Melophorus eumorphus 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 : 211-214

Melophorus eumorphus Heterick, Castalanelli & Shattuck sp. n.

Types.

Holotype minor worker (bottom ant) from 53 km E Vokes Hill, Victoria Desert, South Australia, 9 October 1976, P.J. M. Greenslade [ANIC32-900173] (ANIC). Paratypes: 2 minor workers on same pin and with same details as holotype (ANIC); 2 minor workers from Cambrai, South Australia, 24-28 January 1972, P.J. M. Greenslade (ANIC); minor worker from Koonamore, South Australia, 25 February 1972, P.J. M. Greenslade, (5) (BMNH); 2 minor workers from Observatory Hill, Victoria Desert, South Australia, 7 October 1972, P.J. M. Greenslade, (4), 26) (SAM); major and media worker from intersection of Holland track and Norseman Road 32°24'51"S, 119°27'33"E, Western Australia, 2 January 2006, B.E. Heterick, sandplain/laterite heathland, foraging on ground [JDM32-001981] (WAM); minor worker from 64 km E of Southern Cross, Western Australia, 18 April, 1987, B. Heterick, soil, native vegetation, rural environment, 245, 8MelBH26, [JDM32-001982] (WAM).

Other material examined.

New South Wales: CSIRO Lake Mere Field Station, near Louth (Bryannah, M. ). South Australia: Cambrai (Greenslade, P.J. M. ), Cambrai (Greenslade, P.J. M. [ANIC32-900102]), Cambrai (Greenslade, P.J. M. ), Cambrai (Greenslade, P.J. M. ), Koonamore (Greenslade, P.J. M. ), Koonamore (Greenslade, P.J. M. ). Western Australia: 1 km W Canna (Heterick, B.E. [M320]).

Diagnosis.

Melophorus eumorphus 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. fieldi species-complex because of the appearance of the anteriorly placed clypeal psammophore, the compact propodeum, the presence of more than one preapical spine on the metatibia, at least in the major worker, the long, even spindly legs and the unmodified mandible in the major worker. The appressed setae on the gaster in all workers of M. eumorphus are very small and inconspicuous when the gaster is moderately distended, and are separated from one another by at least their own length, these appressed setae also being inconspicuous on the mesosoma and never long and silvery. The mesosoma is glabrous in the minor worker or has one or a few flexuous, erect setae. The node of the minor worker is often squamiform and most commonly the cuticle is shining or even glossy with vestigial or weak shagreenation. These features serve to differentiate M. eumorphus from most of the members of its complex. This ant may be distinguished from the few remaining similar species (notably M. longipes , M. turneri and M. vitreus ) by the following characters: the minor worker is very small (HW <0.55 mm), the frons of the head capsule is smooth and shining, the eye is large (eye length approximately 0.40 × length of head capsule), the mesopleuron has distinct, wrinkled or scalloped sculpture that may extend to the mesonotum (this is a particularly good feature to help distinguish this ant from the similar-sized M. vitreus ) and the propodeum is a rounded cube. The major worker is also very small (HW ≤ 0.73 mm) with a large eye (eye length approximately 0.38 × length of head capsule) and the mesopleural sculpture as for the minor worker

Minor worker description.

Head. Head approximately oval with straight sides; posterior margin of head strongly convex; frons shining and smooth except for piliferous pits; 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 large (eye length ≥ 0.50 × length of side of head capsule), or moderate (eye length 0.20-0.49 length of side of head capsule); in full-face view, eyes set at about midpoint of head capsule; in profile, eye set around midline of head capsule; eyes elliptical or slightly reniform. In full-face view, frontal carinae distinctly concave; frontal lobes curved toward antennal insertion. In full-face view, anteromedial clypeal margin broadly convex with anteromedial dimple; clypeal psammophore set below midpoint of clypeus; 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; anterior mesosoma in profile broadly convex; appearance of erect pronotal setae long (i.e., longest erect setae longer than length of eye) and unmodified, or erect pronotal setae absent; in profile, metanotal groove deep, ‘V’ -shaped; propodeum shining, with multiple hair like striolae; propodeum smoothly rounded or with indistinct angle; 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 subcuboidal, vertex bluntly rounded; in full-face view, shape of petiolar node square with rounded angles; node shining and smooth throughout. Gaster. Gaster smooth and glossy; 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 and gaster chocolate, mesosoma tan.

Major worker description.

Head. Head square; posterior margin of head planar or weakly convex; cuticle of frons shining and smooth except for piliferous pits; 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 at about 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 convex with anteromedial dimple; clypeal psammophore set at or above 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 with very superficial microreticulation, entire lower mesopleuron distinctly shagreenate; anterior mesosoma in profile pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; erect pronotal setae long (i.e., longer than length of eye) and unmodified; in profile, metanotal groove deep, V-shaped; propodeum shining, dorsum and declivitous face of propodeum mainly smooth, but with weak to strong vertical striolae arising from metapleuron; propodeum smoothly rounded or with indistinct angle; propodeal dorsum and declivity confluent; erect propodeal setae present and sparse to moderate (1-12); appressed propodeal setae long and separated by at least own length; 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 smooth throughout. 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 as for minor worker.

Measurements.

Worker (n = 6): CI 105-110; EI 26-33; EL 0.16-0.21; HL 0.46-0.73; HW 0.49-0.73; ML 0.64-0.91; MTL 0.38-0.56; PpH 0.07-0.11; PpL 0.23-0.33; SI 91-105; SL 0.51-0.73.

Comments.

Melophorus eumorphus is a small, shining species that appears to be widespread in arid and semi-arid habitats in temperate Australia (in NSW, SA and WA). The ant can be separated from similar species in its clade by a combination of its bimodal mesosoma when seen in profile, its scalloped mesopleuron, its total or almost total lack of erect setae on the mesosoma and its thick, knob-like petiolar node. Superficially, it is similar in appearance to several members of the M. ludius complex, but has the spindly legs, the posteriorly placed clypeal psammophore and the long maxillary palps that are typical of many of the members of the M. fieldi complex. One WA specimen has been genetically sequenced. On a five-gene tree this species is linked to M. perthensis ; however a close evolutionary relationship between the pair does not have strong branch support. The ant is sister to M. longipes on a three-gene tree but, again, branch support is relatively weak. There are little ecological data on the species: the sequenced worker from Canna, WA, was collected in mallee woodland over red loam, while five samples were taken from dunes in Cambrai, SA and a single worker was taken from a paddock at the Lake Mere Field Station in NSW.

Etymology.

Greek eu ( ‘well’, ‘good’) plus Latinized Greek morphus (Greek morphé ‘shape’, ‘form’); adjective in the nominative singular.