Polyrhachis pseudothrinax

Polyrhachis pseudothrinax appears to be somewhat more common than other species of the P. gravis-group. It ranges from north Queensland westwards across the Northern Territory to the Kimberley region of Western Australia.

Identification
A member of the Polyrhachis gravis species-group. Kohout (2013): Throughout its distribution, P. pseudothrinax is relatively morphologically uniform, however, the Queensland populations appear to have a longer antennal scapes (SI 118-126 versus 112-120 in NT populations), with the exception of a single specimen from Melville Island (SI 127). When describing this species, Hung (1967) also noted differences in sculpturation of the propodeal dorsum, however, following examination of numerous specimens across the whole range of this species it is apparent that the variability in striation is similar to that displayed by other species of the P. gravis-group. Some specimens also appear to differ in the shape and length of the propodeal dorsum (Andersen, personal communication), however, subsequent examination failed to reveal any other associated taxonomically important characters and I consider they represent only variants from the “prototype” of this species.

With its single middle petiolar spine, P. pseudothrinax is easily recognised. Only Polyrhachis unicornis shares this character, however, it differs in having the spine less acute and shorter (Fig. 5D, G) and in some specimens weakly emarginate apically. They also differ in the shape of their eyes which, in P. unicornis, are larger and distinctly less convex (Fig. 5C). In addition, the sculpturation on the pronotal dorsum is distinctly transverse in P. unicornis, while it is more-or-less longitudinal in P. pseudothrinax and the bristle-like pubescence is distinctly longer and rather abundant in P. pseudothrinax, while it is much shorter and rather sporadic in P. unicornis. Their colour patterns are very similar with a black body and very distinct, light reddish-brown or orange-coloured legs, however, the anterior portion of clypeus in P. unicornis is distinctly lighter reddish-brown, while it is black throughout in the other species.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Male and immature stages unknown.

Nomenclature

 *  pseudothrinax. Polyrhachis pseudothrinax Hung, 1967a: 199, figs. 1-6 (w.) AUSTRALIA. Combination in P. (Campomyrma): Kohout & Taylor, 1990: 512.

Worker
HW 1.84 mm, HL 2.09 mm, SL 2.17 mm, CI 88, SI 118, PW 1.67mm, propodeal width 1.09 mm, propodeal length 0.67 mm.

Head sub oblong with occipital border fiat on each side and somewhat convex in the middle; genae parallel; truncate behind the eyes; angulate at the occipital corners. Eyes close to the occipital corners; maximum diameter 0.49 mm. Frontal carinae subparallel. Clypeus truncate and dentate at the anterior border; carina poorly marked. Antennal scape a little longer than head, surpassing occipital corners by an amount greater than the length of the first two funicular joints. Mandibles 5-dentate.

Alitrunk robust, more or less convex and arched in profile, sides angulately margined, and slightly laminate on the prothorax. Pronotum broader than long; humeral angles slightly dentate. Promesonotal suture very distinct, with the sides of the conjunction sinuate. Mesonotum longer than broad. Metanotum indicated by a distinct transverse carina. Propodeum broader than long, with two tubercular teeth; declivous face perpendicular. Petiolar node with a short spine on each side and a long middle spine which is as high as the mesonotum in profile, and bent slightly backward. Legs slender. Gaster short, dorsum of the first segment with a transverse ridge at the basal third of the segment.

Subopaque. Mandibles finely and densely rugulose. Head with longitudinal rugae, passing through frontal area, becoming rather obscure on the c1ypeus, curved around the antennal fossa. Pronotum with several transverse rugae immediately behind the "neck" and a few longitudinal rugae continuing onto the propodeum, with only a few transverse and some irregular rugae at the center immediately behind the promesonotal suture. Basal two-thirds of the pleura with wavy rugae which extend from the propleuron onto the dec1ivous face of the propodeum; remainder of pleura smooth. Petiolar node with transverse rugae on both faces. Gaster very finely and densely striate, opaque dorsally and moderate shining ventrally.

Black. Mandibles reddish brown; mandibular teeth black. Antennae dark red, scape darker than funiculus. Legs brown. Fore coxae black. The first quarter of the tibia darker than the remainder. Gaster black dorsally and dark red ventrally; dorsal ridge dark red.

Antennae, head, legs and the dorsum of the alitrunk with erect hairs. Pleura hairless. Petiolar node with some erect hairs on the crest. Gaster with erect hairs mostly on the dorsum. Acidopore (i. e. cloacal orifice of other authors; c.f. Hung and Brown, 1966) with fringe of hairs.

Paratype worker: HW 1.75 mm, HL 2.09 mm, SL 2.17 mm, CI 84, SI 123, PW 1.67 mm, propodeal width 0.92 mm, propodeal length 0.75 mm. Mandibular teeth worn. Propodeum longer than broad, with V-shaped rugae. Gastric ridge as black as the dorsum of the gaster.

Kohout (2013) - (holotype cited first, paratype second): TL c. 8.37, 8.47, 7.00-9.22; HL 2.06, 2.06, 1.72-2.25; HW 1.75, 1.72, 1.43-2.01; CI 85, 83, 83-90; SL 2.09, 2.12, 1.81-2.34; SI 119, 123, 112-127; PW 1.62, 1.62, 1.31-1.87; MIL 2.65, 2.65,2.25-2.90 (1+1+18 measured).

Queen
Kohout (2013) - TL c. 9.42; HL 2.21; HW 1.81; CI 82; 5L 2.15; SI 119; PW 2.06; MTL 2.81 (1 measured).

Queen very similar to worker with usual characters identifying full sexuality, including three ocelli, complete thoracic structure, wings and distinctly larger eyes. Pronotal humeri armed with distinct, somewhat dorsally flattened teeth. Mesoscutum marginally wider than long with widely rounded anterior margin in dorsal view; median line distinct; parapsides flat; anterior face in profile rounding onto relatively low, flat dorsum. Mesoscutellum only marginally elevated above dorsal plane of mesosoma. Propodeal dorsum with lateral margins strongly converging posteriorly, terminating in upturned, dorsolaterally directed, acute teeth; dorsum between them descending into steep declivity in medially uninterrupted line. Petiole very similar to worker, only median spine distinctly shorter. Sculpturation, pilosity and colour scheme virtually as in worker.

Type Material


Both the and  "claim" to have the holotype.

References based on Global Ant Biodiversity Informatics

 * Andersen A. N., B. D. Hoffmann, and S. Oberprieler. 2016. Diversity and biogeography of a species-rich ant fauna of the Australian seasonal tropics. Insect Science DOI 10.1111/1744-7917.12402
 * Kohout R.J. 2013. A Review of the Polyrhachis gravis and micans species-groups of the subgenus Campomyrma Wheeler (Hymenoptera: Formicidae: Formicinae). Memoirs of the QLD Museum-Nature 56: 92-117