| | The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels) |
Morphology. Snails, with a conspicuous, spiral, univalve shell.
The shell operculate (the operculum calcareous and solid, with an apophysis); rising-spiral; 3 whorled; typically dextral; wider than high; about (7.3–)8–11.6 mm high; (8.25–)9–13 mm wide; height about 0.9 x the width; with the body whorl predominating and the spire small and short. The height of the spire about 0.15 x that of the shell. The shell semi-lunate, very asymmetric about the vertical axis, with the spire much displaced to one side. The shell very asymmetic about its vertical axis, with a large body whorl and a small, displaced spire; deeply sutured (at the junction of the body whorl and the spire). The whorls shouldered. The aperture with neither teeth nor calluses. The shell without an umbilicus. The shell thick-lipped; opaque; basically whitish or yellow to brown or even black; conspicuously colour-patterned (with irregular purple, pink or white variegations, or transverse bands, or spirally marked with three dark bands).
General biology, ecology. Freshwater aquatic. Breathing via a single gill attached within the mantle cavity. Restricted to well oxygenated waters, in rivers, canals and lakes.
The individuals either male or female (not hermaphrodite).
Classification. Gastropoda; Prosobranchia.
Representation in Britain and Ireland. Theodoxus (1, “River Nerite”).
Illustrations. • Theodoxus fluviatilis (Reeve). NERITIDAE. Theodoxus fluviatilis (L.), "River Nerite". From Reeve (1863), with approximate scale added. • Theodoxus fluviatilis, 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’.
