Monomorium eremum

This is a cryptic species and is only separable from its sister species Monomorium eremoides by analysis of genetic data. M. eremoides has a disjunct distribution with one population found on the northwest coast of Western Australia and one in central Australia. Monomorium eremum has a more continuous distribution that spans the northwestern and central deserts of Australia and together with 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 large, very dark brown glossy species with large eyes and a heavily sculptured mesonotum. This species cannot be separated from Monomorium eremoides using morphology however, both M. eremoides and M. eremum are two of the most distinctive species in the M. rothsteini complex and can be distinguished from all other species by combination of dark cuticular colour, sinuous clypeal margin and sculptured mesonotum.

Distribution
This species has a widespread distribution that spans the northwestern and central desert region of Western Australia and the Northern Territory.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Genetics
COI sequences. Genbank accession numbers for this species are KC572904–KC572906, KC572941, KC572942 and KC572948–KC57952.

Nomenclature

 *  eremum. Monomorium eremum Sparks, in Sparks, Andersen & Austin, 2015: 502, figs. 4m–o, 11b (w.) AUSTRALIA.

Worker
(n=9). HW 0.84–0.86, HL 0.90–0.98, EL 0.2–0.22, PMH 0.29–0.35, PH 0.27–0.33, PNH 0.18–0.23, LHW 0.51–0.57, EW 0.13–0.14, PML 0.53–0.60, ML 0.94–1.03, PL 0.43–0.47, PNWdv 0.21–0.27.

Large species with a medium sized, rectangular head, posterior cephalic margin mildly depressed centrally to almost straight. Anterodorsal margin of the clypeus sinuous to almost straight, frontolateral carinae forming smooth ridges; anteroventral margin without a small median projection, margin appears straight. Sculpture on frons limited to a few strigae only present on antennal lobes; coarse lateral cephalic strigae reach anterior margin of eye or if not reaching, with a few very fine strigae reaching eye margin. Eyes large and bulbous, EW > 0.23 x LHW, 15 ommatidia in longest vertical axis, 12 in longest horizontal axis.

Mesonotum strigate/rugose over most of surface posteriad of promesonotal suture; metanotal groove deep and broad. Mesopleuron alveolate, dorsally with strigae extending from metanotal groove to promesonotal suture. Propodeum in lateral view with dorsolateral angles almost forming a right angle; posterior margin appears vertical, propodeum appears long and rectangular; sculpture alveolate, laterally with strigae curving from metanotal groove on to dorsal surface, extending over metapleural gland bulla to metanotal groove and over posterior half; dorsally with longitudinal strigae mostly absent, posterodorsal corners prominent and diverging; posterolateral corners with sharp carinae that extend from propodeal lobe onto dorsal surface. Petiole node narrow, less than 2 x eye width when viewed from above; shape in posterior view tapering from widest point just below midline and narrowly rounded dorsally, in lateral view anterior and posterior faces converging to rounded point. Posterior surface of petiole node without sculpture, rarely with fine reticulation along basal posterior margin only, postpetiole with fine reticulation. T1 commonly with very fine reticulate pattern covering most of surface, rarely smooth and shining.

Dorsal surface of head and antennal scapes dark chestnut brown, ventral surface of head and area laterad of clypeus, mandibles and antennal flagellum light brown, mesosoma and legs dark brown although lighter than dorsal surface of head, metasoma very dark brown, almost black, cuticle with a high gloss.

Type Material
Holotype worker. Northern Territory, 33km N Barkley Hmstd, -19.4512, 135.9795, 7 Jun 2009, K.S. Sparks, KSS77 (deposited in NTM). Paratypes. Northern Territory. 9 workers, same data as holotype; 10 workers, same data as holotype KSS78; 12 workers, Stuart Hwy, 44km N Barrow Ck, -21.2165, 134.1349, 10 Jun 2009, K.S. Sparks, KSS91; 14 workers, Tanami Tk, 50km from Stuart Hwy, -23.5097, 133.3840, 12 Jun 2009, K.S. Sparks, KSS93; 20 workers KSS94; 20w, Tanami Rd, 150km from Stuart Hwy, -23.2746, 132.9335, 12 Jun 2009, K.S. Sparks, KSS98; 16 workers, Kintore Rd, 45km W Tanami Rd, -23.2685, 132.4263, 13 Jun 2009, K.S. Sparks, KSS106; 4 workers, Uluru NP, - 25.3512, 131.0636, Oct 2011, A. Andersen, ANA11–40; 6w, ANA11–41; 4 workers ANA11–42 (deposited in, , NTM, , , WAM).

Etymology
The specific name is taken from the Latin word for desert wilderness.

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.