| | The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels) |
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.
Hermaphrodite.
Classification. Gastropoda; Prosobranchia.
Representation in Britain and Ireland. Valvata (3, “Valve snails”).
Illustrations. • Valvata cristata and Valvata piscinalis (Reeve). VALVATIDAE. 1, Valvata cristata Müller, "Flat Valve Snail". 2, Valvata piscinalis (Müller), "Common Valve Snail". From Reeve (1863), with approximate scales added. • Valvata cristata and Valvata piscinalis, with other Gastropoda-Prosobranchia (Adams). NERITIDAE. 4, Theodoxus fluviatilis (Linn.), "River Nerite". VIVIPARIDAE. 5, Viviparus contectus (Millet), "Lister's River Snail"; 6, Viviparus viviparus (Linn.), "Common River Snail". BITHYNIIDAE. 7, Bithynia tentaculata (Linn.), "Common Bithynia"; 8, Bithynia leachii (Sheppard), "Leach's Bithynia". VALVATIDAE. 9, Valvata piscinalis (Müller), "Common Valve Snail"; 10, Valvata cristata Müller, "Flat Valve Snail". HYDROBIIDAE. 11, Mercuria confusa (Frauenfeld), "Swollen Spire Snail". 12, Hydrobia ventrosa (Montagu), "Spire Snail". 13, Potamopyrgus antipodarum (Gray), "Jenkins's Spire Snail". POMATIASIDAE. 14, Pomatias elegans (Müller), "Round-mouthed Snail". ACICULIDAE. 15, Acicula fusca (Montagu), "Point Snail", with detail of the operculum. From Adams (1896).
We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, 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. See also Guidelines for using data taken from Web publications.
Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels). Version: 5th August 2019. delta-intkey.com’.
