Polyrhachis kohouti

Polyrhachis kohouti is currently known only from the type locality, based on 2 specimens collected when their nest was disturbed by overturning a log. The species appears to be uncommon because extensive ant collections throughout NE Arnhem Land conducted since 2003, including in the type locality, have failed to find this species again. The vegetation of the type location is open savanna woodland dominated by Eucalyptus oligantha with an understorey of dense grasses, on gently sloping, seasonally waterlogged, loamy soil.

Identification
Polyrhachis kohouti can be easily recognised by the form of its petiole which has a deeply medially concave dorsum and is armed with rather massive, bull horn-shaped spines. The petiole in lateral view is relatively slender, in contrast to other species of the penelope-group where the posterior face of the petiole is usually more-or-less convex or distinctly swollen. Other distinguishing characters of P. kohouti include the strongly transverse pronotal dorsum with widely rounded humeri and strongly posteriorly converging lateral margins that are shallowly emarginate before terminating at the distinctly impressed promesonotal suture. The presence of numerous setae on most of the body surfaces also separates P. kohouti from other species of the penelope-group, which lack hairs, except Polyrhachis hoffmanni which has distinctly longer and sparser hairs on the body.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  kohouti. Polyrhachis (Hagiomyrma) kohouti Hoffmann, 2015: 54, figs. 1-4 (w.) AUSTRALIA.

Worker
holotype cited first: TL c. 6.95, 5.80; HL 1.65, 1.50; HW 1.40, 1.25; CI 85, 83; SL 1.75, 1.59; SI 125, 127; PW 1.34, 1.20; MW 0.75, 0.72; PMI 179, 167; MTL 1.93, 1.78 (1+1 measured).

Median flange of anterior clypeal margin with two distinct acute teeth medially, laterally flanked by acute, somewhat laterally directed teeth. Clypeus with median, anteriorly distinct, longitudinal carina; straight in profile, posteriorly rounding into moderately impressed basal margin. Frontal triangle poorly indicated. Frontal carinae weakly raised; central area relatively wide, rather flat, with only anteriorly indicated frontal furrow. Sides of head in front of eyes converging towards mandibular bases in virtually a straight line; behind eyes sides rounding into convex occipital margin. Eyes moderately convex, in full face view marginally exceeding lateral cephalic outline. Ocelli lacking, position of median ocellus indicated by a shallow pit in cephalic structure. Pronotal dorsum distinctly wider than long with humeri widely rounded, dorsally shallowly concave; lateral pronotal margins weakly raised, converging posteriorly towards clearly impressed promesonotal suture. Mesonotal dorsum with margins converging posteriorly towards indistinct metanotal groove. Propodeal dorsum with lateral margins terminating in moderately long, rather strongly divergent spines with tips weakly turned outwards. Propodeal spiracles situated on moderately projecting tubercles. Petiole with dorsum deeply concave medially, armed with pair of divergent, rather massive, bull horn-shaped spines with tips turned downwards and slightly outwards. Anterior face of first gastral tergite widely rounding onto dorsum.

Mandibles finely, longitudinally striate with numerous piliferous pits. Head, mesosoma and petiole finely reticulate-punctate; somewhat semipolished on vertex of head and dorsum of mesosoma; sides of head and dorsum of spines more coarsely sculptured. Gaster finely shagreened.

Mandibles with numerous golden hairs, longer and curved at masticatory border, shorter and anteriorly inclined towards mandibular bases. Anterior clypeal margin with several anteriorly directed setae medially and a few shorter setae fringing margin laterally. Several, mostly paired, relatively short hairs on clypeus, along frontal carinae and on sides of head, with distinctly longer, anteriorly inclined hairs on vertex and along occipital border. Dorsum of mesosoma and petiole, including spines, with numerous, variously inclined, mostly silvery hairs, longest more than half greatest diameter of eyes. Gaster with abundant, rather long, silvery or pale golden, posteriorly inclined hairs. Closely appressed, silvery pubescence, very sporadic over dorsal body surfaces; pubescence somewhat denser on sides of mesosoma and posterior face of petiolar dorsum and spines. Dorsum of garter with somewhat longer and more abundant silvery pubescence, almost hiding underlying sculpturation.

Body black; appendages very dark reddish-brown or black.

Etymology
Named after Rudy Kohout in recognition of his outstanding contribution to Polyrhachis taxonomy.

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