Tetramorium susannae

Tetramorium susannae is a formerly unrecognized but fairly abundant and common species in Central and West African rain forests.

Identification
The strongly squamiform and transverse petiolar node (DPeI 271 - 354) together with the strongly transverse and sharply cuneiform postpetiole (DPpI 216 - 263, LPpI 54 - 63), and the conspicuous hexagonal ground striation on head and mesosoma distinguish Tetramorium susannae from the other species of the muralti complex.

Distribution
Known from Angola, Cameroon, Central African Republic, Democratic Republic of Congo, Gabon and Ghana.

This taxon was described from Ghana.

Nomenclature

 *  susannae. Tetramorium susannae Hita Garcia, Fischer & Peters, 2010b: 58, figs. 4B, 6B, 7B, 67-69 (w.) GHANA.

There is a distinct variation observable in some characters of Tetramorium susannae that need to be discussed. First, the propodeal spine length is usually constantly long and spinose in material from Cameroon, Gabon, and Ghana (PSLI 26 - 33) while it is more elongate-triangular and shorter in the Central African Republic and the D.R. Congo (PSLI 22 - 24). The other geographically variable character is the appendage coloration that, interestingly, shows a similar pattern as already discussed for Tetramorium muralti. The T. susannae type material from Ghana as well as all specimens from Angola, the D.R. Congo and Gabon all possess whitish yellowish appendages. In contrast to this, the appendage coloration is strongly bicoloured in material from Cameroon and the Central African Republic with whitish tibiae while the remaining leg segments, mandibles, and antennae are of dark brown colour. However, the observed variation in appendage coloration and propodeal spine length is at present not considered as sufficient and consistent enough to allow a splitting of the T. susannae material.

The absence of longitudinal rugae on the mesosomal dorsum and the entire and convex anterior clypeal margin group T. susannae together with T. muralti and separate them from the rest of the species complex. Yet, the latter species does not possess the characteristic hexagonal ground striation on head and mesosoma observed in T. susannae, and additionally, the postpetiole is only rounded cuneiform without sharp dorsal margin. Furthermore, the cephalic sculpturation of T. muralti , usually consisting of 3 longitudinal rugae, differs from the 1 median ruga present in T. susannae. However, the best single diagnostic character to distinguish T. susannae from other species in the complex is the strongly transverse cuneiform postpetiole with its sharp dorsal transverse margin (DPpI 216 - 264). Although the postpetiole of Tetramorium flavithorax is sharply cuneiform, too, it is less transversely developed (DPpI 192 - 209) and the dorsal transverse margin is not as sharp as in T. susannae. Besides, both species cannot be confused with each other because of the obvious colour pattern of T. flavithorax that evidently differs with the uniform coloration of T. susannae.

Worker
HL 0.489 - 0.556 (0.519); HW 0.456 - 0.528 (0.491); SL 0.300 - 0.372 (0.333); EL 0.106 - 0.139 (0.125); PW 0.333 - 0.433 (0.384); WL 0.533 - 0.633 (0.594); PSL 0.111 - 0.172 (0.143); PTL 0.067 - 0.089 (0.078); PTH 0.200 - 0.250 (0.226); PTW 0.206 - 0.261 (0.236); PPL 0.111 - 0.139 (0.127); PPH 0.189 - 0.244 (0.220); PPW 0.250 - 0.328 (0.296); CI 92 - 99 (95); SI 64 - 73 (68); OI 23 - 28 (25); PSLI 22 - 33 (28); PeNI 54 - 66 (61); LPeI 30 - 39 (34); DPeI 271 - 354 (304); PpNI 67 - 86 (77); LPpI 54 - 63 (58); DPpI 216 - 263 (232); PPI 117 - 135 (126) (42 measured).

Head longer than wide (CI 92 - 99). Anterior clypeal margin entire and convex. Frontal carinae strongly developed and sinuate, curving down ventrally shortly before posterior margin of head, sharply defining posterior and ventral margins of well-developed and broad antennal scrobe. Antennal scape short (SI 64 - 73). Eyes moderate to large (OI 23 - 28), with 7 to 9 ommatidia in longest row. Metanotal groove in profile never impressed. Propodeal spines usually long and spinose, sometimes medium sized and elongate-triangular to spinose (PSLI 22 - 33). Propodeal lobes moderate, triangular and acute. Petiolar node strongly squamiform, in dorsal view highly transverse and between 2.7 to 3.5 times wider than long (DPeI 271 - 354), in lateral view between 2.5 to 3.3 times higher than long (LPeI 30 - 39). Postpetiole strongly cuneiform with sharp dorsal margin, in dorsal view well transverse, between 2.1 to 2.6 times wider than long (DPpI 216 - 264), and distinctly wider than petiolar node (PPI 117 - 135); in profile around 1.6 to 1.8 times higher than long (LPpI 54 - 63). Mandibles unsculptured, smooth and shiny. Clypeus usually with 3 longitudinal rugae, median ruga always well developed, lateral rugae variable and sometimes reduced. Most of head unsculptured, median longitudinal ruga present between frontal carinae, rarely traces of short rugulae present anteriorly near posterior clypeal margin or posteriorly near posterior margin of head, antennal scrobe with median longitudinal ruga anteriorly usually ending before posterior eye level. Mesosoma generally unsculptured and shiny. Ground sculpturation on head and mesosoma a very conspicuous hexagonal striation, in material from Cameroon and Central African Republic often partly reduced. Both waist segments and gaster completely unsculptured, smooth and shiny. All dorsal body surfaces with simple, fine, long standing hairs. Fine pubescence on antennal scapes and tibiae generally appressed. Head, mesosoma, waist segments, and gaster very dark brown to black, appendage coloration variable: appendages uniformly whitish to yellowish in material from Angola, D.R. Congo, Gabon, and Ghana, specimens from Cameroon and Central African Republic with whitish tibiae strongly contrasting with remaining leg segments, mandibles and antennae.

Etymology
The new species is dedicated to Mrs. Susanne Fromm from Oberdürenbach-Büschhöfe, Germany, for her enormous support of the first author's studies over several years.