Polyrhachis melanura

Polyrhachis melanura is a widespread and relatively common species along the northern and northeastern Australian seaboard. It ranges from the Kimberley region in the north-west, to Cape York Peninsula in the east, and south to Rundle Range near Gladstone. It seems to prefer open forests and savannah woodlands, where it builds nests in the ground with the entrances usually hidden under a rock or piece of wood.

Identification
A member of the penelope species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (2013) - Polyrhachis melanura is one of several species that is very similar to Polyrhachis penelope, but can be easily separated by its distinctly dull appearance, the swollen posterior face of its petiole and its obliquely elevated petiolar spines. In contrast, the sculpturation in P. penelope is somewhat more lucid and semi-polished, the oblique posterior face of the petiole is only weakly convex and the petiolar spines are horizontal.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Males unknown; immature stages (larvae in various stages of development and pupae from holotype colony) present in the QM spirit collection.

Nomenclature

 *  melanura. Polyrhachis (Hagiomyrma) melanura Kohout, 2013: 539, figs. 7G-H (w.) AUSTRALIA.

Worker
(holotype cited first): TL c. 6.70, 5.85-6.77; HL 1.65, 1.50- 1.72; HW 1.37, 1.22-1.43; CI 84, 80-84; SL 2.06, 1.81-2.06; SI 150, 144-151; PW 1.28, 1.12-1.31; MW 0.97, 0.81-0.97; PMI 132, 129-145; MTL 2.12, 1.87-2.25 (15 measured).

Anterior clypeal margin with denticulate, median flange, laterally flanked by acute angles. Clypeus with median carina; weakly sinuate in profile (almost straight in some specimens), posteriorly rounding into moderately impressed basal margin. Frontal triangle indistinct. Frontal carinae sinuate with weakly raised margins; central area flat. Sides of head in front of eyes converging towards mandibular bases in very weakly convex line; behind eyes, sides rounding into convex occipital margin. Eyes only moderately convex, in full face view not or only marginally exceding lateral cephalic outline. Ocelli lacking, position of median ocellus indicated by shallow pit in some specimens. Pronotal humeri widely rounded with anterior margins weakly raised; pronotal dorsum widest at mid-length, lateral margins weakly emarginate medially before terminating in distinctly impressed promesonotal suture. Mesonotal dorsum with lateral margins converging towards indistinct metanotal groove. Propodeal dorsum armed with slender, moderately long, subparallel spines with tips weakly curved outwards. Petiole with posterior face distinctly swollen; dorsum weakly concave medially, laterally armed with pair of slender, obliquely elevated, divergent spines with tips curved upwards. Anterior face of first gastral tergite widely rounding onto dorsum.

Mandibles densely and closely longitudinally striate with piliferous pits. Head, mesosoma and petiole very densely, reticulate-punctate; sculpturation rather flat with distinctly matt-opaque appearance, including on spines. Gaster very closely shagreened, opaque.

Mandibles at masticatory borders with numerous, curved, golden hairs. Anterior clypeal margin with only a few, anteriorly directed setae medially. Dorsa of head and mesosoma with several, rather scattered, very short, bristle-like, pale golden hairs; only a few short hairs on anterior face of fore coxae and venter of mid and hind coxae and femora; no hairs fringing lateral outline of head or antennal scapes. Gastral dorsum with several, very short, posteriorly inclined hairs; somewhat more abundant, marginally longer and posteriorly inclined, pale golden or silvery hairs around apex and on venter of gaster. Rather short, appressed, silvery pubescence in various densities over most body surfaces; pubescence pale golden and denser, hiding underlying sculpturation medially, on dorsum of gaster.

Black; mandibles and appendages black or very dark reddish-brown.

Queen
TL c. 7.16-7.71; HL 1.68- 1.75; HW 1.31-1.40; CI 78-80; SL 1.90-1.93; SI 138-1.47; PW 1.68-1.72; MTL 2.15-2.18 (3 measured).

Apart from sexual characters, very similar to worker except: pronotal humeri widely rounded with indication of blunt humeral angles. Mesoscutum wider than long, with relatively low and virtually flat dorsum in lateral view; anterior margin evenly rounded in dorsal view; median line distinct; parapsides flat. Mesoscutellum only marginally elevated above dorsal plane of mesosoma. Propodeal spines shorter than in worker, tips weakly curved outwards. Petiolar spines short, weakly elevated and divergent. Sculpturation, pilosity, pubescence and colour identical to worker.

Etymology
Derived from the Greek word melanos, meaning black, for its uniformly black colour.

Determination Clarifications
Polyrhachis melanura was listed as P. ‘Hagio 11’ by Kohout (2000: 199).

References based on Global Ant Biodiversity Informatics

 * Heterick B. E. 2013. A taxonomic overview and key to the ants of Barrow Island, Western Australia. Records of the Western Australian Museum Supplement 83: 375-404.
 * Kohout R.J. 2013. Revision of Polyrhachis (Hagiomyrma) Wheeler, 1911 (Insecta: Hymenoptera: Formicidae: Formicinae). Memoirs of the Queensland Museum  Nature 56: 487577