Melophorus castaneus

This species is most common in drier habitats, where it is likely to be a generalized forager. Some workers have been collected in modified habitats such as paddocks and rehabilitated grasslands.

Identification
Heterick et al. (2017) - Melophorus castaneus is a member of the Melophoprus 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 Melophoprus 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 M. castaneus the tibiae possess stout, socketed, appressed to subdecumbent setae only, with fine, appressed pubescence lacking. In profile, the mesosoma of the minor worker tends to linear in orientation, its dorsal outline straight or describing a weak arc (the mesosternal outline and the dorsum of the mesonotum being weakly convergent to subparallel anteriorly). The minor worker of Melophorus castaneus can readily be distinguished from its nearest relatives (Melophorus clypeatus, Melophorus praesens and Melophorus rufoniger) by the uniformly rounded appearance of the vertex of the head when seen in full-face view, and by the uniformly convex propodeum. The major worker is less distinctive, but generally has the rounded propodeum seen in the minor worker, wheareas the M. praesens major worker propodeum is more sloping. The major worker clypeus also lacks the well-developed medial flange found in the major worker of M. rufoniger and is smaller (HW of the former has a HW of ≤ 2.10mm versus > 3 mm in M. rufoniger). The major worker of M. clypeatus also has a more protrusive clypeal flange than does the major worker of M. castaneus.

This very typical member of the M. aeneovirens species-group is distinguished from similar species by the combination of its rounded propodeum (rather angulate in the similar M. praesens), the shape of its clypeus (less projecting than in M. rufoniger) and the lack of asymmetry in the vertex of the head capsule in the minor worker. The tibiae have socketed setae only, enabling it to be distinguished from morphologically similar populations of Melophorus curtus.

Distribution
A wide distribution in mainland Australia. However, this ant seems to be more common in eastern and central parts of the country.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  castaneus. Melophorus castaneus Heterick, Castalanelli & Shattuck, 2017: 88, fig. 9 (w.) AUSTRALIA.

Worker
(n = 8): CI 84-111; EI 18-26; EL 0.21-0.37; HL 0.95-1.88; HW 0.79-2.08; ML 1.41-2.25; MTL 0.83-1.41; PpH 0.13-0.27; PpL 0.63-0.93; SI 77-147; SL 1.16-1.60.

Minor. Head. Head approximately oval with straight sides; posterior margin of head strongly convex; frons shining with superficial shagreenation or microreticulation only, or matt or with weak sheen, shagreenate; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only, or consisting exclusively or almost exclusively of well-spaced, appressed setae only (small, erect setae, if present, usually confined to ocular triangle or posterior margin of head). 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 concave; frontal lobes straight in front of antennal insertion. 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 moderately shining and shagreenate throughout; anterior mesosoma in profile broadly convex; erect pronotal setae absent; in profile, metanotal groove shallow, broadly V or U-shaped; propodeum shining and finely striolate and microreticulate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae always absent; appressed propodeal setulae long, each reaching setae behind and in front, but not forming pubescence, or short, separated by more than own length and inconspicuous; 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 rectangular, its vertex blunt, directed posteriad; in full-face view, shape of petiolar node uniformly rounded; node shining and smooth with vestigial sculpture. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour of foreparts and appendages brown, gaster dark brown.

Major. Head. Head quadrate (i.e., heart-shaped); posterior margin of head weakly concave; cuticle of frons matt or with weak sheen, microreticulate; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. Eye moderate (eye length 0.20–0.49 length of head capsule); in full-face view, eyes set above midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; roughly ovoid, eye narrowed posteriad. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes straight in front of antennal insertion. Anterior clypeal margin narrowly convex and protruding anteromedially, clypeal midpoint notched; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Five to six mandibular teeth in major worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron with weak to moderate sheen, shagreenate on pronotum and dorsum of mesonotum, otherwise microreticulate; anterior mesosoma in profile broadly convex; erect pronotal setae short, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove deep, V-shaped; propodeum matt or with a weak sheen and microreticulate; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae absent; propodeal spiracle situated on or beside declivitous face of propodeum, and shorter (length less than 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node uniformly rounded; node shining and smooth with vestigial microreticulation anteriad. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, short, thick, erect setae interspersed with minute, appressed setae. General characters. Colour of head and legs reddish-tan, mesosoma brownish-orange, gaster black.

Type Material
Holotype minor worker (bottom ant) from Gawler Ranges, South Australia, 5 October 1972, P.J.M. Greenslade, (8) [ANIC32-900180]. Paratypes: major worker and media worker on same pin and with same details as holotype (ANIC); minor worker from 2 km E of Cowangie 35°14'S, 141°24'E, Victoria, 5 November 1991, S. Shattuck #2617.7 (ANIC); 3 minor workers from Kunoth Paddock, near Alice Springs, Northern Territory, 24-26 September 1980, P.J.M. Greenslade, Part A., ; minor worker from Sturt National Park, New South Wales, November 1979, P.J.M. Greenslade, Traps 2, 40) ; 2 minor workers from Kunoth Paddock, near Alice Springs, Northern Territory, 24 [September]- 8 October 1974, P.J.M. Greenslade, G. ; minor worker from 105 km N of Yuendumu, Northern Territory, 23 May 1986, P.J.M. Greenslade, (12), (Mu15) ; media worker from Ethel Creek, Western Australia, 1993-4, P.A. Varris, ID: Melophorus froggatti Forel [sic], Det. by: Heterick, B.E., Date: 14 November 2006, checked against syntype specimen [M. froggatti is here regarded as a junior synonym of the closely related and similar M. aeneovirens-BEH] [ANIC32-004580).

Etymology
Latin castaneus (‘chestnut', i.e., coloured); adjective in nominative singular.