Polyrhachis submarginata, 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) : 39-41

Polyrhachis submarginata n. sp.

( Figures 12 a–c)

Diagnosis. A relatively large species in the revoili -group, with somewhat slender head and appendages, incomplete and weak pronotal margination, and very weak propodeal ridges.

Holotype worker. HL 1.66, HW 1.25, CI 75, SL 2.02, SI 162, FW 0.45, FI 36, PW 1.13, WL 2.17, HTL 1.98.

Clypeus medially subcarinate and with anterior margin bearing a protruding rectangular lobe, whose lateral corners are right angled. Head in full face view moderately elongate, oval, wider behind than in front, posterior margin widely convex. Eyes moderately large and convex. Mesosoma stout and evenly convex in profile. In dorsal view pro- and mesonotum distinctly transverse; propodeal dorsum somewhat longer than wide. Pronotum laterally weakly marginate and armed with two small diverging teeth; the margination incomplete and somewhat difficult to see even because of sculpturation and pubescence. Mesonotum and propodeum immarginate. Propodeal dorsum with two faint posterolateral ridges at its posterior corners, medially propodeal dorsum and declivity confluent in a blunt curvature. Promesonotal suture slightly impressed, metanotal suture faint. Petiole with a dorsal pair of widely separated, moderately long and diverging spines and a pair of lateral sharp teeth; the space between dorsal spines straight. First gastral tergite anteriorly weakly concave.

Mandibles faintly longitudinally striolate and with sparse piligerous pits, mostly shining. The whole body and appendages finely reticulate-punctate. Body opaque, appendages weakly shining. Head and mesosomal dorsum with a superimposed, fine, irregular longitudinal rugulation.

Standing hairs abundant everywhere and longer on head and mesosoma. Hairs on scapes at most a little longer than scape diameter at midlength; hairs on tibiae at most about as long as half the maximum tibial width. Body and appendages coated with dense, short and silvery to slightly golden pubescence, not masking the sculpturation and longer on mesosoma and petiole.

Colour black, most of the funicular joints and mandibular apices ferrugineous.

Paratype worker. HL 1.62, HW 1.22, CI 75, SL 1.98, SI 162, FW 0.47, FI 39, PW 1.19, WL 2.3, HTL 1.98. All main features as in the holotype.

Holotype. CENTRAL AFRICAN REPUBLIC: Res. Dzanga–Sangha, 12.7 km, 326° NW Bayanga, 3°00.27’ N 16°11.55’ E, 420 m, 10–11.v.2001 (S. van Noort) (CAS: CASENT0087089 CAR01-M78).

Paratype. CENTRAL AFRICAN REPUBLIC: same data as the holotype, except 14–15.v.2001 (S. van Noort) (1 w, CAS: CASENT0088752 CAR01-M123).

Comment. Polyrhachis submarginata is characterised by weak pronotal margination and propodeal ridges, and a relatively high SI. Polyrhachis submarginata is similar to P. otleti and the main differences between them are reported in the key. Polyrhachis submarginata seems to link revoili -group species with immarginate mesosoma and with well defined, although incomplete, margination. Polyrhachis volkarti Forel is similar but is smaller, has a usually immarginate pronotum, distinctly more slender mesosoma. well developed propodeal ridges, and a higher SI.

Polyrhachis kohli , P. submarginata and P. volkarti look very similar, and share some important features: 1) a shallow clypeal lobe; 2) relatively long scapes, SI> 150; 3) abundant pilosity on body and appendages; 4) mesosoma completely immarginate or almost so; 5) propodeal dorsum and declivity separated by a pair of small, more or less developed, ridges; 6) petiole armed with a pair of moderately long median spines and a pair of lateral much shorter teeth; 7) rough, mostly irregularly longitudinal rugulose sculpturation on head and mesosoma; 8) Body coated with abundant, relatively short and moderately dense greyish pubescence never hiding the sculpturation.

The main differences can be summarized as follows:

Diagnosis. The largest species of the revoili -group known so far, with almost complete lateral marginations of the mesosoma and a continuous well developed ridge separating propodeal dorsum from declivity.

Holotype worker. HL 2.60, HW 2.37, CI 91, SL 2.50, SI 105, FW 0.80, FI 34, PW 2.05, WL 3.5, HTL 2.77.

Clypeus subcarinate, with anterior margin arcuate and medially bearing a faint shallow rounded lobe. Head trapezoidal, wider behind than in front, posterior margin and sides widely convex. Eyes moderately large and convex, close to the posterior corners. Mesosoma in profile evenly weakly convex, mesonotum almost flat. Promesonotal suture well-developed, metanotal suture weak and hardly interrupting the dorsal sculpturation. Pronotum with a pair of strong teeth at its anterior corners and laterally clearly marginate, the margination interrupted just before the promesonotal suture. Mesonotum with a weaker margination, interrupted before the metanotal suture. Lateral margination of propodeal dorsum faint, detectable along about its anterior half. Propodeal dorsum and declivity well-separated by a continuous ridge which is slightly higher medially. Petiole with a dorsal pair of distant, moderately long and diverging spines and a pair of lateral shorter ones; the space between the dorsal spines straight. First gastral tergite anteriorly weakly concave.

Mandibles distinctly longitudinally striolate and with sparse piligerous pits. Clypeus superficially finely reticulate-punctate. Head dorsum prevailingly longitudinally costulate with a faint ground sculpture; head sides and cheeks (malar space) mostly reticulate-rugose with finely reticulate-punctate ground sculpture. Mesosomal dorsum finely longitudinally rugulose with reticulate-punctate ground sculpture. Mesosomal sides mostly finely longitudinally rugulose; mesopleuron less evidently so. Petiole finely reticulate-punctate with superimposed rugulation. Gaster finely reticulate-punctate throughout.

Short to moderately long standing hairs abundant on all body surfaces and appendages. On the legs hairs are shorter than the maximum tibial width. Hairs on scapes are at most slightly longer than scape diameter at midlength. Body and appendages coated with dense, short and greyish pubescence, not masking the sculpturation and sparser on head dorsum and clypeus.

Colour black, except a brown dorsal strip on femurs and tibiae and pale ferrugineous gastral apex.

Holotype. TANZANIA: Morogoro, Kilombero, Zoosite 2, 11.3 km ESE Mbingu, 8.20483 S 36.36055 E, 277 m, 23.x.2007, closed miombo woodland, pitfall trap, FRO 2007_2_P (E. Jew & L. Williams) (SAM: CASENT0250168).

Comment. Polyrhachis terminata is unique for its large size and the complete ridge running between propodeal dorsum and declivity. This ridge is much stronger than the incomplete and weak margination of the propodeal sides.

Figures

FIGURE 12. Polyrhachis submarginata, holotype worker: A, body profile; B, dorsum of mesosoma; C, head in full-face view. (Photos by M. Zilioli)