Tetramorium sentosum

The type was collected on the grounds of Calicut University Campus.

Identification
A member of the Tetramorium scabrosum-species group.

Sheela and Narendran (1998) - This species comes close to Tetramorium mixtum in the following features (1) base of first gastral tergite concave behind post petiole and anterolateral corners of gaster prominent (2) mandibles striate in both species. But it differs from mixtum in (1) Anterolateral corners though projecting forward, not produced into blunt teeth or horn) (2) anterior margin of clypeus entire, not indented medially (in mixtum anterior clypeal margin slightly indented medially). Tetramorium sentosum is smaller in size than mixtum.

Distribution based on Regional Taxon Lists
Oriental Region: India.

Nomenclature

 *  sentosum. Tetramorium sentosus Sheela & Narendran, 1998a: 42, figs. 17-20 (w.) INDIA.

Worker
Holotype. Head anteriorly evenly rugulose, regulae diverging posteriorly and tending to be reticulate beyond level of posterior margin of eyes, posteriorly rugosoreticulate; genae and ventral portions of head longitudinally rugosoreticulate, scrobe with sculpture like that of nearby places; posterior margin of head transverse in front view, sides nearly straight, mandible closely longitudinally striate, masticatory margin with two acute apical teeth followed by two or three small teeth; clypeus with a narrow flange in front; a median strong carina accompanied by two pairs of weak carinae on either side present on mid lobe of clypeus; anterior margin entire, transverse, posterior clypeal margin arched, indistinct, frontal area very small, triangular; frontal lobes short, frontal carinae weak, extending well beyond eyes; posterior margin of scrobe faintly indicated, frontal carina reaching beyond eye by 1.25x length of eye, scrobes not distinctly marked; eyes elongate situated on mid transverse line, but in profile more close to mandibular base. Antennae 12-jointed, scape extending up to vertex, flagellar segments 2-8 transverse, 2-6 very short, club 3 jointed, terminal club segment longer than preceding two together (10:7) flagellum excluding club subequal to terminal club segment.

Thorax: Dorsally rugosoreticulate, sides rugulose, propodeum in between spines rugoso punctate; pronotum anteriorly transverse, sides not sharply pointed but giving a square shouldered appearance, in dorsal view margins straightly converging to propodeal spines; no sutures on thorax, episternum with a shallow diagonal depression, promesosternal separation faintly indicated, propodeal spines long, laterally compressed, directed backwards and upwards, tips acute and a little curved upwards, in dorsal view spines slightly diverging, distinctly longer than distance between its bases (7:5), length 2.3x basal width; propodeal spiracles situated below base of spines, almost at mid length of episternum, but towards posterior margin, metapleural lobes large, flat, shorter than propodeal spines, rounded at tip, subtriangular, length: basal width = 5:4; legs smooth, polished and shining, femora medially swollen, tibiae completely swollen, mid and hind tibiae with simple spurs.

Abdomen: Peduncle of petiole short smooth, petiole node rugosoreticulate with short ventral flange, post petiole weakly sculptured, peduncle subequal to metapleural lobes and shorter than propodeal spines; petiole massive, blocky, no constriction behind node, petiole height and length subequal, nearly convex above, anterior and posterior margins sub-parallel and vertical, postpetiole shorter and a little lower than petiole, in dorsal view petiole length and breadth subequal and posteriorly broader than anterior side; post petiole in dorsal view distinctly broader than long, junction between post petiole and gaster with cross ridge. Gaster smooth polished and shining, anterior margin highly concave, anterolateral corners acute, projecting distinctly forward beyond posterior margin of post petiole; first tergite covering more than 3/4 its length.

Colour of head, thorax and pedicel brownish red, first tergite of abdomen excluding posterior margin dark reddish brown, posterior margin and remaining tergites reddish yellow; mandibles and antennae almost concolourous with head, legs reddish yellow; head, thorax, pedicel and gaster with brownish yellow, short, erect and suberect hairs, hairs abundant on gaster, legs with appressed very shmt hairs, tibiae with few long (as long as those on thorax) suberect hairs.

Total length-2.16mm; head length-0.58mm; Head width-0.53mm: Cephalic index-91; Eye diameter-0.12mm; Scape 1ength-0.40mm; Scape index-75; pronotal width-0.37mm; Alitrunk length-0.64mm.

Type Material
Holotype: Worker, India: Kerala, Calicut University Campus. Sheela. S. 12.3.1995 (Department of Zoology, University of Calicut).

Etymology
The species is named as sentosus to indicate the peculiar metapleural spine.

References based on Global Ant Biodiversity Informatics

 * Sheela S.; T.C. Narendran. 1998. On five new species of Tetramorium (Hymenoptera: Formicidae: Myrmicinae) from India. Entomon 23: 37-44.