Melophorus xouthos 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 : 322-324

Melophorus xouthos Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype media worker from Little Sandy Desert 25°16'07"S, 120°27'33"E, Western Australia, 11-12 August 2012, N. A. Guthrie, dune crest: scattered shrubs and spinifex over red sand. Site 12.2, Melophorus revision sequenced specimen M138 [ANIC32-900211] (WAM). Paratypes: minor worker from 142.1 km SSE of Newman 24°31'53"S, 120°17'24"E, Western Australia, October 1996, S. van Leeuwen & R. N. Bromilow, Temp. invert. Pitfall trap, B3: Sand dune [JDM32-004852] (ANIC).

Other material examined.

South Australia: 26 km SSE Illintjitja (collector?? [SAMA database 32-005279]). Western Australia: 142.1 km SSE Newman (van Leeuwen, S. & Bromilow, R.N. [ANIC32-0900217]), Little Sandy Desert (Guthrie, N. A. [ANIC32-900211]), Little Sandy Desert (Guthrie, N. A. [ANIC32-900216]).

Diagnosis.

Melophorus xouthos 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. xouthos 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. These characters serve to differentiate M. xouthos from all other Melophorus except M. parvimolaris . However, M. xouthos is tawny orange-and-black whereas M. parvimolaris is uniformly brown. The major worker is unknown. Odd, wingless, worker-like Melophorus males are tentatively placed in this species.

Minor worker description.

Head. Head square tending to trapezoid; posterior margin of head planar or 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; eyes elliptical or slightly reniform. In full-face view, frontal carinae straight, divergent posteriad; frontal lobes curved towards antennal insertion. Anteromedial clypeal margin straight; clypeal psammophore set at or above midpoint of clypeus; palp formula 6,4. Five mandibular teeth in minor worker; narrow, strap-like, internal and external margins parallel or nearly so; third mandibular tooth only slightly smaller than tooth no. 4 but much smaller than tooth no. 2 in two specimens seen; masticatory margin of mandibles strongly oblique. Mesosoma. Integument of pronotum, mesonotum and mesopleuron matt or with a weak sheen and shagreenate throughout; anterior mesosoma in profile weakly elevated anteriad, thereafter gently sinuate, pronotum and mesonotum on same plane; erect pronotal setae absent; in profile, metanotal groove a weak or vestigial furrow; propodeum matt or with a weak sheen and indistinctly shagreenate; propodeum smoothly rounded or with indistinct angle; length ratio of propodeal dorsum to its declivity not applicable, 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 narrowly rectangular, vertex blunt, directed posteriad; in full-face view, node tapered with blunt vertex; node matt with indistinct microsculpture. Gaster. Gaster weakly shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, long, whitish, appressed setae with occasional erect non-marginal setae present in at least some workers, as well as a few marginal setae on the first gastral sclerite. General characters. Colour a dingy orange with some brownish infuscation on head and anterior mesosoma, legs black with bluish iridescence, gaster chocolate.

Measurements.

Worker (n =): CI; EI; EL; HL; HW; ML; MTL; PpH; PpL; SI; SL.

Comments.

Only a handful of minor workers are known for this small M. wheeleri complex species, which appears to be confined to remote inland areas of SA and WA but may also occur in the southern NT. The long, whitish setae on the gaster and the appearance of the clypeus help separate this ant from all except one other species in the laticeps cluster, and the attractively mottled appearance distinguishes this ant from the very similar M. parvimolaris . While the five-gene tree places it as the sister to M. fulvidus , and the three-gene tree places the species as sister to M. perthensis (both of these ants being in the M. fieldi complex), both groupings are only weakly supported. Specimens taken from the Little Sandy Desert, WA, were collected on a dune crest over red sand with a scattered shrub and spinifex vegetative layer. However, the habits of the species are unknown.

Etymology.

Greek xouthos ( ‘yellowish-brown’); adjective in the nominative singular.