Polyrhachis gobini

The type material was collected from "secondary rainforest on limestone karst hills". Polyrhachis gobini is an arboreal species.

Identification
A member of the Polyrhachis vestita species group.

Kohout (2008) - P. gobini is a very distinct member of its species-group. Altough it shares several characters with the other species of the group, it does not seem closely related to any species in particular. The rather narrow and elongated mesosomal dorsum somewhat resembles that of Polyrhachis philippinensis but their other characters differ widely. The pronotal spines in P. philippinensis are relatively long and project anterolaterally, while in P. gobini they are rather short and project anteriorly. Moreover, the petiole in P. philippinensis is slender, with its dorsolateral edge armed with a pair of spines, while in P.gobini the petiolar dorsum is entire and unarmed.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Indonesia, Sulawesi.

Biology
Kohout (2008) - Polyrhachis gobini appears endemic to Sulawesi with its known distribution limited to the type locatity. The following information on the species nesting habits are an extract from the field observations made by the collector Bruno Gobin: “[…] I was especially interested in the Diacamma sp. and kept confusing them with the foragers of Polyrhachis sp. Nest sites and foraging workers really looked alike. It (Polyrhachis gobini) is an arboreal ant nesting in cavities in trees. They more-or-less seal the nest entrance with detritus and pulp of rotten wood which they seem to excavate. They appear to forage singly. I sampled 2 nests in which there were larvae and cocoons, but no queen(s), suggesting they are polydomous. [Later] I found a founding queen with two workers in a small cavity without nest material […] I tried to raise the nest but the queen died.” (B. Gobin, pers. comm.).

Nomenclature

 *  gobini. Polyrhachis gobini Kohout, 2008a: 277, figs. 4G-H (w.q.) INDONESIA (Sulawesi).

Worker
(holotype cited first): TL c. 10.03, 9.07-10.78; HL 2.50, 2.32-2.72; HW 1.59, 1.51-1.71; CI 64, 63-65; SL 3.15, 2.87-3.33; SI 198, 190-198; PW 1.03, 0.91-1.11; MTL 3.21, 2.82-3.43 (12 measured).

Anterior clypeal margin arcuate, entire. Clypeus in profile weakly sinuate with median carina, that is low and blunt anteriorly, more distinctly elevated posteriorly; clypeus rounding into moderately impressed basal margin that is well defined laterally. Frontal triangle weakly impressed. Frontal carinae sinuate, with highly raised, laminate margins; central area concave, very narrow anteriorly, flat and wider posteriorly; frontal furrow indistinct. Head widest just in front of eyes with sides weakly convex and converging anteriorly towards mandibular bases; behind eyes sides converging in weakly convex line into a very narrow occipital margin. Eyes convex, almost protuberant, situated well forward from occipital corners; in full face view clearly breaking lateral cephalic outline. Ocelli lacking, relative position of median ocellus indicated by distinct puncture. Pronotal dorsum with pair of relatively short, acute, anteriorly directed, horizontal spines; their lateral edges continued for a short distance and merging with rather blunt, parallel, pronotal margins that run to about mid length; posterior half of pronotal dorsum immarginate. Mesonotal dorsum transverse, with distinct lateral margins anteriorly, rounding onto sides posteriorly. Propodeal dorsum convex in profile with lateral margins narrowly rounded anteriorly, poorly defined posteriorly and terminating in more-or-less distinct denticles or tuberculae; propodeal dorsum rounding into declivity in medially uninterrupted, oblique curve. Petiole biconvex, only marginally higher than width at base, with virtually hexagonal outline in frontal view; dorsal margin blunt, rather flat medially, angular laterally and descending towards blunt lateral angles. Anterior face of first gastral segment low, distinctly lower than height of petiole; rather flat at base and rounding onto dorsum of segment.

Mandibles at masticatory borders smooth and polished; finely, longitudinally striate towards bases. Head reticulate-punctate with sculpturation distinctly increasing in intensity to rugose along sides and somewhat rugose-striate between eyes and frontal carinae. Dorsum of mesosoma and gaster finely shagreened, weakly polished, with sides of mesosoma more-or-less reticulate-punctate.

Mandibles along outer margins and masticatory borders with numerous, curved, golden hairs and with closely appressed hairs towards bases; several longer, erect hairs arising from outer margins near bases. Anterior clypeal margin with a few long, anteriorly directed golden setae medially and several short setae fringing margin laterally. Head with abundant, medium length to long, erect and somewhat anteriorly directed, mostly yellow hairs. Antennal scapes with shorter, erect hairs, most numerous along leading edge, and with fringe of hairs at apex. Mesosomal dorsum and petiole with numerous erect, semierect and variously curved, medium length, yellow and light yellowish-brown hairs, with those on sides somewhat shorter and less abundant. Legs with numerous, medium length, erect hairs on most surfaces, except dorsa of middle and hind femora where they are rather diluted; hairs completely absent from dorsa of front femora. Gaster with relatively long, erect, somewhat posteriorly curved, yellow or yellowish-brown hairs, most abundant and more golden around apex. Relatively long, closely appressed, mostly golden pubescence in various densities over most body surfaces, somewhat diluted near occipital corners, pronotal dorsum between spines and laterally on first gastral segment.

Colour. Black, with only tips of mandibular teeth reddish-brown; extreme tip of apical funicular segments yellowish-brown. Legs distinctly light orange or yellowish-red, with distal ends of femora and proximal ends of tibiae shade darker; tarsi black.

Queen
TL c. 11.14; HL 2.72; HW 1.79; CI 66; SL 3.17; SI 177; PW 1.66; MTL 3.17 (1 measured).

Queen slightly larger than worker with usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings. Pronotum with pair of short, broad-based, anteriorly and weakly downward directed spines. Mesoscutum almost as long as wide; lateral margins strongly converging anteriorly into rather narowly rounded anterior margin; median line distinct; parapsides flat, only weakly raised posteriorly; mesoscutum in profile with relatively low, widely rounded anterior face and flat dorsum. Mesoscutellum very weakly convex and only marginally elevated above dorsal plane of mesosoma; metanotal groove distinct. Propodeum convex in outline with sides terminating posteriorly into very short, medially directed ridges; propodeal dorsum descending into oblique declivity in medially uninterrupted line. Sculpturation of body, pilosity, pubescence and colour virtually as in worker.

Larvae
Immature stages (larvae and pupae) in KULB (B. Gobin private collection).

Type Material
HOLOTYPE: SULAWESI SELATAN, Cagar Alam Karaenta, Kabupaten Maros, c. 05°00’S, 119°45’E, c. 265-315m, iii.1996, secondary rf. on limestone karst hills, B. Gobin (worker). PARATYPES: data as for holotype (10 workers, 1 dealate queen). Holotype (QMT144148), 1 paratype worker and paratype queen in ; 1 paratype worker each in, , , , and ; 3 paratype workers in KULB (B. Gobin private collection).