Aenictus cylindripetiolus

This species mainly inhabits lowland primary forests; only one colony was collected from a longkong orchard. The type series was found under a log in a rainforest during the rainy season. No worker activity was seen around the log and no immatures were found in the bivouac.

Identification
A member of the ceylonicus group. Aenictus cylindripetiolus is similar to Aenictus thailandianus in having a mandible with more than 4 teeth, and entirely sculptured promesonotum. (Jaitrong and Yamane 2013)

Distribution based on Regional Taxon Lists
Oriental Region: Thailand.

Nomenclature

 * . Aenictus cylindripetiolus Jaitrong & Yamane, 2013: 180, fig. 5A-G (w.q.) THAILAND.
 * Type-material: holotype worker, 27 paratype workers, 1 paratype queen.
 * Type-locality: holotype Thailand: Trang Prov., NaYong Dist., Khao Chong Botanical Garden, 10.viii.2009, WJT09-TH2023, evergreen forest (W. Jaitrong); paratypes with same data.
 * Type-depositories: TNHM (holotype); BMNH, MCZC, SKYC, TNHM (paratypes).
 * Distribution: Thailand.

Worker
(holotype and paratypes, n = 10). TL 2.90–3.15 mm; HL 0.60–0.65 mm; HW 0.60–0.65 mm; SL 0.53–0.58 mm; ML 0.98–1.05 mm; PL 0.26–0.28 mm; CI 100–102; SI 88–92.

Head in full-face view subrectangular, almost as long as broad, sides weakly convex, posterior margin almost straight or feebly convex. Antennal scape relatively long, slightly extending beyond 2/3 of head length. Frontal carina relatively long, extending beyond the level of posterior margin of torulus. Parafrontal ridge feeble and incomplete. Anterior clypeal margin weakly concave, concealed by curved anterior extension of frontal carina. Masticatory margin of mandible with large acute apical tooth followed by a medium-sized subapical tooth, 2 denticles, and a medium-sized basal tooth; basal margin feebly concave. Maximum width of gap between anterior clypeal margin and mandibles about 1.4 times as broad as maximum width of mandible. Promesonotum convex dorsally and sloping gradually to metanotal groove; mesopleuron relatively short, demarcated from metapleuron by a shallow groove; metapleural gland bulla relatively small, its maximum diameter about 1.7 times as long as distance between propodeal spiracle and metapleural gland bulla. Propodeum in profile with straight dorsal outline; propodeal junction acutely angulated, overhanging declivitous face; declivity of propodeum broadly and shallowly concave, encircled with a distinct rim. Petiole cylindrical, distinctly longer than high, with its dorsal outline slightly elevated posteriorly, posterior face of petiole flat, and encircled with an indistinct carina; subpetiolar process generally weakly developed, with its ventral outline sinuate, and anteroventral corner acutely angulated. Postpetiole almost as long as petiole, seen in profile with its dorsal outline slightly elevated posteriorly and its ventral outline concave.

Head and gaster entirely smooth and shiny. Mandible very finely striate. Antennal scape superficially reticulate. Mesosoma entirely reticulate, but the sculpturation on pronotum weaker than elsewhere; mesopleuron with longitudinal rugae. Petiole and postpetiole entirely reticulate. Legs entirely smooth and shiny except basal portions of femora and tibiae superficially microreticulate.

Head and mesosoma dorsally with relatively sparse standing hairs mixed with sparse shorter hairs; longest pronotal hair 0.15-0.18 mm long. Head including antennal scape reddish brown; mandible, mesosoma, petiole, and postpetiole dark reddish brown; gaster and legs yellowish brown; mesosoma reddish brown.

Queen
(paratype). TL 6.15 mm; HL 1.03 mm; HW 1.18 mm; SL 0.58 mm; ML 1.68 mm; PL 0.50 mm; CI 115; SI 49.

Head in full-face view subrectangular, slightly shorter than broad, with sides weakly convex, posterior margin weakly concave. Head with a weakly impressed furrow from tip of indistinct frontal carina to occipital margin. Antennal scape relatively short, about half as long as the head, basally narrow, gradually widening apicad; antennal segments II-X each longer than broad; II-V almost of same length. Frontal carina indistinct. Parafrontal ridge absent. Anterior clypeal margin almost straight. Mandible half as long as head, subfalcate, slender, broadest at base, with sharp apex; masticatory margin lacking denticles. Mesosoma rather stout, its dorsal outline almost flat; pronotum and mesonotum fused, with a very shallow suture between them; pronotum slightly broader than mesonotum and propodeum, its median part strongly steeply declining anteriorly; metanotal groove recognizable but shallow; propodeal declivity almost flat, not encircled by a rim. Petiole slightly shorter than high, with its dorsal outline slightly elevated posteriorly, anterior face of petiole concave and posterior face flat; subpetiolar process large, subrectangular, anterior corner and posterior corner each bluntly angulate. Gaster large and elongate; first tergite narrower and much shorter than second, with a very shallow furrow running longitudinally; second tergite longest; third as long as fourth; pygidium small, triangular, with subtruncate tip. Legs relatively long and slender; femora and tibiae clavate.

Entire body smooth and shiny except for lateral face of propodeum and propodeal declivity superficially reticulate but shiny.

Entire body with relatively dense standing hairs; hairs slightly shorter on pronotum than on head, mandible and antennal scape; longest pronotal hair 0.15-0.18 mm long. Head including antennal scape and clypeus yellowish brown; mandible slightly darker; lower gena and large marking on upper frons and vertex dark brown. Mesosoma with ground colour yellowish brown; lateral faces of pronotum and mesonotum, and posterior 2/3 of dorsum of mesonotum dark brown; anterior slope of pronotum reddish brown with a pair of black spots below. Mesopleuron, metapleuron and lateral face of propodeum partly darker. Anterior face of petiole yellowish brown; posterior face extensively and lateroventral portion dark reddish brown; gaster with ground colour yellowish brown to reddish brown; seen from above first tergite with a median spot connected to dark apical band; second tergite with a large triangular median marking, third and fourth tergites with a basal band that is medially widened. Legs yellowish brown.

Type Material
Holotype. THAILAND: Worker from S. Thailand, Trang Prov., Na Yong Dist., Khao Chong Botanical Garden, evergreen forest, 10.VIII.2009, leg. W. Jaitrong, WJT09-TH2023 (THNHM). Paratypes. Twenty-seven workers, same data as holotype (BMNH, MCZC, SKYC, THNHM) and one queen, same data as holotype (THNHM).

Etymology
The specific name refers to the cylindrical petiole of the worker.

References based on Global Ant Biodiversity Informatics

 * Borowiec M. L. 2016. Generic revision of the ant subfamily Dorylinae (Hymenoptera, Formicidae). ZooKeys 608: 1–280.
 * Jaitrong W. 2015. A revision of the Thai species of the ant genus Aenictus Shuckard, 1840 (Hymenoptera: Formicidae: Dorylinae). The Thailand Natural History Museum Journal 9(1): 1-94.
 * Jaitrong W., and S. Yamane. 2013. The Aenictus ceylonicus species group (Hymenoptera, Formicidae, Aenictinae) from Southeast Asia. Journal of Hymenoptera Research 31: 165-233.