Melophorus hexidens 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 : 298-300

Melophorus hexidens Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) from Fowlers Gap, New South Wales, 18 November 1979, P.J. M. Greenslade, (9) [ANIC32-066603] (ANIC). Paratype: minor worker on same pin and with same details as holotype (ANIC); 3 minor workers from Lake Mere, 40 km NNW of Louth, New South Wales, 7 June 1986, P.J. M. Greenslade, (3), LM (ANIC); 3 minor workers from Cobbadah, 30°08'S, 150°46'E, NSW, March 2009, I. Oliver, Pitfall MEROO, 94T, ' Melophorus wheeleri ' (MCZ); 3 minor workers from Cobbadah, 30°08'S, 150°46'E, NSW, March 2009, I. Oliver, Pitfall MEROO, 96, ' Melophorus wheeleri ' (BMNH).

Diagnosis.

Melophorus hexidens 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. 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 hexidens resembles common members of the M. fieldi species-complex in that it has an evenly protuberant clypeus and a psammophore that is set at the midpoint of the clypeus. However, it differs from such species in having six mandibular teeth and short maxillary palps that barely reach the neck sclerite. These features serve to distinguish M. hexidens from all other Melophorus of similar appearance. The major worker is unknown.

Minor worker description.

Head. Head square; posterior margin of head planar or weakly convex; frons 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 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 distinctly concave; frontal lobes curved toward antennal insertion. Anteromedial clypeal margin broadly and evenly convex; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Mandibular teeth in minor worker six; mandibles triangular, weakly incurved; third mandibular tooth distinctly shorter than apical tooth, but equivalent in length to remaining teeth; masticatory margin of mandibles approximately vertical or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron moderately shining and shagreenate throughout; anterior mesosoma in profile broadly convex; 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 microreticulate; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae always absent; appressed propodeal setulae sparse or absent, if present then not regularly spaced; 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 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, erect and semi-erect setae interspersed with regularly placed appressed setae. General characters. Colour of foreparts orange tan, gaster brown.

Measurements.

Worker (n = 2): CI 106-108; EI 23-26; EL 0.24-0.25; HL 0.88-0.98; HW0.93-1.06; ML 1.21-1.29; MTL 0.75-0.81; PpH 0.13-0.16; PpL 0.50-0.54; SI 90-96; SL 0.89-0.96

Comments.

This species is known from four pins of minor workers collected at Fowler’s Gap, Lake Mere (presumably the Research Station near the lake) and Cobbadah, respectively, all sites being in NSW. These workers are very similar in general morphology to M. turneri , but differ in the number of mandibular teeth (six rather than five) and their short palps. They also resemble the (probably closely related) M. purpureus , but differ in the appearance of the clypeus and in the biogeography. The Cobbadah specimens were collected in pitfall traps. Nothing more is known of the species.

Etymology.

Compound of ancient Greek hex ( ‘six’) and Latin dens ( ‘tooth’); adjective in the nominative singular.