Polyrhachis tapini

Identification
A member of the Polyrhachis continua species group in the subgenus Myrma

Polyrhachis tapini is a very characteristic and easily recognisable species. It features virtually flat pronotal and mesonotal dorsa with lateral margins that are rather abruptly and very narrowly (only about 0.1 mm) upturned. The pronotal spines are long and slender with their tips weakly downturned. The petiole has long and divergent dorsal spines and lateral spines reduced to mere angles. The dorsa of the mesosoma and petiole are completely hairless and with only very sparsely distributed, appressed pubescence.

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

Castes
Immature stages unknown.

Nomenclature

 *  tapini. Polyrhachis tapini Kohout, 2013: 42, figs. 46, 49-50 (w.q.m.) PAPUA NEW GUINEA.

Worker
Dimensions (holotype cited first): TL c. 11.39, 11.24-11.89; HL 2.81, 2.81-2.90; HW 2.06, 1.96-2.15; CI 73, 70-74; SL 4.03, 3.93-4.08; SI 196, 190-200; PW 1.90, 1.87-1.93; MTL 4.13, 4.03-4.33 (4 measured).

Anterior clypeal margin arcuate, medially truncate. Clypeus without distinct median carina, very weakly sinuate in profile, with almost flat basal margin. Frontal triangle distinct. Frontal carinae sinuate with strongly raised margins; central area relatively narrow with weakly impressed frontal furrow. Sides of head in front of eyes subparallel, before rounding into mandibular bases; behind eyes sides with distinct postocular carina extending towards occipital corners. Eyes convex; in full face view clearly exceeding lateral cephalic outline. Ocelli lacking. Pronotal dorsum with relatively long, slender, anterolaterally directed, acute spines; lateral edges of spines acute, merging posteriorly with narrowly upturned, smoothly rounded pronotal margins. Promesonotal suture distinctly impressed laterally, rather flat medially; posteriorly rounding into medially flat metanotal groove. Propodeum with lateral margins only weakly raised anteriorly, flat for most of their length and terminating in poorly raised, blunt tuberculae; propodeal dorsum descending into declivity in weakly curved, medially uninterrupted line. Petiole scale-like, distinctly slender in lateral view, armed with two rather long and slender, posteriorly curved, acute spines with inner margins forming ‘U’-shaped petiolar dorsum; lateral margin of petiole below base of each spine with very short, acute tooth. Anterior face of first gastral segment flat at base, widely rounding onto dorsum.

Mandibles finely, longitudinally striate with numerous piliferous pits towards masticatory borders. Clypeus reticulate-punctate; sculpturation obliquely striate on sides and mostly longitudinally striate on vertex and between frontal carinae and eyes. Pronotal dorsum finely, longitudinally striate at base, with striae diverging anteriorly towards bases of spines. Mesonotal and propodeal dorsa finely, rather regularly, longitudinally striate, with propodeal declivity finely reticulate-punctate. Petiole reticulate-punctate, with spines towards tips almost smooth. Gaster shagreened.

Mandibles along outer margin and towards masticatory borders with numerous suberect, relatively long, golden hairs. Anterior clypeal margin with a few, rather long setae medially and several shorter setae fringing margin laterally. Numerous, semierect or erect, relatively long hairs rather abundant on clypeus and front of head; numerous somewhat shorter hairs fringing outline of head in full face view; antennal scapes with numerous, relatively long hairs along leading edge; hairs lacking on dorsum of mesosoma and petiole. Legs, including coxae, with numerous, medium length hairs along ventral margin. Gaster with numerous, medium length, posteriorly directed hairs. Closely appressed, relatively sparse, silvery pubescence over most body surfaces, except dorsum of mesosoma and petiole; pubescence denser with distinct reddish tint on gastral dorsum.

Colour. Black; wide band along masticatory borders and apical funicular segments reddish brown. Legs medium to dark reddish brown with trochanters and apical tarsal segments a shade lighter. Gaster black or very dark brown dorsally, apex reddish brown.

Queen
Dimensions: TL c. 12.10-13.15; HL 2.93-2.99; HW 2.18; CI 73-74; SL 4.08-4.13; SI 187-189; PW 2.46-2.59; MTL 4.03-4.08 (2 measured).

Queen marginally larger than worker with usual characters identifying full sexuality, including three ocelli, complete thoracic structure and wings. Pronotal spines shorter. Mesoscutum only marginally wider than long; lateral margins converging into moderately rounded anterior margin; median line distinct; parapsides virtually flat; mesoscutum in profile with widely rounded anterior face and virtually flat dorsum. Mesoscutellum weakly convex, marginally elevated above dorsal plane of mesosoma. Propodeum with lateral margins weakly raised anteriorly, terminating posteriorly in short ridges; propodeal dorsum in lateral view descending into declivity in medially unbroken curve. Petiole with dorsal spines distinctly shorter. Sculpturation on mesoscutum with longitudinal striae curving anteriorly and medially towards median line, with those on mesoscutellum weakly diverging posteriorly. Pilosity and pubescence similar to that in worker, except numerous erect, medium length hairs present on dorsum of mesosoma that are completely absent in worker. Colour scheme very similar to worker.

Male
A single callow male present in the spirit collection (Bottle no. 39/4).

Type Material
Holotype worker: Papua New Guinea, Central Distr., Tapini, 1000-1200 m, rf., viii.1962, ex nest in soil, R.W. Taylor acc. 2200. Paratypes: data as for holotype (2 workers, 2 queens); New Guinea, Morobe Distr., Herzog Mts., Wagau. C. 4,000 ft, 4-17.i.1965; M.E. Bacchus, B.M. 1965-120; Stn. No. 137. Holotype, 1 paratype worker and 1 paratype queen in ANIC; 1 paratype worker and paratype queen in ; 1 paratype worker in.

Etymology
Named after the type locality, Tapini village, nestled along the southern slopes of the Owen Stanley Range in Papua.

References based on Global Ant Biodiversity Informatics

 * Kohout R. J. 2013. A review of the Polyrhachis continua species-group of the subgenus Myrma Billberg (Hymenoptera: Formicidae: Formicinae) with keys and descriptions of new species. Australian Entomologist 40(1): 13-46.