Aenictus ceylonicus

Little is known about the biology of .

Identification
A member of the ceylonicus group.

Key to Aenictus species groups

Jaitrong and Yamane (2013) – Aenictus ceylonicus is most similar to Aenictus watanasiti in having the mandible with only 3 teeth including apical tooth. It can be separated from the latter by the postpetiole being short and clearly shorter than high (mandible with more than 3 teeth and postpetiole almost as long as high or longer in the other members of the group). See also under Aenictus formosensis.

Distribution
Aenictus ceylonicus is probably restricted to the western part of the Oriental region (India and Sri Lanka) (Jaitrong & Yamane, 2013). The Australian records shown on the occurrence map below are subspecies that have been raised to full species.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, New Guinea, Philippines. Oriental Region: India, Sri Lanka. Palaearctic Region: China, Japan.

Nomenclature

 *  ceylonicus. Typhlatta ceylonica Mayr, 1866a: 505 (w.) SRI LANKA. Wheeler, G.C. & Wheeler, J. 1984: 265 (l.). Combination in Aenictus: Dalla Torre, 1893: 7. Senior synonym of formosensis, latro: Wilson, 1964a: 452. See also: Shattuck, 2008c: 16.
 * latro. Aenictus ceylonicus var. latro Forel, 1901a: 477 (w.) INDIA. Junior synonym of ceylonicus: Wilson, 1964a: 452.
 * papuanus. Aenictus papuanus Donisthorpe, 1941c: 129 (w.) NEW GUINEA. Junior synonym of ceylonicus: Wilson, 1964a: 452.
 * similis. Aenictus similis Donisthorpe, 1948g: 131 (w.) NEW GUINEA. Junior synonym of ceylonicus: Wilson, 1964a: 452.

Shattuck (2008) offers the following taxonomic notes on this species:

As previously conceived (Wilson, 1964: 452) this species extended from India and Sri Lanka eastward to Taiwan and south to Australia and contained eight junior synonyms (formosensis Forel, latro Forel, orientalis Karavaiev, papuanus Donisthorpe, similis Donisthorpe, and turneri Forel (with its junior synonyms deuqueti Crawley and exiguus Clark)). When discussing the specimens placed in ceylonicus Wilson (1964) recognised at least some of the variation noted in this study (for example, see Wilson’s figs. 37–44), but interpreted this variation as intraspecific. For example he mentioned that the subpetiolar process varies considerably in its development, but did not appreciate that this variation occurs in discrete states and shows a strong geographic pattern suggesting that a series of species are involved. A careful re-examination of these characters, combined with considerably more material, has resulted in significantly different conclusions being drawn compared to Wilson (1964).

An examination of currently available material has found that the old “ceylonicus” contains a large number of species, including Aenictus ceylonicus (strict sense), Aenictus acerbus, Aenictus orientalis, Aenictus papuanus, Aenictus prolixus and Aenictus turneri. To determine the identity of A. ceylonicus itself will require considerable work and is beyond the scope of the present study. However, there are a wealth of morphological characters which allow the development of robust species hypotheses as has been demonstrated above for the Australian fauna. Having said that, morphological differences among species are often subtle and require considerable attention to detail to decipher. The following notes are provided as a starting point for a full revision of these ants.

Most of the Indian specimens share the configuration of the subpetiolar process, which forms a rounded anterior lobe followed by a posterior flat to concave extension ending at the junction with the postpetiole. Others have an elongate rectangular subpetiolar process, including the types of A. latro. Specimens with both of these morphologies can be found throughout Asia including in Taiwan, the Philippines, Vietnam and Indonesia. But while material from Vietnam has a rectangular subpetiolar process it has the dorsal surface of the mesosoma smooth and lacking any indication of the metanotal groove (most other species have at least a weak angle at the metanotal groove). Thus while the shape of the subpetiolar process is important it must be used in conjunction with other characters when determining species boundaries.

While the work undertaken here is preliminary, it clearly shows that the situation surrounding this species, and close relatives, is much more complex than that recognised by earlier workers. As a first step in clarifying this situation the names A. orientalis and A. turneri are treated as valid species, A. papuanus and A. similis are transferred to synonymy with A. orientalis while A. formosensis and A. latro are retained as junior synonyms of A. ceylonicus. However this should be treated as preliminary until all relevant material can be studied in detail.

Worker
Jaitrong and Yamane (2013) - (lectotype and paralectotypes of A. ceylonicus, n = 3). TL 3.15–3.20 mm; HL 0.63–0.70 mm; HW 0.58–0.63 mm; SL 0.48–0.53 mm; ML 1.00–1.03 mm; PL 0.25–0.28 mm CI 89–92; SI 83–84. (lectotype and paralectotypes of A. ceylonicus).

Head in full-face view subrectangular, slightly longer than broad, sides convex and posterior margin almost straight or feebly concave. Antennal scape reaching 2/3 of head length; antennal segments II longer than broad and slightly longer than each of III-VI; III slightly longer than broad; IV-VI each almost as long as broad; terminal segment (X) almost as long as VII+VIII+IX. Frontal carina short, reaching the level of posterior margin of torulus. Parafrontal ridge absent. Anterior clypeal margin weakly concave, lacking denticles. Masticatory margin of mandible with 3 teeth, including a large apical tooth; basal margin weakly concave, lacking denticles. 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; metapleural gland bulla relatively large, its maximum diameter about 3.1 times as long as distance between propodeal spiracle and metapleural gland bulla. Propodeum in profile with feebly convex dorsal outline; propodeal junction angulated, nearly right-angled; declivity of propodeum wide, shallowly concave, and encircled with a distinct rim. Petiole sessile and short, almost as long as high, with its dorsal outline elevated posteriorly; subpetiolar process weakly developed. Postpetiole distinctly shorter than petiole and shorter than high, with its dorsal outline slightly elevated posteriorly.

Head entirely smooth and shiny. Mandible with fine longitudinal striation, except along masticatory margin smooth and shiny. Antennal scape smooth and shiny. Promesonotum smooth and shiny except anteriormost portion punctate; mesopleuron, metapleuron and propodeum with several longitudinal rugae. Lateral faces of petiole and postpetiole microreticulate but the dorsal faces smooth and shiny. Legs smooth and shiny.

Head and mesosoma dorsally with relatively sparse standing hairs; longest pronotal hair 0.15–0.18 mm long. Head, mesosoma, petiole and postpetiole reddish brown; gaster, antennae and legs yellowish brown, paler than head, mesosoma and waist.

Wilson (1964) - Syntypes: HW 0.62 mm, HL 0.62 mm, SL 0.50 mm; HW 0.54 mm, HL 0.60 mm, SL 0.44 mm. Antenna 10-segmented. Mandible narrow, bearing 1 large apical and 1 large preapical tooth; the basal portion right-angulate, which can be interpreted as a 3rd "basal" tooth. When mandibles are closed there remains a gap between their posterior borders and center of anterior clypeal border almost as wide as maximum width of mandible. Clypeus emarginate, not armed. Parafrontal ridge rudimentary. Occiput very feebly convex, lacking a collar. Propodeal junction surmounted by low, rounded, transverse ridge, which in side YIGW appears as a "rounded" right angle. Subpetiolar process a long, thin, evenly rounded lobe which projects anteriorly. Pilosity abundant and relatively long; length of longest hairs on pronotum about 0.16 mm.

Head entirely shining. Pronotum shining. Mesothorax and propodeum bearing 15-20 longitudinal rugae, their interspaces weakly microreticulate and feebly shining. Sides of petiole and postpetiole microreticulate and subopaque, their tops shining. Concolorous clear yellow.

Type Material
Jaitrong and Yamane (2013) – Typhlatta ceylonica: Three syntype workers from Sri Lanka (NHMW, examined). One worker among them is selected as the lectotype (Fig. 27E). Aenictus ceylonicus var. latro: Six syntype workers from India, Poona (MHNG, examined).