Melophorus graciliceps 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 : 164-167

Melophorus graciliceps Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) from Heathcote, near Bendigo, Victoria, 26 May 1961, B.B. Lowery, 1000 ft, dry sclerophyll, ANIC ants vial 20.238 [ANIC32-900175] (ANIC). Paratypes: 2 major workers on same pin and with same details as Holotype (ANIC); 1 major and 2 minor workers from Heathcote near Bendigo, Victoria, 29 May 1961, B.B. Lowery, 1000ft, dry sclerophyll, ANIC Ants Vial 20.239 (BMNH); 3 minor workers from Yathong Nature Reserve 145°40'33"S, 32°37'39"S, New South Wales, 3-25 October 2003, C. Lambkin & N. Starwick, 205m, ANIC Bulk Sample 2154, open woodland, field of flowers, Malaise [ANIC32-030855] (MCZ); 6 major and 2 minor workers from St George, Queensland, 7 January 1966, B.B. Lowery, ' Melophorus ', Reddish soil, savannah woodland, R10 (back of label–‘ strange nest–deep narrow cone, smooth, a perfect insect trap’) (QM); 2 major and one minor worker from Calca, South Australia, 26 September 1957, B.B. Lowery, mallee scrub, ANIC Ants Vial 22.188 (SAM); 2 major workers from Westonia, Western Australia, coll. approx. 2000; Environmental Biology Department, Curtin University of Technology, [JDM32-001979] (WAM).

Other material examined.

New South Wales: 24 km E Rankins Spring (Lowery, B.B.), 4 km N Coombah Road House, Route 79 (Crozier, R.H., Imai, H.T. & Ward, P.S.), CSIRO Lake Mere Field Station, near Louth (Bryannah, M. ), Queensland: ‘Merigol’ (Beutel, T.). South Australia: Brookfield Conservation park (Shattuck, S.O. [ANIC32-900110]), Cambrai (Greenslade, P.J. M. ), Cambrai (Greenslade, P.J. M. ), Cambrai (Greenslade, P.J. M. ). Victoria: Sea Lake (Goudie [ANIC32-900111]). Western Australia: 30 km N Billabong RH (Heterick, B.E. [M25/M35/M36]), 7 km E of Burakin (Heterick, B.E. [JDM32-001978]), Dryandra SF (Norwood, C. [JDM32-001980]).

Diagnosis.

Melophorus graciliceps 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. mjobergi clade but differs from the most derived species, and the major worker does not have the deeply recessed area around the frontal carinae and medial sector of clypeus or the impressed setae-bearing sockets visible in the major and media workers that is seen in M. mjobergi , M. postlei and M. compactus . Minor and major workers workers of M. graciliceps are clothed with fine, appressed silvery setae that form pubescence in the minor worker, at least, in conjunction with multiple scattered, modified erect setae (the modified setae varying from distally slightly flattened to clavate) on the head, mesosoma and gaster. This species can only be confused with its near relation, M. lissotriches , but differs in having an only weakly convex eye in the minor worker (strongly convex in M. lissotriches ), the eye barely interrupting the outline of head capsule. In profile, the pronotum of the minor worker rises gently, and the mesosoma is thereafter more-or-less straight, the mesonotum does not dip towards the propodeum and the metanotal groove is not demarcated by a v-shaped notch. The frontal carinae of the major worker is concave (straight or weakly convex in M. graciliceps ) and the cuticle of its head is smooth and shining (matt or weakly shining in M. graciliceps ).

Minor worker description.

Head. Head square; posterior margin of head planar to strongly convex; frons shining with superficial shagreenation or microreticulation only; frons consisting almost completely of appressed setae that may form pubescence (tiny, erect setae, if present, usually confined to ocular triangle). Eye moderate (eye length 0.20-0.49 length of side of head capsule); in full-face view, eyes set above mid point 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 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 with weak to moderate sheen and superficial microreticulation (more pronounced on mesopleuron); anterior mesosoma in profile weakly elevated anteriad, thereafter gently sinuate, pronotum and mesonotum on same plane; appearance of erect pronotal setae short and often expanded distally, at times clavate; in profile, metanotal groove a weak or vestigial furrow; propodeum shining and shagreenate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (greater than 12), or present and sparse to moderate (1-12); appressed propodeal setulae long and closely aligned, creating pubescence; 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 square with sharp angles; node shining and distinctly shagreenate-microreticulate. Gaster. Gaster weakly shining with indistinct shagreenation; pilosity of first gastral tergite consisting of thick, appressed setae that form pubescence, interspersed with numerous short, modified (sometimes clavate), erect setae. General characters. Colour brown to blackish-brown.

Major worker description.

Head. Head square; posterior margin of head planar or weakly concave; cuticle of frons shining and smooth except for piliferous pits; frons consisting mainly of well-spaced appressed and a few mainly modified, clavate (feather-like) erect setae. 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 and evenly convex; clypeal psammophore set below midpoint of clypeus; 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 and mainly smooth, vestigial shagreenation most noticeable on humeri and mesopleuron; anterior mesosoma in profile broadly convex; erect pronotal setae short and often expanded distally, at times clavate; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and generally smooth, with only weak, indistinct shagreenation; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (at least a dozen); appressed propodeal setae long and closely aligned, creating pubescence; 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 square with rounded angles; node shining and faintly shagreenate-microreticulate. Gaster. Gaster shining with superficial microreticulation; pilosity of first gastral tergite consisting of thick, often distally flattened, erect setae over well-spaced, short, appressed setae. General characters. Colour reddish-orange, gaster brown.

Measurements.

Worker (n = 8): CI 90-117; EI 20-32; EL 0.19-0.31; HL 0.67-1.32; HW 0.60-1.55; ML 0.98-1.87; MTL 0.71-0.95; PpH 0.09-0.15; PpL 0.43-0.69; SI 70-158; SL 0.95-1.08

Comments.

Melophorus graciliceps has a very wide distribution and has been recorded from all mainland Australian states except the ACT. This ant is distinguishable from all others except M. lissotriches by virtue of the combination of silvery appressed pubescence and modified, erect setae. The species differs from M. lissotriches in terms of the appearance of the frontal carinae (major worker) which are concave in this ant and weakly convex in M. lissotriches , and the appearance of the mesonotal groove and the position of the compound eyes (minor worker). Molecular sequencing has been only partially successful, but a three-gene tree indicates a close relationship between M. graciliceps and M. biroi . On the basis of morphology, however, we predict that more inclusive sampling will reveal the former will still fall within the M. mjobergi clade.

In general, this species prefers drier areas that support mallee or savanna vegetation, and appears to favour dunes. However, there is one record from a paddock (Coombah, NSW). One interesting note refers to the nest of this ant as being (verbatim) 'strange nest, deep, narrow cone, smooth, a perfect insect trap.' However, the principal author of this paper found a nest that was unremarkable, and it seems more likely the author of the label (B. B. Lowery) may have somehow confused the entrance burrow of an Aphaenogaster species (known to make that sort of nest) with the domicile of this Melophorus . Six workers collected at Yathong, NSW, were also taken in a malaise trap, indicating this ant may climb on vegetation if the need arises.

Etymology.

Latin gracilis ( ‘slender’) plus -ceps ( ‘-headed’ [from caput]); adjective in the nominative singular.