Aenictus sonchaengi

All material examined of this species was collected from lowland primary rainforests, except for the single colony from Surat Thani Province (southern Thailand) which was collected from a disturbed forest. Two colonies from Khao Nan National Park, southern Thailand, were found during the night, while a colony from Songkhla Province (southern Thailand) was found in early morning. This species is probably sympatric with Aenictus rotundicollis in at least Borneo. (Jaitrong and Yamane 2011)

Identification
A member of the laeviceps species group. This species is closely related to Aenictus rotundicollis in having only 2 long standing hairs on the vertex of the head and the promesonotum which is, seen in profile, strongly convex dorsally and forming a high dome. However, it is easily separated from A. rotundicollis as follows: promesonotum with 2–4 standing hairs (more than 4 hairs in A. rotundicollis); dorsal surface of propodeum smooth and shiny (propodeum entirely sculptured in A. rotundicollis); pronotal dorsum superficially shagreened and shiny and somewhat wrinkled (smooth and shiny in A. rotundicollis). Also see Aenictus breviceps and Aenictus laeviceps.

Distribution
Malay Peninsula (S. Thailand) and Borneo (Sarawak and Brunei).

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

Castes
Known only from the worker caste.

Nomenclature

 *  sonchaengi. Aenictus sonchaengi Jaitrong & Yamane, 2011: 43, figs. 38-40 (w.) THAILAND.

Worker
Measurements. Holotype and paratypes (n = 10): TL 4.20–4.35 mm; HL 0.85–0.95 mm; HW 0.83–0.85 mm; SL 0.68–0.73 mm; ML 1.33–1.35 mm; PL 0.30–0.33 mm; CI 89–97; SI 82–85.

Holotype and paratypes -Head in full-face view subrectangular, slightly longer than broad, with sides convex and posterior margin almost straight; occipital carina complete. Antennal scape relatively short, only reaching 3/4 of head length; antennal segments II–X each longer than broad; II almost as long as each of III–V; terminal segment (X) slightly shorter than VII+VIII+IX. Frontal carina short, slightly extending beyond posterior margin of torulus. Anterior margin of clypeus slightly convex, bearing 5–6 denticles. Masticatory margin of mandible with a large apical tooth followed by a medium-sized subapical tooth, 5 denticles, and a medium-sized basal tooth; basal margin bearing 2–3 denticles. Mesosoma rather stout; promesonotum in profile strongly convex and forming a dome, mesonotum sloping to metanotal groove; propodeum distinctly lower than promesonotum, with its dorsal outline almost straight; propodeal junction round or weakly angulate; declivity seen in profile almost vertical, not margined dorsally and laterally with a carina. Petiole relatively short, globular, almost as long as high; subpetiolar process well developed and triangular, its apex directed downward and backward; postpetiole slightly larger than petiole.

Entire head smooth and shiny. Mandible very finely striate except along masticatory and outer margins. Antennal scape superficially sculptured and shiny. Pronotum entirely smooth and shiny except for its anteriormost portion being punctate; mesonotum and upper portion of mesopleuron longitudinally rugulose; remainder of mesopleuron, metapleuron and lateral face of propodeum punctate; dorsal surface of propodeum smooth and shiny. Petiole densely reticulate; postpetiole dorsally smooth and shiny, its lateral face weakly reticulate. Legs entirely smooth and shiny.

Vertex with a pair of standing hairs; promesonotum with relatively sparse standing hairs; longest pronotal hair 0.20–0.23 mm long; propodeum with a pair of standing hairs near posterolateral corners. Entire body dark reddishbrown. Typhlatta spot located anterior to occipital corner.

Type Material
Holotype worker from S. Thailand, Nakon Si Thammarat Prov., Khao Nan, 12 XII 2007, W. Jaitrong leg. . Fourteen paratype workers, same data as holotype (,, THNHM).

Etymology
The specific name is dedicated to Dr. Pichai Sonchaeng, the president of the National Science Museum, Thailand.