Melophorus curtus

Based on label data, this ant has a predilection for black soil, and has been taken in both dry sclerophyll woodland and savannah. Pitfall traps are a common means of capture. In all likelihood this species is a generalized scavenger. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus curtus 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 Melophorous curtus the tibiae possess fine, appressed pubescence in addition to stout, socketed, appressed to subdecumbent setae This species differs from Melophorus sulconotus in the appearance of the mesosoma, which, in profile, has a pronotum and mesonotum that are weakly to strongly convex in the minor worker, The antennal scapes and tibiae lack bristly erect and semi-erect setae, and short, erect setae are normally sparse on dorsum of mesosoma. The head of the minor worker is oval or squared and the frontal triangle is triangular in appearance. This combination of characters separates M. curtus from Melophorus gibbosus and Melophorus griseus, which share the pilosity pattern seen on the metatibae in M. curtus. Both M. griseus and M. gibbosus have erect setae on the antennal scape and the tibiae. The major worker of M. curtus can also be distinguished from that of M. gibbosus (the major worker of M. griseus is unknown) by its partially shagreenate frons, the frons being microreticulate in the M. gibbosus major worker.

There is some doubt that the taxon, as defined here, is monophyletic: although it is characterized by the presence of fine, appressed pubescence of the tibiae in addition to stout, socketed, appressed to subdecumbent setae, and also the absence of erect setae on the antenna and hind tibiae, other features are very variable, especially in the minor worker. Quite compressed, short-legged, relatively hairy workers are common in the Armidale area of NSW, while larger, more elongate and glabrous or near glabrous workers are common further north. In northern Australia a very elongate form with long, silvery, appressed setae on the head and body occurs. (However, this ant may represent the media worker of Melophorus tenuis, which is here described on the basis of the minor only.) The moderately gracile morphotype, which is the most common, can also easily be mistaken for Melophorus praesens or Melophorus castaneus, and the tibiae of specimens must be examined carefully to distinguish the former species from the latter two.

Distribution
Most collections of Melophorus curtus have been made in Eastern Australia, where it is quite common.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  curtus. Melophorus curtus Forel, 1902h: 485 (s.w.q.) AUSTRALIA.

The possibility that there could be at least two or three cryptic species cannot be discounted, and further investigation involving genetics work is desirable in order to unravel the phylogenetics of the variable populations of this species.

Worker
Heterick et al. (2017) - (n = 8): CI 87–109; EI 15–31; EL 0.18–0.40; HL 0.68–2.40; HW 0.59–2.62; ML 0.94–2.81; MTL 0.57–1.81; PpH 0.11–0.35; PpL 0.49–1.23; SI 72–149; SL 0.88–1.90.

Minor. Head. Head approximately oval with straight sides; posterior margin of head strongly convex; frons matt or with weak sheen, shagreenate; frons consisting almost completely of appressed setae that may form pubescence (tiny, erect setae, if present, usually confined to ocular triangle). 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 margin entire or very weakly indented; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Five to six 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; appearance of erect pronotal setae short, (i.e., longest erect setae shorter than length of eye) and unmodified, or erect pronotal setae absent; in profile, metanotal groove shallow, broadly V or U-shaped; propodeum shining and shagreenate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae variable in number, may be absent; appressed propodeal setulae long and closely aligned, creating pubescence; propodeal spiracle situated on or beside 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 square with rounded angles; node shining and distinctly shagreenate-microreticulate. Gaster. 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, or consisting of long, closely aligned, whitish, appressed setae, with erect setae (present in at least some workers) confined to margin of the sclerite. General characters. Colour brown, gaster slightly darker in some workers.

Major. Head. Head quadrate (i.e., heart-shaped); posterior margin of head weakly concave; cuticle of frons shining with superficial shagreenation or microreticulation only; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. Eye small (eye length less than 0.2 × 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; eyes elliptical. In full-face view, frontal carinae concave; frontal lobes curved inward in front of antennal insertion. Anterior clypeal margin narrowly convex and protruding anteromedially, clypeal midpoint notched; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five 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 matt or with weak sheen and microreticulate throughout; anterior mesosoma in profile broadly convex; erect pronotal setae short, (i.e., 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 sparse to moderate (1-12); appressed propodeal setae long and closely aligned, creating pubescence; 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, or generally rounded with median indentation; node shining and faintly shagreenatemicroreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of thick, appressed setae that form pubescence, interspersed with numerous short, bristly, erect setae. General characters. Colour of foreparts orange-red, gaster brown to black.

Type Material
Heterick et al. (2017) - Syntype small major worker, Mackay, Queensland, here designated lectotype: (examined: ANIC specimen ANIC32-053434). Also examined: syntype minor worker with same details as lectotype (ANIC), here designated a paralectotype; AntWeb images of syntype major and minor worker, Mackay, Queensland  (CASENT0903264, CASENT0903265), here designated paralectotypes; AntWeb images of syntype major and minor worker, Mackay, Queensland  (CASENT0909810, CASENT0909811), here designated paralectotypes. Also designated a paralectotype is a syntype queen (MHNG) (Taylor and Brown 1985), not seen.

A small syntype major worker from Mackay is here designated lectotype. This specimen not only represents the most common morph of M. curtus but has clearly recognizable defining features that belong to this taxon. The other syntypes here become paralectotypes.



References based on Global Ant Biodiversity Informatics

 * Heterick B. E., M. Castalanelli, and S. O. Shattuck. 2017. Revision of the ant genus Melophorus (Hymenoptera, Formicidae). ZooKeys 700: 1-420.