Aenictus appressipilosus

Known only from lowland rainforests of Borneo. Seiki Yamane collected the type series at night.

Identification
A member of the ceylonicus species group. Jaitrong and Yamane (2013) - Aenictus appressipilosus is a distinct species within the group in having 2 long standing hairs mixed with few short appressed hairs on the vertex and has a few appressed hairs mixed with few decumbent hairs on promesonotum (the other species have sparse to dense long standing hairs on head and pronotum).

Key to Aenictus species groups / Key to southeastern Asian Aenictus ceylonicus group species

Distribution
Borneo (Sabah)

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

Castes
Known only from the worker caste.

Nomenclature

 *  appressipilosus. Aenictus appressipilosus Jaitrong & Wiwatwitaya, 2013: 172, figs. 1A-C (w.) MALAYSIA.

Worker
(holotype and paratypes, n = 9). TL 2.70-2.85 mm; HL 0.58-0.60 mm; HW 0.54-0.55 mm; SL 0.45-0.48 mm; ML 0.90-0.95 mm; PL 0.25 0.28 mm; CI 92-93; SI 84-88.

Head in full-face view clearly longer than broad, anterior portion slightly broader than posterior portion, sides convex, posterior margin almost straight; occipital margin bearing a carina. Antennal scape relatively long, extending beyond 2/3 of head length but not reaching posterolateral corner of head. Frontal carina relatively long, slightly extending beyond the level of posterior margin of torulus. Parafrontal ridge indistinct, slightly extending beyond the level of posterior margin of torulus. Anterior clypeal margin almost straight or feebly concave. Masticatory margin of mandible with large acute apical tooth followed by a medium-sized subapical tooth, and 5-6 denticles; basal margin almost straight. Maximum width of gap between anterior clypeal margin and mandibles about 1.8 times as broad as maximum width of mandible. Promesonotum convex dorsally and sloping gradually to metanotal groove; metanotal groove indistinct; mesopleuron relatively long, not clearly demarcated from metapleuron; metapleural gland bulla relatively small, its maximum diameter about 1.8 times as long as distance between propodeal spiracle and metapleural gland bulla. Propodeum in profile with straight dorsal outline; propodeal junction acutely angulate, overhanging the declivitous face; declivity of propodeum seen from back tapering above, shallowly concave, and encircled with a thin rim. Petiole in profile trapezoidal, slightly longer than high, with straight dorsal outline; anterior slope of petiole seen in profile feebly concave; subpetiolar process low with anterior corner angulated and posteroventrally produced into a spine with acute tip, margin connecting anterior corner and base of the spine weakly concave. Postpetiole shorter than petiole, with its dorsal outline convex.

Head and gaster entirely smooth and shiny. Mandible very finely striate. Antennal scape superficially microreticulate, apical half slightly shiny. Mesosoma reticulate (reticulation coarser on lateral face of pronotum than on propodeum) except for anteriormost portion of pronotum punctate; promesonotal dorsum smooth and shiny; mesopleuron with relatively irregular longitudinal rugae.

Head with a pair of long standing hairs mixed with sparse short appressed hairs over the surface; mesosoma dorsally with relatively sparse appressed hairs mixed with 2-4 decumbent hairs; longest pronotal hair (decumbent hair) 0.10-0.13 mm long. Antennal scape, mesosoma, petiole and postpetiole reddish brown; head, gaster and legs yellowish brown.

Type Material
Holotype. MALAYSIA: Worker from E. Malaysia, Borneo, Sabah, Tawau Hills N.P., 7.VII.1996, leg. Sk. Yamane, SB96-SKY-01 (UMS). Paratypes. Eight workers, same data as holotype (SKYC, THNHM).

Etymology
The specific name refers to the appressed hairs on promesonotum.