Polyrhachis dimoculata

Polyrhachis dimoculata appears to be a rather rare species and, in spite of extensive collecting undertaken in recent years at Danum Valley and Kinabalu Park, the holotype and paratype remain the only specimens known. The holotype was collected foraging on low vegetation along the Segama River walking track and the paratype by fogging the rainforest canopy at Poring Hot Springs. (Kohout 2013)

Identification
A member of the Polyrhachis aculeata species group in the subgenus Myrma

Polyrhachis dimoculata is similar to other species of the aculeata complex; however, it is easily recognised by its very fine body sculpturation that produces a very characteristic, somewhat semi-polished appearance to the head, mesosoma and petiole, which contrasts with the highly polished gaster. Also, unlike other species of the complex, P. dimoculata has virtually no pubescence and pilosity on all the dorsal body surfaces. (Kohout 2013)

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia.

Castes
Sexuals and immature stages unknown.

Nomenclature

 *  dimoculata. Polyrhachis (Myrma) dimoculata Kohout, 2013: 147, figs. 3, 8-9 (w.) MALAYSIA.

Worker
Description. Dimensions (holotype cited first): TL c. 7.66, 7.41; HL 1.90, 1.84; HW 1.53, 1.43; CI 80, 78; SL 2.43, 2.37; SI 159, 166; PW 1.37, 1.34; MTL 2.62, 2.50 (2 measured).

Mandibles with 5 teeth. Anterior clypeal margin arcuate, narrowly medially truncate. Clypeus with blunt median carina, virtually straight in profile, posteriorly rounding into weakly impressed basal margin. Frontal triangle distinct. Frontal carinae sinuate with rather strongly raised margins; central area narrow with distinct median furrow. Sides of head in front of eyes converging towards mandibular bases in evenly convex line; behind eyes sides converging into smoothly rounded occipital corners. Eyes convex, strongly posteriorly truncate, in full face view clearly breaking lateral cephalic outline. Ocelli lacking; positions of lateral ocelli indicated by weakly raised cephalic sculpturation. Dorsum of mesosoma evenly convex in profile; pronotal humeri armed with rather long, acute spines; dorsum of each spine with distinct, rather acute, longitudinal carina running from base towards and almost reaching tip; outer edges of spines acute, weakly notched basally and continuous with lateral margins of pronotal dorsum. Promesonotal suture distinctly impressed. Mesonotal dorsum with lateral margins narrowly rounded and weakly raised anteriorly; metanotal groove impressed laterally, rather flat medially. Propodeal dorsum with lateral margins distinctly converging posteriorly and terminating in narrowly rounded, weakly raised ridges that are continued medially and merge into a dorsally bowed, somewhat medially notched carina dividing propodeal dorsum from shallowly concave declivity; secondary carinae extending from propodeal margins towards propodeal spiracles dividing declivity from sides of propodeum. Petiole biconvex in profile, armed with a pair of dorsolaterally and posteriorly directed, acute spines, situated on dorsolateral angles close to posterior face of petiole; dorsal margin of petiole with intercalary tooth visible in lateral view; distinctly shorter, rather blunt tooth situated laterally below base of each spine. Anterior face of first gastral segment concave to accommodate posterior face of petiole, anterodorsal margin distinctly lower than full height of petiolar node.

Mandibles finely, longitudinally striate with numerous piliferous pits. Body surfaces very finely sculptured, reticulate-punctate, rather semi-polished to opaque, sculpture on pronotal dorsum, notably along lateral margins, somewhat longitudinally directed; bases of pronotal spines more distinctly longitudinally striate. Propodeal declivity, tips of pronotal and petiolar spines and gaster, smooth and polished. Mandibles along masticatory borders with a few semierect, relatively short, golden hairs. Anterior clypeal margin with a few moderately long, anteriorly directed, golden setae medially. A few pairs of moderately long, erect, golden hairs along basal margin of clypeus and along frontal carinae. Hairs totally absent from vertex of head, antennal scapes, dorsum of mesosoma, petiole and dorsum of gaster. Only a few, moderately long hairs on anterior and posterior faces of fore coxae. Gaster with numerous, posteriorly directed hairs around apex and on venter.

Colour. Black throughout, with only extreme tip of apical funicular segment reddish brown.

Etymology
Derived from the combination of the Latin words dimidiatus, meaning halved, and oculus, meaning eye, in reference to the rather peculiar truncate eyes.

References based on Global Ant Biodiversity Informatics

 * Kohout R. J. 2013. A review of the Polyrhachis aculeata species-group of the subgenus Myrma Billberg (Hymenoptera: Formicidae: Formicinae), with keys and descriptions of new species. Australian Entomologist 40(3): 137-171.