 3.0 times higher than long (LPeI 33–36) and around 2.3 to 2.4 times wider than long (DPeI 228–238), while T. karthala has a high nodiform petiolar node which is around 1.8 to 2.0 times higher than long (LPeI 50–54) and around 1.5 to 1.6 times wider than long (DPeI 148–158). The smallest species of the complex, T. rumo (HW 0.43–0.49; WL 0.56–0.67), differs from T. karthala (HW 0.51–0.55; WL 0.72–0.79) not only in body size but also in the shape of the petiolar node. The node of T. rumo is thinly cuneiform and moderately squamiform, in profile 2.3 to 2.7 times higher than long (LPeI 37–43) while, as noted above, the node of T. karthala is high nodiform and thicker, only 1.8 to 2.0 times higher than long (LPeI 50–54). Furthermore, in T. aspis the propodeal spines and lobes are strongly inclined towards each other, whereas the spines and lobes of T. karthala are not. The latter species also has two to four pairs of long, standing hairs on the dorsal pronotum and mesonotum while T. aspis has at least six on the pronotum and mesonotum and usually one or two on the anterior propodeum. The last species in the complex, T. cognatum, appears morphologically very close to T. karthala, but has noticeably shorter antennal scapes (SI 61–67) and propodeal spines (PSLI 12–16) than T. karthala (SI 70–74; PSLI 20–22).

To our knowledge, there is no significant intraspecific variation in T. karthala.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  karthala. Tetramorium karthala Hita Garcia & Fisher, 2014: 82, figs. 20A, 24C, 27D, 28D, 29B, 35, 63 (w.) MADAGASCAR.

Worker
(N=10). L 0.59–0.63 (0.61); HW 0.51–0.55 (0.53); SL 0.36–0.39 (0.38); EL 0.15–0.16 (0.15); PH 0.27–0.31 (0.29); PW 0.38–0.42 (0.40); WL 0.72–0.79 (0.75); PSL 0.12–0.14 (0.13); PTL 0.12–0.14 (0.13); PTH 0.23–0.26 (0.24); PTW 0.18–0.21 (0.19); PPL 0.15–0.17 (0.15); PPH 0.22–0.25 (0.23); PPW 0.22–0.25 (0.24); CI 86–87 (87); SI 70–74 (72); OI 29–30 (29); DMI 51–55 (54); LMI 37–39 (39); PSLI 20–22 (21); PeNI 45–49 (47); LPeI 50–54 (51); DPeI 148–158 (151); PpNI 55–61 (58); LPpI 65–68 (66); DPpI 138–158 (151); PPI 112–131 (124).

Head much longer than wide (CI 86–87); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly to moderately developed, only weakly raised, and ending between posterior head margin and posterior head margin. Antennal scrobes very weakly developed to almost absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 70–74). Eyes very large (OI 29–30). Mesosomal outline in profile flat to weakly convex, moderately low and long (LMI 37–39), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present and distinctly developed. Propodeal spines short to moderately long, elongate-triangular to spinose, and usually acute (PSLI 20–22), propodeal lobes short and triangular, always much shorter than propodeal spines, spines and lobes never strongly inclined towards each other. Petiolar node in profile rounded high nodiform, around 1.8 to 2.0 times higher than long (LPeI 50–54), usually anterior and posterior faces more or less parallel, anterodorsal and posterodorsal margins both well-rounded and usually situated at about same height, petiolar dorsum moderately convex; node in dorsal view around 1.5 to 1.6 times wider than long (DPeI 148–158), in dorsal view pronotum between 2.0 to 2.2 times wider than petiolar node (PeNI 45–49). Postpetiole in profile subglobular, between 1.4 to 1.6 times higher than long (LPpI 65–68); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 138–158), pronotum around 1.6 to 1.8 times wider than postpetiole (PpNI 55–61). Postpetiole in profile usually appearing of more or less same volume as petiolar node, postpetiole in dorsal view around 1.1 to 1.3 times wider than petiolar node (PPI 112–131). Mandibles completely unsculptured, smooth, and shiny; clypeus usually irregularly longitudinally rugulose with three to five, often broken, rugulae, sometimes rugulae reduced to one or two, median ruga/rugula often developed, but usually broken, rarely completely absent; cephalic dorsum between frontal carinae longitudinally rugose/rugulose with seven to nine rugae/rugulae, rugae usually running from posterior clypeal margin to posterior head margin, often interrupted, rarely with cross-meshes; scrobal area mostly unsculptured with ground sculpture only, lateral head reticulate-rugose to longitudinally rugose. Dorsum and sides of mesosoma mostly irregularly longitudinally rugose/rugulose. Forecoxae dorsally with few traces of rugulae, otherwise mostly unsculptured, smooth, and shining. Ground sculpture on head and mesosoma very distinct, usually reticulate-punctate with few areas very finely reticulate-rugulose. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with numerous pairs of standing, long, fine hairs; mesosoma usually with two to four pairs: one long pair on anterior pronotum and one long pair on anterior mesonotum, sometimes two shorter pairs present, one on posterior pronotum and one on posterior mesonotum; propodeum, waist segments and first gastral tergite without any standing hairs; first gastral tergite with short, moderately dense, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Head, mesosoma, waist segments and gaster uniform light brown, appendages often lighter, more yellowish brown.

Type Material
Holotype, pinned worker, COMOROS, Grande Comore, Karthala, 11.82699°S, 43.4295°E, 1000 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF19734, 14.–15.III.2008 (B.L. Fisher et al.) (: CASENT0137302). Paratypes, three pinned workers with same data as holotype (CAS: CASENT0137426; CASENT0137440; CASENT0137510); two workers with same data as holotype except collected from rotten log and collection code BLF19750 (: CASENT0135232); six pinned workers from Grande Comore, Karthala, 11.81336°S, 43.41945°E, 1125 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF19700, 13.–14.III.2008 (B.L. Fisher et al.) (: CASENT0136774; CAS: CASENT0136766; CASENT0137214; CASENT0137221; CASENT0137244; CASENT0137263;).

Etymology
The new species is named after the type locality, Karthala Forest on Mount Karthala volcano on the island of Grand Comore. The species epithet is a noun in apposition, and thus invariable.

References based on Global Ant Biodiversity Informatics

 * Hita Garcia F, and B. L. Fisher. 2014. The hyper-diverse ant genus Tetramorium Mayr (Hymenoptera, Formicidae) in the Malagasy region - taxonomic revision of the T. naganum, T. plesiarum, T. schaufussii, and T. severini species groups. ZooKeys 413: 1-170.