Depressed globose shell, very thin, glassy white, shiny, smooth; short spire with three whorls which grow rapidly, the body whorl very large and ventricose (this species, in its general aspect, is very similar to the freshwater mollusc Valvata piscinalis (Muller, 1774)); deep sutures, obtuse apex, aperture wide and rounded, umbilical slit rather wide with a deep round umbilicus. Dimensions: mm 1-1.3 x mm 0.7-1

Distribution and habitat
Species present from the northern Atlantic to the English Channel and to the Atlantic coasts of France. In literature there is only one record for the Mediterranean (Palazzi, 1985 - Ciucca di Cinisi beach, Terrasini, Palermo), plus those of specimens similar to the species in question (Palazzi, in Biondi et al., 1983 - for the coast of Leghorn). Therefore its presence in the Mediterranean needs confirmation. Never recorded for the Gulf of Naples, though Bogi & Nofroni (1986) recorded a finding, but Gaglini (1987) questions this, relating it to another species. It is a littoral species, living on algae and laminarians.

Diagnostic characters
A minute, globular shell, but with a distinct spire; broader than high, smooth, transparent and glossy; umbilicus large. Snout rather deeply bifid.

Other characters
There are 3-4 tumid whorls which meet at deep sutures. When the shell is viewed from the base the umbilicus is seen to be bounded or slightly covered on one side by the inner lip. Up to 1 mm high and about 1 mm broad; last whorl occupies 80-85% of shell height, the aperture over half.
R. globularis has short tentacles each with an eye behind the base.The flesh is pale and has dark brown markings. The scarcity of records of this animal (mainly from Scotland) suggests that it is rarer than the other two species of the genus, though they all live in the same habitat. R. globularis may well prove to be commoner than believed, having been overlooked or taken to be juveniles of the other species. Breeding has not been described.