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Rissoina (Rissoina) fasciata A. Adams, 1851

Description: Shell variable in size, shape and sculpture, spire weakly to strongly convex. Protoconch of 1 whorls, with distinct junction with teleoconch. Teleoconch of 4 - 7 weakly to strongly rounded whorls in adult shells. Whorls sculptured with weak or strong axial ribs on all whorls or only on early whorls; when present on last whorl, fading out just below periphery. Spiral sculpture of fine threads over whole surface, not crossing axial ribs. Aperture lens or D-shaped, with broad anterior canal and narrow posterior canal; outer lip expanded, thickened but smooth internally, sometimes with weak varix externally; inner lip callused, thickened at top and bottom. Colour uniformly white, fawn or brown, or white with broad brown spiral bands.

Size: Up to 9.3 mm in length.

Distribution: Endemic to Australia; Moreton Bay, Queensland, southwards and around southern Australia as far as Port MacDonnell, SA, including Tasmania.

Habitat: Lives under rocks intertidally and in the shallow subtidal. Common.

Synonymy: Due to the variability of this species, there are many synonyms. Those given by Sleurs (1992) are Rissoina hanleyi Schwartz, 1860; R. flexuosa Gould, 1861; R. cincta Angas, 1867; R. smithi Angas, 1867; R. variegata Angas, 1867; Moerchiella deleta Laseron, 1956.

Remarks: This is one of the most common and one of the most variable shells in beach washup in NSW. Adult specimens, recognised by the flared outer lip of the aperture, vary in length from 4.3 - 9.3 mm, in shape from narrow to wide, in sculpture from almost smooth to strongly axially ribbed, in whorl shape from nearly flat to strong rounded, and in colour from white to brown to banded. The axial ribs may be present on all whorls, or on just some of the whorls. Recent Australian literature has commonly recognised two species, R. fasciata A. Adams, 1851 and R. variegata Angas, 1867, but Sleurs (1992), who studied a wide range of shells and animal anatomy, including penial characters, concluded there is one variable species.

Fig. 1:  a. Manly Cove, North Harbour (C.314666) b. Tuggerah Beach, NSW (C.314624)

Fig. 2:  All specimens Pebbly Beach, NSW (DLB5359)

 

Copyright Des Beechey 2010