Tetramorium aspis

Tetramorium aspis was mainly sampled from leaf litter or general collecting on the ground, which suggests that it might be a ground-active species.

Identification
A member of the Tetramorium cognatum species complex of the Tetramorium schaufussii species group. Hita Garcia and Fisher (2014) - The following character combination clearly diagnoses T. aspis within the T. cognatum species complex: relatively large eyes (OI 25–27); frontal carinae weakly developed; propodeal spines short, triangular to elongate-triangular, and acute (PSLI 18–21), propodeal lobes always only weakly shorter than propodeal spines, and spines and lobes strongly inclined towards each other; petiolar node in profile high rounded nodiform, weakly squamiform and relatively thin, in profile around 2.0 to 2.2 times higher than long (LPeI 46–51), and in dorsal view around 1.4 to 1.6 times wider than long (DPeI 146–161); mesosoma with six or more pairs of long, standing hairs on pronotum and mesonotum, propodeum usually with one or two pairs located anteriorly.

With its large eyes (OI 25–27) and the presence of six or more pairs of long, standing hairs on the mesosoma Tetramorium aspis is unlikely to be confused with the small-eyed Tetramorium gladius (OI 19–20), or Tetramorium freya, which lacks standing pilosity on the mesosomal dorsum. Furthermore, the weakly developed frontal carinae separate it from the species with strong frontal carinae Tetramorium myrmidon, Tetramorium proximum, and Tetramorium tenuinode. The latter three are also mostly larger species (HW 0.58–0.81; WL 0.76–1.07) compared to T. aspis (HW 0.51–0.55; WL 0.72–0.81). The remaining four species are morphologically closer to T. aspis. Of these, Tetramorium camelliae differs significantly from T. aspis on the basis of petiolar node development. In the latter the node is only weakly squamiform, in profile around 2.0 to 2.2 times higher than long (LPeI 46–51), and in dorsal view between 1.4 to 1.6 times wider than long (DPeI 146–161). This shape contrasts with the node of T. camelliae, which is around 2.8 to 3.0 times higher than long (LPeI 33–36) and around 2.3 to 2.4 times wider than long (DPeI 228–238). The best character for separating T. aspis from the remaining three species is the development and arrangement of propodeal spines and lobes. In T. aspis the spines are short, triangular to elongate-triangular, and acute (PSLI 18–21), the lobes relatively long, only weakly shorter than the spines, and the spines and lobes are strongly inclined towards each other. This arrangement is not seen in Tetramorium cognatum, Tetramorium karthala or Tetramorium rumo (it is present in T. camelliae though) since they either have short to moderate spines (T. karthala + T. rumo: PSLI 20–26), much longer than the lobes, or the spines are very short (T. cognatum: PSLI 12–16) and approximately same length as lobes or even shorter. Beyond this conspicuous character, T. aspis also has longer antennal scapes (SI 68–72), a broader petiolar node (DPeI 146–161), and a narrower postpetiole (DPpI 126–135) than T. cognatum (SI 61–67; DPeI 129–142; DPpI 137–153). Tetramorium karthala, which is only found on the Comoros, has only two to four pairs of long, standing hairs on the pronotum and mesonotum while T. aspis has least least six pairs. The last species, T. rumo, has very short antennal scapes (SI 60–66), a thinly cuneiform and moderately squamiform petiolar node, and is usually very bright yellow to light brown.

Intriguingly, T. scutum from the T. sikorae complex, which is endemic to the same geographic area, bears a strong superficial resemblance to T. aspis. However, they are in different species complexes based on their differences in pilosity on the first gastral tergite (present in T. scutum but absent in T. aspis). Apart from this key character they also differ slightly in eye size and propodeal spine length.

To our best knowledge, there is no apparent intraspecific variation in T. aspis.

Distribution
So far T. aspis is known only from a few localities in the southeast of Madagascar around Ivohibe and Andringitra, where it was collected in rainforests or montane rainforests at elevations ranging from 785 to 1680 m.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  aspis. Tetramorium aspis Hita Garcia & Fisher, 2014: 61, figs. 22C, 27B, 28C, 29A, 30, 63 (w.) MADAGASCAR.

Worker
(N=12). HL 0.60–0.63 (0.61); HW 0.51–0.55 (0.54); SL 0.36–0.39 (0.37); EL 0.14–0.15 (0.14); PH 0.26–0.30 (0.28); PW 0.40–0.44 (0.43); WL 0.72–0.81 (0.77); PSL 0.11–0.13 (0.13); PTL 0.11–0.13 (0.12); PTH 0.23–0.25 (0.24); PTW 0.16–0.19 (0.18); PPL 0.16–0.19 (0.18); PPH 0.23–0.24 (0.24); PPW 0.22–0.24 (0.23); CI 85–88 (87); SI 68–72 (70); OI 25–27 (26); DMI 54–57 (55); LMI 35–37 (36); PSLI 18–21 (21); PeNI 40–44 (42); LPeI 46–51 (49); DPeI 146–161 (152); PpNI 51–56 (54); LPpI 70–81 (74); DPpI 126–135 (131); PPI 121–137 (129).

Head much longer than wide (CI 85–88); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly developed, only faintly raised, slightly diverging posteriorly, merging with surrounding sculpture halfway between posterior eye margin and posterior head margin. Antennal scrobes weak to absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 68–72). Eyes relatively large (OI 25–27). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 35–37), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove usually present, but very weakly developed. Propodeal spines short, triangular to elongate-triangular, and acute (PSLI 18–21), propodeal lobes triangular to elongate-triangular, always slightly shorter than propodeal spines, in profile spines and lobes strongly inclined towards each other. Petiolar node in profile high rounded nodiform, weakly squamiform and relatively thin, around 2.0 to 2.2 times higher than long (LPeI 46–51), anterior and posterior faces approximately parallel, anterodorsal margin usually situated slightly higher and more angulate than posterodorsal margin, petiolar dorsum relatively flat to weakly convex; node in dorsal view around 1.5 to 1.6 times wider than long (DPeI 146–161), in dorsal view pronotum around 2.3 to 2.5 times wider than petiolar node (PeNI 40–44). Postpetiole in profile globular, between 1.2 to 1.4 times higher than long (LPpI 70–81); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 126–135), pronotum around 1.8 to 2.0 times wider than postpetiole (PpNI 51–56). Postpetiole in profile appearing more voluminous than petiolar node, postpetiole in dorsal view around 1.2 to 1.4 times wider than petiolar node (PPI 121–137). Mandibles completely unsculptured, smooth, and shiny; clypeus weakly irregularly longitudinally rugulose, median ruga never fully developed, usually reduced to few traces, one or two mostly unbroken lateral rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with seven to nine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, often irregularly shaped, interrupted or with cross-meshes; scrobal area mostly unsculptured; lateral head reticulate-rugose to longitudinally rugose, often with larger areas with reduced sculpture. Ground sculpture on head weakly to moderately reticulate-punctate, especially laterally. Dorsum and sides of mesosoma mostly irregularly longitudinally rugose/rugulose, sides of mesosoma often with some reticulate-rugose areas. Ground sculpture on dorsal mesosoma mostly absent, lateral mesosoma usually weakly to moderately reticulate-punctate. Forecoxae usually unsculptured, smooth and shining. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with six or more pairs on pronotum and mesonotum, propodeum usually with one or two pairs anteriorly; waist segments and first gastral tergite without any standing hairs at all; first gastral tergite with short, moderately dense, appressed pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments and gaster usually of uniform brown to dark brown, appendages yellowish to light brown; sometimes waist segments and gaster lighter than head and mesosoma but still darker than appendages.

Type Material
Holotype, pinned worker, MADAGASCAR, Fianarantsoa, R.S. Ivohibe 8.0 km E Ivohibe, 22.48333°S, 46.96833°E, 1200 m, montane rainforest, sifted litter, (leaf mold, rotten wood), collection code BLF01747, 15.–21.X.1997 (B.L. Fisher) (: CASENT0344940). Paratypes, eleven workers with same data as holotype (CAS: CASENT0189115; CASENT0198990; CASENT0198991; CASENT0198995; CASENT0198998; CASENT0217756; CASENT0247396; CASENT0247397; CASENT0247398; CASENT0247399; CASENT0247400); three workers with same data as holotype except sampled from rotten stick on ground and collection code BLF01746 (CAS: CASENT0189124); fourteen workers from Fianarantsoa, 8.0 km NE Ivohibe, 22.4217°S, 46.8983°E, 1200 m, montane rainforest, sifted litter, (leaf mold, rotten wood), collection codes BLF01751 and BLF01753, 3.–9.XI.1997 (B.L. Fisher) (: CASENT0247403; CAS: CASENT0189123; CASENT0189156; CASENT0198992; CASENT0198993; CASENT0198994; CASENT0198996; CASENT0247402; CASENT0247404; CASENT0247405; : CASENT0247401).

Etymology
The name of the new species is Old Greek and means “shield,” referring to the weakly squamiform condition of the petiolar node. The species epithet is a nominative noun, and thus invariant.

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.