Polyrhachis gerstaeckeri

Nothing is known about the biology of .

Identification
Rigato (2016) - A species in the viscosa-group with this distinctive character combination: 1) propodeal dorsum and declivity separated by a thin, medially arched ridge; 2) petiole quadrispinose (the mid-pair of spines longer); 3) all mesosomal segments distinctly transverse in dorsal view; 4) sculpture finely reticulate-punctate with an ill-defined longitudinal rugulation on mesosomal dorsum and cephalic vertex.

P. gerstaeckeri does not correspond to the description of Polyrhachis cubaensis provided by Bolton (1973). Polyrhachis gerstaeckeri differs for its transverse propodeal dorsum, less developed median prominence of the propodeal ridge between the propodeal teeth (Bolton also reported propodeal spines instead of teeth for “cubaensis”), a weaker longitudinal rugosity, and absence of standing hairs from the dorsum of the body (some hairs are mentioned as occurring on head and gastral dorsum of the specimen described by Bolton, 1973).

Polyrhachis gerstaeckeri shares several features with Polyrhachis wilmsi, but the latter has a better defined margination between the propodeal dorsum and the declivity, with a stronger median prominence, and a more conspicuous rugulation on the head.

The main differences between P. gerstaeckeri and P. wilmsi can be summarized as follows:

Distribution based on Regional Taxon Lists
Afrotropical Region: Kenya, United Republic of Tanzania.

Nomenclature

 *  gerstaeckeri. Polyrhachis gerstaeckeri Forel, 1886f: 197 (w.) TANZANIA. Combination in P. (Myrma): Wheeler, W.M. 1922a: 994. Subspecies of cubaensis: Mayr, 1893: 196; Forel, 1894b: 71; Emery, 1896d: 379. Junior synonym of cubaensis: Bolton, 1973b: 325. Status as species: Rigato, 2016: 22. Senior synonym of striolatorugosa: Rigato, 2016: 22.
 * striolatorugosa. Polyrhachis cubaensis var. striolatorugosa Mayr, 1893: 195 (w.) TANZANIA. Combination in P. (Myrma): Wheeler, W.M. 1922a: 994. Junior synonym of cubaensis: Bolton, 1973b: 325; of gerstaeckeri: Rigato, 2016: 22.

Worker
Rigato (2016) - Holotype. HL 1.60, HW 1.43, CI 89, SL 1.70, SI 119, FW 0.45, FI 31, PW 1.47, WL 2.08, HTL 1.72. (N.B.: gaster missing from the holotype)

Clypeus faintly carinate, its anterior margin evenly convex. Head in full face view oval, wider behind than in front; sides and posterior margin weakly convex. Eyes placed close to posterior corners and moderately protruding. Scapes moderately long. Mesosoma stout, in profile pronotum anteriorly and propodeum slightly convex, mesonotum almost flat. In dorsal view pronotum, mesonotum and propodeum distinctly wider than long. Pronotal teeth mostly anteriorly directed, well developed and strong. Pronotum and mesonotum transversely weakly convex, propodeum more arched. Mesosoma distinctly marginate along its sides, the marginations not forming flanges or lobes. Promesonotal and metanotal sutures distinct, but not impressed. Propodeal dorsum and declivity separated by a distinct margin, medially more raised and almost toothlike. Propodeal teeth small, upturned and blunt. Petiole with four spines: dorsal pair almost parallel, upward directed and moderately bent backward, distinctly longer than the lateral pair. In frontal (or posterior) view the space between the dorsal pair very weakly concave, almost straight.

Mandibles mostly finely shagreened. The whole body finely reticulate-punctate with superimposed fine and moderately developed rugulosity especially on cephalic and mesosomal dorsum. Head mostly reticulate-rugulose; mesosomal dorsum with longitudinal rugulosity. Propodeal declivity superficially finely reticulate.

Standing hairs almost absent, except for those fringing the anterior clypeal margin. Pubescence on the body very short and sparse.

Colour black throughout.

A recently collected worker from Zanzibar (figs. 6a-c), the type locality of gerstaeckeri, has the following data:

HL 1.50, HW 1.38, CI 92, SL 1.66, SI 120, FW 0.42, FI 30, PW 1.37, WL 1.93, HTL 1.63.

Very similar to gerstaeckeri holotype, except that the margin between propodeal dorsum and declivity is more evenly convex and less medially pronounced.

Also, it bears the following features, which cannot be seen in the gasterless holotype:

First gastral tergite finely reticulate-punctate and faintly shining, widely and slightly concave anteriorly. Scattered standing hairs occurring on gastral tergites IV-V and all sternites. Gastral pubescence very short, sparse and inconspicuous (distance between adjacent hairlets at least twice the pubescence length).

Also, I assign to gerstaeckeri 3 workers from coastal continental Tanzania and 1 from coastal Kenya: HL 1.45– 1.58, HW 1.31–1.47, CI 87–95, SL 1.60–1.76, SI 118–123, FW 0.38–0.43, FI 29–31, PW 1.15–1.36, WL 1.85– 2.08, HTL 1.52–1.72. (n=4)

Type Material
Rigato (2016) - Holotype worker, TANZANIA: Zanzibar (M. Hildebrandt) [examined].

References based on Global Ant Biodiversity Informatics

 * André E. 1887. Description de quelques fourmis nouvelles ou imparfaitement connues. Rev. Entomol. (Caen) 6: 280-298.
 * Forel A. 1886. Études myrmécologiques en 1886. Annales de la Société Entomologique de Belgique. 30: 131-215.
 * Rigato F. 2016. The ant genus Polyrhachis F. Smith in sub-Saharan Africa, with descriptions of ten new species. (Hymenoptera: Formicidae). Zootaxa 4088: 1-50.
 * Wheeler W. M. 1922. Ants of the American Museum Congo expedition. A contribution to the myrmecology of Africa. VIII. A synonymic list of the ants of the Ethiopian region. Bulletin of the American Museum of Natural History 45: 711-1004