Tetramorium rotundatum

Know from three queens, the two Democratic Republic of the Congo type specimens and a third collected in Gabon.

Identification
Bolton (1980) - This species is known only from the female (queen) but definitely represents a separate good species, closely related to Tetramorium africanum. The shape and proportions of the petiole in T. rotundatum are the same as in T. africanum and both species are clothed with dense short pilosity on the head and alitrunk. However, in T. africanum this pilosity is also present on the first gastral tergite whereas it is absent here in T. rotundatum or at most represented only by a narrow band on the extreme apex of the sclerite, the greater part being hairless. Pilosity is distinctly denser on the appendages (at least) in T. africanum, where the short hairs form a dense mat or pelt on the scapes and tibiae. In T. rotundatum the hairs are sparser and quite widely spaced out on the scapes and tibiae, and in general the length of each hair is about equal to the distance between hairs in the same row. Finally the mesopleuron of T. africanum is densely sculptured with fine disorganized rugulae whereas in T. rotundatum the mesopleuron is almost smooth, at most with fine superficial shagreening or punctulation over most or all of its surface. Females of T. africanum and T. rotundatum together separate from the much more common Tetramorium aculeatum as follows.

Tetramorium aculeatum females
 * Head narrower, CI < 95 (range 83-90).
 * Eyes strongly convex, very prominent; diameter of head across eyes 1.20-1.25 x HW.
 * Scapes longer, SI > 110.
 * Sides of pronotum and mesopleuron strongly and quite regularly longitudinally rugose.
 * Hairs on dorsal (outer) surfaces of hind tibiae and on scapes as long as or longer than the maximum width of the appendage on which they arise.
 * Body hairs elongate, fine, usually flexuous.
 * Length of petiolar peduncle greater than thickness of node in profile.
 * Palp formula 3, 2.

Tetramorium africanum and Tetramorium rotundatum females
 * Head broader, CI > 95 (range 96-103).
 * Eyes less convex, not as prominent; diameter of head across eyes 1.10-1.12 x HW.
 * Scapes shorter, SI < 110.
 * Sides of pronotum and mesopleuron unsculptured or with very irregular fine dense rugulation; sometimes with pronotum unsculptured, mesopleuron sculptured.
 * Hairs on dorsal (outer) surfaces of hind tibiae and on scapes shorter (usually obviously shorter) than the maximum width of the appendage on which they arise.
 * Body hairs short, commonly more so less straight or only slightly curved.
 * Length of petiolar peduncle less than thickness of node in profile.
 * Palp formula 4, 2 (T. africanum).

As stated above the worker of T. rotundatum remains unknown. However, as workers and females of T. africanum and T. aculeatum each show the same basic characters there is a good chance that the worker of T. rotundatum will resemble that of T. africanum but lack hairs (or have very reduced pilosity) on the first gastral tergite.

Distribution based on Regional Taxon Lists
Afrotropical Region: Democratic Republic of Congo, Gabon.

Nomenclature

 *  rotundatum. Macromischoides africanus var. rotundatus Santschi, 1924b: 209 (q.) DEMOCRATIC REPUBLIC OF CONGO. Combination in Tetramorium: Bolton, 1980: 357. Raised to species: Bolton, 1980: 357.

Description
Bolton (1980) - TL 6.1-7.0, HL 1.18-1.26, HW 1.16-1.30, CI 98-103, SL 1.16-1.30, SI 100-103, PW 1.20-1.34, AL 1.90-2.10 (4 measured).

Type Material
Bolton (1980) - Syntype female, ZAIRE: Région des Lacs (Sagona) [examined].

References based on Global Ant Biodiversity Informatics

 * Bolton B. 1980. The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Ethiopian zoogeographical region. Bulletin of the British Museum (Natural History). Entomology 40: 193-384.