Acanthomyrmex concavus

Specimens have been found in leaf litter from a rainforest and a mature wet forest.

Identification
Moffett (1986) - Minors with head deeply concave dorsad and thus resembling Acanthomyrmex luciolae and Acanthomyrmex basispinosus, except: propodeal spines without a distinct thickened base, strongly directed caudad; mandibles each with a ventral tooth; medial clypeal lobes well-developed, projecting; postpetiole with only two pairs of hairs dorsally. Major worker unknown.

A Sabah specimen has a distinctive, bilobed petiolar node.

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

Worker
Minor

Nomenclature

 * . Acanthomyrmex concavus Moffett, 1986c: 80, figs. 39B-C, 44-47 (w.) BORNEO (East Malaysia: Sarawak, Sabah).
 * Status as species: Bolton, 1995b: 53; Pfeiffer, et al. 2011: 44; Yamada, Ito, et al. 2018: 10.{nomenplus}}

Worker
Minor. Holotype and single paratype measure HW 1.10, HL 0.90 (CI 122), ML 0.78 to 0.79 (MI 87 to 88), SL 0.90 (SI 82), EL 0.16 to 0.17, HFL 1.00 to 1.03 (FLI 111 to 114; FWI 24) mm. Posterior margin of head deeply concave in dorsal full-face view; head shape similar to A. luciolae, but with lateral margins of head less strongly convex. Head widest above the eyes. Head with rounded foveae having thick walls; dorsally the longest hairs extend 0.10 to 0.12 mm. Scapes short (SI < 90). Clypeal index 140 to 144. Lobe to each side of medial clypeal hair strongly produced, but widely separated from the hair; lateral clypeal hairs in a completely enclosed fovea. Smooth medial area of clypeus not bordered laterally by rugae. Mandibles with a small but distinct ventral tooth.

Spines on trunk virtually straight, with propodeal spines extending more directly caudad than in other species; pronotal spines short, stubby, and lacking conspicuous hairs. Pronotal angle forming a feeble tooth. Sculpture on trunk particularly deeply impressed. Propodeal declivity transversely rugose, and bordered on each side by two adjacent rugae.

Petiolar node rounded, without dorsolateral teeth, so that PWI not measurable. Anterior peduncle of petiole long and narrow, and lacking lateral and sublateral hairs; subpetiolar declivity present. Postpetiole subrectangular, about one third wider than it is long, rounded dorsad and only feebly rugose on sides; with two pairs of hairs dorsally. Femora hairy, and with ventral surfaces distinctly concave; hind femora relatively short (FLI < 120). Color dark orange red, with legs and gaster lighter and more orange.

Type Material
Holotype. Minor worker deposited in from Malaysia; Sarawak; 4th Div., Gunung Mulu National Park, RGS Exped., Long Pala, lowland rainforest leaf litter, 19/X/1977 (B. Bolton).

Paratypes. One minor worker, same collection data as holotype.

Etymology
Name refers to strongly concave posterior margin of head.

References based on Global Ant Biodiversity Informatics

 * Moffett, M. W. 1986. Revision of the myrmicine genus Acanthomyrmex (Hymenoptera: Formicidae). Bulletin of the Museum of Comparative Zoology 151:55-89.
 * Pfeiffer M., D. Mezger, and J. Dyckmans. 2013. Trophic ecology of tropical leaf litter ants (Hymenoptera: Formicidae) - a stable isotope study in four types of Bornean rain forest. Myrmecological News 19: 31-41.
 * Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58
 * Yamane S., T. Itino, and A.R. Nona. 1996. Ground ant fauna in a Bornean dipterocarp forest. Raffles Bulletin of Zoology 44(1): 253-262.
 * Yamane S.; Nona, A. R. 1994. Ants from Lambir Hills National Park, Sarawak. Pp. 222-226 in: Inoue, T.; Hamid, A. A. (eds.) 1994. Plant reproductive systems and animal seasonal dynamics. Long-term study of dipterocarp forests in Sarawak. Kyoto: Center for Ecological Research, Kyoto University, vii + 255 pp.
 * Yamane Sk., T. Itino, and A. Rahman Nona. 1996. Ground ant fauna in a Bornean dipterocarp forest. The Raffles Bulletin of Zoology 44(1): 253-262.