Acropyga oceanica

Acropyga oceanica has been recorded from leaf litter, and been collected in bamboo forest from a pitfall trap. An Eumyrmoccus sp. mealybug was recorded with this species by Williams (1998), but the record must be considered questionable given the difficulty in the past in identifying this Acropyga species. (LaPolla 2004)

Identification
LaPolla (2004) - Worker: 7-8 segmented antennae; small species (TL: 1.16-1.43); 4 distinct teeth on mandible; torulae very closely set together; antennal apical segment long, about as long as preceding 4 segments combined. Queen: unknown. Male: unknown. Compare with Acropyga yaeyamensis.

This is the smallest known Acropyga and the antennal segment count is the lowest of any known Old World species. Its torulae are also extremely closely set together with virtually no space between them. It can relatively easily be separated from other small Acropyga species by its low antennal segment count (7-8) and the resence of 4 distinct teeth on the mandible. Morphologically the worker of this species resembles Acropyga smithii of the New World. Both of those species have as few as 7 antennal segments, 4 distinct mandibular teeth and similar mesosomal structures. This similarity however is probably the result of convergence.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia, New Guinea, Singapore, Solomon Islands. Palaearctic Region: China.

This species ranges throughout the Indo-Australian region, reaching as far north as southern China.

Nomenclature

 *  oceanica. Acropyga (Rhizomyrma) oceanica Emery, 1900c: 333, pl. 8, fig. 44 (w.q.m.) NEW GUINEA. Senior synonym of septemstruma: LaPolla, 2004a: 76.
 * septemstruma. Acropyga (Rhizomyrma) septemstruma Terayama, Fellowes & Zhou, 2002: 24, figs. 7-10 (w.) CHINA. Junior synonym of oceanica: LaPolla, 2004a: 76.

LaPolla (2004) - The lack of worker-associated males for this species is frustrating since Old World males have not been recorded with antennal segment counts below 12 segments. With the worker of this species only possessing up to 8 segments, males would be expected with as few as 9 antennal segments. This could be phylogenetically very interesting, but will have to await future discovery of the males.

Emery recorded the worker as having up to 9 segments, but that is erroneous, because one of the specimens he determined as this species was in actuality an Acropyga ambigua specimen with 9 segments. Nine segmented antennae have not been recorded in the worker of this species.

Worker
LaPolla (2004) - (n=5): TL: 1.16-1.43; HW: 0.329-0.351; HL: 0.345-0.396; SL: 0.22-0.264; ML: 0.34-0.415; GL: 0.437-0.653; CI: 87.83-95.36; SI: 66.87-79.52.

Head: yellow; head longer than broad; posterior margin entire; 7-8 segmented, incrassate antennae; apical antennal segment about as long as preceding 4 segments combined; scape fails to reach posterior margin by about length of pedicel; torulae very closely set together, so that little space exists between them; clypeus narrow, slightly convex medially, with erect hairs on surface; mandible narrow with 4 distinct, nearly even teeth; dorsal surface of mandibles with dense cluster of hairs near masticatory margin (only easily seen with SEM examination); gap exists between inner mandibular margin and anterior clypeal margin. Mesosoma: yellow; in lateral view pronotum with short anterior shelf; pronotum rises steeply toward mesonotum; pronotum without hairs except for a few erect hairs posteriorly; mesosomal dorsum flat; mesonotum with a dense layer of appressed to erect hairs; propodeum with erect hairs; declivity steep. Gaster: petiole thick and erect; gaster yellow, covered in a thick layer of appressed hairs, with scattered erect hairs throughout.

Type Material
LaPolla (2004):

Acropyga (Rhizomyrma) oceanica Emery, 1900: 333 (w.q.m.). 2 syntype workers, PAPUA NEW GUINEA: N.E.: Friedrich-Wilhelmshaften (L. Birö) [examined]. The designated lectotype is a worker labeled JSL TYPE # 128 and is deposited at MCSN. The lectotype is the worker specimen whose head is off of the card; the worker whose head is glued to the card is Acropyga ambigua. Though the queen and male were briefly described in the original description they were not part of the collection at MCSN, and were not able to be located in other collections known to contain a large number of Emery type material.

Acropyga (Rhizomyrma) septemstruma Terayama, Fellowes, and Zhou, 2002: 24 (w.). Holotype worker, CHINA: Hong Kong, Northeast New Territories, Sha Lo Tung (J.R. Fellowes) (ICKH) [not examined]. NEW SYNONYM.