Polyrhachis expressa

All of the 270 specimens of the type series were collected foraging on stems of Bambusa forbesi (=Neololeba atra) within a small area of monsoonal rainforest. Their nesting habit is unknown, but it is very probable that they use hollow bamboo internodes. (Kohout 2006)

Identification
Very similar to Polyrhachis emeryana from the Solomons. Both species have widely rounded pronotal shoulders, a propodeum armed with spines and distinctly elongated lateral petiolar spines. However, P. expressa differs by its finer sculpturation, notably on the dorsum of the head and mesosoma, and its less convex pronotal dorsum. The propodeal spines in P. expressa are quite long, columnar and bluntly terminated, while in P. emeryana they are short, triangular and acute. Also, the appressed pubescence in P. expressa is extremely short and inconspicuous, while it is distinctly longer and more prominent in P. emeryana. (Kohout 2006)

Distribution
Known only from the type locality at Iron Range.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Abundance
Only known from two collections in the Iron Range.

Castes
Known only from workers.

Nomenclature

 *  expressa. Polyrhachis expressa Kohout, 2006b: 99, figs. 2B, F-G (w.) AUSTRALIA.

Worker
Dimensions (holotype cited first): TL c. 5.64, 5.49-6.15; HL 1.47, 1.43-1.56; HW 1.47, 1.42-1.56; CI 100, 99-103; SL 1.78, 1.72-1.84; SI 121, 116-122; PW 1.12, 1.06-1.18; MTL 2.18, 2.12-2.31 (16 measured).

Clypeus in profile straight anteriorly, rounding posteriorly into moderately impressed basal margin. Head about as wide as long; sides of head in front of eyes weakly convex; behind eyes sides converging into convex occipital margin. Eyes only moderately convex, in full face view just breaking lateral cephalic outline. Ocelli lacking. Pronotal humeri widely rounded in dorsal view. Mesosoma in profile with pronotal dorsum strongly convex, rising steeply towards short summit and descending towards distinct promesonotal suture; mesonotum weakly convex, metanotal groove indistinct, indicated only by depression in lateral outline; propodeal dorsum rather ﬂat, armed with a pair of relatively long, slender, bluntly terminated spines. Petiole with anterior face almost straight, posterior face moderately convex; dorsal margin armed with four spines, dorsal pair broad-based and tooth-like, lateral pair widely diverging, slender, more than twice as long as dorsal pair. Subpetiolar process acute anteriorly, narrowly rounded posteriorly. Anterior face of first gastral segment ﬂat, narrowly rounding onto dorsum of segment.

Head and gaster finely shagreened with dense cover of minute punctures and piliferous pits. Mesosoma and petiole more strongly sculptured with intensity of sculpturation distinctly increasing laterally; lower portions of pronotum, meso- and metapleurae and petiole, strongly reticulate-rugose.

Several curved or semierect hairs on masticatory borders, with distinctly shorter, mostly appressed hairs towards mandibular bases. Anterior clypeal margin medially with several rather long, anteriorly directed setae and with fringe of shorter setae lining margin laterally. A few medium length hairs along ventral margins of gastral segments. Very short, appressed hairs, arising from minute punctures and pits, rather densely distributed over all dorsal body surfaces. Dorsum of head, antennal scapes, mesosoma, petiole, first gastral segment and tarsi black. Mandibles, condylae, antennal scapes distally, narrow bands on funicular segments, and legs, including coxae, medium to dark reddish-brown. Extreme tip of apical funicular segment distinctly lighter. Clypeus, sides of head and posterior margins of gastral segments somewhat diffusely reddish-brown.

Type Material
HOLOTYPE: QUEENSLAND, Cape York Pen., Iron Ra. NP, nr Gordon Ck x-ing, 12°42’S, 143°18’E, 1-6.x.2000, R.J. Kohout acc. 2000.177 (worker). PARATYPES: data as for holotype (269 workers). Holotype (QMT99336) and most paratypes in ; 4 paratypes each in, and ; 2 paratypes each in , , , ,  and.