The families of British non-marine molluscs (slugs, snails and mussels)


L. Watson and M. J. Dallwitz


Morphology. Snails, with a conspicuous, spiral, univalve shell.

Eyes at the bases of the tentacles.

The shell operculate (this thick, somewhat calcified, concentrically lined); rising-spiral; 5 whorled, or 6 whorled; typically dextral; 5–13(–16) mm in its maximum dimension; higher than wide; 5–13(–16) mm high; about 3.25–8.5(–10.4) mm wide; height about 1.5–1.55 x the width; with the body whorl predominating and the spire small and short. The height of the spire about 0.3–0.35 x that of the shell. The spire acute to obtuse. The shell inverted-pyriform; deeply sutured (very deeply so in B. leachii). The whorls neither shouldered nor keeled. The aperture round to oval; with neither teeth nor calluses. The shell with an umbilicus to without an umbilicus. The umbilicus small (small). The shell thick-lipped; thin and translucent to opaque; horn-coloured; plain (glossy).

General biology, ecology. Freshwater aquatic. Breathing via a single gill attached within the mantle cavity. In large bodies of well oxygenated, slow moving or still, hard water.

The individuals either male or female (not hermaphrodite).

Classification. Gastropoda; Prosobranchia.

British representation. Bithynia (2, “Bithynia snails”).

Illustrations. • Bithynia leachii and Bithynia tentacula (Reeve). • Bithynia leachii and Bithynia tentaculata, 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.’.