Tetramorium tantillum

This relatively large and conspicuous species is known only from a handful of sampling events from a few rainforest localities in Eastern Madagascar. This is surprising because the other species of the T. tosii group, Tetramorium tosii, is relatively common across nearly all of the rainforest zone of Eastern Madagascar. The more abundant T. tosii could have the ability to displace the morphologically close T. tantillum, although presently no evidence supports this theory. More than half of the specimens were collected from lower vegetation, implying that T. tantillum lives predominantly in this stratum; fewer specimens were collected on the ground, where this ant also may forage.

Identification
The antennal scapes of moderate length (SI 79 - 87) and the long propodeal spines (PSLI 30 - 33) render T. tantillum easily identifiable within the T. tosii species group. Tetramorium tantillum possesses distinctly shorter antennal scapes and propodeal spines than Tetramorium tosii (SI 97 - 104; PSLI 42 - 49). Also, the petiolar node shape is different, though this character should be considered with caution. Generally, the dorsum of the petiolar node of T. tantillum is less convex and the anterodorsal and posterodorsal angles are equally well-developed and of about the same height whereas the node of T. tosii shows a much more convex dorsum and the posterodorsal angle is always situated higher than the anterodorsal. However, some smaller specimens of T. tosii show a petiolar node shape that approaches the one viewed in T. tantillum.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  tantillum. Tetramorium tantillum Bolton, 1979: 152, figs. 30, 31 (w.) MADAGASCAR. See also: Hita Garcia & Fisher, 2011: 41.

Description
HL 1.010 - 1.080 (1.052); HW 0.900 - 0.970 (0.939); SL 0.750 - 0.810 (0.780); EL 0.180 - 0.205 (0.195); PW 0.695 - 0.720 (0.708); WL 1.294 - 1.338 (1.314); PSL 0.325 - 0.360 (0.343); PTL 0.345 - 0.370 (0.357); PTH 0.320 - 0.340 (0.327); PTW 0.350 - 0.380 (0.360); PPL 0.295 - 0.310 (0.303); PPH 0.330 - 0.350 (0.340); PPW 0.350 - 0.390 (0.371); CI 88 - 91 (89); SI 79 - 87 (83); OI 19 - 21 (21); PSLI 30 - 33 (33); PeNI 49 - 53 (51); LPeI 108 - 111 (109); DPeI 99 - 103 (101); PpNI 50 - 55 (52); LPpI 84 - 94 (89); DPpI 119 - 126 (123); PPI 99 - 107 (103) (5 measured).

Head distinctly longer than wide (CI 88 - 91). Anterior clypeal margin entire and convex. Frontal carinae well-developed, almost reaching posterior head margin. Antennal scrobes weakly developed, almost absent. Antennal scapes of moderate length, not reaching posterior margin of head (SI 79 - 87). Eyes relatively small (OI 19 - 21), with 11 to 13 ommatidia in longest row. Mesosomal profile relatively flat and only weakly convex, metanotal groove absent. Propodeal spines long, spinose, and acute (PSLI 30 - 33). Propodeal lobes triangular, short, and blunt. Node of petiole rectangular nodiform without sharp angles, in profile anterior and posterior faces roughly parallel, antero- and posterodorsal angles situated at about same height, dorsum moderately convex, node weakly longer than high (LPeI 108 - 111), in dorsal view roughly as long as wide (DPeI 99 - 103). Postpetiole in profile rounded, higher than long (LPpI 84 - 94), in dorsal view clearly wider than long (DPpI 119 - 126), as wide as petiolar node to weakly wider (PPI 99 - 107). Mandibles finely striate. Clypeus with 3 longitudinal rugae, median ruga more strongly developed. Head ventrally and laterally with distinct reticulate-rugose sculpturation, cephalic dorsum longitudinally rugose, with 6 to 8 rugae between frontal carinae; ground sculpturation on head weak and faint. Mesosoma and waist segments weakly reticulate-rugose without any distinct ground sculpturation. First gastral tergite completely unsculptured, smooth, and shiny. All dorsal surfaces of head, mesosoma, waist segments, and gaster with numerous long, standing hairs; hairs on antennal scapes and tibiae appressed. Colouration uniformly dark brown to blackish brown.

Type Material
Holotype worker, MADAGASCAR, Mangabe Island, Antongil Bay, 19.II.1977, primary rain forest, AB 42 litter, (W. L. & D. E. Brown) [not examined]. Paratypes, 3 workers with same data as holotype (MCZ, ) [partly examined].