Tetramorium amissum

Identification
Tetramorium amissum is a member of the lucayanum-complex and as such it has strongly sculptured pedicel segments and striate mandibles. Only two species in the complex, and indeed in the group as a whole, have raised pubescence on the outer tibial surface, T. amissum and Tetramorium tychadion. This single character isolates them but it is interesting to note that both of them belong in the lucayanum-complex. The two differ as follows.

 Tetramorium amissum
 * Median clypeal impression absent.
 * Pronotal dorsum irregularly rugose.
 * Metanotal groove deeply impressed.
 * Petiole in dorsal view broader than long.
 * Head and alitrunk yellow, gaster dark brown.
 * Ventral surface of head with a pair of extremely long fine hairs immediately behind the buccal cavity.

 Tetramorium tychadion
 * Median clypeal impression present.
 * Pronotal dorsum longitudinally rugose.
 * Metanotal groove vestigial.
 * Petiole in dorsal view longer than broad.
 * Entire ant uniform dark brown.
 * Ventral surface of head without long hairs immediately behind the buccal cavity.

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

Nomenclature

 *  amissum. Tetramorium amissum Bolton, 1980: 336, fig. 113 (w.) DEMOCRATIC REPUBLIC OF CONGO.

Worker
HOLOTYPE. TL 3.5, HL 0.82, HW 0.72, CI 88, SL 0.61, SI 85, PW 0.52, AL 0.94.

Mandibles longitudinally striate. Anterior clypeal margin with a narrow median apron but without a median impression. Median clypeal carina strong on anterior two-thirds but posteriorly weak. Frontal carinae elongate, running back well beyond the level of the posterior margins of the eyes and merging into the occipital rugular sculpture. Eyes moderate, maximum diameter 0.16, about 0.22 x HW and with 9 ommatidia in the longest row. With the alitrunk in profile the metanotal groove forming a conspicuous U-shaped concavity in the dorsal outline. Propodeal spines straight, narrow, elevated, much longer than the broadly triangular metapleural lobes. Petiole in profile with an elongate anterior peduncle and a fairly stout node, the dorsal length of which is less than the height of the tergal portion. In dorsal view the node is distinctly broader than long. Dorsum of head with irregular but strongly developed longitudinal rugae which are quite widely spaced, there being 10-11 of them between the frontal carinae at the level of the eyes. Close to the occipital margin a very few cross-meshes are present but there is no occipital rugoreticulum developed. Sides of head between eye and frontal carina less strongly but more irregularly rugose. Groundsculpture of head faint and superficial so that the surfaces between the rugae are polished and glossy. Dorsal alitrunk coarsely, densely irregularly rugose, without a defined rugoreticulum but with numerous transverse components which are as strongly developed as the longitudinals. Ground-sculpture vestigial, almost effaced. Dorsal surfaces of petiole and postpetiole finely rugulose, the rugulae sharply defined, irregular on the petiole but predominantly longitudinal on the postpetiole. First gastral tergite absolutely smooth. All dorsal surfaces of head and body with numerous standing hairs, the longest of those on the alitrunk distinctly longer than the maximum diameter of the eye. Hairs on ventral surface of head markedly finer than those on dorsum; one pair, which is situated just behind the buccal cavity, very long, exceeding those on the dorsal alitrunk. Dorsal (outer) surfaces of hind tibiae with suberect to subdecumbent fine, fairly long pubescence. Shorter subdecumbent pubescence also present on scapes. Head, alitrunk and appendages glossy dull yellow, the gaster dark brown.

Type Material
Holotype worker, Zaire (‘B. Congo’ on data label): Lwiro River, 47 km N. Bukavu, 1950 m, 27.viii.57 (E. S. Ross & R. E. Leech).