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RISSOIDAE


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Rissoina (Rissoina) iredalei Laseron, 1950

Description: Shell with spire convex. Protoconch of 1 smooth whorl, with distinct junction with teleoconch. Teleoconch of 3-5 moderately convex whorls, shouldered below deeply impressed suture. Axial sculpture of narrow, widely and irregularly spaced axial grooves; spiral sculpture of deep grooves covering entire surface. Aperture lens or D-shaped, with broad anterior canal and narrow posterior canal; outer lip expanded, not thickened and smooth internally, with weak varix externally; inner lip callused, thickened at top and bottom. Colour translucent fawn when fresh, aging to opaque white.

Size: Up to 6.0 mm in length.

Distribution: Endemic to Australia; Tweed Heads, NSW, southwards and around southern Australia to south-western WA, including Bass Strait.

Habitat: On the continental shelf, at depths of 20-150 m. Moderately common.

Comparison: The unusual sculpture of widely-spaced axial grooves makes this species distinctive within the genus.

Synonymy: Rissoina axiscalpta Cotton, 1952, from South Australia, is the same species (NEW SYNONYM).

Fig. 1:  Off Jervis Bay, NSW, in 37 m (C.395971)

 

Copyright Des Beechey 2010