Polyrhachis eureka

The type series of P. eureka, from the Gulf Country of north-western Queensland, are the only specimens known of this apparently rare species. The specimens were collected foraging on the ground in savannah woodland.

Identification
A member of the Polyrhachis micans species-group. Kohout (2013) - Polyrhachis eureka is very similar to Polyrhachis micans but differs in several characters including distinctly coarser and less regular sculpturation of the mesosomal dorsum. The eyes in P. eureka are more convex (Fig. 6A) and the propodeal teeth distinctly longer and wider (Fig. 6F), about as wide as the distance between their bases. In contrast, the eyes in P. micans are relatively flat (Fig. 7A) and the propodeal spines shorter, more acute and relatively slender (Fig. 7F), with their basal width about half of the distance between their bases. Dorsal margin of petiole strongly rising medially and dorsally, armed with a pair of closely approximate dorsal spines that are dorsoposteriorly directed and form, in lateral view, a single continuous line with anterior face of petiole (Fig. 6F). In contrast, the dorsal petiolar spines in P. micans are distinctly longer, more widely separated and distinctly more dorsally directed in lateral view.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Sexuals and immature stages unknown.

Nomenclature

 *  eureka. Polyrhachis (Campomyrma) eureka Kohout, 2013: 110, figs. 6A-B, E-F (w.) AUSTRALIA.

Worker
(holotype cited first): TL c. 8.87, 8.87-9.58; HL 2.21, 2.14-2.25; HW 2.00, 1.87-2.03; CI 90, 87-90; SL 2.34, 2.31-2.37; SI 117, 117-123; PW 1.75, 1.63-1.78; MTL 2.74, 2.65-2.78 (1 +4 measured).

Mandibles with 5 teeth. Anterior clypeal margin widely medially truncate, truncate portion more-or-less regularly denticulate, laterally delimited by distinct teeth. Clypeus with rather blunt median carina; virtually straight in profile, basal margin flat. Frontal triangle distinct. Frontal carinae sinuate with weakly raised margins; central area shallowly concave with flat frontal furrow. Sides of head in front of eyes rounding towards mandibular bases; behind eyes sides with a short, postocular lateral ridges and narrowly rounded occipital corners. Eyes distinctly convex, in full face view breaking lateral cephalic outline. Ocelli lacking. Pronotal dorsum distinctly wider than long; humeri bluntly angular with rather distinct anterior margins converging towards occipital collar; lateral pronotal margins converging towards moderately impressed, anteriorly bowed promesonotal suture. Mesonotal lateral margins converging posteriorly into flat metanotal groove. Propodeal margins raised, converging posteriorly and terminating in very distinct, somewhat dorsomedially flattened, broad-based, propodeal teeth with rounded tips; basal width of teeth about as wide as distance between their bases; propodeal dorsum curving in medially uninterrupted line into steep, shallowly concave declivity. Petiole With dorsal margin strongly rising medially and dorsally, terminating in a pair of closely approximate, slender, divergent spines; inner margins of spines continuous medially into open 'U'-shaped dorsum of petiole; outer margins of spines descending into distinctly shorter, slender, lateral spines. Anterior face of first gastral segment virtually flat, lower than full height of petiole, narrowly rounding onto dorsum of gaster.

Mandibles closely and finely, longitudinally striate with piliferous pits. Clypeus reticulate-punctate. Head reticulate-ptulctate with sculpturation on vertex organised into more-or-less longitudinal striae. Pronotal dorsum very finely striate, median striae somewhat barrel-shaped. Dorsa of mesonotum and propodeum more distinctly, somewhat irregularly, longitudinally striate; sides of mesosoma wrinkled. Petiole, including spines, very finely reticulate. Gaster very closely and finely reticulate-punctate, semiopaque.

Mandibles towards masticatory borders with numerous curved, medium length, golden hairs. Anterior clypeal margin with several, anteriorly directed, longer golden setae medially and numerous shorter setae fringing margin laterally. A pair of medium length golden hairs near anterior clypeal margin and pair of shorter hairs near base; a few hairs on fore coxae and venter of middle and hind coxae and femora. Hairs absent from dorsum of head, mesosonla, petiole and dorsum of gaster. Venter and apex of gaster with relatively long, posteriorly inclined, golden hairs. Very short, appressed, golden pubescence in various densities over most body surfaces, except dorsum of mesosoma, most abundant on dorsum of gaster.

Mandibles medium reddish-brown at masticatory borders, becoming progressively darker towards bases; teeth dark, reddish-brown. Clypeus reddish-brown with rest of head black. Antennal scapes and basal funicular segments black or very dark reddish-brown, subsequent segments progressively lighter towards apices. Coxae and femora relatively light reddish-brown with tibiae a shade darker; tarsi very dark, almost black, with apical segments very light orange. Petiole reddish-brown, lateral borders and teeth almost black. Gaster, including venter and apex, distinctly reddish-brown.

Etymology
Derived from a Greek word heureka, meaning ‘I have found it’ (an exclamation of discovery).

References based on Global Ant Biodiversity Informatics

 * 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