Melophorus sericothrix

One mention of ‘mallee woodland’ is the only ecological note, but specimens from southwestern Australia collected at Worsley and Boddington would have come from the tall sclerophyll woodland found in these localities. As with most other Melophorus the habits of this ant are unstudied. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus sericothrix 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. Melophorus sericothrix possesses several characters which, taken, together, combine to define the species adequately: in profile, the head of the minor worker is weakly to moderately dorsoventrally compressed, also, when seen in profile, the eye is set above the midpoint of the gena, the clypeal psammophore of the major worker is set at around the midpoint of the clypeus to halfway between midpoint and anterior margin, and that of media and minor workers from below the midpoint to just above the anterior margin. The head, body and legs of the minor worker are strongly pubescent, all worker subcastes having many short, unmodified, prickly, erect setae on the head and body with a couple to a moderate number of such setae also distributed along the antennal scapes. However, these setae are mainly or wholly absent from the tibiae. The propodeum has an obliquely declivitous face. Small members of the Melophorus mjobergi clade which have many unmodified erect setae may be confused with this species, but major workers of Melophorus compactus, Melophorus mjobergi and Melophorus postlei have only one preapical metatibial spine, and the head of the major worker of M. sericothrix is very typically that of the M. fieldi complex members and not at all like the head of the major worker of M. compactus, M. mjobergi or M. postlei.

This hirsute member of the genus is identifiable by the combination of many mostly short, erect, unmodified setae on the body and antennal scapes but absent from the legs, the placement of the clypeal psammophore and the presence of more than one preapical spur on the metatibiae. Sequencing of old material has been unsuccessful, but the ant is here presumed to belong to the M. fieldi complex despite its superficial resemblance to several members of the M. mjobergi complex.

Distribution
Heterick et al. (2017) - Populations of the ant are known from southwestern Australia and southeastern SA, but it probably also occurs in suitable habitat in northern Victoria and southwestern NSW.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  sericothrix. Melophorus sericothrix Heterick, Castalanelli & Shattuck, 2017: 298, fig. 69 (w.) AUSTRALIA.

Worker
(n = 8): CI 87–120; EI 18–33; EL 0.17–0.26; HL 0.58–1.20; HW 0.50–1.44; ML 0.80–1.66; MTL 0.51–1.00; PpH 0.07–0.16; PpL 0.30–0.68; S 84–149I; SL 0.75–1.22.

Minor. Head. Head rectangular; posterior margin of head planar or weakly convex; frons matt or with weak sheen, microreticulate or microreticulate-shagreenate; frons consisting of appressed pubescence, with many short, unmodified, erect setae. 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 broadly and evenly convex; 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 matt with indistinct shagreenate sculpture throughout; anterior mesosoma in profile weakly elevated anteriad, thereafter gently sinuate, pronotum and mesonotum on same plane; appearance of erect pronotal setae short, (i.e., longest erect setae shorter than length of eye) and unmodified; in profile, metanotal groove a narrow but deep slit; propodeum matt or with a weak sheen and indistinctly shagreenate; propodeum smoothly rounded or with indistinct angle, or angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about 1:1, or not applicable, propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (greater than 12); 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 uniformly rounded; node matt and 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. General characters. Colour concolorous smoky, dark greyish-brown to black or variegated blackish-brown and tan.

Major. Head. Head square; posterior margin of head planar or weakly concave; cuticle of frons striolate anteriad, smooth and shining posteriad; 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 concave; frontal lobes straight in front of antennal insertion. Anterior clypeal margin broadly and evenly convex; clypeal psammophore set below 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, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum matt or with weak sheen and microreticulate-striolate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 1:1 and1:2; erect propodeal setae present and abundant (at least a dozen); 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; node shining and faintly shagreenate-microreticulate. Gaster. Gaster weakly shining with indistinct shagreenation; pilosity of first gastral tergite consisting of a mixture of curved, erect and semi- erect setae and decumbent setae that form a variable pubescence. General characters. Colour of foreparts orange to dark tan, gaster dark brown.

Type Material
Holotype minor worker (bottom ant) from Brookfield Conservation Park 34°19'S, 139°29'E, South Australia, 29 October 1991, S. Shattuck #2506.3 [ANIC32-900174]. Paratypes: 2 minor workers on same pin and with same details as holotype (ANIC); 3 major workers from Brookfield Conservation Park 34°19'S, 139°29'E, South Australia, 29 October 1991, S. Shattuck #2507.3 [ANIC32-900103] (ANIC); 2 minor workers from Worsley 32°23'S, 115°56'E, Western Australia, February 2014, G. Orabi, WP92, litter [JDM32-001557] ; 3 minor workers, a media worker and 3 major workers from 9 miles E of Newdegate, Western Australia, 4 October 1947, T. Greaves, ‘Melophorus’ ; 3 major workers, ‘Grs(?), Brookfield, 198h 5(?)’ [South Australia], 128 ; minor and media worker from Eneabba-Leeman Road 29°52.26'S, 115°05.45'E, Western Australia, April 2004, R. Dunn, pitfall trap (L57), 1.5m shrubland, white sand on limestone, ‘ID: Melophorus mjobergi Forel det. by: B.E. Heterick [sic], Date: 14 Nov. 2004’, ‘Checked against syntype specimen’ [Note: this identification is now determined to be incorrect, despite the very similar appearance of the minor worker of these two species-BEH] [JDM32-001559] ; 2 minor workers from 2 km S of Worsley 32°24'S, 115°56'E, Western Australia, 11 February 2004, G. Orabi, WP (West Pit) 92, hand-collected, litter [JDM32-001558] (WAM).

Etymology
Compound of Latin sericus (‘silky’) plus Greek thrix (‘hair’).