Monomorium subapterum

Specimens of this species have been observed feeding at flowers of Melelauca sp. in the northwest of Australia. M. subapterum is the most commonly found species in the M. rothsteini complex in the arid centre of the country.

Identification
Sparks et al. (2015) - A member of the M. rothsteini species group. A small, glossy dark brown species with large eyes and a slightly concave to sinuous clypeus. The mesonotum is without sculpture except in the posterior region, the propodeal dorsolateral angles clearly form an obtuse angle or are rounded and the petiole node is narrow.

This species cannot be separated from Monomorium stagnum using morphology alone. Evidence for its separation from M. subapterum comes from a species delimitation study undertaken by (Sparks et al. 2014).

Distribution
This species has the broadest distribution of all the species dealt with here and can be found throughout most of the arid interior of Australia.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Genetics
COI sequences. Genbank accession numbers for this species are KC572878, KC572885–KC572888, KC572895–KC572897, KC572901, KC572907, KC572909, KC572910, KC572922, KC572940, KC572946, KC572954, KC572960–KC572965, KC572967–KC572969, KC572971–KC572976, KC572984, KC572987–KC572991 and KC572993–KC572996.

Nomenclature

 *  subapterum. Monomorium subapterum Wheeler, W.M. 1917b: 112, fig. 2 (w.q.m.) AUSTRALIA. Combination in M. (Notomyrmex): Emery, 1922e: 170; in Chelaner: Ettershank, 1966: 97; in Monomorium: Taylor, 1987b: 4. Junior synonym of rothsteini: Heterick, 2001: 408. Revived from synonymy: Sparks, Andersen & Austin, 2015: 520.

Worker
Sparks et al. (2015) - (n=9). HW 0.68–0.82, HL 0.74–0.86, EL 0.14–0.2, PMH 0.27–0.35, PH 0.21–0.31, PNH 0.17–0.18, LHW 0.43–0.49, EW 0.10–0.12, PML 0.43–0.53, ML 0.64–0.88, PL 0.27–0.39, PNWdv 0.16–0.20.

Small species with a small, rectangular head; posterior cephalic margin shallowly depressed medially. Anterodorsal margin of the clypeus sinuous to almost straight, frontolateral carinae forming smooth ridges; anteroventral margin with or without a small median projection. Frons strigate, restricted to antennal lobes and area in between or with a few strigae only present on antennal lobes; coarse lateral cephalic strigae reach anterior eye margin or if not reaching then a few very fine strigae may reach eye margin. Eyes large, EW > 0.23 x LHW, 12–13 ommatidia in longest vertical axis, 11 in longest horizontal axis.

Mesonotum smooth and shining, metanotal groove sculpture extending just into lateral portion of posterior region in some specimens, in others with posterior mesonotum rugulose strigulate. Mesopleuron and lateral surface of propodeum alveolate, strigae restricted to metapleural gland bulla. Propodeum in lateral view with dorsolateral angles clearly forming an obtuse angle; dorsally with anterior transverse carinae weakly present, transverse and longitudinal strigae absent. Petiole node narrow, less than 2 x eye width when viewed from above; shape in posterior view tapering to a narrow point, in lateral view anterior and posterior faces converging to a narrowly rounded point. Petiole node smooth and shining, some specimens with fine reticulate sculpture along posterior basal margin, postpetiole without sculpture.T1 completely smooth and without sculpture.

Head and mesosoma brown to very dark brown, dorsally infuscated in lighter specimens; mandibles light brown, legs brown to dark brown, trochanters and apical margins of femur and tibia distinctly lighter in colour than remainder of legs, antennal scapes and metasoma dark brown to very dark brown, lighter in colour than flagellum, cuticle with a high gloss.

Queen
Sparks et al. (2015) - (n=2). HW 1.5–1.52, HL 1.35, EW 0.25–0.27, EL 0.35, ML 2.40–2.42, PeH 0.62–0.66, PNWdv 0.55–0.57, PPH 0.57.

Head triangular, broader behind the eyes that in front, vertex straight sculpture strigulate to smooth over frontal surface, laterally strigulate. Frontal clypeal margin very mildly concave. Mandibles strigate with a large apical and two smaller preapical teeth. When angled towards eye antennal scapes not surpassing dorsal eye margin.

Mesoscutum in profile evenly rounded from pronotum to scutellum, scutellum rounded and raise only slightly above surface of mesoscutum, surface smooth and shining except for pitted setal insertion points and lateral margins which are rugulose strigate. Pronotum finely reticulate, mesopleuron above central groove finely reticulate to smooth, strigate along posterior margin; below central groove medially reticulate, strigate on anterior and posterior third. Propodeum strigate with many raised ridges over entire surface, finely reticulate in between ridges on posterior surface. Petiole node triangular in profile, trapezoidal in posterior view with a rounded dorsal margin, petiole and postpetiole alveolate to reticulate, petiole laterally with transverse ridges on ventral half, postpetiole with irregular ridges on lateral and posterior surfaces. Metasomal tergites and sternites finely reticulate.

Colour entirely dark reddish-brown, head and mesosoma slightly darker than antennal scapes, anterior clypeal margin and metasoma. Head and mesosoma with many long and short, erect, dull setae except for a broad glabrous area of that spans entire length of mesoscutum.

Male
Sparks et al. (2015) - (n=3). HW 1.39–1.40, HL 1.0, EW 0.33, EL 0.45–0.46, ML 2.34–2.40, PeH 0.57–0.6, PNWdv 0.55–0.59, PPH 0.52–0.56.

Head triangular with three ocelli. Eyes large, bulbous, oval in shape and positioned at an angle in lateral view such than longest axis point towards nearest lateral ocellus. Clypeus raised and rounded centrally, anterior margin straight. Mandibles with large apical tooth and two smaller teeth. When angled towards the eye antennal scapes, not surpassing dorsal eye margin. Sculpture coarsely rugose over entire surface, a few raised, transverse strigae present on clypeus and in between antennal insertion points.

Mesoscutum in profile evenly convex from anterior to posterior margin, sculpture coarsely aerolate-rugose tending towards rugulose-strigate anteriorly except for a narrow triangle that runs centrally from anterior margin to approximately one third of length is finely reticulate. Parapsidal lines present. Pronotum reticulate, rugose along dorsal margin. Scutellum large and bulbous with a central depression, sculpture aereolate-rugose. Mesopleuron aereolate, rugose along anterior margin to strigate along posterior margin. Propodeum aereolate laterally to reticulate on dorsal and posterior surfaces, a few raised ridges on ventral third of lateral surfaces. Petiole and postpetiole with a flattened dorsal surface in lateral view, in dorsal view with a small median depression giving a slightly bilobed appearance, sculpture aereolate to reticulate, rugulose strigate on posterior surface of petiole, and posterolateral corners of postpetiole, petiole only slightly taller than postpetiole.

Metasomal tergites and sternites finely reticulate over entire surface.

Head and mesosoma dark brown to black, mandibles, scape and femora and metasoma dark brown, antennal flagellum and remainder of legs and posterior margin of tergites light brown. Head mesosoma and ventral surface of legs and metasomal with large numbers of long, erect light brown setae except for central triangle on mesoscutum which is glabrous.

References based on Global Ant Biodiversity Informatics

 * Sparks K. S., A. N. Andersen, and A. D. Austin. 2014. Systematics of the Monomorium rothsteini Forel species complex (Hymenoptera: Formicidae), a problematic ant group in Australia. Zootaxa 3893(4): 489-529.