Melophorus chrysus

Several ANIC specimens have been collected in mallee and this may be the usual habitat for the ant, but it has also been collected in marri forest just south of Perth, WA, and from a dune in SA. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus chrysis is a member of the Melophorus anderseni species-group (maxillary palp segments short [not reaching neck sclerite], narrow and terminating in a subulate [awl-shaped segment]; PF 6,4; metatibial apical spur absent; in full-face view, masticatory margin of mandible strongly oblique with four teeth in known major workers [except chrysus], and four to six teeth in minor worker). This species is distinguished from others in the group by having, in profile, the petiolar node thickly squamiform in the minor worker, the major worker smooth and glossy in appearance, and also by having, in profile, the pronotum smoothly rounded and inclined at angle > 30°, and, in profile, the clypeus evenly convex or more strongly convex posteriorly, but not bulbous. The “pillipes” condition (whorls of fine, erect setae on appendages) occurs in some populations.

Most populations are glabrous, but several exhibit the very hairy ‘pillipes’ condition. This species is treated as a member of the anderseni group. All four taxa possess short palps with an acuminate final segment, and the metatibial apical spur is absent. The close relationship of Melophorus chrysus to members of the Melophorus fieldi complex is rendered more likely because it exhibits the ‘pillipes’ condition, otherwise seen only in ants belonging to that complex. The morphology is also similar.

Distribution
This species is rarely seen but has been collected in all Australian mainland states except NSW.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  chrysus. Melophorus chrysus Heterick, Castalanelli & Shattuck, 2017: 152, fig. 28 (w.) AUSTRALIA.

Worker
(n = 6): CI 101–117; EI 22–32; EL 0.18–0.25; HL 0.56–0.96; HW 0.57–1.12; ML 0.81–1.32; MTL 0.56–0.80; PpH 0.09–0.11; PpL 0.36–0.58; SI 76–116; SL 0.66–0.85.

Minor. Head. Head square; posterior margin of head weakly convex; frons shining with superficial shagreenation or microreticulation only; pilosity of frons a mixture of short, erect and semi-erect setae interspersed with shorter decumbent setae and well-spaced, short, appressed setae. Eye moderate (eye length 0.20–0.49 length of side of head capsule); in full-face view, eyes set at about midpoint of head capsule; in profile, eye set around midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes curved toward antennal insertion. Anteromedial clypeal margin broadly and evenly convex; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five mandibular teeth in minor worker; mandibles narrow, strap-like, internal and external margins parallel or nearly so; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles strongly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron shining and mainly smooth, vestigial shagreenation most noticeable on humeri and mesopleuron; 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, indicated mainly by an angle; propodeum shining and smooth or with superficial and almost invisible microsculpture; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae variable in number, may be absent; appressed propodeal setulae sparse or absent, if present then not regularly spaced; 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 smooth throughout. Gaster. Gaster smooth and glossy; pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly placed appressed setae, or consisting wholly or mainly of long, curved setae, appressed setae apparently absent. General characters. Colour light yellow to gamboge yellow.

Major. Head. Head horizontally rectangular, broader than wide; posterior margin of head planar or weakly concave; cuticle of frons shining and smooth except for piliferous pits; 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, midpoint of head capsule; in profile, eye set anteriad of midline of head capsule; eyes elliptical. In full-face view, frontal carinae distinctly concave; frontal lobes curved toward antennal insertion. Anterior clypeal margin broadly convex with anteromedial dimple; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five mandibular teeth in major worker; mandibles narrow, strap-like, internal and external borders parallel or nearly so; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles strongly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron shining and mainly smooth, vestigial shagreenation most noticeable on humeri and mesopleuron; 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 shining and generally smooth, with only weak indistinct shagreenation; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (at least a dozen); appressed propodeal setae sparse or absent, if present then not regularly spaced; 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 tapered with blunt vertex; node shining and smooth with vestigial microreticulation anteriad. Gaster. Gaster weakly shining with indistinct shagreenation; pilosity of first gastral tergite consisting mainly of well-spaced short, semi-erect and decumbent setae. General characters. Colour gamboge yellow.

Type Material
Holotype minor worker from Wungong Catchment 32°16'40"S, 116°08'12"E, Western Australia, 6-13 February 2009, D. Kabay, Water Corporation thinning: thinning plot dieback tree upland jarrah forest, 2A, 3Y [JDM32-004655]. Paratypes: Major worker and 2 minor workers from Streaky Bay, South Australia, 3 October 1957, B.B Lowery, mallee scrub, [folded paper label] ‘Melophorus, Streaky Bay: SA 450 m[iles] W of Adelaide, mallee scrub, sandy nest in [sic] among galleries of Melophorus laticeps Wh. 3.10.57 B.B. Lowery’ [ANIC32-900127] ; minor worker from Cambrai, South Australia, 1-4 February 1972, P.J.M. Greenslade, dune Ib (SAM); 2 minor workers from Mount Bruce 22°37'32"S, 118°17'05"E, September 1991, S van Leeuwen, Fire/Mulga Research 1-2a [JDM32-004804] (WAM).

Etymology
Chrysus (Greek) was the spirit of gold; noun in the nominative singular standing in apposition to the generic name.