Melophorus orthonotus 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 : 249-252

Melophorus orthonotus Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype media worker from 85 km E Meentheena OC 21°17'44"S, 121°15'50"E, Western Australia, 29 July 2003-11 October 2004, CALM Pilbara Survey, Site NE13, Ethylene glycol pitfalls [JDM32-004590] (WAM). Paratype: Major(?) worker from 23 km NE of Warrawagine Hstd 20°41'54"S, 120°51'23"E, Western Australia, 22 May 2006-21 August 2006, CALM Pilbara Survey, Site: PHYEO1: Ethylene glycol pitfalls [JDM32-004589] (ANIC).

Diagnosis.

Melophorus orthonotus can be placed in the M. biroi species-group on the basis of characters of the clypeus, mandible and palps. The elongate propodeum, however, is unique in the species-group and resembles more closely the typical form of the propodeum in the M. aeneovirens species-group (see below). The species is also placed in the M. 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. Uniquely among the Melophorus seen, where rare species are often only represented by minor workers, here it is the major and media worker of this species that are the sole representatives in the collections examined. Even so, the species cannot be confused with any other Melophorus . In profile, the major and media worker have a smooth, elongate propodeum, with the propodeal angle indicated only by a faint curve, the metanotal groove being a weak impression so that the mesonotal and propodeal outline is barely interrupted. The mesonotum and mesopleuron are not separated by any impression or suture, and the mesosternal outline is strongly convergent anteriad with the outline of mesonotum, similar to some ants in the M. aeneovirens species-group.

Media worker description.

Head. Head square; posterior margin of head weakly convex; 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 large (eye length ≥ 0.50 × length of side of head capsule); in profile, eye set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae distinctly concave; frontal lobes straight in front of 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 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 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, or erect pronotal setae absent; in profile, metanotal groove shallow, broadly V or U-shaped; propodeum shining and smooth or with superficial and almost invisible microsculpture; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae variable in number, may be 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 subcuboidal, vertex bluntly rounded; 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. General characters. Colour of foreparts orange tan to reddish brown, gaster brown to blackish-brown.

Major worker description.

Head. Head square; posterior margin of head planar or weakly convex; cuticle of frons matt or with weak sheen, microreticulate; 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 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 straight, divergent posteriad; frontal lobes straight in front of antennal insertion. Anterior clypeal margin straight; clypeal psammophore set at or above 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, indicated mainly by an angle and metathoracic spiracles; propodeum shining, with multiple hair like striolae; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae absent; appressed propodeal setae short, separated by more than own length and inconspicuous; 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 generally rounded with median indentation; node shining and faintly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae, erect setae (present in at least some workers) confined to margin of the sclerite. General characters. Colour of head orange tan, mesosoma and legs orange, gaster blackish-brown.

Measurements.

Worker (n = 1): CI 104; EI 22; EL 0.25; HL 1.11; HW 1.16; ML 1.80; MTL 0.97; PpH 0.13; PpL 0.85; SI 111; SL 1.28.

Comments.

This species is described from two specimens taken in the Pilbara region, WA. As with M. teretinotus , in the M. aeneovirens species-group, this member of the M. fieldi group has a very weak to vestigial metanotal groove, which distinguishes it from other species in its complex. No samples were available for sequencing. The known specimens were collected in ethylene glycol pitfall traps, but no other information is available.

Etymology.

Compound of Greek: othos ( ‘straight’) plus notus (Neo-Latin ‘back’); adjective in the nominative case.