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RISSOIDAE |
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Rissoina (Rissoina) cretacea Tenison-Woods, 1878 Description: Shell with spire slightly convex. Protoconch of 1¼ whorls, with distinct junction with teleoconch. Teleoconch of 5½ - 6 weakly convex whorls, weakly angled at top. Whorls sculptured with weak, irregularly spaced axial ribs, weaker on bottom of whorls, fading out on latter whorls; on last whorl present as weak folds on top third of whorl. Spiral sculpture absent. Aperture lens or D-shaped, with broad anterior canal and narrow posterior canal; outer lip expanded, slightly thickened but smooth internally, with minute varix externally; inner lip callused, thickened at top and bottom. Colour uniformly white or yellowish, polished and shining, translucent when fresh, becoming opaque with age. Size: Up to 6.8 mm in length. Distribution: Endemic to Australia; Cape Moreton, Queensland, southwards to Gabo Island, Victoria. Habitat: Subtidal, in 27-120 m. Moderately common. Comparison: R. cretacea is similar to R. rhyllensis, both having fairly smooth shells, and occurring subtidally. R. rhyllensis has a relatively large protoconch of 2 whorls, while that of R. cretacea is small, of 1¼ whorls. The whorls of R. cretacea are more convex than those of R. rhyllensis, and the aperture is narrower. Synonymy: None. Fig. 1: Off Gabo Island, Victoria, 27 m (C.135037) |
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