Polyrhachis danum

Nothing is known about the biology of Polyrhachis danum.

Identification
Previously misidentified as Polyrhachis semiinermis, a very similar species described by Donisthorpe from the Philippines. Polyrhachis danum also resembles Polyrhachis brevinoda from north Queensland. All three species have widely rounded pronotal shoulders and virtually parallel-sided petioles with greatly reduced or rudimentary spines. Polyrhachis brevinoda differs in having the propodeal declivity descending in an oblique curve while in P. semiinermis and P. danum the declivity is virtually vertical. Although the petiolar spines in P. brevinoda are short, the dorsal spines are relatively well defined, while the dorsal spines are more-or-less obsolete in the other two species. Polyrhachis brevinoda is also distinctly smaller than P. danum (HL 1.31-1.53 versus 1.65-1.87 respectively) and has dark brown to black legs (always distinctly red in P. danum). (Kohout 2006)

Distribution
Endemic to Borneo.

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

Abundance
Relatively common in suitable lowland rainforest habitat.

Castes
The males and immature stages are unknown.

Nomenclature

 *  danum. Polyrhachis danum Kohout, 2006b: 112, figs. 6E-F (w.q.) BORNEO.

Worker
Dimensions (holotype cited first): TL c. 7.76, 6.60-7.76; HL 1.84, 1.65-1.87; HW 1.62, 1.37-1.62; CI 88, 81-88; SL 2.50, 2.18-2.50; SI 154, 150-164; PW 1.37, 1.22-1.37; MTL 3.12, 2.68-3.17 (31 measured).

Clypeus in profile weakly, evenly convex with basal margin weakly impressed. Frontal triangle indistinct. Frontal carinae sinuate with raised margins; central area concave with weakly indicated frontal furrow. Sides of head in front of eyes weakly convex, converging anteriorly towards mandibular bases; behind eyes sides rounding into highly convex occipital margin. Eyes relatively large, convex, in full face view clearly breaking lateral cephalic outline. Ocelli lacking, position of median ocellus marked by distinct pit; relative positions of lateral ocelli poorly indicated. Pronotum in dorsal view with humeri widely rounded; greatest pronotal width at mid-length of segment. Mesosoma in profile convex; promesonotal suture moderately strongly impressed; position of metanotal groove indicated by very weak impression; propodeum widely rounding into virtually vertical declivity. Petiole low, anterior, posterior and dorsal faces flat; dorsal spines reduced to minute denticles. Subpetiolar process rather long, acute anteriorly, obtusely angular posteriorly. Anterior face of first gastral segment in lateral view relatively low, widely rounded.

Mandibles finely, longitudinally rugose with numerous piliferous pits. Head, mesosoma and gaster rather smooth and polished, very finely, microscopically and uniformly shagreened with numerous very shallow punctures. Anterior face of petiole finely, transversely wrinkled.

Mandibles with numerous, relatively short, erect to semierect hairs. A few, medium length, anteriorly directed setae medially on anterior clypeal margin, several shorter setae lining margin laterally. Rather short, paired, erect hairs near anterior and basal clypeal margins and along frontal carinae; pair of longer, somewhat curved hairs on summit of mesosoma. A few, isolated, long, erect hairs anteriorly on fore coxae and along ventral surfaces of trochanters and femora, hairs absent in some specimens. Medium length hairs along posterior margins of apical gastral segments, hairs more abundant on gastral venter.

Colour. Black with mandibular masticatory borders, condylae and extreme tips of apical funicular segments reddish-brown. Legs, including trochanters, red or reddish-brown with distal ends of femora very narrowly darker; proximal ends of tibiae and tarsi very dark brown or black.

Queen
Dimensions (paratype queen cited first): TL c. 8.32, 8.21; HL 1.87, 1.81; HW 1.59, 1.62; CI 85, 89; SL 2.37, 2.50; SI 149, 1.54; PW 1.72, 1.72; MTL 3.03, 3.15 (2 measured). Apart from sexual characters, closely resembling worker except: pronotal humeri widely rounded; mesoscutum slightly wider than long with lateral margins distinctly converging anteriorly, forming narrowly rounded anterior margin; median line weakly indicated, very short; parapsides rather flat; in profile mesoscutum with dorsum gently curved anteriorly, rather flat posteriorly. Mesoscutellum convex, slightly elevated above dorsal plane of mesosoma; metanotal groove distinct, well impressed. Propodeal dorsum convex in profile, evenly rounded into vertical declivity. Very fine, microscopic sculpturation, rather sporadic dorsal pilosity and polished appearance as in worker.

Type Material
HOLOTYPE: EAST MALAYSIA, SABAH, Danum Valley Conservation Area, 04°57’N, 117°48’E, Segama R. Trail, rf., 11.xi.2000, R.J. Kohout acc. 2000.217 (worker). PARATYPES: data as for holotype (21 workers, 1 dealate queen); ditto, Nature Trail, rf, 11.xi.2000, RJK acc. 2000.227 (2 workers); ditto, Western Trail, rf, 12.xi.2000, RJK acc. 2000.237 (12 workers). Holotype (QMT99343), most paratype workers and paratype queen in ; 2 paratypes each in, , , , , , and.

References based on Global Ant Biodiversity Informatics

 * Kohout R.J. 2006. Review of Polyrhachis (Cyrtomyrma) Forel of Australia, Borneo, New Guinea and the Solomon Islands with descriptions of new species. Memoirs of the Queensland Museum 52: 87-146.
 * Kohout R.J., and M. Mohamed. 2008. A preliminary list of the Polyrhachis ants of the Maliau Basin Conservation area in Sabah, Borneo (Hymenoptera: Formicidae: Formicinae). Asian Myrmecology 2: 63-70.
 * Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58