Melophorus argus Heterick, Castalanelli & Shattuck

Heterick, Brian E., Castalanelli, Mark & Shattuck, Steve O., 2017, Revision of the ant genus Melophorus (Hymenoptera, Formicidae), ZooKeys 700, pp. 1-420 : 145-147

Melophorus argus Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (top ant) from Kapalga, Alligator Rivers area, Northern Territory, 7-9 September 1983, P.J. M. Greenslade, 8 i traps, [ANIC32-066597] (ANIC). Paratypes: minor worker on same pin and with same details as holotype (ANIC); two minor workers from Kapalga, Alligator Rivers area, Northern Territory, 7-9 September 1983, P.J. M. Greenslade, 8 ii traps, (13), (MCZ).

Diagnosis.

Melophorus argus can be placed in the M. biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is also 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]). The minor worker of Melophorus argus (the major worker is unknown) can be recognised by a combination of a promently scalloped mesopleuron, a thickish, dorsall rounded petiolar node and a glabrous mesosoma that is bimodal when viewed in profile.

Minor worker description.

Head. Head approximately oval with straight sides; posterior margin of head strongly convex; frons shining and smooth except for piliferous pits; 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. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes curved toward antennal insertion. Anteromedial clypeal margin broadly and evenly convex, or narrowly protrusive anteromedially, the protrusion with a square border; 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 shining and smooth on dorsum, entire lower mesopleuron distinctly striolate-microreticulate; anterior mesosoma in profile pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; erect pronotal setae absent; in profile, metanotal groove deep, ‘V’ -shaped; propodeum shining, with multiple hair like striolae; 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 shorter (length <0.50 × height of propodeum). Petiole. In profile, petiolar node broadly squamiform, almost a tubercle; 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 short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour concolorous brown.

Measurements.

Worker (n = 2): CI 87-90; EI 29-32; EL 0.12-0.11; HL 0.42-0.43; HW 0.36-0.39; ML 0.54-0.58; MTL 0.26-0.27; PpH 0.07-0.08; PpL 0.21-0.21; SI 113-116; SL0.37-0.44.

Comments.

This small, northern species is definitely known from the minor worker only, but the principal author of this paper has noted that a possible TERC major worker is similar to that of M. biroi . Only two pins, one of two workers from Kapalga, NT and one without any label data, were available for analysis. However, additional material for this species from the NT (Kakadu NP; Howard Springs; Wildman Riv.; Berry Springs; Brydle Hill) and also the Kimberley, WA (4 km W King Cascade) was briefly noted in the TERC Collection. Melophorus argus is recognizable by its completely glabrous appearance and its bimodal mesosomal profile. The Kakadu specimens were pitfall trapped by Greenslade, but nothing more is known of this ant.

Etymology.

Latinized Greek argus (Greek argos ‘shining’); participle in the nominative singular.