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Craspedoplax variabilis (H. Adams & Angas, 1864)

Description: Shell valves very variable in sculpture and colour. Jugal area triangular, with longitudinal grooves between smooth or pustulose ridges. Lateral and pleural areas either not differentiated or with lateral areas elevated; both areas pustulose, pustules either in rows or randomly placed. Girdle with sutural tufts of strong bristles, naked between tufts, foot edged with strong bristles. Valve colour variable from white to black, but often mottled fawn.

Size: Up to 16 mm in length, but generally less that 12 mm.

Distribution: Endemic to Australia: southern Qld, southwards and around southern Australia to south-western WA, including Tas.

Habitat: Lives on rocky shores, under rocks. Macpherson & Gabriel (1962) commented it lives below half tide, usually among calcareous algae.

Comparison: This species is very variable in valve sculpture and colour, so these characters are of little use in identification. The broadly triangular jugal zone with longitudinal groves is a constant character. In NSW, the small size of less than 12 mm, longitudinally grooved jugal zone, allied with a girdle with sutural tufts but otherwise bare is usually sufficient for identification.

Synonymy: Both Craspedoplax variabilis cambrica Iredale & Hull, 1925 from Port Jackson, and Craspedoplax variabilis diminuta Iredale & Hull, 1925 from northern Qld are geographical variants.

Remarks: Iredale & Hull (1927, p. 86) included in the description the comment "The girdle shows the usual sutural tufts, but scale-like spicules otherwise cover it". Inspection of wet preserved specimens at 300X magnification shows the surface to be pustulose but no spicules are apparent.

Fig. 1: Photo by Leon Altoff (used by permission)

Fig. 2: Twofold Bay, NSW. (C.147915). Valve V & VI detail.


Copyright Des Beechey 2019