Iridomyrmex cyaneus

Iridomyrmex cyaneus is an ant of the dry, desert regions of the Australian interior, and has been recorded from Western Australia, South Australia and New South Wales. It has been collected in pitfall traps in mulga woodland over calcrete (Western Australia), but otherwise there are no ecological data on labels or in the original description.

Identification
This striking little species cannot be mistaken for any other Iridomyrmex, its truncate and sharply declivitous propodeum and its metallic blue or pinkish sheen being a unique combination for the genus. Indeed, their iridescence, their compact form and their narrow node can lead to workers being mistaken for Ochetellus. However, they are distinguished from that genus by the clypeal protuberance and the more posterior position of the eyes on the head capsule. As regards other Iridomyrmex, the more extreme morphologies in I. difficilis, probably the species most closely related to this ant, strongly resemble those of I. cyaneus, but iridescence of any sort is always lacking in the former taxon.

Identification Keys including this Taxon

 * Key to Iridomyrmex species

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  cyaneus. Iridomyrmex cyaneus Wheeler, W.M. 1915g: 812 (w.) AUSTRALIA. See also: Heterick & Shattuck, 2011: 71.

Description
Worker Description. Head. Posterior margin of head weakly concave; erect setae on posterior margin absent; sides of head noticeably convex; erect genal setae absent from sides of head in full-face view (one to a few small setae may be present near mandibular insertion). Ocelli absent; in full-face view, eyes set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eye asymmetrical, curvature of inner eye margin more pronounced than that of its outer margin. Frontal carinae convex; antennal scape barely attaining posterior margin of head, or surpassing it by less than 1 x its diameter. Erect setae on scape absent, except at tip; prominence on anteromedial clypeal margin present as an indistinct swelling or undulation; mandible regularly triangular with oblique basal margin; long, curved setae on venter of head capsule absent. Mesosoma. Pronotum strongly inclined anteriorly. Erect pronotal setae lacking or very minute (one or two tiny setae may be present). Mesonotum evenly curved. Erect mesonotal setae lacking or very minute (one or two tiny setae present). Mesothoracic spiracles always inconspicuous; propodeal dorsum protuberant; placement of propodeal spiracle posteriad and near propodeal declivity; propodeal angle present as sharply defined angle, the dorsal and declivitous propodeal faces often separated by a carina. Erect propodeal setae lacking or very minute (one or two tiny setae present). Petiole. Dorsum of node convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster absent on first gastral tergite; marginal erect setae of gaster absent on first tergite. General characters. Allometric differences between workers of same nest absent. Colour uniformly brown to black, with bluish to pink iridescence throughout. Erect setae completely absent from almost all specimens seen.

Measurements. Worker (n = 5)—CI 88–94; EI 25–28; EL 0.17–0.19; EW 0.14–0.15; HFL 0.73–0.84; HL 0.71–0.84; HW 0.63–0.75; ML 0.82–1.00; MTL 0.51–0.62; PpH 0.11–0.15; PpL 0.34–0.44; SI 80–86; SL 0.54– 0.62.