Tetramorium rimytyum

Identification
Bolton (1980) - This fascinating primary forest species is an almost exact intermediate between members of the aculeatum-group and those of the setigerum-group close to Tetramorium metactum. The decision to place T. rimytyum in the aculeatum-group is based on the presence of a clypeal notch, the reduction of the frontal carinae and the presence of elevated tibial pubescence in this species. These characters are general in the aculeatum-group but not in Tetramorium setigerum and its allies, but the overall similarity in body form between T. metactum and T. rimytyum is obvious. Within the aculeatum-group rimytyum is separated from both Tetramorium aculeatum and Tetramorium africanum by its conspicuous triangular metapleural lobes and its possession of elevated pubescence on the tibiae as opposed to the long hairs seen in the other two species. Apart from this it is separated from T. africanum by having the head coarsely sculptured, the petiole node as broad as long in dorsal view, the petiole shaped as in figure, and the clypeus with coarse carinae. In T. africanum the head is very weakly or not sculptured, the petiole node is much broader than long in dorsal view, the petiole is shaped as in figure, and the clypeal carinae are fine and widely separated. In the case of T. aculeatum the petiole node is much shorter in profile with a correspondingly longer peduncle than in T. rimytyum, and again the node in dorsal view is much broader than long.

Distribution based on Regional Taxon Lists
Afrotropical Region: Ghana.

Nomenclature

 *  rimytyum. Tetramorium rimytyum Bolton, 1980: 356, fig. 129 (w.) GHANA.

Worker
Holotype: TL 4.8, HL 1.04, HW 0.90, CI 87, SL 0.98, SI 109, PW 0.66, AL 1.34.

Mandibles longitudinally striate, armed with three teeth followed by a series of 5 denticles which decrease in size basally. Anterior clypeal margin with a conspicuous median notch, the median portion of the clypeus with 3 strong longitudinal carinae and with 1-2 weaker carinae outside these on each side. Frontal carinae hardly distinguishable from the remaining cephalic sculpture, being only slightly more strongly developed; they can be distinguished to the level of the eyes but behind this are inseparable from the other sculpture. Antennal scrobes absent, the scapes long (SI > 100). Eyes prominent, roughly hemispherical in full-face view, their maximum diameter 0.20, about 0.22 x HW. Number of ommatidia in longest row difficult to count due to curvature of the eye, but approximately 12-13. With the head in full-face view the occipital margin shallowly convex, rounding broadly and evenly into the sides, the curvature including almost all the space between the posterior margins of the eyes and the occipital margin. Metanotal groove in profile broadly but shallowly impressed. Propodeum armed with a pair of long narrow spines which are much longer than the acutely triangular metapleural lobes. Petiole and postpetiole in profile shaped as in Fig. 129; in dorsal view the petiole node as broad as long. Dorsum of head strongly but irregularly longitudinally rugose with a few scattered cross-meshes. Occipitally the rugae even more irregular and with more numerous and stronger cross-meshes which form a loose reticulum in places. Sides of head above and behind eyes with a loose, broad-meshed rugoreticulum. Ground-sculpture minimal, the spaces between rugae generally glossy, at most with very faint superficial markings. Dorsal alitrunk rugose, predominantly longitudinally so on the promesonotum although the rugae are very irregular and are stronger and more widely spaced on the pronotum than on the mesonotum. Rugae on propodeal dorsum weaker and very irregular. Ground-sculpture vestigial or absent. Both petiole and postpetiole with rugose sculpture dorsally, but those on the latter segment much weaker, more widely spaced and more regularly longitudinal than those on the former. First gastral tergite unsculptured. All dorsal surfaces of head and body with abundant long fine acute hairs, the longest of those on the alitrunk easily exceeding the maximum diameter of the eye. Dorsal (outer) surfaces of middle and hind tibiae with fine suberect to subdecumbent dense pubescence. Colour uniform dark brown.

Type Material
Holotype worker, Ghana: Mt Atewa, 1.xii.1968, on fallen tree trunk (B. Bolton).