Melophorus tenuis 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 : 117-119

Melophorus tenuis Heterick, Castalanelli & Shattuck sp. n.

Type.

Holotype minor worker from 1.3 km NE of Morgan River, 15°08'10"S, 126°09'09"E, Western Australia, 20 August 2012, A. Cross; 345m elevation, ethylene glycol pitfall, open savannah [sic] woodland over sandy soil; sp. C [ANIC32-900210] (WAM).

Diagnosis.

Melophorus tenuis is a member of the M. aeneovirens species-group (in full-face view, the anterior clypeal margin convex, apron-like and covering whole or part of the retracted mandible, except in M. nemophilus , the medial clypeal sector often produced so that it is protrusive when seen in profile; the psammophore frequently with coarse and well-separated ammochaetae, these always placed on or just above anterior margin; in profile, the propodeum elongate and oblique or broadly rounded), and the M. aeneovirens species-complex (in full-face view, psammophore ranged along or just above anterior margin of clypeus and following the curve of the margin; anterior margin of clypeus broadly medially produced, and often with central notch that may be deeply impressed, but is never acuminate at its midpoint; metatibia with maximum of two rows of preapical spines). In M. tenuis the tibiae possess stout, socketed, appressed to subdecumbent setae only, with fine, appressed pubescence lacking. In profile, the mesosoma of the minor worker tends to linear in orientation, its dorsal outline straight or describing a weak arc (the mesosternal outline and the dorsum of the mesonotum being weakly convergent to subparallel anteriorly). Only the minor worker of Melophorus tenuis is known. This species can be distinguished from all others in its species-complex its dorsoventrally flattened head, its long maxillary palps (short in the superficially similar M. platyceps ) and its weakly sinuous mesosomal outline when seen in profile.

Minor worker description.

Head. Head approximately oval, sides of head divergent towards mandibular insertions; posterior margin of head extended posteriad as a convex, sloping surface with a slight medioccipital protuberance; cuticle of frons with weak sheen, finely shagreenate; in single specimen pilosity of frons consisting exclusively of well-spaced, appressed setae only. 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, eyes set around midline of head capsule; eye shape elliptical. Antennal carinae straight in full-face view; antennal lobes curved toward 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 minor worker; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth and teeth numbers two and four; masticatory margin of mandibles ap proximately vertical or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron moderately shining and shagreenate throughout; anterior mesosoma in profile flattened, promesonotum on same plane as propodeum; erect pronotal setae absent; in profile, metanotal groove shallow, indicated mainly by an angle; propodeum shining and shagreenate; propodeum elongate, smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and completely inconspicuous; propodeal spiracle situated at least twice its width from the declivitous face of propodeum, and shorter (length <0.50 × height of propodeum). Petiole. In profile, petiolar node subcuboidal, its vertex bluntly rounded; in full-face view, shape of petiolar node uniformly rounded; node shining and faintly shagreenate. 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 uniformly dark olive-brown.

Measurements.

Worker (n = 1): CI 82; EI 30; EL 0.25; HL 0.99; HW 0.82; ML 1.72; MTL 1.18; PpH 0.16; PpL 0.67; SI 168

Comments.

Melophorus tenuis has an appearance somewhat reminiscent of Melophorus attenuipes and Melophorus mullewaensis , but, although it is likely closely related to these taxa, it can be distinguished from them by the much flattened head and the appearance of the femur and clypeus. This ant has been collected from a number of sites in the far north of Australia, but only one minor worker was available for this project. TERC material from WA has been collected from King Edward River, Bachesten Creek, Purnululu NP, Parry Lagoon and the Mitchell Plateau. TERC also holds specimens from Bradshaw Stn, Barunga, Nitmuluk NP, Bullo Gorge and Kakadu in the NT.

Pitfall-trapped specimens collected by Adam Cross in Doongan and Theda Stations in the Kimberley were found in four study plots on shallow, sandstone-derived soils overlying Pentecost sandstone. The vegetation was open savannah woodland dominated by Eucalyptus tetradonta and E. miniata over shrubs and low annual grasses. Three of the four plots were near the Morgan River, and the fourth was on Noongallah Creek (A. Cross, pers. comm.). The holotype is one of the Morgan River specimens from that project.

Etymology.

Latin ( ‘thin’, ‘slender’); adjective in the nominative singular.