Acanthomyrmex minus

Colonies nest in downed twigs on the forest floor and were found to be (n=2) monogynous. In one colony an additional virgin ergatoid queen was found. Colonies were small with less than 20 minor workers and a few majors. One colony had no majors, although it produced two major pupae in the laboratory. Acanthomyrmex minus ergatoid queens and both subcastes of workers had a single ovariole per ovary. (Terayama et al. 1998)

Identification
Terayama et al. (1998) - This species belongs to the Acanthomyrmex notabilis species group of Moffett (1986), which is characterized by the convex and not bilobed posterior margin of head in major workers. Within the group, this new species is easily distinguished from the others by the smooth and impunctate frons and vertex, and smaller body size (HL 1.58 mm, HW 1.60 mm) of major workers, and straight dorsal margin of petiolar node in major and minor workers.

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

Nomenclature

 * . Acanthomyrmex minus Terayama, Ito & Gobin, 1998: 259, figs. 7-12, 22-24 (s.w.q.) INDONESIA (Sumatra).
 * Type-material: holotype major worker, 1 paratype major worker, 25 paratype minor workers, 2 paratype ergatoid queens.
 * Type-locality: holotype Indonesia: Sumatra, Padang, Ulu Gadut, 28.iii.1997 (F. Ito); paratypes with same data.
 * Type-depositories: BZBC (holotype); BZBC, MNHA, NIAS (paratypes).
 * Status as species: Yamada, Ito, et al. 2018: 10.
 * Distribution: Indonesia (Sumatra).

Worker
Major. (holotype). HL 1.58 mm; HW 1.60 mm; SL 0.63 mm; CI 101; SI 39;WL 0.65 mm; PL 0.35 mm; PH 0.28 mm; DPW 0.26 mm; PPL 0.20 mm; PPH 0.28 mm; PPW 0.25 mm; TL 2.8 mm.

Head as long as wide, with weakly convex posterior margin in full face view; posterior margin very slightly notched medially; median furrow shallow, and recognized in posterior 2/5 of frons and vertex; frons and vertex smooth, without hairs; gena with shallow punctures moderately; shallow punctures also present near frontal carina. Mandible smooth, without any tooth. Anterior margin of clypeus straight, wihout a median projecting lobe. Antennal scape broadest at posterior 1/ 5 of its length, with about 10 erect hairs; 2nd segment slightly longer than wide; 3rd to 9th segments each 0.5 X as long as wide. Antennal scrobe moderately developed, but without funicular scrobe. Eye 0.10 mm in diameter.

Pro- and mesonotum with large punctures which are ca. 0.05 mm. Propodeal spine 0.24 mm long, turned to the posterior portion; declivitous surface subopaque.

Petiole longer than high, with acute triangular node in profile; posterodorsal margin with a pair of erect hairs; lateral petiolar hairs absent; in posterior view, node rectangular, with parallel sides and straight dorsal margin. Postpetiole rectangular, 0.76 X as long as wide in profile; 2 pairs of dorsal hairs and a pair of lateral hairs present; in dorsal view, 0.70Xas long as wide, with slightly concave anterior and straight dorsal margins.

Gaster smooth and impunctate, without hairs.

Body reddish brown; mandibles dark brown; antennae and legs yellowish brown.

Minor. HL 0.73 mm; HW 0.90 mm; SL 0.60 mm; CI 123; SI 67; WL 0.80 mm; PL 0.30 mm; PH 0.24 mm; DPW 0.18 mm; PPL 0.18 mm; PPH 0.23 mm; PPW 0.20 mm; TL 2.5 mm.

Head wider than long, with feebly concave posterior margin in full face view; frons and vertex with large coarse punctures which are ca. 0.06 mm in diameter. Mandible largely smooth. Antennal scape with about 10 erect hairs; 2nd segment slightly longer than wide; 3rd to 9th segments each 0.5 X as long as wide. Clypeus with 2 longitudinal rugae; median clypeal lobes feebly developed; clypeal index 84. Eye 0.11 mm in diameter.

Alitrunk with convex dorsal outline in profile; pro- and mesonotum punctate as in head; pronotal spine 0.13 mm long; propodeal spine thin and straight, 0.28 mm long. Petiole 1.25 X as long as high, with a pair of posterodorsal hairs; lateral petiolar hairs absent; in posterior view, node with parallel sides and straight dorsal margin. Postpetiole 0.78 X as long as high, with straight dorsal margin in profile; dorsum with 2 pairs of erect hairs; lateral postpetiolar hairs present; in dorsal view, 0.76 Xas long as wide.

Gaster smooth and shining, without hairs.

Body reddish brown, gaster slightly darker; antennae reddish brown; mandibles and legs brown.

Queen
Ergatoid. HL 0.90 mm; HW 1.08 mm; SL 0.65 mm; CI 119; SI 60; WL 0.83 mm; PL 0.35 mm; PH ; 0.26 mm; DPW 0.21 mm; PPL 0.18 mm; PPH 0.28 mm; PPW 0.24 mm; TL 2.5 mm.

Head wider than long, with concave posterior margin in full face view; frons and vertex with shallow punctures sparsely; the punctures ca. 0.05 mm in diameter, and separated by 1.5-2.0 X their own diameters; interspaces smooth. Mandible large, without tooth as in major worker. Anterior margin of clypeus straight, without distinct teeth. Antennal scape with about 10 erect hairs; 2nd segment longer tthan wide; 3rd to 9th segments each wider than long. Eye 0.11 mm in diameter.

Alitrunk, petiole, postpetiole, and gaster as in major worker.

Body reddish brown; mandibles, antennae and legs yellowish brown.

Type Material
Holotype. Major worker, Vlu Gadut, Padang, Sumatra, Indonesia, 28.III.1997, F. Ito leg. Paratypes. 1 major worker, 17 minor workers, 1 ergatoid queen, same colony as holotype; 8 minor workers, 1 ergatoid queen, same data as holotype.

Etymology
The specific epithet is named after the small body size of major workers.

References based on Global Ant Biodiversity Informatics

 * Terayama M., F. Ito, and B Gobin. 1998. Three new species of the genus Acanthomyrmex Emery (Hymenoptera: Formicidae) from Indonesia, with notes on the reproductive caste and colony composition. Entomological Science 1: 257-264.