Tetramorium pialtum

Identification
Bolton (1980) - This small species is most closely related to the more common Tetramorium dumezi and shares most characters with it. Separation of the two is based on sculpture differences as T. dumezi lacks the pronotal median costa seen in T. pialtum and has only 5 rugulae between the frontal carinae at eye-level as opposed to 7 in T. pialtum. Apart from these the pronotal sculpture is coarser in T. pialtum where a broken reticulum is present, whereas in T. dumezi the sculpture is feeble and predominantly longitudinal, at most with a few cross-meshes.

Distribution based on Regional Taxon Lists
Afrotropical Region: Central African Republic, Ghana, Kenya.

Nomenclature

 *  pialtum. Tetramorium pialtum Bolton, 1980: 350 (w.) GHANA.

Worker
Holotype: TL 3.1, HL 0.69, HW 0.58, CI 84, SL 0.43, SI 74, PW 0.42, AL 0.86.

Mandibles smooth and shining with scattered minute pits. Anterior clypeal margin entire, without a median notch. Clypeus with three weak longitudinal carinae, the median and a flanking pair. Frontal carinae fine and narrow, extending back to the occiput and merging there with the sculpture. The left carina continuous but the right broken near its base and with a distinct gap. This implies that variation in carinal development such as is seen in candidum may also occur here. Maximum diameter of eye 0.15, about 0.26 x HW and with 8 ommatidia in the longest row. With the head in full-face view the sides approximately parallel and more or less straight. Propodeum armed with a pair of short triangular teeth which are about as long as their basal width and which are shorter and narrower than the triangular metapleural lobes. Petiole node in profile with the posterodorsal angle much broader and more broadly rounded than the anterodorsal. Node in dorsal view subglobular and slightly broader than long. Dorsum of head with fine, more or less straight, widely spaced longitudinal rugulae. Some of these are continuous from clypeus to vertex but some are broken or interrupted; 7 are present between the frontal carinae at the level of the eyes. Occipital region without a rugoreticulum. Ground-sculpture of head a very superficial faint patterning only. Dorsal alitrunk irregularly rugulose, strongest on the pronotum where a loose, broken reticulum is present but much weaker and less conspicuous posteriorly. Midline of pronotum with a strong longitudinal costa, which is distinctly stronger than the rugulae on each side of it. Ground-sculpture of alitrunk dorsum a fine, almost effaced granulation. Petiole and postpetiole almost smooth, with only the faintest vestiges of sculpture. Gaster unsculptured and smooth. All dorsal surfaces of head and body with standing short hairs. Scapes and tibiae only with short decumbent to appressed pubescence. Colour brownish yellow.

Type Material
Holotype worker, Ghana: Tafo, G-block, 11.xi.1968, on bark of tree (C. A. Collingwood).