Polyrhachis achterbergi

Polyrhachis achterbergi is known only from the type locality where it is sympatric with Polyrhachis bruehli and Polyrhachis widodoi. Nothing is known about its nesting habits but most specimens have been collected by fogging or Malaise traps and it is apparently arboreal, probably building nests high in the rainforest canopy (Kohout 2006).

Identification
Kohout (2006): Polyrhachis achterbergi is a spectacular species, the blue colour of the head, mesosoma and petiole, strongly contrasting with the orange appendages. It is similar to Polyrhachis bruehli and Polyrhachis widodoi, and also to Polyrhachis vitalisi. All four species share the dense reticulate-punctate sculpturation of the head, mesosoma and petiole but only Polyrhachis achterbergi, Polyrhachis bruehli and Polyrhachis widodoi have the same striking colour scheme. Polyrhachis achterbergi differs from Polyrhachis bruehli by the absence of propodeal spines and from Polyrhachis widodoi by shape of the anterior clypeal margin. In Polyrhachis achterbergi the margin has a central, blunt, projecting tooth, while in widodoi it is deeply emarginate medially. (Kohout 2006)

Distribution
Known only from the type localities (see below).

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

Abundance
Known only from the few collections that comprise the type series.

Worker
Known only from (type) workers.

Nomenclature

 *  achterbergi. Polyrhachis achterbergi Kohout, 2006b: 110, figs. 5A, 6A-B (w.) BORNEO.

Worker
Dimensions (holotype cited first): TL c. 8.06, 7.46-8.06; HL 2.25, 2.12-2.25; HW 2.28, 2.15-2.28; CI 101, 101-105; SL 2.09, 2.03-2.18; SI 92, 91-99; PW 1.78, 1.68-1.81; MTL 2.71, 2.62-2.81 (14 measured).

Anterior clypeal margin convex with central, blunt, projecting tooth. Clypeus in profile very weakly sinuate, almost straight, with weakly impressed basal margin; laterally basal margin indicated by very distinct line. Frontal triangle weakly impressed. Frontal carinae relatively short, margins only weakly raised; central area wide with distinct, flat frontal line. Head very broad, distinctly wider than long. Sides of head almost straight in front of eyes; widely rounding behind eyes into broad, medially concave occipital margin. Lateral carina separating gena from ventral parts of head lacking. Eyes relatively small, rather flat, situated well forward and inward from occipital corners; in full face view eyes not reaching lateral cephalic outline. Median ocellus distinct; lateral ocelli absent, relative positions indicated by slightly raised cephalic sculpture. Pronotum in dorsal view with humeri armed with strong, blunt teeth. Mesosoma in profile convex anteriorly, summit relatively flat, posteriorly sloping in weakly convex curve into very short propodeal declivity; promesonotal suture distinct; metanotal groove lacking. Petiole with weakly convex anterior, and virtually flat posterior face; dorsum armed with pair of broad-based, blunt teeth and pair of longer, slender lateral spines. Subpetiolar process angular anteriorly, widely rounded posteriorly. Anterior face of first gastral segment relatively low and flat, widely rounding onto dorsum of segment.

Mandibles very finely, mostly longitudinally, striate-rugose with numerous shallow piliferous pits. Clypeus with smooth, median line, running from anterior clypeal process towards base, reaching weakly impressed frontal triangle. Most of head, mesosoma and petiole distinctly and regularly reticulate-punctate. Gaster very finely shagreened.

Several short, curved hairs present on mandibular masticatory borders, a number of short, appressed hairs arising from pits towards mandibular bases. Only a few, rather short, anteriorly directed setae fringing anterior clypeal margin. Short to very short, erect hairs, mostly in pairs, near anterior and basal clypeal margins and along frontal carinae; 1 or 2 pairs of short hairs on summit of mesosoma. Gaster with several medium length hairs lining posterior margins of apical segments, with hairs more abundant on venter. Extremely short, closely appressed pubescence over all body surfaces, most distinct on gaster.

Head, mesosoma and petiole medium to deep blue with weak metallic sheen. Mandibles black with small reddish patch near masticatory borders. Antennae brown with distal end of scapes blotched reddish-brown. Funicular segments very narrowly at their joints, and tips of apical segments widely, yellowish-brown. Coxae of front legs and subpetiolar process medium reddish-brown, coxae of mid- and hind legs a shade lighter; rest of legs very bright, light to medium orange; proximal ends of tibiae and tarsi very dark brown to black. Gaster very dark reddish-brown, almost black in some specimens, with posterior margins of segments diffusely reddish-brown.

Type Material
HOLOTYPE: EAST MALAYSIA, SABAH, Danum Valley Conservation Area, 04°57’N, 117°48’E, Segama R. trail, c. 150m, rf., 11.xi.2000, R.J. Kohout acc. 2000.217 (worker). PARATYPES: data as for holotype (2 workers); nr Danum Valley Field Centre, c. 150m, 20-26.iii.1987, Malaise Trap 5, C.van Achterberg (3 workers); ditto, C.van Achterberg & D. Kennedy (2 workers); ditto, Malaise Trap 10, C.van Achterberg (worker); ditto, 14.x.1999, fogging, L. Ellwood (T1 – fog 4-2; fog 4-17; fog 4-20; fog 4-24) (5 workers). Holotype (QMT99341) and 1 paratype in ; 2 paratypes in, , and ; 1 paratype 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.
 * 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