Melophorus chauliodon

Existing label data for dry, pinned material is scanty, but a specimen from SA was taken in cane grass. Sequenced material has been collected from red clay soil, mulga woodland and from suburban lawns. This species is particularly common in and around the Perth metropolitan area, and can occur in highly built up locations. The phylogenetic position the species occupies and the nature of the mandible suggests it is largely or wholly granivorous. (Heterick et al. 2017)

Identification
Heterick et al. (2017) - Melophorus chauliodon 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 wheeleri species-complex because it agrees with the following apomorphies possessed by the complex: the minor worker often has more than five teeth, the largest major worker has a short, massive, elbowed mandible directed posteriad; in profile, the maxillary palps are short in the major and generally short in minor workers (in the minor worker, usually only attaining the neck sclerite at their maximum extent when the head is moderately inclined) and, in full-face view, the anterior margin of the clypeus in the large major worker is usually planar or weakly concave (variable in other subcastes but planar or narrowly protuberant anterior clypeal margins predominate). Melophorus chauliodon major and media workers are readily identifiable by virtue of their having a variably offset tusk-like basal mandibular tooth. This feature is not found in any other Melophorus. The minor worker is less distinctive, but is glabrous, its eye is an elongated ellipse (length of eye ≥ 0.3 × length of side of head) and in full-face view it has a square head shape, and this combination of features sufficiently characterise it when compared with other members of the species-complex.

Melophorus chauliodon is a morphologically and genetically compact species. The major and media workers are easily identified by the large and often tusk-like basal tooth that is variably situated along the basal margin. In many WA populations this tooth is highly-developed and, at the rear of the gape, virtually occludes the gap between the mandible and the anterior margin of the clypeus. In eastern populations the tooth is situated more anteriorly along the apical margin of the mandible and is less strongly developed. Minor workers lack this anatomical feature but can be distinguished from similar species by a combination of their glabrous mesosoma, the straight anterior margin of the clypeus, the appearance of the head capsule and the elongate eye. The five-gene tree suggests that this species falls within the Melophorus fieldi complex; however the three-gene tree indicates otherwise, and places this species within the M. wheeleri species-complex, and this is likely to be the more correct placement in view of the morphology.

Distribution
Heterick et al. (2017) - Found in all mainland states except the ACT and Vic. The species is also absent from Tasmania.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  chauliodon. Melophorus chauliodon Heterick, Castalanelli & Shattuck, 2017: 338, fig. 79 (w.) AUSTRALIA.

Worker
(n = 8): CI 114–125; EI 14–32; EL 0.21–0.38; HL 0.57–2.22; HW 0.64–2.77; ML 0.85–2.34; MTL 0.58–1.49; PpH 0.10–0.26; PpL 0.34–0.90; SI 54–101; SL 0.65–1.51.

Minor. Head. Head square; posterior margin of head planar or weakly convex; frons shining with superficial shagreenation or microreticulation only, or matt or with weak sheen, microreticulate or microreticulate-shagreenate; frons consisting exclusively or almost exclusively of well-spaced, appressed setae only (small, erect setae, if present, usually confined to ocular triangle or posterior margin of head). 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 anteriad of midline of head capsule; eyes elliptical or slightly reniform, or elongate. In full-face view, frontal carinae straight or weakly convex; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin straight and retrousse anteromedially or weakly convex; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five to seven 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 shining and mainly smooth, vestigial shagreenation most noticeable on humeri and mesopleuron; anterior mesosoma in profile broadly convex; erect pronotal setae absent; in profile, metanotal groove shallow, indicated mainly by an angle; propodeum shining and shagreenate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about1:1; 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 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 throughout. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour variable, ranging from foreparts orange or orange tan with dark brown gaster to concolorous brownish-black.

Major. Head. Head horizontally rectangular, broader than wide; posterior margin of head 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 small (eye length less than 0.2 × length of head capsule); in full-face view, eyes set above midpoint of head capsule, or set at about 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 emarginate, or weakly crenulate at midpoint; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five mandibular teeth in major worker; mandibles strongly incurved, apical sector uniformly carinate and forming a bifurcate, horizontal ledge that terminates in the basal and pre-basal teeth; 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 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 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 tapered with sharp vertex, or 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 short, bristly, erect setae over well-spaced, short, appressed setae. General characters. Colour of foreparts brownish-orange to orange-brown, gaster dark brown to blackish-brown.

Type Material
Holotype minor worker (middle ant) from Sandringham Station 25.03S, 139.03E, 55 km NW of Bedourie, Queensland, 21 February 1980, S. R. Morton, S2, 4 [ANIC32-900189]. Paratypes: minor worker and major worker on same pin with same details as holotype (ANIC); 3 minor workers from 16 km W of Mt Aloysius 26.01S, 128.26E, Western Australia, 16 November 1977, J. E. Feehan, associated collector, T. A. Weir [ANIC32-900067] (ANIC); major worker from 80 km E of Emu, Victoria Desert, South Australia, 8 October 1976, P.J.M. Greenslade, (3) ; 3 media workers from Sturt National Park, New South Wales, 24 November 1979, P. J. M. Greenslade, (4), 37 ; major worker and media worker from 20 km W of Cameron Corner, South Australia, 25 November 1979, P.J.M. Greenslade, (1) ; major and minor worker and male from Lexia 31°36'48"S, 115°56'49"E, Western Australia, 9 October 2005, B.E. Heterick, Banksia open woodland, Adenanthos understorey, white quartz sand [JDM32-001877] ; 2 media workers and minor worker from Hope Valley 32°11'53"S, 115°50'14"E, Western Australia, 21 October 2007, B.E. Heterick, Banksia/Allocasuarina sandplain, grey over yellow sand [JDM32-001878] (WAM).

Etymology
Greek chaulios (‘outstanding’/’impressive’) plus odon (‘tooth’); noun in the nominative singular standing in apposition to the generic name.