Polyrhachis angusta

This species nests in soil and appears to be much less common and more localised than the widespread Polyrhachis ammon.

Identification
A member of the ammon species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (1988): This species stands close to Polyrhachis ammon, but is consistently separable by its distinctly slender, more gracile stature. The pronotum in dorsal view is almost quadrate, 0.7-0.8 times as wide as the head, with narrowly rounded shoulders, and the lateral margins distinctly sinuate behind. The propodeal spines are oblique to the main axis of the mesosoma in side view and slightly divergent from above. In P. ammon the pronotum is more or less transverse with the shoulders broadly rounded and the lateral margins narrowed posteriorly and almost straight in outline. The propodeal spines project horizontally, and are subparallel. The appressed pubescence in P. angusta is shorter and more dilute, and the pilosity distinctly longer, than in P. ammon.

Kohout (2013): Polyrhachis angusta is very similar to Polyrhachis ammon, however it is consistently separable by its distinctly more slender body and longer spines and hairs. The reddish-golden midline patch on dorsum of the first gastral tergite is rather narrow in dorsal view and widely bordered with very distinct, silvery, appressed pubescence. In contrast, the patch in P. ammon is distinctly wider, covering most of the dorsum, and is only narrowly diffused into pale golden pubescence on the sides and venter of the gaster.

Distribution
Patchily distributed from Eungella in northern Queensland to central New South Wales.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  angusta. Polyrhachis ammon r. angusta Forel, 1902h: 524 (w.q.m.) AUSTRALIA. Combination in P. (Hagiomyrma): Forel, 1915b: 108. Raised to species: Kohout, 1988c: 431.

Worker
Kohout (2013) - (syntypes cited first): TL c. 8.12-8.52, 7.41-9.17; HL 2.07- 2.12, 1.81-2.15; HW 1.69-1.71, 1.42-1.72; CI 81-82, 77-82; SL 2.52-2.57, 2.18-2.62; SI 149-152, 148-159; PW 1.06-1.25, 1.15-1.33; MW 0.62-0.70, 0.64-0.75; PMI 167-178, 172-180; MTL 2.97-3.07, 2.67-3.17 (3 + 17 measured).

Median flange of anterior clypeal margin usually with three acute teeth along its shallowly emarginate margin; laterally flange delimited by acute angles. Clypeus with distinct, median carina; sinuate in profile with relatively shallow basal margin. Frontal carinae with moderately raised margins; central area with rather flat frontal furrow. Sides of head in front of eyes converging anteriorly in almost straight line before rounding into mandibular bases; behind eyes, sides rounding into moderately convex occipital margin. Eyes situated close to occipital corners, convex, clearly breaking lateral cephalic outline in full face view. Ocelli lacking. Pronotal dorsum virtually quadrate, only marginally wider than long; humeri dilated, rounded and dorsally shallowly concave with margins narowly raised dorsally; lateral margins subparallel, distinctly emarginate at midlength. Promesosonal suture distinct; mesonotal dorsum with lateral margins rather strongly converging posteriorly towards dorsally indistinct metanotal groove. Propodeum with lateral margins diverging posteriorly, terminating in relatively long, slender, moderately elevated, acute spines with tips weakly turned outwards. Petiole with pair of slender, horizontal, divergent, acute spines.

Mandibles finely longitudinally striate with numerous piliferous pits towards bases. Mesosoma and petiole finely reticulate-punctate with sculpturation on head, notably on vertex and sides, somewhat coarser and organised into more-or-less distinct longitudinal pattern. Gaster finely shagreened.

Mandibles with numerous, medium length, curved, golden hairs at masticatory and outer borders; only a few closely appressed, very short hairs towards mandibular bases. Several anteriorly directed setae arising from median clypeal flange and a few very short setae fringing anterior clypeal margin. Several medium length, erect hairs on clypeus, along frontal carinae and vertex, with a few breaking occipital outline in full face view. Numerous, relatively long, erect golden hairs on most body surfaces, some almost as long as greatest diameter of eye. Hairs more numerous, but marginally shorter and posteriorly inclined on gaster. Closely appressed, rather sparse, mostly silvery pubescence on head, sides of mesosoma, petiole and venter and sides of gaster; pubescence rich golden with distinct reddish hue along midline of mesosoma and on gaster, where it forms a relatively wide, laterally diffused patch in centre of first gastral tergite that virtually hides underlying sculpturation.

Black with only mandibular teeth and condylae reddish-brown.

Queen
Kohout (2013) - (syntype queen cited first): TL c. 9.93, 9.83-10.43; HL 2.27, 2.18-2.27; HW 1.81, 1.72-1.81; CI 80, 78-82; SL 2.57, 2.46-2.57; SI 142, 140-144; PW 2.17, 1.87-2.17; MTL 3.02, 2.97-3.06 (8 measured).

Apart from sexual characters, very similar to worker except: pronotal humeri widely rounded with lateral margins only very narrowly raised; mesoscutum only marginally wider than long or subquadrate; anterior margin rather narrowly rounded with distinct medial line; parapsides flat. Mesoscutum virtually flat, mesoscutellum only weakly convex, not elevated above dorsal plane of mesosoma in lateral view. Propodeal dorsum evenly rounded into weakly convex declivity. Propodeal and petiolar spines slender, but distinctly shorter than in worker. Body sculpturation similar to that in worker, sculpturation on vertex and sides of head somewhat coarser. Pilosity and pubescence on head and gaster similar to that in worker, but more sporadic and shorter on dorsa of mesosoma and petiole.

References based on Global Ant Biodiversity Informatics

 * Kohout R.J. 2013. Revision of Polyrhachis (Hagiomyrma) Wheeler, 1911 (Insecta: Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum  Nature 56: 487577
 * Robson Simon Database Polyrhachis -05 Sept 2014