Polyrhachis brisbanensis

Polyrhachis brisbanensis is a relatively common species in open eucalypt forests and woodlands of the greater Brisbane region. Its distribution extends north to Fraser Island and the Cooloola coast and south to the Queensland-New South Wales border and almost reaches the Great Dividing Range in the west. It is a ground-nesting species with nest entrances usually hidden under pieces of wood or rock. Colonies are relatively small with examined nests containing about 50-60 workers and one dealate queen.

Identification
A member of the ammon species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (2013) - Polyrhachis brisbanensis is similar to several species, notably Polyrhachis ammon and Polyrhachis brutella. It differs from the former by its almost quadrate pronotal dorsum, closely spaced, parallel petiolar spines and the narrow patch of dark reddish pubescence on the gastral dorsum. In contrast, in P. ammon the pronotal dorsum is rectangular and wider than long, the petiolar spines are distinctly divergent and rich golden pubescence is distributed over most of the gastral dorsum. Besides its generally smaller size (HL 2.15-2.37 in P. brisbanensis versus 2.28-2.56 in P. brutella), P. brisbanensis differs from P. brutella in several other characters, including the straight profile of the clypeus, the weakly sinuate propodeal and parallel petiolar spines and the abundant, brassy golden pubescence of the body. In contrast, the clypeus in P. brutella is shallowly, but distinctly concave in profile, the tips of the propodeal and petiolar spines are curved outwards and the rather sporadic body pubescence is mostly pale silvery. Differences between the queens of the species are even more pronounced. The queen of P. brutella features an exceptionally massive mesosoma, which lacks any pilosity or pubescence.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Males and immature stages present in the QM and ANIC collections.

Nomenclature

 *  brisbanensis. Polyrhachis (Hagiomyrma) brisbanensis Kohout, 2013: 508, figs. 2A-B (w.q.m.) AUSTRALIA.

Worker
(holotype cited first): TL c. 10.43, 9.42-10.58; HL 2.21, 2.15- 2.37; HW 1.81, 1.65-1.87; CI 82, 76-82; SL 2.90, 2.87-3.12; SI 160, 158-174; PW 1.47, 1.40-1.72; MW 1.00, 0.97-1.15; PMI 147, 133-150; MTL 3.48, 3.38-3.68 (21 measured).

Median flange of anterior clypeal margin with usually three teeth, flanked by acute angles laterally. Clypeus with distinct, longitudinal carina, straight in profile, narrowly rounding into weakly impressed basal margin. Frontal carinae sinuate, distinctly raised in midlength; central area with distinct frontal furrow. Sides of head in front of eyes converging towards mandibular bases in straight line; behind eyes, sides narrowly rounding into moderately convex occipital margin. Eyes convex, clearly breaking lateral cephalic outline in full face view. Ocelli lacking. Pronotal dorsum almost quadrate, only slightly wider than long; humeri widely rounded, dorsally shallowly concave, lateral margins behind humeri usually notched or shallowly emarginate and subparallel towards promesonotal suture. Mesonotal lateral margins converging posteriorly, weakly raised and rounding into poorly indicated metanotal groove. Propodeal dorsum with lateral margins subparallel, terminating in more-or-less horizontal, weakly sinuate, acute spines. Petiole armed with pair of parallel, horizontal, posteriorly directed, acute spines. Mandibles finely longitudinally striate with numerous piliferous pits. Head and mesosoma reticulate-punctate, sculpturation on front of head and pronotal dorsum organised into somewhat longitudinaly striate rugulations. Spines smooth and polished towards tips. Gaster finely shagreened.

Mandibles at masticatory borders with numerous, curved golden hairs. Anterior clypeal margin with two longer setae medially and only a few very short setae fringing margin laterally. A few, paired, medium length, erect hairs on clypeus, along frontal carinae and on vertex, no hairs breaking lateral cephalic outline. Dorsum of mesosoma and petiole, fore coxae and ventral surfaces of femora with numerous, erect and variously curved, relatively long golden hairs, longest hairs almost equal to greatest diameter of eye. Gaster with numerous, moderately long, posteriorly inclined golden hairs. Relatively abundant, appressed, golden pubescence with distinct brassy tint, somewhat medially radiating on pronotal and mesonotal dorsa; pubescence silvery and distinctly more diluted on head and sides of mesosoma. Gastral dorsum with abundant, golden-brassy pubescence virtually hiding underlying sculpturation; first gastral tergite with distinct, reddish-coloured, rather small, median patch, surrounded by golden and diffused into silvery pubescence on sides and venter of gaster.

Black; mandibles very dark reddish-brown with narrow, transverse, light reddish band at bases of mandibular teeth. Appendages black or very dark reddish-brown.

Queen
TL c. 10.38-10.89; HL 2.09- 2.15; HW 1.59-1.68; CI 76-78; SL 2.71-2.78; SI 163-172; PW 2.25- 2.37; MTL 3.33-3.53 (6 measured).

Apart from sexual characters, very similar to worker except: longitudinal clypeal carina less distinct; eyes more convex, virtually protuberant. Pronotal humeri subangular; mesoscutum as long as wide, anterior margin evenly rounded; median line distinctly bifurcate; dorsum flat with parapsides only weakly raised posteriorly. Mesoscutellum with dorsum convex, distinctly raised above dorsal plane of mesosoma. Propodeum with spines parallel, shorter than in worker; dorsum rounding evenly into virtually vertical declivity. Petiole armed with very short, posteriorly curved spines. Sculpturation, pilosity, pubescence and colour identical to that in worker.

Type Material


Type deposition: Holotype, most paratypes and paratype queen in, 3 paratype workers and paratype queen in ; 2 paratype workers each in , , , , , and.

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