Tetramorium tanaense

Identification
The subsequent character combination separates Tetramorium tanaense from the rest of the species complex: propodeal spines long and acute (PSLI 34 - 37); eyes moderate to large (OI 26 - 29); mesosoma with longitudinal rugulae, ground sculpturation smooth and shiny; first gastral tergite without standing hairs.

Distribution
This taxon was described from Kenya. It is also found in Tanzania.

Nomenclature

 *  tanaense. Tetramorium tanaense Hita Garcia, Fischer & Peters, 2010b: 83, figs. 13B, 14B, 94-96 (w.) KENYA.

Tetramorium tanaense shares many morphological similarities with Tetramorium bendai, Tetramorium humbloti, and Tetramorium sepultum. Nonetheless, it can be best separated from them by the sculpturation of the mesosoma, pilosity and shape of petiole and postpetiole. The best separation from T. bendai can be performed by comparing the ground sculpturation on the mesosoma which is densely packed reticulate-punctate in the latter, while it is generally unsculptured in T. tanaense. They also differ in the shape of the postpetiolar node in dorsal view, since this is much more transverse in T. bendai (DPpI 206 - 238) than in T. tanaense (DPpI 188 - 200). Furthermore, the latter cannot be confused with T. sepultum since the eyes of this species are smaller (OI 21 -22) and the propodeal spines much shorter (PSLI 22 - 23) than in T. tanaense (OI 26 - 29, PSLI 34 -37). Another difference between these two species is the pilosity on the mesosomal dorsum because T. sepultum has 7 to 8 pairs of standing hairs there while in T. tanaense there are only 4 pairs. As already pointed out in the description of T. humbloti, the latter and T. tanaense share most characters except the sculpturation on the mesosoma. Especially the pronotal dorsum is unsculptured and shiny in all examined T. humbloti specimens from all over its distribution range, whereas the pronotal dorsum of T. tanaense is fully longitudinally rugulose. Apart from the sculpturation on the mesosoma they share most other characters and the same morphometric range. Therefore, it is possible that they are in fact one and the same species, though, more material is needed to prove or reject this. Finally, the absence of standing hairs on the first gastral tergite distinctly separates T. tanaense from the remaining species of the weitzeckeri complex.

Worker
HL 0.706 - 0.739 (0.720); HW 0.689 - 0.733 (0.704); SL 0.533 - 0.556 (0.542); EL 0.183 - 0.200 (0.194); PW 0.544 - 0.567 (0.555); WL 0.867 - 0.989 (0.896); PSL 0.250 - 0.267 (0.258); PTL 0.089 - 0.106 (0.098); PTH 0.333 - 0.356 (0.340); PTW 0.311 - 0.328 (0.319); PPL 0.183 (0.194); PPH 0.344- 0.367 (0.356); PPW 0.356 - 0.367 (0.361); CI 95 - 100 (98); SI 74 - 81 (77); OI 26 - 29 (28); PSLI 34 - 37 (36); PeNI 56 - 59 (58); LPeI 27 - 32 (29); DPeI 305 - 350 (326); PpNI 62 - 67 (65); LPpI 52 - 56 (53); DPpI 188 - 200 (192); PPI 108 - 114 (113) (6 measured).

Head slightly longer than wide to as long as wide (CI 95 - 100). Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, ending shortly before posterior margin of head. Antennal scrobe narrow, shallow, and without defined ventral margin, not reaching posterior margin of head. Antennal scape of medium size, not reaching posterior margin of head (SI 74 - 81). Eyes of moderate size to relatively large (OI 26 - 29), with 10 to 12 ommatidia in longest row. Metanotal groove slightly impressed. Propodeal spines elongate-triangular to spinose, very long and acute (PSLI 34 - 37). Propodeal lobes small, triangular and acute. Node of petiole strongly squamiform, in dorsal view distinctly transverse, more than 3 times wider than long (DPeI 305 - 350), in lateral view around 2.8 to 3 times higher than long (LPeI 27 - 32). Postpetiole distinctly squamiform, in dorsal view around 2 times wider than long (DPpI 188 - 200); in lateral view only weakly thicker than petiolar node, and around 1.9 times higher than long (LPpI 52 - 56). Mandibles distinctly longitudinally striate. Clypeus rugose, mostly longitudinally, median ruga always strongly developed. Head longitudinally rugose, dorsum of head with 10 to 11 rugae between frontal carinae, most running to posterior margin of head. Spaces between dorsal rugae and scrobal area mostly with distinctly reticulate-punctate ground sculpture, but some parts unsculptured. Mesosoma dorsally and laterally with fine, longitudinal, widely spaced rugulae; generally no ground sculpturation present. Petiole, postpetiole and gaster completely unsculptured, smooth and shiny. Head with numerous fine, long, erect hairs; mesosoma with up to 4 pairs of erect hairs (1 on pronotum, 2 on mesonotum, and 1 on propodeum), petiole and postpetiole each with 2 pairs of hairs; first gastral tergite without standing hairs. Fine pubescence on tibiae and antennal scapes always appressed. Body colour uniformly brown to dark brown.

Type Material
Holotype worker, KENYA, Tana River Delta, Lake Shakababo, near Ngao, 28.X.1977, leg. V. Mahnert & J.L. Perret (: ZFMK_HYM_2009_6081). Paratypes, 5 workers with same data as holotype (BMNH: 2 workers ZFMK_HYM_2009_6082, ZFMK_HYM_2009_6083; : 3 workers ZFMK_HYM_2009_6084).

Etymology
The name of the new species refers to the type locality, the Tana River Delta in Coastal Kenya.