Melophorus castanopus

Identification
Heterick et al. (2017) - Melophorus castanopus can be placed in the Melophorus biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is placed in the M. biroi species-complex on the basis of a further suite of characters (viz, metatibia of major worker with only one preapical spur [except rarely in the mjobergi clade]; clypeal psammophore placed anteriorly at or just above anterior margin of clypeus in the minor worker and often in the major worker; head dorsoventrally compressed to varying degrees in the minor worker of most species with the eyes placed high on the sides; compact legs, and small body size [[(excluding mjobergi clade) HW of smallest minor 0.36 mm, average HW of smallest minors 0.46 mm; HW of largest known major 1.29 mm, average HW of largest majors (where known) 1.05 mm]). Melophorus castanopus can be most easily confused with M. biroi but the appearance of the major and minor workers, seen in profile, is slightly more flattened than the corresponding major and minor workers of the latter species, and the minor worker has erect setae on first gastral tergite, including a line of marginal setae. The minor worker mesosoma also possesses a couple to a few, usually stout erect setae (several specimens may need to be seen because of abrasion). Such setae are abundant and modified in a few isolated populations.

The ant is very similar to Melophorus biroi, but minor workers rarely have a glabrous mesosoma, unlike M. biroi, and they always have erect setae on the margin of the first gastral tergite (lacking in M. biroi minor workers). Major workers are more difficult to distinguish, but majors for M. castanopus have a gently convex pronotum (mostly flattened in M. biroi major workers). The genetics of the species are unknown as old wet material from SAMA did not produce a signal.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  castanopus. Melophorus castanopus Heterick, Castalanelli & Shattuck, 2017: 168, fig. 32 (w.q.) AUSTRALIA.

Worker
(n = 8): CI 93–116; EI 20–29; EL 0.14–0.25; HL 0.51–0.11; HW 0.47–1.29; ML 0.69–1.50; MTL 0.36–0.77; PpH 0.07–0.16; PpL 0.28–0.67; SI 75–124; SL 0.58–0.96.

Minor. Head. Head square; posterior margin of head planar or weakly convex; 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 moderate (eye length 0.20–0.49 length of side of head capsule); in full-face view, eye set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight or weakly convex; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin broadly and evenly convex; 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 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 shagreenate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about 1:1; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle situated on or beside declivitous face of propodeum, and longer (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 distinctly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting mainly of short, appressed setae, together with a few erect and semi-erect setae. General characters. Colour of most populations concolorous light to dark brown, a few populations with orange foreparts and dark brown gasters.

Major. Head. Head square; posterior margin of head planar or weakly concave; cuticle of frons shining and smooth except for piliferous pits and a few striolae around antennal insertions and Frontal carinae; 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; eyes elliptical. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes straight in front of antennal insertion. Anterior clypeal margin broadly and evenly convex; clypeal psammophore set at or just above anterior clypeal margin; 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 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; erect pronotal setae short and unmodified, or weakly expanded distally; in profile, metanotal groove shallow, indicated mainly by an angle and metathoracic spiracles; propodeum matt or with a weak sheen and microreticulate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 1:1 and 1:2; erect propodeal setae present and sparse to moderate (1-12); appressed propodeal setae short, separated by more than own length and inconspicuous; 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 distinctly microreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae. General characters. Colour brownish-orange with brown gaster to concolorous chocolate.

Type Material
Minor worker (middle ant) from 4 km S of Auburn, South Australia, 14 February 1974, P.J.M. Greenslade [ANIC32-900113]. Paratypes: 2 minor workers on same pine and with same details as holotype (ANIC); major, media and minor worker from Bridgewater, South Australia, 23 September 1972, P.J.M. Greenslade (ANIC); major worker from Belair, South Australia, 20-23 December 1971, P.J.M. Greenslade, traps-7 (ANIC); 2 major and a minor worker from Calca, South Australia, 26 September 1957, B.B. Lowery, mallee scrub, ANIC Ants Vial 22.188 ; 3 minor workers from Harveys Return, Kangaroo Island, South Australia, 15 January 1973, P.J.M. Greenslade, (5) (MCZ); 3 major workers from Morialta Reserve, Lofty Ranges, South Australia, 8 September 1957, B.B. Lowery, 1000ft, dry sclerophyll, ANIC Ants Vial 22.197 [ANIC32-900114] ; major worker and dealate queen from Belair, South Australia, March 1971, P.J.M. Greenslade, Traps 1217 [ANIC32-900176].

Etymology
Greek kastanos (‘chestnut-tree’; hence the colour) plus pous (‘foot’); adjective in the nominative singular.