Tetramorium securis

The type material was collected from the litter and a pitfall trap, all from forest habitat.

Identification
Roncin (2002) - A member of the Tetramorium scabrosum-species group. Of all the known Tetramorium species of the Oriental Region, Tetramorium securis is the smallest; the only one along with Tetramorium kraepelini with a head width inferior to 0.50 mm. The former species is similar to Tetramorium kieti by its overall sculpture, proportions of the head, weakness of the posterior part of antennal scrobes, pilosity of scapes and hind tibiae, and moderate development of gastral tubercles, but differs by its size, the shape and sculpture of the petiole, the width of the basis of the propodcal spines, and the sculpture of the basis of the first gastral tergite.

Distribution based on Regional Taxon Lists
Oriental Region: Vietnam.

Nomenclature

 *  securis. Tetramorium securis Roncin, 2002: 283, figs. 1, 3, 5 (w.) VIETNAM.

Worker
Holotype. TL 1.9. HL 0.506, HW+E 0.489, HW 0.453, CI 90, SL 0.362, SI 80, EL 0.114, PrW 0.326, ML 0.535, DPW 0.139, DPpW 0.194. Paratypes: TL 1.9-2.0, HL 0.506-0.531, HW+E0.486-0.502, HW0.547-0.455, CI 86-88, SL0.375-0.379. SI 83-84, EL 0.110, PrW 0.346-0.354, ML 0.573-0.582, DPW 0.143-0.150, DPpW 0.202-0.235.

Head nearly as long as wide with feebly concave posterior margin in full face view: sides weakly convex, and head width moderately decreasing from eyes to anterior clypeus margin. Mandibles with faint striation, with three strong apical teeth, the two first closer to each other than to the third one: followed by a series of four minor denticles. Anterior clypeal margin entire, moderately and regularly convex. Clypeus with three main longitudinal rugae. Anterior clypeus margin with a small horizontal rim below the anterior declivity bordering the basal margin of the mandibles when closed. F'rontal carinae extending back almost to occipital corners, but behind level of eyes becoming weak and no more strongly developed than cephalic rugae. Eyes situated in front of the middle of sides of head, their maximum length 0.114 mm, about 0.25 x HW. Dorsal head sculpture between frontal carina longitudinally rugulose, the rugae being slightly sinuous, turning to a rugoreticulum dorsally in the 1/5 posterior part of head from the level of the superior limit of the scrobes to occiput in full face view. This rugoreticulum also covers lateral and ventral parts of head from the lower margins of the scrobes, and from mandibular insertions to occiput, and becomes very weak posteromedioventrally. Spaces between frontal rugae and in inner parts of the reticulation filled with small reticulate-puncturations. Upper part of scrobes possesses only this fine puncturation and appears less sculptured than neighboring areas. Scrobes not really delimited by a margin posteriorly and laterally.

Dorsal surface of scapes with one or two erect hairs and with decumbent pubescence.

Mesosoma without any trace of dorsal sutures, and regularly convex in profile. Pronotal humeri angulate in dorsal view. Propodeal lobes well developed, acute, slightly shorter than the propodeal spines and with dorsal and ventral outlines concave in lateral view. Propodeal spines semi-translucent, acute, flattened in the sagittal plan, slightly upcurved at their extremities, and almost parallel in dorsal view. Mesosoma with fine reticulate-puncturations superimposed to coarse rugoreticulations. Former sculpture reduced on lateral parts of propodeum.

Node of petiole in profile bent backwards with tergal portion slightly higher than long, posterior and dorsal face meeting through a curve, not separated by an angle. Anterior face of node concave. In dorsal view node 1/3 longer than wide, its lateral portions steeply sloping downward and meeting on the top in a sharp longitudinal edge. Sternal part of the node visible in dorsal view and wider than the tergal part (maximum width ofthe tergal part of the petiole= 0.118).

Petiole and postpetiole quite bright but with superficial reticulation. In profile, dorsal outline of the anterior peduncle of the petiole backwards prolonged by a strong diagonally ascending ruga that almost reaches the upper posterior part of the node. Postpetiole transverse and rectangular in dorsal view. Dorsal face of the tibia III with a few suberect hairs.

Base of first gastral tergite concave, widely connected with postpetiole. Anterolateral parts of first tergite gaster forming blunt tubercles anterior to the level of medioanterior margin of gaster in dorsal view. Posterior visible part of the abdominal pretergite IV with a transverse groove armored with short longitudinal costae. Gaster fairly shining but with superficial fine reticulation (visible in alcohol under high magnification and saturated light reflection).

All dorsal surfaces of the body with erect, stout, and rather small hairs, the longer of them situated on the back of head, mesosome and gaster reaching 0.055 mm.

Color light yellowish brown, the appendages yellowish.

Type Material
The holotypes of the new species are deposited in the Museum National d'Histoire Naturelle de Paris and the paratypes in the author's collection.

Holotype worker, Vietnam: Dong Nai Province: Binh Chau, forest, 35m, litter surface, 22.i.1995, pitfall (VIET 173), L. Deharveng, A. Bedos coll. Paratypes workers: 2 workers, same locality, 22.i.1995, pitfall traps (VIET 154), L. Deharveng, A. Bedos coll.

Etymology
From the latin securis which means axe; refers to the shape of the petiole.

References based on Global Ant Biodiversity Informatics

 * Roncin E. 2002. Two new Tetramorium species (Hymenoptera: Formicidae) from Vietnam with a discussion of the mixtum, tonganum, and scabrosum groups. Sociobiology 40: 281-292.