Melophorus majeri Agosti

Heterick, Brian E., Castalanelli, Mark & Shattuck, Steve O., 2017, Revision of the ant genus Melophorus (Hymenoptera, Formicidae), ZooKeys 700, pp. 1-420 : 342-344

Melophorus majeri Agosti

Melophorus majeri Agosti 1997: 166, figs 6-9.

Types. Holotype minor and paratype major workers Hassel Road, Jerramungup, Western Australia [AMNH, ANIC, CASC] (examined: ANIC holotype (second ant on pin of three workers) and paratypes CASENT0172019, CASENT017020, AntWeb images of AMNH (CASENT0104674) and CASC (CASENT0173922, CASENT0173922) specimens). The AntWeb Automontage image for the holotype erroneously depicts a paratype major worker from the same pin as the holotype. specimens, Note. Syntype label also erroneously displayed for CASENT0104674 (paratype).

Other material examined.

Western Australia: Eneabba-Leeman Rd. (Dunn, R. [JDM32-001553]), Mettler Lake Rd. (15 km SW of Wellstead) (Heterick, B.E. [JDM32-001552]).

Diagnosis.

The armed propodeum in all worker sub-castes, the flattened and laterally carinate pronotum and mesonotum in the minor worker, the raised antennal lobes, and the absence of a metatibial apical spur distinguish Melophorus majeri from all other Melophorus and cause it to be placed in its own, unique species-group.

Minor worker description.

Head. Head elongate, truncate posteriad; posterior margin of head planar to strongly 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 small (eye length less than 0.2 × length of side of head capsule); in full-face view, eyes set above midpoint of head capsule; in profile, eye set around midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight or weakly convex; frontal lobes straight, elevated. Anteromedial clypeal margin narrowly convex and protruding, clypeal margin entire or very weakly indented; clypeal psammophore set at or just above anterior clypeal margin; palp formula 6,4. Five to six 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 matt or with weak sheen and microreticulate throughout; anterior mesosoma in profile gently undulate, dorsal and lateral surfaces separated by carinae; erect pronotal setae absent; in profile, metanotal groove a weak or vestigial furrow; propodeum matt or with a weak sheen and microreticulate; propodeum distinctly angulate, propodeal angles produced as short, erect denticles; length ratio of propodeal dorsum to its declivity about 3:2; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle situated at least twice its width from the declivitous face of propodeum, and longer (length ≥ 0.50 × height of propodeum). Petiole. In profile, petiolar node trapezoidal with sharply defined flange posteriad; in full-face view, shape of petiolar node tapered with squared-off vertex; node matt and microreticulate. Gaster. Gaster matt with distinct microreticulate pattern; pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour blackish-brown.

Major worker description.

Head. Head square; posterior margin of head planar or weakly concave; 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 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 or weakly convex; frontal lobes straight, elevated. Anterior clypeal margin convex, acuminate anteromedially, margin entire; clypeal psammophore set at or just above anterior clypeal margin; 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 matt or with weak sheen and microreticulate throughout; anterior mesosoma in profile gently sinuous after initial steep pronotal incline; erect pronotal setae short, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove a narrow but deep slit; propodeum matt or with a weak sheen and microreticulate; propodeum distinctly angulate, propodeal angles produced as short denticles; length ratio of propodeal dorsum to its declivity between 1:1 and 1:2; erect propodeal setae absent; appressed propodeal setae short, separated by more than own length and inconspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and shorter (length less than 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 matt, and microreticulate. Gaster. Gaster matt with a distinct microreticulate pattern; pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae. General characters. Colour generally dark brown, head brown.

Measurements.

Worker (n = 2): CI 70-102; EI 21-30; EL 0.14-0.19; HL 0.65-0.89; HW 0.46-0.91; ML 0.92-0.24; MTL 0.44-0.64; PpH 0.09-0.14; PpL 0.32-0.47; SI 96-223; SL 0.88-1.01

Comments.

This enigmatic species can be distinguished from all other Melophorus by reason of its armed propodeum in all worker subcastes. Other apomorphies include the absent metatibial apical spur (shared only with the unrelated M. anderseni group and M. fulvidus ) and the peculiarly flattened and carinate mesosoma in the minor worker, hence our tentative placement of M. majeri in its own species-group. The affinities of this ant are unknown, as no specimens were available for sequencing, but the appearance of the major worker suggests it may be close to the M. biroi species-group, if not a very aberrant member of that group. The only known specimens (one nest series and a couple of strays) have come from white sand in southwestern WA. The minor worker, in particular, has more than a suggestion of being a mimic of a pselaphid beetle inquiline, with an extraordinary antennal scape that becomes incrassate distally and a flattened mesosoma. Could this be a kleptoparasite or subterranean nest raider of other ants? However that may be, minor workers are also active on the soil surface and have been collected as foragers. The nest series was associated with a piece of wood ( Agosti 1997).