Melophorus dicyrtos 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 : 161-164

Melophorus dicyrtos Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) from slopes above Baroalba Spring 12.475S, 132.51E, Northern Territory, 17 November 1972, R.W.Taylor & J.E. Feehan, Euc. Savanna, Acc. 72.1006, ANIC ANTS VIAL 38.92 [ANIC32-900177] (ANIC). Paratypes: 2 major workers on same pin and with same details as holotype (ANIC); major and 2 minor workers from Gove Nhulumbuy, Northern Territory, 1 November 1972, R.W. Taylor Accession 72.824, ANIC Ants Vial 15.198 [ANIC32-002772] (ANIC); 2 minor and major worker from 22 km SW of Katherine, Northern Territory, 26 October 1977, P.J. M. Greenslade (2), 10 (BMNH); 3 media workers from slopes above Baroalba Spring 12.475S, 132.51E, Northern Territory, 16 November 1972, R.W.Taylor & J.E. Feehan, Euc. Savanna, Acc. 72.1015, ANIC ANTS VIAL 38.104 [ANIC32-900115] (MCZ); major worker and 2 minor workers from Horn Island 10.37S, 142.17E, Torres Strait, 10-27 June 1974, H. Heatwole & E. Cameron, No. HOR.64 [ANIC32-900116] (QM); minor, media and major worker from Yampi 2 Stn, Kimberley Area, Western Australia, C. Palmer, May 2002 [JDM32-004529] (WAM).

Other material examined.

Northern Territory: 1 km NNE Bullita, Gregory Nat. Park (Weir, T. & Bouchard, P. [ANIC32-051712]), 22 km WSW Borroloola (Feehan, J.E.), Caranbirini Water Hole, 33 km SW Borroloola (Feehan, J.E.), Jabiru (Greenslade, P.J. M. ), Jabiru, Alligator Rivers area (Greenslade, P.J. M. ), Jabiru, Alligator Rivers area (Greenslade, P.J. M. ), Kapalga, Alligator Rivers area (Greenslade, P.J. M. ). Queensland: 13 km E by S Weipa (Zborowski, P. & Shattuck, S.O. [ANIC32-043330]), 3.5 km SWbyS Mt. Baird (Naumann, I.D.), Clermont, 7.5 km E (Burwell, C.), Hann River (Zborowski, P. & Horak, M. [ANIC32-031071]), Lolworth NP (Wright, S.), Proserpine, Airport Drive (Raven, R.), Red Falls (Monteath, G.), Somerset, Cape York (Cameron, E.), Weipa (Majer, J.D.). Western Australia: Argyle Diamond Mine via Kununurra (Postle, A.T. [JDM32-004621]), Argyle Diamond Mine via Kununurra (Postle, A. [JDM32-004988]), Marillana Ck (Dunlop, N. [JDM32-005034]), Mt. Whaleback (Walker, K.J. [JDM32-004942]), Zuytdorp (WAM/CALM [JDM32-001975]).

Diagnosis.

Melophorus dicyrtos can be placed in the M. biroi species-group on the basis of characters of the clypeus, propodeum, mandible and palps. The species is placed in the M. biroi species-complex on the basis of a further suite of characters (viz, metatibia of major worker with only one preapical spur [except rarely in the mjobergi clade]; clypeal psammophore placed anteriorly at or just above anterior margin of clypeus in the minor worker and often in the major worker; head dorsoventrally compressed to varying degrees in the minor worker of most species with the eyes placed high on the sides; compact legs, and small body size [[(excluding mjobergi clade) HW of smallest minor 0.36 mm, average HW of smallest minors 0.46 mm; HW of largest known major 1.29 mm, average HW of largest majors (where known) 1.05 mm]). Melophorus dicytos can be recognised and distinguished from species of similar appearance (e.g., M. biroi and M. castanopus ) by virtue of the propodeum of the minor and major worker being protuberant, strongly truncate, and with an elevated dorsal surface which is much shorter than its declivitous surface. This is also a relatively large member of the M. biroi complex (HW of minor worker 0.65 mm ≥, HW of major worker 1.25 mm ≥) and is largely tropical ( M. castanopus in contrast is largely southeastern in distribution and apparently does not occur in NT, QLD and WA, so is probably not sympatric with M. dicyrtos ). The metanotal groove characteristically is a deep V-shaped notch and most workers have long, flexuous setae on the mesosomal surface but these may be short and bristly.

Minor worker description.

Head. Head square; posterior margin of head planar or weakly convex, or planar or weakly concave; frons shining with superficial shagreenation or microreticulation only; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. 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 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 smooth on dorsum, entire lower mesopleuron distinctly striolate-microreticulate, or with weak to moderate sheen and superficial microreticulation (more pronounced on mesopleuron); anterior mesosoma in profile pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; appearance of erect pronotal setae long (i.e., longest erect setae longer than length of eye) and unmodified, or short, (i.e., longest erect setae shorter than length of eye) and unmodified; in profile, metanotal groove deep, ‘V’ -shaped; propodeum shining and finely striolate and microreticulate; propodeum angulate, propodeal angle blunt, or distinctly angulate, propodeal angle sharp; length ratio of propodeal dorsum to its declivity greater than 1:2; erect propodeal setae variable in number, may be absent; appressed propodeal setulae long and separated by at least own length, or short, separated by more than own length and inconspicuous; propodeal spiracle situated on or beside declivitous face of propodeum, and longer (length ≥ 0.50 × height of propodeum), or 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 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. General characters. Colour concolorous orange tan to dark reddish-brown.

Major worker description.

Head. Head square; posterior margin of head weakly concave; cuticle of frons striolate anteriad, smooth and shining posteriad; pilosity of frons a mixture of a few well-spaced, erect setae interspersed with appressed setae only. 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 or weakly convex in full-face view, or straight, divergent posteriad; frontal lobes curved inward in front of antennal insertion. Anterior clypeal margin broadly convex with anteromedial dimple; 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; mastica tory margin of mandibles approximately aligned vertically 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 broadly convex; erect pronotal setae long (i.e., longer than length of eye) and unmodified; in profile, metanotal groove deep, V-shaped; propodeum matt or with weak sheen and microreticulate-striolate; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity greater than 1:2; erect propodeal setae present and sparse to moderate (1-12); appressed propodeal setae short, separated by more than own length and inconspicuous; 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 uniformly rounded; node shining and faintly striolate and microreticulate. Gaster. Gaster shining, shagreenate ('LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced, erect and semi-erect setae interspersed with regularly spaced appressed setae. General characters. Colour of foreparts orange tan to dark reddish-black, gaster dark chocolate to blackish.

Measurements.

Worker (n = 6): CI 100-117; EI 19-26; EL 0.17-0.24; H 0.66-1.09L; HW 0.66-1.28; ML 0.91-1.42; MTL 0.53-0.84; PpH 0.12-0.13; PpL 0.38-0.58; SI 81-120; SL 0.79-1.04.

Comments.

Melophorus dicyrtos is preeminently a species of the northern half of Australia, and most samples collected come from the Torresian phytogeographic zone. A dry husk of a worker that is doubtfully placed in this species and that comes from the Zuytdorp area near Kalbarri, WA, represents the most southerly record for the ant, which has been collected in the NT, QLD and WA. No specimens were available for sequencing. Although small, this is a reasonably spectacular species from the biroi clade; with its shining cuticle, rounded mesonotum, sharply incised and v-shaped metanotal groove, and its truncate propodeum with an acutely angled division between the dorsal and declivitous faces helping to distinguish the species from similar ants. Several worker samples have been taken in flight intercept traps, suggesting the ant may climb on vegetation. Two NT samples were taken in eucalyptus savannah, and material from the QM has been collected in yellow pan traps in vinescrub growth over yellow basalt, from a faeces-baited pitfall trap in eucalypt woodland, and from closed woodland including one sample from a dung trap. The association of a Melophorus species with dung is likely to be merely fortuitous (Burwell, C., pers. comm.).

Etymology.

Greek dikyrtos ( ‘two-humped’); adjective in the nominative singular.