Tetramorium myrmidon Hita Garcia & Fisher

Hita Garcia, Francisco & Fisher, Brian L., 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, pp. 1-170 : 64-66

Tetramorium myrmidon Hita Garcia & Fisher sp. n. Figs 23C, 25B, 26C, 36, 64

Type material.

Holotype, pinned worker, MADAGASCAR, Toliara, Réserve Spéciale d’Ambohijanahary, Forêt d’Ankazotsihitafototra, 35.2 km 312° NW Ambaravaranala, 18.26667°S, 45.40667°E, 1050 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF07020, 13.-17.I.2003 (B.L. Fisher et al.) (CAS: CASENT0028635). Paratypes, two workers with same data as holotype (CAS: CASENT0028642; CASENT0028643); and three workers MADAGASCAR, Toliara, Réserve Spéciale d’Ambohijanahary, Forêt d’Ankazotsihitafototra, 34.6 km 314° NW Ambaravaranala, 18.26°S, 45.41833°E, 1100 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF07086, 16.I.2003 (B.L. Fisher et al.) (CAS: CASENT0029810; CASENT0029821; CASENT0030099).

Diagnosis.

Tetramorium myrmidon can be easily distinguished from the other members of the group by the following combination of characters: eyes relatively large (OI 24-25); antennal scapes short (SI 74-76); frontal carinae well developed, noticeably raised, ending shortly before posterior head margin; petiolar node high rounded nodiform, in profile around 1.7 times higher than long (LPeI 58-60), in dorsal view around 1.2 to 1.3 times wider than long (DPeI 121-129); in dorsal view postpetiole around 1.3 to 1.5 times broader than petiolar node (PPI 133-141); dorsum of mesosoma with two pairs of long, standing hairs on pronotum and mesonotum.

Worker measurements

(N=6). HL 0.70-0.76 (0.73); HW 0.62-0.69 (0.65); SL 0.47-0.52 (0.49); EL 0.16-0.18 (0.16); PH 0.33-0.37 (0.35); PW 0.45-0.50 (0.47); WL 0.85-0.94 (0.89); PSL 0.13-0.16 (0.14); PTL 0.14-0.16 (0.15); PTH 0.24-0.27 (0.25); PTW 0.18-0.20 (0.19); PPL 0.18-0.21 (0.19); PPH 0.24-0.28 (0.26); PPW 0.24-0.28 (0.26); CI 88-91 (90); SI 74-76 (75); OI 24-25 (25); DMI 52-54 (53); LMI 38-40 (39); PSLI 18-20 (19); PeNI 39-40 (39); LPeI 58-60 (59); DPeI 121-129 (125); PpNI 52-55 (54); LPpI 73-77 (76); DPpI 129-136 (133); PPI 133-141 (138).

Worker description.

Head much longer than wide (CI 88-91); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae well developed, noticeably raised, diverging posteriorly, merging with surrounding sculpture shortly before posterior head margin. Antennal scrobes very weakly developed, almost absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 74-76). Eyes relatively large (OI 24-25). Mesosomal outline in profile flat to weakly convex, moderately low and long (LMI 38-40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, but weakly developed. Propodeal spines short to moderate, elongate-triangular, and acute (PSLI 18-20), propodeal lobes triangular and short, always much shorter than propodeal spines. Petiolar node in profile high nodiform with well rounded margins, around 1.7 times higher than long (LPeI 58-60), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height, anterodorsal margin slightly more angulate than posterodorsal, more rounded margin, petiolar dorsum relatively flat to weakly convex; node in dorsal view 1.2 to 1.3 times wider than long (DPeI 121-129), in dorsal view pronotum between 2.5 to 2.6 times wider than petiolar node (PeNI 39-40). Postpetiole in profile globular, between 1.3 to 1.4 times higher than long (LPpI 73-77); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 129-136), pronotum around 1.8 to 1.9 times wider than postpetiole (PpNI 52-55). Postpetiole in profile appearing more voluminous than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 133-141). Mandibles completely unsculptured, smooth, and shiny; clypeus irregularly longitudinally rugulose with three to seven rugulae, median ruga usually fully developed, one to three mostly unbroken lateral rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with seven to nine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, often interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured with ground sculpture only, lateral head reticulate-rugose to longitudinally rugulose. Ground sculpture on head well developed and distinct, mostly reticulate-punctate. Dorsum and sides of mesosoma irregularly longitudinally rugulose to reticulate-rugulose. Forecoxae dorsally weakly rugulose, but mostly unsculptured, smooth, and shining. Ground sculpture on mesosoma weakly to moderately punctate. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of standing, long, fine hairs; dorsum of mesosoma with two pairs only, one on anterior pronotum and one on anterior mesonotum; propodeum, waist segments, and first gastral tergite without any standing hairs; first gastral tergite with very short, scarce, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments, and gaster uniformly brown to dark brown, appendages yellowish to light brown.

Etymology.

The name of the new species is inspired by the ancient Greek “myrmidons”, which were skilled warriors and known as the legendary “ant-people” who inhabited the Greek island of Aegina. The species epithet is a noun in apposition, and thus invariant.

Distribution and biology.

The new species is so far only known from Ambohijanahary, which is an isolated montane rainforest located in the midwest of Madagascar (Fig. 64), where it was collected only twice. With only six known specimens it represents an extremely rare species. Tetramorium myrmidon was collected from leaf litter at elevations of 1050 to 1100 m.

Discussion.

Based on its larger body size and very well developed frontal carinae, Tetramorium myrmidon differs strongly from the smaller species Tetramorium aspis , Tetramorium camelliae , Tetramorium cognatum , Tetramorium karthala and Tetramorium rumo , all with more weakly developed frontal carinae, while being presumably morphologically closer to Tetramorium gladius , Tetramorium proximum and Tetramorium tenuinode . Of these, Tetramorium gladius possesses very small eyes (OI 19-20), while the eyes of Tetramorium myrmidon are much larger (OI 24-25). Tetramorium tenuinode has shorter antennal scapes (SI 66-70) and a thinner petiolar node, in profile 1.8 to 2.2 times higher than long (LPeI 45-54), in contrast to Tetramorium myrmidon with its longer scapes (SI 74-76) and lower and thicker petiolar node, which is in profile around 1.7 times higher than long (LPeI 58-60). The widespread Tetramorium proximum , however, appears to be the species morphologically closest to Tetramorium myrmidon and most of their morphometric ranges and characters overlap. Nonetheless, we consider both sufficiently demarcated from each other since they are found to co-occur in sympatry in Ambohijanahary. The specimens of Tetramorium proximum from this locality differ from Tetramorium myrmidon by having five to six pairs of long, standing hairs on the mesosoma and a generally thinner and higher petiolar node. Finally, Tetramorium myrmidon is unlikely to be confused with the last species of the complex, Tetramorium freya , since the latter lacks long, standing pilosity on the mesosomal dorsum (present in Tetramorium myrmidon ).

The small number of specimens from just two collection events in the same locality does not permit proper assessment of intraspecific variation.