Polyrhachis placida

Polyrhachis placida is apparently a ground-nesting species with the known specimens collected from under a rock in savannah woodland.

Identification
A member of the penelope species-group in the Polyrhachis subgenus Hagiomyrma. Kohout (2013) - Polyrhachis placida is similar to Polyrhachis lydiae, but has a virtually black body while in P. lydiae the body is bright metallic green with the front of head and anterior portion of the pronotum distinctly light reddish-brown. It also closely resembles Polyrhachis stricta described below, however they differ in numerous characters, including the more strongly posteriorly converging promesonotal margins in P. stricta (PMI >190 versus PMI <168 in P. placida).

Key to Polyrhachis Hagiomyrma group species

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Castes
Known only from the worker caste.

Nomenclature

 *  placida. Polyrhachis (Hagiomyrma) placida Kohout, 2013: 543, figs. 8E-F (w.) AUSTRALIA.

Worker
(holotype cited first): TL c. 6.80, 6.60-6.80; HL 1.59, 1.56- 1.59; HW 1.23, 1.22-1.25; CI 77, 77-79; SL 1.78, 1.75-1.78; SI 145, 142-146; PW 1.09, 1.03-1.09; MW 0.65, 0.62-0.65; PMI 168, 163-168; MTL 2.09, 1.93-2.09 (3 measured).

Anterior clypeal margin with acutely denticulate, median flange. Clypeus with median carina; distinctly sinuate in profile with moderately impressed basal margin. Frontal carinae sinuate with weakly raised margins at midlength, flat posteriorly; central area relatively wide, flat with poorly indicated frontal furrow. Sides of head in front of eyes converging towards mandibular bases in straight line; behind eyes, sides widely rounding onto convex occipital margin. Eyes convex, in full face view clearly exceeding lateral cephalic outline. Ocelli lacking. Pronotal dorsum with weakly raised, bluntly angular humeri; lateral margins converging towards distinct promesonotal suture. Mesonotal margins converging posteriorly; metanotal groove indistinct. Propodeal margins terminating in divergent, relatively short, weakly curved, spines. Petiole with anterior face straight, posterior face convex; dorsum shallowly concave medially, armed with slender, divergent, weakly elevated spines. Anterior face of first gastral tergite distinctly higher that full height petiole, widely rounding onto dorsum.

Mandibles finely striate at bases, rather smooth with numerous piliferous pits towards masticatory borders. Head, mesosoma and petiole distinctly reticulate-punctate. Spines sculptured from bases up to midlength, smooth and polished towards tips. Gaster shagreened.

Mandibles with numerous, curved, golden hairs and closely appressed hairs towards bases. Anterior clypeal margin with several longer setae medially and fringe of shorter setae laterally. Numerous, mostly medium length, erect, golden hairs on most body surfaces, including appendages; antennal scapes with very short, bristle-like hairs; head in full face view with a few short hairs between eyes and mandibular bases and numerous, distinctly longer hairs fringing occipital margin. Gastral pubescence posteriorly directed and somewhat longer around apex and on venter.

Black; mandibles and legs, including coxae, light to medium reddish-brown; antennae and gaster dark reddish-brown.

Etymology
Derived from the Latin placidus, meaning quiet, tranquil, in reference to the peaceful and serene western slope of the Atherton Tableland that surrounds the type locality

Determination Clarifications
Polyrhachis ‘Hagio 17’ listed by Kohout (2000: 200) actually consisted of two species, Polyrhachis placida and Polyrhachis stricta.