Melophorus setosus

Andersen (2007) notes the apparent association of this ant with Monomorium rothsteini (‘rothsteini group’ in Andersen) nests and queries whether this may be another nest raider. Queensland Museum specimens were hand collected as foragers in brigalow scrub. No other data are known for this species. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus setosus can be placed in the Melophorus biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is also placed in the Melophorus fieldi species-complex because of the appearance of the anteriorly placed clypeal psammophore, the compact propodeum, the presence of more than one preapical spine on the metatibia, at least in the major worker, the long, even spindly legs, and the unmodified mandible in the major worker. The vestiture of short modified setae that clothe the head and body of this ant (but not the legs or antennal scape), and the distinctive frontal carinae that are straight or weakly convex and converge anteriad rather than diverging, as in most Melophorus, make this species unmistakeable.

This species has a distinctive facies, with straight rather than concave frontal carinae and stout, modified setae that are especially abundant in the minor worker. This combination enables the ant to be distinguished from all other Melophorus, although the bulbous clypeus associates it superficially with Melophorus caeruleoviolaceus. This ant is possibly also more distantly related to Melophorus solitudinis.

Distribution
The rather uncommon but widespread Melophorus setosus is well represented in the TERC Collection (as ‘Group H’) with specimens from northern NT, QLD and WA. Material in other collections has come from NT (ANIC), QLD (QM) and WA (WAM).

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  setosus. Melophorus setosus Heterick, Castalanelli & Shattuck, 2017: 302, fig. 70 (w.) AUSTRALIA.

Worker
(n = 4): CI 108–118; EI 22–28; EL 0.26–0.33; HL 0.86–1.27; HW 0.93–1.49; ML 1.20–1.52; MTL 0.78–0.93; PpH 0.17–0.17; PpL 0.48–0.61; SI 75–105; SL 0.98–1.11.

Minor. Head. Head square; posterior margin of head weakly convex; frons matt or with weak sheen, microreticulate or microreticulate-shagreenate; frons consisting mainly of stout, appressed and erect setae, both sets of setae modified and thickened and occasionally clavate (featherlike) in appearance. 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 curved inward in front of antennal insertion. Anteromedial clypeal margin broadly and evenly convex and protrusive; clypeal psammophore set below midpoint of clypeus; 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 with weak to moderate sheen, shagreenate on pronotum and dorsum of mesonotum, otherwise microreticulate; anterior mesosoma in profile smoothly rounded anteriad, thereafter pronotum and whole of mesonotum flattened and on same plane as propodeum; appearance of erect pronotal setae short and unmodified, or weakly expanded distally; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and uniformly striolate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about 3:2; erect propodeal setae present and abundant (greater than 12); appressed propodeal setulae long, each reaching setae behind and in front, but not forming 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 uniformly rounded; node shining and smooth with vestigial sculpture. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of thick, often distally flattened, erect setae over well-spaced, short, appressed setae. General characters. Colour of foreparts orange tan to brick red (head may be darker), gaster black with or without violet iridescence.

Major. Head. Head horizontally rectangular, broader than wide; posterior margin of head weakly concave; cuticle of frons matt or with weak sheen, indistinctly shagreenate; frons consisting mainly of appressed and stout erect setae, the latter bristly in appearance and distinctly modified (flattened) distally. 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; eyes elliptical. In full-face view, frontal carinae straight or weakly convex; frontal lobes curved inward in front of antennal insertion. Anterior clypeal margin broadly and evenly convex; 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 moderately shining and shagreenate throughout; anterior mesosoma in profile broadly convex; erect pronotal setae short and often expanded distally, at times clavate; in profile, metanotal groove deep, V-shaped; propodeum shining, with multiple hair-like striolae; 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 at least twice its width from the 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 tapered with squared-off vertex; node shining and faintly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of thick, often distally flattened, erect setae over well-spaced, short, appressed setae. General characters. Colour of foreparts orange tan, gaster black.

Type Material
Holotype minor worker (middle ant) from Colyer Creek, 8 km N of Alice Springs 23°37'S, 133°52'E, Northern Territory, 25 January 1991, S. Shattuck #2180-7 [ANIC32-066657]. Paratypes: Major worker and minor worker on same pin with same details as holotype (ANIC); 3 minor workers from 27 km SE of Katherine, Northern Territory, 8 April 1978, P.J.M. Greenslade, (5) ; minor worker from Ethel Creek, Western Australia, 1993-4, P.A. Varris, ‘Melophorus sp. O’, 96 [JDM32-004549].

Etymology
Latin setosus (‘bristly’); adjective in the nominative singular.