Polyrhachis unicornis

Identification
Similar to Polyrhachis pseudothrinax with which it shares the single median spine on the petiole. However, the spine in P. unicornis is distinctly shorter and blunt and in some specimens, including the holotype, its apex is shallowly emarginate. Most of the characters distinguishing the species are given in the identification section of P. pseudothrinax.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Sexuals and immature stages unknown.

Nomenclature

 *  unicornis. Polyrhachis (Campomyrma) unicornis Kohout, 2013: 107, figs. 5C-D, G-H (w.) AUSTRALIA.

Worker
TL c. 8.62, 6.90-8.62; HL 2.06, 1.72-2.06; HW 1.81, 1.51-1.81; 088, 86-89; SL 2.12, 1.84-2.12; SI 117, 117-126; PW 1.56, 1.26-1.56; MTL 2.81, 2.25-2.81 (1+6 measured).

Mandibles with 5 teeth, distinctly reducing in length towards base. Anterior clypeal margin widely truncate, truncate portion bluntly denticulate, laterally delimited by blunt corners. Clypeus without distinct median carina; very shallowly concave in profile with flat basal margin. Frontal triangle distinct. Frontal carinae sinuate with only moderately raised margins; central area with poorly distinct frontal furrow. Sides of head in front of eyes converging towards mandibular bases in virtually straight line before rounding into mandibular bases; behind eyes sides rounding into distinct occipital corners. Eyes relatively large, onlymoderately convex, in full face view breaking lateral cephalic outline. Ocelli lacking. Pronotal humeri armed with distinct blunt teeth, lateral margins behind narrowly emarginate before converging posteriorly and rounding into relatively shallow promesonotal suture. Mesonotal dorsum with anterior lateral margins converging posteriorly towards flat, indistinct metanotal groove. Propodeal dorsum with lateral margins converging posteriorly and terminating in upturned, somewhat dorsomedially flattened, acute teeth; dorsum shallowly concave medially, before curving into steeply descending declivity in medially uninterrupted line. Petiole scale-like, virtually triangular in lateral view; dorstum armed with relatively short, weakly posteriorly curved, median spine; in some specimens, including holotype, spine is weakly emarginate apically; lateral petiolar spines distinct, acute. Gaster in lateral view with anterior face flat, distinctly lower than full height of petiole; antelior margin of first gastral tergite with blunt transverse carina.

Mandibles very finely striate with numerous piliferous pits. Clypeus reticulate-punctate; head along frontal carinae and on sides and vertex rather regularly, longitudinally striate. Pronotal dorsum transversely striate, striae somewhat medially bowed and curving towards posterior corners of segment. Mesonotal and propodeal dorsa finely striate, striae converging posteriorly along lateral margins of segments. Propodeal declivity, petiole and anterior face of gaster finely, transversely striate. Dorsum and sides of gaster very finely, longitudinally striate.

Mandibles at masticatory borders and along outer margins with numerous, medium length, curved, golden hairs. Anterior clypeal margin with several, anteriorly directed, relatively long, golden setae medially and shorter setae fringing margin laterally. Head with numerous, erect to semierect, bristle-like, short hairs, only few hairs breaking lateral cephalic outline at occipital corners in full face view. Dorsum of mesosoma virtually witthout hairs, except a few, very short, erect hairs towards propodeal teeth and declivity. Dorsum of first gastral tergite without hairs; medium length, posteriorly directed hairs rather abundant on subsequent tergites, venter and apex of gaster. Antennae and legs, including coxae, with numerous short, bristle-like, semierect hairs.

Black; mandibles and anterior portion of clypeus distinctly light reddish-brown; teeth, mandibular borders and anterior clypeal margin narrowly bordered black. Antennae reddish-brown with funiculi towards apices a shade lighter. Fore coxae dark, reddish-brown, in some specimens somewhat blotched light brown. Legs, including mid and hind coxae, distinctly orange, tarsi a shade darker. Gastral apex reddish-brown.

Type Material


Type deposition: Holotype in ; 2 paratypes in ; 1 paratype each in, , and.

Etymology
Derived from the combination of the Latin unicus, meaning sole, and cornu, meaning horn, in reference to the single dorsal petiolar spine.