Melophorus prominens 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 : 311-313

Melophorus prominens Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) Coolawanyah Station, Western Australia, 1953, K.C. Buller, ANIC ANTS VIAL 27.89 [ANIC32-900142] (ANIC). Paratypes: 2 major workers on the same pin and with the same details as the holotype (ANIC); 2 major workers and media worker from 28 miles SE of Roebourne, Western Australia, 21 April 1963, McInnes & Dowse, Central & NW Aust. 1963, Series A276 (ANIC); 2 major workers and minor worker from 18 miles ESE of Roebourne, Western Australia, 20 April 1963, McInnes & Dowse, 29170, Central & N.W. Aust. 1963, Series A273 (BMNH); 2 major workers from 15 miles S of Roebourne, Western Australia, 24 June 1967, G. Campbell, on grass flats carrying grass seeds (MCZ); 2 minor workers from 6 km N of Yalgoo, 19 March 1987, B. Heterick, 168, 8MelBH28 [JDM32-001868] (WAM).

Diagnosis.

Melophorus prominens 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). The broadly angulate projection of the clypeus in major and media workers automatically identifies them as belonging to this species. The minor worker is less distinctive, but is large (HW nearly 1 mm), has a convex, protrusive clypeus with a stout psammophore near the anterior margin, a minutely striate mandible and six or more teeth on the masticatory margin. These features separate it from numerous, smaller minor workers in the same species-complex. The M. prominens minor worker is most easily confused with the minor worker of M. wheeleri but is quite hairy and has erect setae on the mesosoma, including more than a dozen on the propodeum.

Minor worker description.

Head. Head rectangular; posterior margin of head weakly concave; frons matt or with weak sheen, shagreenate; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with 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, eye set anteriad of midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight or weakly convex; frontal lobes curved inward in front of antennal insertion. Anteromedial clypeal margin broadly and evenly convex and protrusive; clypeal psammophore set at or just above anterior clypeal margin; palp formula 3,4. Mandibular teeth in minor worker six to nine; mandibles triangular, weakly incurved; third mandibular tooth may be separated from tooth no. 3 and tooth no. 4 by one or more intercalary teeth, size appears to vary; masticatory margin of mandibles approximately vertical or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron with weak to moderate sheen, shagreenate on pronotum and dorsum of mesonotum, otherwise microreticulate; anterior mesosoma in profile weakly elevated anteriad, thereafter gently sinuate, pronotum and mesonotum on same plane; appearance of erect pronotal setae long (i.e., longest erect setae longer than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V or U-shaped; propodeum shining and microreticulate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (greater than 12); appressed propodeal setulae long and separated by at least own length; 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, or tapered with blunt vertex; node shining and distinctly microreticulate. 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 concolorous chocolate.

Major worker description.

Head. Head quadrate (i.e., heart-shaped); posterior margin of head weakly concave; cuticle of frons shining with superficial shagreenation or microreticulation only; 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; in profile, eye set anteriad of midline of head capsule; eyes elliptical. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes curved inward in front of antennal insertion. Anterior clypeal margin convex, acuminate anteromedially, with anteromedial projection protruding at angle of 90° to clypeus; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Mandibular teeth in major worker effectively 3, basal tooth reduced to angle only; mandibles strongly incurved, apical sector weakly carinate or incompletely carinate; third mandibular tooth larger than tooth no.2 (basal tooth represented by an angle or small denticle); masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron shining with very superficial microreticulation, entire lower mesopleuron distinctly shagreenate; anterior mesosoma in profile broadly convex; erect pronotal setae long (i.e., longer than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and microreticulate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about 4:3; erect propodeal setae present and abundant (at least a dozen); appressed propodeal setae long, each reaching setae behind and in front, but not forming pubescence; propodeal spiracle situated at least twice its width from the 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 median indentation; node shining and faintly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae. General characters. Colour concolorous dark chocolate.

Measurements.

Worker (n = 4): CI 108-125; EI 13-25; EL 0.24-0.47; HL 0.91-2.81; HW 0.98-3.52; ML 1.22-2.70; MTL 0.90-2.04; PpH 0.13-0.38; PpL 0.46-1.11; SI 50-91; SL 0.89-1.76.

Comments.

The Melophorus prominens major worker is rendered distinctive by an anteromedian clypeal prominence that is directed outwards at a 90° angle to the clypeus. The minor worker lacks this feature and is more difficult to identify; however, it has a convex anterior clypeal margin and is relatively hairy, enabling it to be distinguished from similar minor workers in the M. wheeleri cluster. All definitive collections of this ant have been taken in the mid-west or Pilbara regions of WA, but a pin of material taken from 30 km S of Strathburn Qld (TERC) may also belong to this species. No specimens of this ant have been sequenced and label records provide no additional data, but the species is likely to be granivorous, based on its undoubted affinities with M. wheeleri .

Etymology.

Latin prominens ( ‘projection’); participle in the nominative singular.