Melophorus oblongiceps 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 : 280-283

Melophorus oblongiceps Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) from c. 7 km SE of William Creek 28.57 S× 136.24E, South Australia, 22 September 1972, J. E. Feehan, ANIC Ants Vial 16.64 [ANIC32-900057] (ANIC). Paratypes: major worker and media worker on same pin and with same details as holotype (ANIC); 2 major workers and a minor worker from Sulphur Peninsula, Lake Eyre North, South Australia, 21 August 1967, G.P. Cross & F.J. Mitchell, nests in damp margin of Lake Eyre, S.A. Mus. specs. [ANIC32-900056] (BMNH); major worker, media worker and minor worker from Sulphur Peninsula on separate pin with same details as the immediately preceding, but without ANIC number (SAM)minor worker and 4 major workers from Curdimurka, South Australia, 1 April 1972, B.B. Lowery, in soft, damp mud margin of Lake Eyre (MCZ).

Other material examined.

South Australia: Curdimurka (Lowery, B.B.), Lake Harris (Hudson, P. [M340]).

Diagnosis.

Melophorus oblongiceps can be placed in the M. biroi species-group on the basis of the characters of the clypeus, propodeum, mandible and palps. However, it occupies a separate, monotypic species-complex. Melophorus oblongiceps can be determined by the following characters: major and minor workers with a combination of long mandibles (i.e., the apical tooth of the retracted mandible reaches to at least the tentorial pit on the opposite side of the head capsule), similar appearance of the head capsule in major and minor workers and short maxillary palps (segments four to six combined barely longer than segment three), in profile, the entire palp reaching only to the middle of the venter of the head capsule in the minor worker when the head is moderately inclined. The head of the major worker is without a short, massive, elbowed mandible directed posteriad. All workers possess five mandibular teeth; the median sector of clypeus is uniformly convex and moderately protuberant with a small, blunt angle at the midpoint of the anterior clypeal margin.

Minor worker description.

Head. Head square; posterior margin of head planar or weakly convex; frons shining with superficial shagreenation or microreticulation only; pilosity of frons a mixture of short, erect and semi-erect setae interspersed with shorter decumbent setae and well-spaced, short, appressed setae. 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 distinctly 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 moderately shining and shagreenate throughout; anterior mesosoma in profile broadly convex; 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, broadly V or U-shaped; propodeum shining and microreticulate; propodeum always smoothly rounded; propodeal dorsum and declivity confluent; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle 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 with superficial microreticulation; pilosity of first gastral tergite consisting of a mixture of curved, erect and semi-erect setae and decumbent and appressed setae that form a variable pubescence. General characters. Colour russet.

Major worker description.

Head. Head horizontally rectangular, broader than wide; posterior margin of head weakly concave; cuticle of frons shining with superficial shagreenation or microreticulation only; pilosity of frons a mixture of well-spaced, distinctly longer erect and semi-erect setae interspersed with shorter decumbent 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 distinctly concave; frontal lobes straight in front of antennal insertion. Anterior clypeal margin broadly and evenly convex; 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 very superficial microreticulation, entire lower mesopleuron distinctly shagreenate; anterior mesosoma in profile broadly convex; erect pronotal setae short, (i.e., shorter than length of eye) and unmodified; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum shining and microreticulate; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae present and abundant (at least a dozen); appressed propodeal setae 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 less than 0.50 × height of propodeum). Petiole. In profile, petiolar node squamiform; in full-face view, shape of petiolar node tapered with blunt vertex, or tapered with sharp vertex; node shining and distinctly microreticulate. Gaster. Gaster shining with superficial microreticulation; pilosity of first gastral tergite consisting of a mixture of curved, erect and semi- erect setae and decumbent setae that form a variable pubescence. General characters. Colour russet.

Measurements.

Worker (n = 2): CI 104-114; EI 18-26; EL 0.23-0.35; HL 0.86-1.74; HW 0.89-1.98; ML 1.26-2.22; MTL 1.01-1.48; PpH 0.13-0.21; PpL 0.49-0.86; SI 71-121; SL 1.08-1.42.

Comments.

Melophorus oblongiceps appears to be restricted to the damp terrestrial environment around Lake Eyre, SA. This species resembles some members of the fieldi and wheeleri complexes, but can be distinguished by the similar appearance of the different subcastes of workers, the short palps and the non-massive five-toothed mandibles. The habits of the ant have not been documented but it may have some specializations, since the only ecological notes mentioned on labels indicate it nests and forages in the damp margins at the edge of Lake Eyre. Sequencing of one specimen has been largely unsuccessful, but sufficient to indicate the species may belong somewhere in the vicinity of the M. wheeleri complex.

Etymology.

Latin oblongus ('longer than broad’) plus -ceps ( ‘-headed’ [from caput]); adjective in the nominative singular.