Polyrhachis enigma

The holotype is the only available worker of this species and nothing is known about its nesting habits.

Identification
Kohout (2006) - In general appearance, including the scale-like petiole, closely resembles some members of the subgenus Cyrtomyrma. However, the shape of the head that almost completely lacks a lateral carina, and the partially developed lateral margins of the pronotum and mesonotum. exclude it from Cyrtomyrma. In particular, the queens closely resemble some members of the recently established P. porcata-group of Aulacomyrma and their distinguishing characters, including the poorly defined lateral margins of the mesosoma and the arcuate dorsal margin of the petiole with short lateral teeth, support the placement of Polyrhachis enigma within this latter subgenus. In spite of the distance (about 260 km) separating their collection localities, the holotype worker and para type queens share most of the specific morphological characters and I am confident that they represent a single biological species.

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

Castes
Male and immature stages unknown.

Nomenclature

 *  enigma. Polyrhachis (Aulacomyrma) enigma Kohout, 2006c: 78, figs. 1-3 (w.q.) NEW GUINEA.

Worker
Dimensions: TL c. 6.05; HL 1.56; HW 1.50; CI 96; SL 1.72: SI 115; PW 1.15; MTL 1.93. Black; mandibles reddish-brown with teeth, inner and outer borders and base narrowly lined dark brown. Antennae dark brown with apex of last funicular segment distinctly lighter, yellowish-brown. Mandibles with 5 teeth, reducing in length towards base. Anterior clypeal margin widely and shallowly emarginate medially. Clypeus in profile very weakly sinuate; posteriorly with rather vague, short, blunt, medial carina; basal margin flat, laterally indicated by thin line. Frontal triangle indistinct. Frontal carinae sinuate, rather short, with moderately raised margins anteriorly, rather flat posteriorly; central area relatively wide with weakly raised medial carina. Sides of head in front of eyes weakly concave, converging towards mandibular bases; widely rounded behind eyes into weakly convex occipital margin. Eyes rather small, moderately convex, situated well forward from occipital corners; in full face view marginally exceeding lateral cephalic outline. Ocelli absent. Pronotal humeri with dorsally flattened triangular teeth, their lateral margins continued for a short distance forming incomplete lateral pronotal margins. Mesosoma in profile weakly convex; promesonotal suture distinct; mesonotum with weakly indicated lateral margins, almost flat in profile; metanotal groove lacking; propodeum laterally emarginate, with dorsum smoothly rounding into oblique declivity. Petiole scale-like, with anterior face almost flat, posterior face weakly convex dorsal margin armed with pair of acute dorsal teeth and pair of more slender, short, lateral spines; margins between dorsal teeth and lateral spines somewhat jagged, with additional pair of blunt denticles. Anterior face of first gastral segment lower than height of petiole, with anterodorsal margin widely rounding onto dorsum of segment. Mandibles at masticatory borders longitudinally rugose, rather polished towards bases. Legs light orange-red with distal ends of femora narrowly and proximal ends of tibiae more widely black: tarsi mostly dark brown with apical segments distinctly lighter, yellowish-brown. Whole body surfaces extremely finely shagreened, with dorsum of head and mesosoma highly polished. Sides of pronotum with numerous shallow striae directed obliquely towards very finely wrinkled lateral lobes; mesonotum und propodeum with numerous, shallow, oblique striae. Abundant shallow punctures scattered over most body surfaces. Mandibles with a few short, curved and semi erect hairs near masticatory borders and along outer margins; towards bases with numerous, very short, appressed hairs arising from pits. Clypeus with several short setae lining anterior margin. All body surfaces with numerous, scattered, rather short, semierect or appressed hairs arising from shallow punctures and pits. Posterior margins of gastral segments lined with medium length. erect hairs, distinctly longer hairs concentrated around gastral apex. Leading edge of antennal scapes with several short, erect hairs. Legs with only a few. Medium length hairs arising from ventral surfaces of femora and dorsal surfaces of middle and hind tibiae.

Queen
TL c. 7.06-7.36; HL 1.75-1.81; HW 1.59-1.68; CI 91- 93; SL 1.68-1.84; SI 104-114; PW 1.25-1.31; MTL 1.93-2.03 (3 measured).

Black, with colour scheme virtually identical to that in worker. Very similar to worker with usual characters identifying full sexuality, including three ocelli and complete thoracic structure. Clypeus in profile straight. with blunt, longitudinal carina medially; basal clypeal margin flat. Eyes more convex than in worker, clearly breaking lateral cephalic outline. Pronotal humeri with blunt triangular teeth; mesoscutum slightly wider than long with lateral margins strongly converging anteriorly, forming narrowly rounded anterior margin; median line very short, poorly indicated; parapsides distinct, rather flat; mesoscutum in profile relatively low, widely rounding onto flat dorsum. Mesoscutellum flat, not elevated above dorsal plane of mesosoma; metanotal groove strongly impressed. Propodeum wide. strongly transverse, convex in profile. laterally terminating into blunt angles; dorsum descending into steeply oblique declivity in medially uninterrupted line. Petiole with dorsal margin sharp, entire, laterally weakly rounding into short, acute, posterolaterally curved spines. Subpetiolar process triangular. Anterior face of first gastral segment low, smoothly rounding onto dorsum. Mandibles rather distinctly, longitudinally rugose. Head, including clypeus with very faint, longitudinal striae, more distinct between eyes and frontal carinae. Mesosoma laterally with striae more distinct than those in worker; mesoscutum anteriorly with longitudinal, medially converging, rather weakly indicated striae. Propodeal dorsum distinctly, longitudinally striate with declivity and petiole very finely, mostly transversely, reticulate. All dorsal surfaces of head, mesosoma and gaster very finely shagreened, highly polished, but not as shiny as in worker.

Type Material
Holotype worker, Papua New Guinea: Morobe Prov., Mt Missim (Mt. Misim on label), 07°20’S. 146°43'E, (no date of collection), Stevens. Paratypes: 3 dealate queens. Eastern Highlands. Mingende. 05°58'S, 144°53' E, 5000 ft, 14.i.1968, H.B. Lowery. Holotype in ; 1 paratype each in, and.

References based on Global Ant Biodiversity Informatics

 * Janda M., G. D. Alpert, M. L. Borowiec, E. P. Economo, P. Klimes, E. Sarnat, and S. O. Shattuck. 2011. Cheklist of ants described and recorded from New Guinea and associated islands. Available on http://www.newguineants.org/. Accessed on 24th Feb. 2011.
 * Kohout R.J. 2006. A new species of Polyrhachis (Aulacomyrma) Emery from Papua New Guinea. Australian Entomologist 33: 77-80.