Chelaner decuria

This appealing little ant is inconspicuous, and probably more abundant than the distribution records suggest. (Heterick 2001)

Identification
Heterick (2001) - A member of the falcatus group. This is the only Australian Chelaner with 10-segmented antennae. Nonetheless, the form of the propodeum and of the body sculpture clearly places Chelaner decuria in the same species-group as Chelaner elegantulus, Chelaner falcatus and Chelaner lacunosus.

Heterick (2009) - Aside from members of some populations of putative Monomorium sydneyense, this is the only Australian Chelaner or Monomorium with a 10-segmented antenna.

Distribution
Heterick (2009) - Confined to the south-west corner of WA, this species has a more localized distribution than most of the other members of its species group. However, it is easily the most common.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Heterick (2001) - In southwestern Australia, the species occupies habitats ranging from wet sclerophyll forest to coastal Banksia and Dryandra scrubland.

I observed activity at a nest in semi-rural bush and parkland in Kwinana, Western Australia, where the ants were foraging nocturnally on sand with sparse ground cover. The workers moved very slowly across the ground surface. The entrance to the nest was a minute hole, barely larger than an individual worker. No excavated soil or other material could be seen around the nest.

Heterick 2009 - Occurs in woodlands, up to the outskirts of towns and cities, including the Perth metropolitan area.

Nomenclature

 *  decuria. Monomorium decuria Heterick, 2001: 379, figs. 24, 69 (w.) AUSTRALIA.
 * Combination in Chelaner: Sparks et al., 2019: 232.

Worker
Holotype. HML 1.70; HL 0.69; HW 0.63: Cel 92; SL 0.43; SI 67; PW 0.39. Other. HML 1.41-1.83; HL 0.56-0.74; HW 0.52-0.72; Cel 92-97; SL 0.36-0.46; SI 65- 74; PW 0.28-0.41 (9 measured).

As for the worker of Chelaner falcatus, but with the following apomorphies.

Head. Frons of head capsule microreticulate and striolate with combination of appressed setulae and erect and suberect setae. (Viewed from front) compound eyes set at midpoint of each side of head capsule; (viewed laterally) compound eyes set posterior of midline ofhead capsule; eye moderate, eye width 0.5-1.5x greatest width of antennal scape. Antennal segments 10. Longest lateral anterior clypeal setae long, extending beyond dorsal margin of closed mandibles. Maximum number of mandibular teeth and denticles: five; mandibles (viewed from front) triangular and striate, with piliferous punctures; apical and basal mandibular margins meeting in tooth or denticle.

Alitrunk. Promesonotum with uniform microreticulation and dorsal foveae; evenly convex dorsally; erect and suberect promesonotal setae absent to >5; setulae appressed. Mesonotal suture absent. Metanotal groove absent. Propodeal processes present on posterior propodeal angles as small denticles or sharp flanges. Propodeal angle absent; propodeal setulae appressed.

Petiole and postpetiole. Ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) near 4:3. Anteroventral process always present as pronounced spur. Ventral lobe present in some individuals. Height-length ratio of postpetiole near 2:1 to near 4:3. Ventral process absent or vestigial.

General characters. Colour light brown, head and gaster darker, appendages tawny yellow. Worker caste monomorphic.

Type Material
Holotype. Worker, Western Australia, Kwinana, 31.i.l987, B. E. Heterick, soil, mixed native/ exotic veg., semi rural environment, 125/6MonBH49. Paratypes. Western Australia: 2x4 workers, Geraldton, 300 miles N of Perth, 22.v.l963, C. Mercovich, 300 ft., ca 15 miles inland, savannah woodland, 10 seg. antennae, Chelaner ( and ).



Etymology
Latin: “division of ten”.

References based on Global Ant Biodiversity Informatics

 * Heterick B. E. 2001. Revision of the Australian ants of the genus Monomorium (Hymenoptera: Formicidae). Invertebrate Taxonomy 15: 353-459.
 * Heterick B. E. 2009. A guide to the ants of south-western Australia. Records of the Western Australian Museum Supplement 76: 1-206.