Acanthomyrmex crassispinus

Identification
Wheeler (1930) - This species is clearly different, especially in the character of the thoracic spines and petiolar node from any of the five previously described species of the rare and interesting lndomalayan genus Acanthomyrmex, namely Acanthomyrmex ferox of Perak and Sumatra, Acanthomyrmex luciolae of Ceylon, Acanthomyrmex notabilis from the island of Batchian, Acanthomyrmex dyak and Acanthomyrmex dusun from Borneo. It will he noticed that, with the exception of ferox, all of these species are known only from islands. The peculiar soldier form of Acanthomyrmex closely resembles that of Pheidole, hut the enormous head projects backward over the thorax, which lacks the long pronotal spines of the worker.

Distribution based on Regional Taxon Lists
Oriental Region: Taiwan.

Nomenclature

 *  crassispinus. Acanthomyrmex crassispina Wheeler, W.M. 1930a: 101, fig. 2 (w.) TAIWAN. Moffett, 1986c: 69 (s.). See also: Lin & Wu, 1998: 86.

Worker
Length 3-3.5 mm.

Head subrectangular, distinctly broader than long, with straight, subparallel cheeks, pronounced anterior angles, broadly excised posterior border and somewhat rounded posterior corners. Eyes small, convex, hemispherical, at the middle of the sides of the head. Mandibles large, broad and convex, with the external borders straight in the middle, the terminal borders long and toothless, except for four or five rather indistinct apical denticles, the basal border concave in the middle but forming a right angle with the terminal border. Clypeus very short and transverse, with feebly and broadly concave anterior border, the upper surface with two median carinae, each terminating in a minute denticle at the anterior border. Frontal carinae widely separated and widely diverging posteriorly, forming the mesial borders of distinct scrobes for the basal two thirds of the scapes. Frontal area distinct, triangular. Antennae rather stout; scapes extending about one fourth their length beyond the posterior corners of the head; distinctly flattened, somewhat expanded and angulate basally, with a ridge on the outer side as far back as the middle of their length; first funicular joint nearly twice as long as broad, joints two to eight slightly longer than broad, the terminal joint as long as the two preceding subequal joints of the club. Thorax of the usual structure, but the two pairs of spines, one on the pronotum and one on the epinotum, as long as the height of the thorax, the former pair being somewhat shorter than the latter. Both pairs are stout, though the epinotal pair is more so, straight, directed upward a:o.d outward and only very slightly bent backward at their tips, which taper rather rapidly and are not very acute. The epinotal spines are flattened and their anterior borders are distinctly ridged. Metasternal angles acutely dentate. Petiolar peduncle as long as the remainder of the segment, the node cuneate in profile and acute above, its superior border rather deeply and angularly excised so that it forms two triangular teeth which are as long as broad at their bases. Postpetiole cuboidal; seen from above rectangular, slightly broader than the petiole, slightly longer than broad and distinctly broader behind than in front, with straight sides, its node in profile with flat dorsal and perpendicularly truncated anterior and posterior surfaces. Gaster broadly elliptical, convex above and below, with rather straight anterior border. Legs stout, the tibiae clavate, the femora thickened in the middle.

Shining; mandibles, legs and gaster more so than the remainder of the body. Mandibles smooth, very finely and obscurely coriaceous. Clypeus smooth in the middle between the carinae, coarsely rugose on the sides. Head covered with circular foveolae separated by coarse rugae which are regularly reticulate on the front and occiput but irregularly longitudinal on the cheeks. Antennal scrobes transversely rugulose. Pro- and mesonotum sculptured like the posterior portion of the head; mesopleurae with a few very coarse rugae, the short base of the epinotum with several finer longitudinal rugae, the declivity, spines and petiole smooth; postpetiole smooth above, coarsely reticulate-rugose on the sides; gaster, legs and scapes smooth and polished.

Hairs yellowish, very delicate, short, blunt, sparse and erect, confined to the head, thorax and scapes; clypeus and tip of gaster with a few longer, pointed hairs.

Head, thorax and funiculi ferruginous red; mandibles, scapes, thoracic spines, pedicel, gaster and legs brownish yellow; terminal borders of mandibles black.

Type Material
Described from five specimens from Botel Tobago.