Melophorus translucens 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 : 339-342

Melophorus translucens Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) from Swanbourne, Western Australia, 30 September 1987, B. Heterick, soil, native vegetation, urban dune, 295, 8MelBH21 [JDM32-001966]. Paratypes: Major worker on same pin and with same details as holotype (WAM); minor worker and two major workers from Bold Park 31°56'S, 115°46'E, Western Australia, 28 March 2002, P. Achour, pitfall trap, coastal woodland [JDM32-001968] (WAM); minor worker from near Perth, Western Australia, 1978, M. Rossbach, A1387C83 [JDM32-001973] (ANIC); minor worker from near Perth, Western Australia, 1978, M. Rossbach, A1387C83 [JDM32-001973] (MCZ).

Other material examined.

Western Australia: Christmas Tree Well (Heterick, B.E. [M17/M53/M54]), Guilderton (Heterick, B.E. [JDM32-001970]).

Diagnosis.

Melophorus translucens is placed in the M. ludius species-group on the basis of molecular data. However, in morphological appearance this taxon shares major diagnostic characters with the M. biroi complex (viz, metatibia of major worker with only one preapical spur; clypeal psammophore placed anteriorly at or just above anterior margin of clypeus in the minor worker and often in the major worker; legs compact, and small body size [HW of smallest minor <0.40 mm, HW of largest major <1.10 mm]). Like the other three members of its species-group, M. translucens is characterised by being weakly sculptured overall, with the cuticle of the mesosoma visibly thin, the mesonotum being translucent to varying degrees and the mesopleuron either smooth or with vestigial sculpture only. In Melophorus ltranslucens the mesonotum is conspicuously translucent and its pale appearance often contrasts with the much more intense colour of the rest of the mesosoma (although some minor workers can be generally pale). Melophorus translucens is distinguished from both M. ludius and M. pusillus by its more elongate propodeum and propodeal spiracle.

Minor worker description.

Head. Head rectangular; posterior margin of head planar or weakly concave; frons shining with superficial shagreenation or microreticulation only; 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, or set at about midpoint of head capsule; in profile, eye set anteriad of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae concave; frontal lobes straight in front of antennal insertion. Anteromedial clypeal margin broadly and evenly convex; 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 shining and mainly smooth, vestigial shagreenation most noticeable on humeri and mesopleuron; anterior mesosoma in profile pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex, or smoothly rounded anteriad, thereafter pronotum and whole of mesonotum flattened and on same plane as propodeum; 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, indicated mainly by an angle; propodeum shining and shagreenate; propodeum smoothly rounded or with indistinct angle; 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 on or beside declivitous face of propodeum, and longer (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 with vestigial sculpture. 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, or consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour of head, pronotum, propodeum orange or orange tan to brown, mesonotum translucent cream-yellow to yellow, gaster dark brown, appendages variably yellowish to brownish.

Major worker description.

Head. Head square; posterior margin of head planar or weakly concave; cuticle of frons shining with superficial shagreenation or microreticulation only; 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 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 concave; frontal lobes straight in front of antennal insertion. Anterior clypeal margin straight; 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 shining with indistinct microsculpture that is most pronounced on lower surfaces; anterior mesosoma in profile pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; erect pronotal setae short, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove shallow, indicated mainly by an angle and metathoracic spiracles; propodeum shining and microreticulate; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae absent; appressed propodeal setae sparse or absent, if present then not regularly spaced; propodeal spiracle situated on or beside declivitous face of propodeum, and longer (length ≥ 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node tapered with squared-off vertex; node shining and smooth with vestigial microreticulation anteriad. Gaster. Gaster shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of thick, appressed setae that form pubescence, interspersed with numerous short, bristly, erect setae. General characters. Colour of foreparts (excluding mesonotum) orange to orange tan, mesonotum yellow, gaster brown to dark brown.

Measurements.

Worker (n = 4): CI 69-111; EI 20-36; EL 0.12-0.15; HL 0.46-0.69; HW 0.32-0.77; ML 0.59-0.90; MTL 0.34-0.48; PpH 0.05-0.07; PpL 0.27-0.43; SI 74-149; SL 0.47-0.57.

Comments.

This species appears to be confined to white sand, with all bar one of the populations sampled occurring on the Swan Coastal Plain, WA (one collection was taken at Christmas Tree Well in the Darling Range). All of these samples have been collected in the vicinity of Perth but the ant probably has a broader distribution in suitable habitats. A nest examined by the principal author in white sand-dunes near Swanbourne Beach, Perth, WA was situated among low, coastal shrubs. The depigmented, almost transparent mesosoma (quite bulbous in the major worker) and obliquely elongate propodeal spiracle serve to distinguish it from most other ants, although pale forms of the tiny minor worker can be difficult to differentiate from those of M. pusillus . In such cases the smaller size of the eye in M. translucens is a useful diagnostic character. Minor workers can be colour variable, ranging from a depigmented yellow-and-white to dark brown-and-white, the depigmented mesonotum contrasting spectacularly with the rest of the mesosoma in the latter.

Given its generally unremarkable appearance, this ant appears to be surprisingly primitive. In both the bar-coding COI and the five-gene tree the species strongly assorts with hirsutus and, more broadly, forms with that latter species a sister-group relationship with potteri and pusillus , but falls within these latter on the three-gene tree. However, the species is retained in the ludius complex for now, based on its morphology, though it may eventually require separate complex or even species-group status. The species seems to have evolved earlier than the M. biroi species-group, based on branch length, and its current localized distribution may indicate a relictual status.

Apart from its being apparently restricted to white, sandy soils, nothing more is known about this ant.

Etymology.

Latin trans ( ‘across’, ‘through’) plus lucens ( ‘shining’); adjective in the nominative singular.