Polyrhachis brevipilosa, Rigato, Fabrizio, 2016

Rigato, Fabrizio, 2016, The ant genus Polyrhachis F. Smith in sub-Saharan Africa, with descriptions of ten new species. (Hymenoptera: Formicidae), Zootaxa 4088 (1) : 11-13

Polyrhachis brevipilosa n. sp.

( Figures 1 a–c)

Diagnosis. A small species in the revoili -group with lobed clypeus, weakly marginate pronotum, minute propodeal teeth, rough reticulate-punctate sculpture, and relatively abundant and short standing hairs on body and appendages.

Holotype worker. HL 1.07, HW 0.89, CI 83, SL 1.21, SI 136, FW 0.33, FI 37, PW 0.79, WL 1.27, HTL 1.21.

Clypeus medially fairly distinctly carinate and with its anterior margin bearing a small protruding rectangular lobe, whose lateral corners are distinctly right-angled. Head in full face view subtrapezoidal, wider behind than in front, posterior margin wide and weakly convex with widely rounded posterior corners. Eyes relatively large and protruding. Mesosoma stout, evenly convex in profile. Pronotum laterally marginate, the margination interrupted a little in front of the promesonotal suture; mesonotum and propodeum immarginate. Pronotal teeth anteriorly diverging, relatively short and sharp. Promesonotal suture distinct, metanotal suture weaker and hardly interrupting the sculpturation. Propodeal teeth reduced to minute tubercles. Propodeal dorsum and declivity confluent in a blunt curvature. Petiole with four thin spines, the dorsal pair directed upward and slightly backward and about 1.5 times as long as the lateral pair. Petiolar dorsum in frontal (or posterior) view obtusely angled in the middle. First gastral tergite anteriorly concave.

Mandibles superficially striolate/shagreened and with sparse piligerous pits. Head, mesosoma, petiole and appendages reticulate-punctate and with a rough appearance, dull. Dorsum of head, pronotum and mesonotum also with a superimposed, relatively dense, coarse longitudinal, sometimes inconspicuous, rugulation. Gaster finely reticulate-punctate and fairly shining.

Pubescence fine, whitish, short and moderately dense on most of the body and appendages, but sometimes poorly visible and never hiding the sculpturation. Standing hairs relatively short and moderately abundant on body and appendages, absent from the petiole. Longest hairs occur on head and leading edge of scapes. Few hairs on scapes longer than scape width at midlength; standing hairs on tibiae distinctly shorter than maximum tibial width.

Body black, legs mostly concolorous with the body, tibiae dark brown; antennal funiculi mostly testaceous, mandibular apex ferrugineous.

Paratype workers (n=2). HL 1.10–1.34, HW 0.91–1.07, CI 80–83, SL 1.27–1.48, SI 138–140, FW 0.34–0.42, FI 37–39, PW 0.82–1.02, WL 1.39–1.65, HTL 1.24–1.42. The smaller specimen does not significantly differ from the holotype. Yet an unexpectedly large specimen has a seemingly stouter mesosoma and pronotal teeth, and stronger petiolar spines (dorsal and lateral pairs more similar in size also). In my opinion, these differences are slight and possibly due to allometry.

Holotype worker. GABON: La Makandé, Forêt des Abeilles, I–II.1999, A. Dejean (BMNH).

Paratypes. REPUBLIC of the CONGO: Niari Region, 2.30921 S 12.82224 E, 754 m, 4.vii.2013, primary forest, canopy fogging (L. Niemand) (1 w, AFRC: LN-RC1-044, CASENT0250041); Niari Region, 2.31500 S 12.82488 E, 710 m, 5.vii.2013, primary forest, canopy fogging (L. Niemand) (1 w, AFRC: LN-RC1-041, CASENT0250033).

Comment. Polyrhachis brevipilosa is the smallest species of the revoili -group. Only P. luteipes n. sp. (see below) and P. re g e s a Bolton have a comparable size. Polyrhachis luteipes differs especially for its much weaker sculpturation, paler appendages and immarginate pronotum. Polyrhachis regesa is very similar to brevipilosa , but they can be distinguished as reported in the key. I examined the holotype of P. regesa Bolton and realized that the metanotal suture is not completely wanting as stated by Bolton and a faint trace remains visible under certain lights. Also, the propodeal “tubercles” (in Bolton’s own words) of regesa look like weak ridges because they are relatively wide and much closer to one another than in brevipilosa , where they are short and tooth-like.

Figures

FIGURE 1. Polyrhachis brevipilosa, holotype worker: A, body profile; B, dorsum of mesosoma; C, head in full-face view. (Photos by M. Zilioli)