Melophorus parvimolaris 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 : 304-307

Melophorus parvimolaris Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (top ant) from Mt Bruce 23°35'42"S, 118°11'43"E, Western Australia, September 1991, S. van Leeuwen, Fire/Mulga research 3-1a [JDM32-004558] (WAM). Paratypes: Minor worker on same pin and with same details as holotype (WAM); major worker from Tanami, Northern territory, 17-21 April 1986, P.J. M. Greenslade, 11) [ANIC32-900134] (ANIC); 3 minor workers from 11 km N of Tennant Creek 19°32'S, 134°13'E, Northern Territory, 11 October 1981, D. Davidson/ S. Morton, 149C (MCZ).

Other material examined.

Northern Territory: Tanami (Greenslade, P.J. M. ). Western Australia: 2 km SW Marda Pool (CALM Pilbara Survey [JDM32-004557]), 3.9 km N Kumarina (Heterick, B.E. [M173/M174]), 5 km N Kumarina (Heterick, B.E. [M283]), Yoothepina [Yoothapina] (Hides, D. [JDM32-001822]).

Diagnosis.

Melophorus parvimolaris 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 clypeus of M. parvimolaris is distinctly folded back towards the mandible and the clypeal psammophore is placed on a ledge in the minor worker, the head, mesosoma and gaster have relatively long, whitish, appressed setae that overlap and form a weak pubescence on the gaster and the ant has a distinct microreticulate or shagreenate sculpture and is matt or has a weak sheen. The minor worker has five mandibular teeth and the HW of the major worker is quite small (HW ≈ 1.45 mm). These characters serve to differentiate M. parvimolaris from all other Melophorus except M. xouthos . However, M. parvimolaris is uniformly brown, whereas M. xouthos is tawny orange-and-black.

Minor worker description.

Head. Head square or rectangular, tending to trapezoid; posterior margin of head weakly convex; frons matt or with weak sheen, 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; roughly ovoid, eye narrowed posteriad. In full-face view, frontal carinae distinctly concave; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin straight; 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 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; erect pronotal setae absent; in profile, metanotal groove shallow, indicated mainly by an angle; propodeum matt or with a weak sheen and microreticulate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae always absent; appressed propodeal setulae long, each reaching setae behind and in front, but not forming pubescence; 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 tapered with blunt vertex; node shining and distinctly microreticulate, or matt and microreticulate. Gaster. Gaster weakly shining with indistinct shagreenation; pilosity of first gastral tergite consisting of well-spaced, long, whitish, appressed setae only, erect setae always absent. General characters. Colour concolorous chocolate.

Major worker description.

Head. Head horizontally rectangular, broader than wide; posterior margin of head planar or weakly concave; cuticle of frons matt or with weak sheen, indistinctly shagreenate; frons consisting mainly of appressed and stout erect setae, the latter bristly in appearance and distinctly modified (flattened) distally. 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 broadly emarginate; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Four mandibular teeth in major worker-5; mandibles strongly incurved, apical sector weakly carinate or incompletely carinate; third mandibular tooth distinctly shorter than apical tooth, but equivalent in length to remaining teeth; masticatory margin of mandibles approximately aligned vertically or weakly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron matt or with weak sheen and microreticulate throughout; anterior mesosoma in profile broadly convex; erect pronotal setae absent; in profile, metanotal groove shallow, indicated mainly by an angle and metathoracic spiracles; propodeum matt or with a weak sheen and microreticulate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity between 1:1 and 1:2; erect propodeal setae variable in number, may be absent; appressed propodeal setae long and closely aligned, creating pubescence; propodeal spiracle situated on or beside 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 blunt vertex; node matt, shagreenate. Gaster. Gaster weakly shining with indistinct shagreenation; pilosity of first gastral tergite consisting of thick, often distally flattened, erect setae over well-spaced, short, appressed setae. General characters. Colour concolorous blackish-brown.

Measurements.

Worker (n = 6): CI 109-123; EI 17-30; EL 0.20-0.27; HL 0.61-1.23; HW 0.67-1.52; ML 0.87-1.38; MTL 0.55-0.91; PpH 0.09-0.16; PpL 0.32-0.57; SI 59-101; SL 0.68-0.89.

Comments.

This small, dull brown member of the M. laticeps species-group can be recognized by features of the clypeus, the presence of long, whitish, appressed setae on the body and gaster, and its mostly matt, shagreenate or microreticulate cuticle. Melophorus xouthos shares these features, but is bicoloured tawny orange-and-black and has legs with a bluish, iridescent sheen. Thus far M. parvimolaris has only been collected in arid and semi-arid regions in the NT and WA, but it probably also occurs in SA in areas of suitable habitat. Sequencing data on a five-gene tree suggests a sister relationship with M. caeruleoviolaceus , but this cannot be not assumed (see comments under the latter species). The ant is likely to be wholly or largely granivorous: on two separate occasions just north of Kumarina, WA, the principal author saw minor workers collecting small, wind-blown seeds.

Etymology.

Latin parvus ( ‘small’) plus molaris ('adapted for grinding’, 'molar tooth’); adjective in the nominative singular.