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 sub- at the bases of the tentacles.

The shell operculate (this circular, horny and thin, concentrically multi-spiral); planispiral (V. cristata), or rising-spiral; 5 whorled, or 6 whorled; typically dextral; 3–6 mm in its maximum dimension; wider than high, or about as high as wide (V. piscinalis); 1.2–1.6 mm high (V. cristata), or 3–4.3 mm high (V. macrostoma), or 4.5–6 mm high (about, in the high spired V. piscinalis); 3–3.5(–4) mm wide (V. cristata), or 3.5–5 mm wide (V. macrostoma), or 4.5–6 mm wide (about, in V. piscinalis); height about 0.6 x the width (V. macrostoma), or 1 x the width (V. piscinalis). The height of the spire about 0.17 x that of the shell (V. macrostoma), or 0.24 x that of the shell (V. piscinalis). The spire when raised, obtuse. The shell when not planispiral, discoid (V. macrostoma), or cochleate to globose (V. piscinalis); when raised, deeply sutured. The whorls neither shouldered nor keeled. The aperture round; with neither teeth nor calluses. The columella smooth. The shell with an umbilicus, or without an umbilicus (V. piscinalis). The umbilicus when present, large and wide (and deep). The shell thick-lipped to thin-lipped; opaque; brownish-yellow or horn-coloured; plain.

General biology, ecology. Freshwater aquatic. Breathing via a single gill attached within the mantle cavity (the left gill feather-like and exsertile, the right thread-like). In slowly flowing or still water, often on muddy or silty substrates.


Classification. Gastropoda; Prosobranchia.

British representation. Valvata (3, “Valve snails”).

Illustrations. • Valvata cristata and Valvata piscinalis (Reeve). • Valvata cristata and Valvata piscinalis, 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.’.