Melophorus pelecygnathus

The nature of the mandibles indicates that this ant is likely specialized for hunting particular prey, whether this is termites (as assumed by Andersen, 2007) or some other arthropod. Unfortunately, available labels do not provide any information on the ant apart from the necessary basics of place, date and collector.

Identification
Heterick et al. (2017) - Melophorus pelecygnathus is one of three members of the Melophorus potteri species-group. These three species have a large, oblique propodeal spiracle situated well before declivitous face of propodeum, the spiracle bisecting much of the propodeum. This species is distinguished from the remaining members of the group by the combination of its reduced palp formula (PF 3,4) and its large, securiform mandible whose masticatory margin is virtually edentate with only minute (often worn), evenly sized teeth except for the long apical tooth.

Melophorus pelecygnathus is a spectacular species with large, securiform (hatchet-shaped) mandibles in both the minor and major workers. The ant cannot be mistaken for any other Melophorus.

Distribution
The species has been recorded from NSW, QLD, SA and WA.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Nomenclature

 *  pelecygnathus. Melophorus pelecygnathus Heterick, Castalanelli & Shattuck, 2017: 405, fig. 97 (w.) AUSTRALIA.

Worker
(n = 4): CI 103–104; EI 22–24; EL 0.22–0.31; HL 0.89–1.35; HW 0.92–1.40; ML 1.18–1.75; MTL 0.66–0.97; PpH 0.18–0.28; PpL 0.53–0.81; SI 73–74; SL 0.68–1.03.

Minor. Head. Head rectangular; posterior margin of head planar to strongly convex; 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; in profile, eye set anteriad of midline of head capsule; eye roughly ovoid, narrowed posteriad. In full-face view, frontal carinae straight, convergent posteriad; frontal lobes curved inward in front of antennal insertion. Anteromedial clypeal margin straight; clypeal psammophore set at or just above anterior clypeal margin; palp formula 3,4. Mandibular teeth in minor worker absent, mandible edentate or with small crenulations only; mandibles securiform; third mandibular tooth absent; masticatory margin of mandibles approximately vertical 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 pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex; erect pronotal setae absent; in profile, metanotal groove shallow, broadly V- or U-shaped; propodeum matt or with a weak sheen and microreticulate; propodeum smoothly rounded or with indistinct angle, or angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about 4:3; erect propodeal setae always absent; appressed propodeal setulae short, separated by more than own length and inconspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and longer (length ≥ 0.50 × height of propodeum). Petiole. In profile, petiolar node narrowly conical, vertex blunt, directed posteriad, or subcuboidal, vertex bluntly rounded; in full-face view, shape of petiolar node uniformly rounded; node shining and distinctly shagreenate-microreticulate, or matt with indistinct microsculpture. Gaster. Gaster shining with superficial microreticulation, or shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. General characters. Colour bicoloured with reddish to chocolate head, orange- or reddish-brown mesosoma and dark brown gaster.

Major. Head. Head square; posterior margin of head planar or weakly concave; 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 small (eye length less than 0.2 × 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; eye roughly ovoid, narrowed posteriad. Frontal carinae straight, convergent posteriad; frontal lobes curved inward in front of antennal insertion. Anterior clypeal margin straight; clypeal psammophore set at or just above anterior clypeal margin; palp formula 3,4. Mandibular teeth in major worker absent, mandible edentate or with small crenulations only; mandibles securiform; third mandibular tooth absent; masticatory 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 pronotum smoothly rounded anteriad and flattened posteriad, mesonotum narrowly convex, or gently sinuous after initial steep pronotal incline; 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 absent; appressed propodeal setae short, separated by more than own length and inconspicuous; propodeal spiracle situated nearer to midpoint of propodeum than to its declivitous face, and longer (length ≥ 0.50 × height of propodeum), or situated nearer to midpoint of propodeum than to its declivitous face, and shorter (length less than 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 faintly shagreenate-microreticulate. Gaster. Gaster shining, shagreenate (‘LP record’ appearance); pilosity of first gastral tergite consisting of well-spaced short, inconspicuous, appressed setae only, erect setae always absent. Colour of foreparts orange to crimson, gaster chocolate.

Type Material
Holotype minor worker (top ant) from 97.6 km SE of Newman 23°52'46"S, 120°30'12"E, Western Australia, April, 1997, S. van Leeuwen & R. N. Bromilow, Perm. invert. pitfall trap S5, Sandstone breakaway [JDM32-001575]. Paratypes: minor worker on same pin and with same details as holotype (WAM); major and minor from 142 km SSE of Newman 24°31'46"S, 120°17'45"E, Western Australia, August 1997, S. van Leeuwen & R. N. Bromilow, Perm. invert., pitfall trap B4, Spinifex sandplain [JDM32-001576] ; minor worker from Gawler Ranges, South Australia, 5 October 1972, P.J.M. Greenslade, (3), ‘Melophorus sp. 1 loan ANIC 1991’ [ANIC32 900030] ; major and media worker from Kwelkan 31°08'36"S, 117°59'43"E, Western Australia, 12 March 2006, M. Russell, Hand-collected, grid survey [JDM32-001574] (WAM).

Etymology
Compound of Latinized Greek pelecys (Greek pelekys ‘hatchet’) plus Neo-Latin gnathus (‘jaw’); noun in the nominative singular standing in apposition to the generic name.