Melophorus griseus

Workers collected in long grass near Dunham River, Western Australia, were extremely timid solitary foragers among (much more numerous) workers of Iridomyrmex minor, which they resemble in the field. The species is both genetically and morphologically closely related to M. canus but is more restricted in its distribution.

Identification
Heterick et al. (2017) - Melophorus griseus is a member of the Melophorus aeneovirens species-group (in full-face view, the anterior clypeal margin convex, apron-like and covering whole or part of the retracted mandible, except in Melophorus nemophilus, the medial clypeal sector often produced so that it is protrusive when seen in profile; the psammophore frequently with coarse and well-separated ammochaetae, these always placed on or just above anterior margin; in profile, the propodeum elongate and oblique or broadly rounded), and the M. aeneovirens species-complex (in full-face view, psammophore ranged along or just above anterior margin of clypeus and following the curve of the margin; anterior margin of clypeus broadly medially produced, and often with central notch that may be deeply impressed, but is never acuminate at its midpoint; metatibia with maximum of two rows of preapical spines). In Melophorus griseus the tibiae possess fine, appressed pubescence in addition to stout, socketed, appressed to subdecumbent setae Melophorus griseus differs from Melophorus curtus by the features mentioned above. The frontal carinae of the minor worker is raised and laminate at the edges, the frontal triangle is narrowly semi-oval, the sides of head are concave below eyes, giving it a bell-shaped appearance and, in profile, the in profile, pronotum and mesonotum form a gentle curve. These features separate it from its likely nearest relative, M. gibbosus.

This ant is differentiated from Melophorus canus in lacking the long, silky setae and the dentiform mandible, the mandible in this case being five-toothed. The lack of a thoracic hump also helps to separate the minor worker from the minor worker of Melophorus gibbosus. Most workers have bristly, erect setae on the antennae and tibiae.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  griseus. Melophorus griseus Heterick, Castalanelli & Shattuck, 2017: 106, fig. 14 (w.) AUSTRALIA.

Worker
(n =1): CI 91; EI 23; EL 0.23; HL 1.10; HW 1.01; ML 1.58; MTL 1; PpH 0.166; PpL 0.62; SI 136; SL 1.40.

Minor. Head. Head approximately oval, sides of head divergent towards mandibular articulations; posterior margin of head planar or weakly convex; frons matt or with weak sheen, microreticulate or microreticulate-shagreenate; frons consisting of appressed pubescence, with many short, unmodified, erect setae. Eye moderate (eye length 0.20–0.49 length of side of head capsule); in full-face view, eyes set above midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes straight, elevated. Anteromedial clypeal margin narrowly convex and protruding, clypeal midpoint distinctly notched; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Five mandibular teeth in minor worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles approximately vertical or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron matt with indistinct shagreenate sculpture throughout; anterior mesosoma in profile broadly convex; appearance of erect pronotal setae short, (i.e., longest erect setae shorter than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V or U-shaped; propodeum matt or with a weak sheen and indistinctly shagreenate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (greater than 12); appressed propodeal setulae long and closely aligned, creating pubescence; propodeal spiracle situated at least twice its width from the declivitous face of propodeum, and shorter (length < 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node generally rounded with median indentation or hollow; node matt with indistinct microsculpture. Gaster weakly shining with indistinct shagreenation; pilosity of first gastral tergite consisting of thick, appressed setae that form pubescence, interspersed with numerous short, bristly, erect setae. General characters. Colour brown, gaster slightly darker than foreparts.

Type Material
Holotype minor worker from Argyle Diamonds via Kununurra, Western Australia, September 1989, A. T. Postle, Site 15 Melophorus sp. [JDM32-004555]. Paratypes: 2 minor workers from Gibb River Road turnoff 15°50.096'S, 128°18.664'E, Western Australia, 9 February 2013 (3.40pm), Heterick, B.E., Sample 35: parking area with tall grass nearby, ABRS M21 (WAM).

Etymology
Latin griseus (‘gray’); adjective in the nominative singular.