Polyrhachis retusa

Known only from the holotype.

Identification
Kohout (2007) - P. retusa is relatively close to Polyrhachis porcata, however, they differ in a number of characters, including their relative size (HL 1.12 in retusa versus 1.50-1.68 in porcata). The pronotal dorsum in lateral view is much less convex in retusa with the pronotal teeth short and broad-based and the petiole is narrow in profile with its dorsal margin distinctly acute. The first gastral segment of retusa is concave, but its dorsal margin is not elevated dorsally. In contrast, the pronotal dorsum in porcata is distinctly convex in lateral view with the humeri armed with laterally and anteriorly directed, acute spines. The petiole, in lateral view, is scale-like, with both faces distinctly convex and the dorsal margin less acute. The first gastral segment is concave with the dorsal margin of the concavity produced above the face of the segment.

Distribution based on Regional Taxon Lists
Indo-Australian Region: New Guinea.

Castes
Known only from the worker caste.

Nomenclature

 *  retusa. Polyrhachis (Aulacomyrma) retusa Kohout, 2007a: 235, figs. 93, 96, 99 (w.) NEW GUINEA.

Worker
holotype: TL c. 4.43; HL 1.12; HW 1.04; CI 93; SL 1.22; SI 117; PW 0.87; MTL 1.12.

Clypeus with anterior margin arcuate, weakly truncate; in profile clypeus straight anteriorly with outline raised towards basal margin due to a short carina formed by median stria; basal margin impressed medially, laterally indicated by break in cephalic sculpture. Frontal triangle indistinct. Frontal carinae with raised laminate lobes. Sides of head in front of eyes converging anteriorly towards mandibular bases; posteriorly rounding into weakly convex preoccipital margin. Eyes strongly convex, clearly breaking cephalic outline in full face view. Pronotal humeri armed with acute, broad-based teeth, lateral margins curving from bases onto sides, pronotal dorsum immarginate. Promesonotal suture distinct. Metanotal groove lacking. Lateral margin of mesonotal dorsum formed by outermost dorsal striae. Propodeum immarginate laterally and posteriorly with dorsum descending into declivity in uninterrupted curve. Dorsal margin of petiole with shallow emargination medially, weakly jagged laterally, lateral spines relatively long, curved outwards, backwards and upwards. Anterior face of first gastral segment concave, with dorsal margin of concavity acute, not elevated above dorsal face of segment.

Sculpture of head and body consisting of more-or-less regularly spaced striae; mostly longitudinal on dorsum of head, those on vertex curving medially towards frontal carinae and central area. Pronotal striation distinctly converging anteriorly, several median striae curving tranversely onto pronotal collar. Mesonotal-propodeal dorsum with striae V-shaped, converging posteriorly and terminating just before propodeal dorsum descends into declivity. Petiole with anterior face wrinkled, transversely at base of segment and vertically on sides; posterior face of petiole finely shagreened. First gastral segment distinctly striate laterally, striae less distinct dorsally and becoming reticulate-punctate centrally.

Head and mesosoma with numerous, yellow, erect hairs, notably on front of head; distinctly shorter hairs arising from vertex and mesosomal dorsum. Petiole with a few short, erect hairs on dorsal margin. First gastral segment with a few, short, posteriorly directed hairs, more erect and distinctly longer on apex and venter. Very sparse, pale yellow, appressed pubescence on dorsum of head, mesosoma and gastral dorsum.

Black, including antennal scapes, femora and proximal ends of hind tibiae. Funiculi, except apices and basal tarsal segments medium to dark reddish-brown. Tibiae, except their proximal ends, apical segments of tarsi and last funicular segments distinctly light reddish-brown.

Type Material
HOLOTYPE: INDONESIA, IRIAN JAYA (New Guinea: Neth. on data label), Vogelkop, Fak Fak, S. coast of Bomberai Pen., 02º55’S, 132º18’E, 10-100m, 3.vi.1959, T. C. Maa (worker). Type distribution: unique holotype in.

Etymology
From the Latin word retusus, meaning blunted, rounded, refering to the bluntly terminated propodeal dorsum of this species.

References based on Global Ant Biodiversity Informatics

 * Janda M., G. D. Alpert, M. L. Borowiec, E. P. Economo, P. Klimes, E. Sarnat, and S. O. Shattuck. 2011. Cheklist of ants described and recorded from New Guinea and associated islands. Available on http://www.newguineants.org/. Accessed on 24th Feb. 2011.
 * Kohout R.J. 2007. Revision of the subgenus Aulacomyrma Emery of the genus Polyrhachis F. Smith, with descriptions of new species (pp. 186-253). In Snelling, R.R., Fisher, B.L. & Ward, P.S. (eds). Advances in ant systematics: homage to E.O. Wilson  50 years of contributions. Memoirs of the American Entomological Institute 80: 690 pp.