Tetramorium scutum 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 : 105-107

Tetramorium scutum Hita Garcia & Fisher sp. n. Figs 41B, 42A, 57, 66

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) (CAS: CASENT0189116). Paratypes, five pinned workers with same data as holotype (BMNH: CASENT0218026; CAS: CASENT0218027; CASENT0248303; CASENT0248304; CASENT0248305); five pinned workers from Fianarantsoa, 8.0 km NE Ivohibe, 22.42167°S, 46.89833°E, 1200 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF01753, 3.-9.XI.1997 (B.L. Fisher) (CAS: CASENT0218022; CASENT0218023; CASENT0218028; CASENT0248309; MCZ: CASENT0248308); seven pinned workers from Fianarantsoa, R.S. Ivohibe, 6.5 km ESE Ivohibe, 22.49667°S, 46.955°E, 1575 m, montane rainforest, sifted litter (leaf mold, rotten wood), collection code BLF01751, 24.-30.X.1997 (B.L. Fisher) (CAS: CASENT0189154; CASENT0218021; CASENT0218024; CASENT0218025; CASENT0248306; CASENT0248307).

Diagnosis.

Tetramorium scutum can be separated from the remainder of the species complex by the following character combination: moderate to large eyes (OI 24-25); short antennal scapes (SI 71-74); frontal carinae moderately to well developed, slightly diverging posteriorly, ending at or shortly before posterior head margin; propodeal spines moderate to long (PSLI 22-24), propodeal lobes elongate-triangular, always weakly shorter than propodeal spines, in profile spines and lobes strongly inclined towards each other; petiolar node in profile around 2.0 to 2.1 times higher than long (LPeI 48-50) and in dorsal view around 1.4 to 1.5 times wider than long (DPeI 144-154); dorsum of mesosoma with six or more pairs of long, standing hairs from anterior pronotum to posterior mesonotum, propodeum without any standing pilosity; waist segments with long, standing pilosity.

Worker measurements

(N=10). HL 0.65-0.70 (0.67); HW 0.60-0.64 (0.61); SL 0.43-0.45 (0.44); EL 0.15-0.16 (0.15); PH 0.31-0.33 (0.32); PW 0.44-0.48 (0.45); WL 0.79-0.86 (0.83); PSL 0.15-0.17 (0.16); PTL 0.12-0.14 (0.13); PTH 0.25-0.28 (0.27); PTW 0.19-0.21 (0.19); PPL 0.18-0.21 (0.19); PPH 0.25-0.29 (0.XX); PPW 0.25-0.29 (0.27); CI 90-92 (91); SI 71-74 (72); OI 24-25 (24); DMI 54-59 (55); LMI 38-39 (38); PSLI 22-24 (23); PeNI 41-44 (43); LPeI 48-50 (49); DPeI 144-154 (148); PpNI 57-62 (59); LPpI 70-74 (72); DPpI 134-140 (138); PPI 133-142 (138).

Worker description.

Head longer than wide (CI 90-92); in full-face view posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae moderately to well developed, slightly diverging posteriorly, ending at or shortly before posterior head margin. Antennal scrobes weak to absent, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 71-74). Eyes moderate to relatively large (OI 24-25). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 38-39), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weak or absent. Propodeal spines moderate to long, elongate-triangular to spinose, and acute (PSLI 22-24); propodeal lobes elongate-triangular, always weakly shorter than propodeal spines, in profile spines and lobes strongly inclined towards each other. Petiolar node in profile high rounded nodiform to weakly squamiform, around 2.0 to 2.1 times higher than long (LPeI 48-50), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height, petiolar dorsum relatively flat; node in dorsal view between 1.4 to 1.6 times wider than long (DPeI 144-154), in dorsal view pronotum between 2.2 to 2.5 times wider than petiolar node (PeNI 41-44). Postpetiole in profile subglobular, around 1.3 to 1.4 times higher than long (LPpI 70-74); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 134-140), pronotum between 1.6 to 1.8 times wider than postpetiole (PpNI 57-62). Postpetiole in profile appearing slightly more voluminous than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 133-142). Mandibles completely unsculptured, smooth, and shiny; clypeus weakly, irregularly, longitudinally rugulose with median area mostly unsculptured, smooth, and shiny, sometimes median rugula present, but then weakly developed and/or interrupted, one or two weak, irregular and broken rugulae present on each side; cephalic dorsum between frontal carinae longitudinally rugulose with six to nine rugae/rugulae, rugae/rugulae usually running from posterior clypeal margin to posterior head margin, often irregularly shaped, interrupted or with cross-meshes; scrobal area partly unsculptured and merging with surrounding sculpture; lateral head anteriorly reticulate-rugose to longitudinally rugose and posteriorly mostly unsculptured. Ground sculpture on head weakly to moderately reticulate-punctate, especially laterally. Dorsum of mesosoma irregularly longitudinally rugose; lateral mesosoma mostly irregularly longitudinally rugose with some reticulate-rugose elements. Ground sculpture on mesosoma weak to absent. Forecoxae 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 from anterior pronotum to posterior mesonotum, propodeum without standing pilosity; petiole with one and postpetiole with one or two pairs of long, standing hairs; first gastral tergite with short, moderately dense, appressed pubescence in combination with several scattered, long, standing hairs. 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 contrasting with yellowish to light brown mandibles, antennae, and legs.

Etymology.

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

Distribution and biology.

This new species is only known from the area around Ivohibe (Fig. 66) where it was collected from a few montane rainforest localities situated at elevations of 1200 to 1575 m. All specimens were sampled from leaf litter.

Discussion.

Tetramorium scutum is relatively easy to distinguish within the species complex since it is the only species in which the moderately long spines (PSLI 22-22) and the comparatively long propodeal lobes are strongly inclined towards each other. In all the other group members the spines are either much shorter or if they are of approximately similar length as in Tetramorium scutum , then the lobes are much smaller and spines and lobes are never strongly inclined towards each other. Interestingly, the species most similar to Tetramorium scutum are Tetramorium aspis and Tetramorium camelliae from the Tetramorium cognatum complex, and we suspect that they are also more closely related to each other than to the rest of the group. These three species all have strongly inclined spines and lobes and are also found in the same small area in the southeast of Madagascar.

The new species is only known from a relatively small area and consequently shows very little intraspecific variation.