Iridomyrmex mirabilis

This species is confined to south-western and southern Western Australia, and is rarely encountered. Recent specimens have been collected at Eneabba and Bandalup Hill near Ravensthorpe (JDMC). Older material was taken at Albany, while specimens held at the California Academy of Sciences in the USA were collected very many years ago at Darlington, on the outskirts of Perth. Ecological data are largely lacking, but the Eneabba specimens were taken by pitfall trap in shrubland over white quartz sand, while the Bandalup Hill workers were collected while foraging on Kunzia similis growing on gravel/laterite cap-rock.

Identification
The small I. mirabilis is probably the most extraordinary Iridomyrmex of all, and cannot be mistaken for any other ant. This species has many apomorphies. The small size, short, strongly concave frontal carinae and its general morphology place it firmly in the I. calvus complex, but the propodeal spiracle on the uniquely flattened propodeum is within the propodeal angle (the propodeum is somewhat reminiscent of the genus Turneria, although lacking the propodeal tubercles of the latter). The broadly concave anterior clypeal margin lacks any sort of medial protuberance, even a vestigial one, the gaster is dorsoventrally compressed, but most peculiar of all is the petiolar node, which is reduced to a vertical carina.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  mirabilis. Iridomyrmex mirabilis Heterick & Shattuck, 2011: 107, fig. 53 (w.) AUSTRALIA.

Description
Worker Description. Head. Posterior margin of head weakly convex; 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 concave; 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 always completely absent; mandible triangular with distinct angle between masticatory and basal margins; long, curved setae on venter of head capsule absent. Mesosoma. Pronotum weakly undulant or almost straight. Erect pronotal setae sparse (6 or fewer) and bristly. Mesonotum evenly curved. Erect mesonotal setae lacking or very minute (one or two tiny setae present). Mesothoracic spiracles always inconspicuous; propodeal dorsum straight and short (equal in length to propodeal declivity); placement of propodeal spiracle posteriad and near confluence of propodeal dorsum and 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 sparse to absent. Petiole. Dorsum of node planar; node reduced to anterior lip only, the rest incorporated in the petiole. Gaster. Non-marginal erect setae of gaster 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 bluish iridescence on foreparts, purple iridescence on gaster. Colour of erect setae pale whitish-yellow.

Measurements. Worker (n = 5)—CI 89–91; EI 27–29; EL 0.18–0.19; EW 0.14–0.15; HFL 0.71–0.75; HL 0.69–0.74; HW 0.63–0.66; ML 0.83–0.90; MTL 0.54–0.56; PpH 0.08–0.11; PpL 0.35–0.39; SI 85–88; SL 0.53– 0.58.

Etymology
Latin: ‘wonderful’, with reference to the unique features of this species.

References based on Global Ant Biodiversity Informatics

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