Iridomyrmex innocens

This ant is confined to south-west Western Australia, but is reasonably common in higher rainfall areas of the Darling Ranges.

Identification
Comments. Iridomyrmex innocens is a very shiny, usually black or dark brown species, although pale workers can occur (I. ‘argutus’). The combination of the shining cuticle with only superficial reticulation and many long, erect setae on the mesosoma is unique for this species within the I. calvus complex.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  innocens. Iridomyrmex innocens Forel, 1907h: 292 (w.q.m.) AUSTRALIA. Senior synonym of argutus, occiduus: Heterick, 2009: 56 (in text). See also: Heterick & Shattuck, 2011: 92.
 * argutus. Iridomyrmex argutus Shattuck, 1993b: 1312, figs. 8, 9, 36 (w.) AUSTRALIA. Junior synonym of innocens: Heterick, 2009: 56 (in text).
 * occiduus. Iridomyrmex occiduus Shattuck, 1993b: 1320, figs. 18, 19, 36 (w.q.m.) AUSTRALIA. Junior synonym of innocens: Heterick, 2009: 56 (in text).

Taxonomic Notes
I. argutus and I. occiduus, discussed by Shattuck (1993b), have been synonymized under the name I. innocens in Heterick (2009). (In his 2009 monograph, Heterick pointed out that one of two workers of I. argutus with the same collection data as the type material, but not discussed by Shattuck (1993b), possesses setae on the venter of the head capsule, the main character used by the latter author to distinguish I. occiduus (setae present) from I. argutus (setae absent)). These workers are held in the Curtin Ant Collection (JDM Collection). In other workers nominally of I. occiduus the setae on the venter of the head capsule were found by Heterick to number between two and over a dozen. The remaining distinguishing character used by Shattuck, namely, the slightly darker head capsule found in I. argutus compared with uniform colouration of head and mesosoma in light-coloured specimens of I. occiduus, was considered by Heterick to be very subtle and difficult to sustain, given the small number of I. argutus workers discussed by Shattuck in his work (i.e., two workers). Heterick also examined a syntype queen of I. innocens, held at WAM, and found its non caste-specific features to be identical with those of I. argutus and I. occiduus. On these grounds the latter two species were synonymised by Heterick under I. innocens.

Description
Worker Description. Head. Posterior margin of head planar to weakly concave; erect setae on posterior margin in full-face view set in a row; sides of head noticeably convex; erect genal setae present on sides of head in full- face view. 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 surpassing posterior margin of head by 1–2 x its diameter. Erect setae on scape present and abundant; prominence on anteromedial clypeal margin always completely absent; mandible regularly triangular with oblique basal margin; long, curved setae on venter of head capsule present. Mesosoma. Pronotum moderately and evenly curved over its length. Erect pronotal setae moderate in number (6– 12), longest setae elongate, flexuous and/or curved. Mesonotum straight. Erect mesonotal setae moderate in number (6–12), long, often curved. Mesothoracic spiracles prominent or inconspicuous; propodeal dorsum protuberant; placement of propodeal spiracle posteriad and near propodeal declivity; propodeal angle present as a bluntly defined right angle, the dorsal and declivitous propodeal faces never separated by a carina. Erect propodeal setae moderate in number (6–12), long, often curved. Petiole. Dorsum of node convex; node thin, scale-like, orientation more-or-less vertical. Gaster. Non-marginal erect setae of gaster present on first gastral tergite; marginal erect setae of gaster present on first tergite. General characters. Allometric differences between workers of same nest absent. Colour shining yellowish-brown to brown, head and gaster may be darker than mesosoma. Colour of erect setae pale, whitish.

Measurements. Worker (n = 22)—CI 91–99; EI 23–28; EL 0.17–0.21; EW 0.10–0.17; HL 0.70–0.90; HW 0.64–0.89; ML 0.28–0.42; MTL 0.59–0.75; PpH 0.09–0.19; PpL 0.33–0.48; SI 86–99; SL 0.61–0.78.

References based on Global Ant Biodiversity Informatics

 * Forel A. 1915. Results of Dr. E. Mjöbergs Swedish Scientific Expeditions to Australia 1910-13. 2. Ameisen. Ark. Zool. 9(16): 1-119
 * Heterick B. E., and S. Shattuck. 2011. Revision of the ant genus Iridomyrmex (Hymenoptera: Formicidae). Zootaxa 2845: 1-174.
 * Shattuck S. O. 1993. Revision of the Iridomyrmex calvus species-group (Hymenoptera: Formicidae). Invertebrate Taxonomy 7: 1303-1325.