Iridomyrmex meridianus

This species is currently known from populations in the extreme south-west of Western Australia and also in Tasmania. Nests have been found under rocks and logs and in rotting wood. Most collections have been made in heavily forested areas.

Identification
Iridomyrmex meridianus is a small-medium, dark brown to black Iridomyrmex that closely resembles Iridomyrmex splendens and Iridomyrmex mattiroloi, but can be separated from both by the absence or virtual absence of erect setae on the mesosoma and the posterior margin of the head. This species also resembles mesic populations of Iridomyrmex mjobergi, but the mandible is dark brown compared with light yellow or orange in I. mjobergi. Western Australian material differs slightly from that from Tasmania in that the workers are fractionally larger and darker with a more distinct bluish-green to yellowish-green iridescence.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  meridianus. Iridomyrmex meridianus Heterick & Shattuck, 2011: 103, figs. 51, 96 (w.) AUSTRALIA.

Description
Worker Description. Head. Posterior margin of head planar to weakly concave; erect setae on posterior margin in full-face view, present singly or as a couple of setae on either side of posterior margin of head; 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 semi-circular, or asymmetrical, curvature of inner eye margin more pronounced than that of its outer margin. Frontal carinae convex; antennal scape surpassing posterior margin of head by 1–2 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 moderately and evenly curved over its length. 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 inconpicuous; propodeal dorsum smoothly and evenly convex; placement of propodeal spiracle posteriad and near propodeal declivity, or mesad, more than its diameter away from propodeal declivity; propodeal angle weakly present or absent, the confluence of the dorsal and declivitous propodeal faces indicated, if at all, by an undulation. Erect propodeal setae lacking or very minute (one or two tiny setae present). Petiole. Dorsum of node convex; node thin, scale-like, orientated anteriad. Gaster. Non-marginal erect setae of gaster present or absent on first gastral tergite; marginal erect setae of gaster present on first tergite, or absent on first tergite. General characters. Allometric differences between workers of same nest absent. Colour dark brown to black, with weak yellowish- to bluish-green iridescence on body and legs. Colour of erect setae on head and coxae light yellow-brown.

Measurements. Worker (n = 6)—CI 84–89; EI 25–31; EL 0.18–0.21; EW 0.14–0.16; HFL 0.82–1.01; HL 0.79–0.87; HW 0.67–0.76; ML 0.97–1.15; MTL 0.58–0.73; PpH 0.13–0.15; PpL 0.40–0.46; SI 98–115; SL 0.68– 0.84.

Etymology
Latin: ‘south’ or ‘southern’.

References based on Global Ant Biodiversity Informatics

 * CSIRO Collection
 * Heterick B. E., and S. Shattuck. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-174.
 * Heterick, B., and S. O. Shattuck. "Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae)." Zootaxa 2845 (2011): 1-174.