Chelaner sublamellatus

This small (TL < 2.5 mm) ant was collected many years ago from a litter berlesate from North Twin Peaks Island in the Recherche Archipelago. The holotype and sole known specimen (a worker) belongs to the WA Museum. (Heterick 2009)

Identification
Heterick (2009) - Three large and four minute teeth on each mandible, sharp propodeal spines (similar to those possessed by the eastern states species Monomorium sculpturatum), and a large, ventrally carinate, subpetiolar process that ends in a spur anteriad.

Heterick (2003) - An unusual Monomorium in having seven teeth and denticles. In M. sublamellatum, the four tiny denticles may be a derived feature, representing a modification of the two basal-most teeth, the primitive number of teeth being five.

The large subpetiolar process is also unique among Australian Monomorium workers, but is paralleled in the South African species Monomorium lubricum. Other features that occur less frequently in Australian Monomorium include the propodeal spines, the relatively small eye, and the strongly striate sculpture of the alitrunk. However, this ant shares several of the characters found in most of those Monomorium formerly placed in Chelaner, namely a 12-segmented, gradually tapering antenna without a discernible club, a protrusive anteromedian clypeal border, a small, laterally placed propodeal spiracle, and a thick petiolar node that is higher than the postpetiole. Nonetheless, this species is sufficiently distinctive that I am unable to assign it to any of the species-groups discussed in Heterick (2001), and its affinities are unclear.

Distribution based on Regional Taxon Lists
Australasian Region: Australia.

Biology
Heterick (2003) - The known location for the ant is an offshore island approximately 100 km east of the small south coastal town of Esperance. Apart from the results of a few attempts at farming and sheep grazing by former settlers, most of the Recherche Archipelago remains in a natural state (Burbidge et al. 1993). Faunistically, the Recherche Archipelago appears to be comparable to the adjacent southern coast of Australia. For instance, the islands support a moderately rich (i.e., 20 spp.) herpetofauna, though one that includes mainly common species found on the nearby mainland and which is unremarkable in terms of conservation values (Smith & Johnstone 1996). However, the flora of these islands includes at least 384 species of vascular plants (Keighery 1995), with many niches available for small invertebrates such as ants. Moreover, the ant fauna of the Esperance region and further to the east is not particularly well-known, and may well yield additional surprises.

Nomenclature

 *  sublamellatum. Monomorium sublamellatum Heterick, 2003: 250, figs. 2, 3, (w.) AUSTRALIA.

Worker
Holotype. HML 1.57; HL 0.58; HW 0.48; CeI 82; SL 0.41; SI 86; PW 0.32.

Head. Head rectangular, vertex planar; frons longitudinally striate-reticulate with inwardly curved, fine, decumbent setae. Compound eyes circular; (viewed from front) eyes set in anterior half of head capsule; (viewed from side) eyes set slightly posterior of midline of head capsule; eye size moderate, about same width as antennal scape. Antennal segments 12; antenna gradually tapering without a clearly differentiated club. Anteromedian portion of clypeus bicarinate, median clypeal carinae protruding narrowly, produced apically as a pair of tiny denticles; median seta present on anterior margin of clypeus; longest lateral anterior clypeal setae long, extending beyond dorsal margin of closed mandibles; posteromedian clypeal margin level with posterior surface of antennal fossae; anterior tentorial pits about equidistant between mandibular insertions and antennal fossae. Frontal lobes parallel, sinuate; venter of head capsule without long, strongly curved setae. Palp formula unclear, but palps visibly short (one or two segments). Mandibles triangular, smooth and shining with scattered piliferous punctures; mandibles each with large apical tooth, two large subapical teeth and four tiny denticles; basal tooth a tiny denticle; basal angle of mandible distinct, apical and basal mandibular margins ending in a denticle. Alitrunk. Promesonotal sculpture in form of longitudinal striae, some reticulate sculpture also present on anterior and posterolateral sectors, cuticle between striae shining; in profile, promesonotum abruptly declivous before its juncture with head capsule, gently convex thereafter throughout most of its length; many (i.e., >20) erect and suberect setae present on promesonotum, all of approximately the same length. Mesonotal suture visible as fine line, terminating at mesothoracic spiracle. Metanotal groove present as feebly impressed furrow between promesonotum and propodeum. Propodeal sculpture present laterally and on anterodorsal sector as longitudinal striae, posterodorsal sector of propodeum more-or-less smooth, enclosed within an arch-shaped carina directed anteriad; dorsal propodeal face flattened; propodeal angle present; propodeal angles produced as short, sharp spines; metapleural lobes blunt, acute-angled flanges; length ratio of dorsal propodeal face to its declivous face near 1:1; declivous face of propodeum smooth except for two faint transverse striae between propodeal spines; erect and suberect propodeal setae sparse; decumbent or appressed propodeal setae apparently lacking; propodeal spiracle lateral and about midway between metanotal grove and declivous face of propodeum; propodeal spiracular vestibule indistinct. Petiole and postpetiole. Petiolar spiracle small, lateral and positioned slightly ahead of petiolar node; in profile, peduncle short, its length about half width of node. In profile, shape of petiolar node subcuboidal; sculpture of node reticulate; ratio of greatest node breadth (i.e., viewed from front) to greatest node width (i.e., viewed in profile) near 1:1; subpetiolar process a large, thick flange, projected anteriad as a spur, underside of process possessing two distinct carinae which converge anteriad, about two thirds of the way along their length. Height ratio of petiolar node to postpetiole between 2:1 and 1:1. In profile, height-length ratio of postpetiole near 1:2; sculpture of postpetiole reticulate; ventral process on postpetiole present and distinct. Gaster. Pilosity of first gastral tergite consisting of abundant, semi-erect yellowish setae of approximately the same length; surface of sclerites smooth and shining. General characters. Colour a uniform, rich yellow. Worker caste differentiation not able to be assessed (only one specimen known).

Type Material
Holotype. Western Australia. Worker, North Twin Peaks Island, Recherche Archipelago, 9.v. 1976, C. Bryce, NE side at face of granite (WAM 94/1679). The single known specimen of Monomorium sublamellatum has been deposited with the Western Australian Museum.



Etymology
Latin adjective sub ‘under’ + lamellatum ‘thin plate’.