Polyrhachis metella

Kohout (2013): Polyrhachis metella is one of only two Hagiomyrma species that does not occur on the Australian mainland (the other is P. denticulata Karavaiev). It is evidently a rare species, manifestly missing from most recent collections.

Identification
The sole member of the metella species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (2013): Polyrhachis metella is a very unusual species that combines several unrelated characters, such as the deeply medially emarginate anterior clypeal margin, rather peculiar, disc-shaped mesonotal dorsum, extremely long and slender propodeal spines and appendages, very high declivity and flat topped petiole. Such a combination of characters, suggests that P. metella may be allied with species in the subgenus Hedomyrma. However, when Viehmeyer (1912) redescribed the worker of P. metella, he considered its unarmed pronotal shoulders a sufficient character to place it in the ammon-group. His decision was followed by Emery (1925) and all subsequent authors have included P. metella in the subgenus Hagiomyrma.

Key to Polyrhachis Hagiomyrma group species

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

Castes
Male and immature stages unknown.

Nomenclature

 *  metella. Polyrhachis metella Smith, F. 1860b: 99, pl. 1, figs. 20, 21 (w.) NEW GUINEA. Kohout, 2013: 526 (w.q.). Combination in P. (Hagiomyrma): Emery, 1925b: 185. See also: Viehmeyer, 1912: 10.

Worker
Kohout (2013) - (holotype cited first): TL c. 10.13, 9.42-11.14; HL 2.52, 2.28- 2.65; HW 1.74, 1.59-1.93; CI 69, 69-74; SL 3.43, 3.17-3.73; SI 197, 189-204; PW (greatest width measured along promesonotal suture) 1.36, 1.31-1.55; MTL 4.18, 3.93-4.43 (12 measured).

Mandibles with 5 teeth. Anterior clypeal margin with open ‘U’-shaped emargination, laterally flanked by distinct, strong teeth; clypeus with rather blunt median carina, virtually straight in profile; basal margin shallow. Frontal triangle indistinct. Frontal carinae weakly sinuate, very strongly raised, almost vertical; central area very narrow, deeply excavated, with poorly indicated frontal furrow. Sides of head in front of eyes subparallel, straight or very weakly convex towards mandibular bases; behind eyes, sides merging into distinct, postocular ridges running on each side from narrow occipital margin along occipital corners, terminating before reaching posterior margin of eyes. Eyes relatively small, moderately convex, in full face view not reaching lateral cephalic outline. Median ocellus present in some specimens; lateral ocelli lacking. Pronotal dorsum with lateral margins strongly converging anteriorly; pronotal humeri with high, almost vertically raised, somewhat angular margins; promesonotal suture deeply impressed laterally. Mesonotal dorsum disc-shaped in dorsal view, lateral margins raised posteriorly; metanotal groove distinctly impressed. Propodeal lateral margins strongly raised for short distance before terminating in long, subparallel or divergent, somewhat sinuate spines, apical third of spines usually weakly curved outwards; propodeal dorsum between somewhat flattened, bases of spines rather short and narrow, abruptly rounding into high, obliquely descending, weakly convex, declivity. Hind coxae dorsoposteriorly carinate with dorsally projecting blunt processes. Petiole with anterior and posterior faces subparallel, or distinctly concave in some specimens; dorsum with posteriorly sloping platform, laterally armed with long, slender, divergent spines with tips weakly curved outwards. Anterior face of first gastral tergite only marginally higher than full height of petiole, widely rounding onto dorsum.

Mandibles densely longitudinally striate at bases, smooth and polished towards masticatory borders with numerous piliferous pits. Head and mesosoma closely reticulate-punctate. Spines sculptured at bases, smooth and polished towards tips. Petiole with anterior face smooth and polished, posterior face finely reticulate. Gaster finely shagreened.

Mandibles at masticatory borders with numerous, rather short, curved, golden hairs. Anterior clypeal margin medially with a few, rather long, anteriorly projecting setae and fringe of shorter setae laterally. Clypeus with a few paired, medium length, golden hairs. A few erect hairs on venter of coxae, fringe of hairs on venter of fore and mid femora. Apex and venter of gaster with numerous posteriorly directed hairs, longest hairs almost reaching greatest diameter of eyes in length. Hairs completely lacking from sides and vertex of head, mesosoma, petiole and most of gastral dorsum. Closely appressed, relatively long, silvery pubescence on sides of head, mesosoma, petiole and venter of gaster; pubescence distinctly golden on vertex of head and dorsum of mesosoma where it is somewhat medially radiating. Dorsum of gaster with rather abundant, medially radiating, golden pubescence, virtually identical to that in members of the Polyrhachis sexspinosa-group of subgenus Myrmhopla.

Black; mandibular masticatory borders, appendages, excluding coxae, and gaster medium reddish-brown. Antennal scapes towards bases and tarsi a shade darker.

Queen
Kohout (2013) - TL c. 11.19; HL 2.56; HW 1.84; CI 72; SL 3.53; SI 192; PW 2.00; MTL 4.28 (1 measured).

Apart from sexual characters similar to worker, except: eyes more convex, clearly exceeding lateral cephalic outline. Mesoscutum wider than long with lateral margins converging into narrowly rounded anterior margin; dorsum relatively low, weakly convex in lateral view; median line distinct; parapsides flat. Mesoscutellum only marginally elevated above dorsal plane of mesosoma. Propodeal spines horizontal, relatively short, about as long as distance between bases. Petiole similar to that in worker with spines divergent and distinctly shorter. Sculpturation, pilosity, pubescence and colour identical to those in worker.

Type Material


Holotype worker in. Labelled “Dor. 15” (= Dory I., New Guinea) and with a Donisthorpe type-label.