The families of British non-marine molluscs (slugs, snails and mussels)
Morphology. Snails, with a conspicuous, spiral, univalve shell.
The shell operculate (this horny and thin or fairly thick, concentrically lined); rising-spiral; 6–7 whorled; typically dextral; 25–35 mm in its maximum dimension (V. viviparus), or 30–40 mm in its maximum dimension (V. contectus); higher than wide; 25–35 mm high (V. viviparus), or 30–40 mm high (V. contectus); about 18–26 mm wide (V. viviparus), or 23.5–31.8 mm wide (V. contectus); height about 1.2–1.3 x the width. The height of the spire about 0.22–0.25 x that of the shell. The shell inverted-pyriform; deeply sutured (between all the whorls). The whorls neither shouldered nor keeled. The aperture almost round; with neither teeth nor calluses. The shell with an umbilicus, or without an umbilicus. The umbilicus small (deep and distinct, in V. contectus only). The shell thick-lipped; opaque; dark greenish with darker bands; conspicuously colour-patterned.
General biology, ecology. Freshwater aquatic. Breathing via a single gill attached within the mantle cavity. In large bodies of well oxygenated, still or slow-moving water. Suspension feeders, lying for long periods in mud with the mouth uppermost.
The individuals either male or female (not hermaphrodite); viviparous.
Classification. Gastropoda; Prosobranchia.
British representation. Viviparus (2, River snails).
Illustrations. • Viviparus contectus and Viviparus viviparus (Reeve). • Viviparus contectus and Viviparus viviparus, with other Gastropoda-Prosobranchia (Adams).
To view the illustrations with detailed captions, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The families of British non-marine molluscs (slugs, snails and mussels). Version: 4th January 2012. http://delta-intkey.com’.