The families of British non-marine molluscs (slugs, snails and mussels)
Morphology. Snails, with a conspicuous, spiral, univalve shell.
The animal with one pair of tentacles only (these broad-based, triangular, and flattened). Eyes at the bases of the tentacles.
The shell inoperculate; rising-spiral; 3–8 whorled; typically dextral, or sinistral (exemplified in particular by aberrant populations of Lymnaea peregra); (7–)10–45(–50) mm in its maximum dimension; higher than wide (mostly), or higher than wide to about as high as wide; (7–)10–45(–50) mm high; height about 1.2–2.8 x the width. The height of the spire about 0.05–0.48 x that of the shell. The spire acute (even when very short). The shell very asymmetric about the vertical axis, with the spire much displaced to one side (notably in Lymnaea auricularia, Myxas glutinosa and forms of L. peregra), or more or less symmetrical about its vertical axis (mostly). The shell when wider than high, very asymmetic about its vertical axis, with a large body whorl and a small, displaced spire; when higher than wide, fusiform (broadly), or ovoid-asymmetric, or inverted-pyriform, or tear-shaped, or turretiform; deeply sutured (especially so at the base of the spire). The whorls neither shouldered nor keeled. The aperture with neither teeth nor calluses. The columella folded, or twisted. The shell thick-lipped (the aperture often strengthened by a thickened rib), or thin-lipped; thin and translucent to opaque; mostly more or less horn-coloured, sometimes brown-, purplish- or greyish-tinged, but sometimes rendered blackish by extraneous matter; plain.
General biology, ecology. Terrestrial to freshwater aquatic, or freshwater aquatic. Breathing air directly via the lung-like mantle cavity (and via the skin in general). Species of diverse wet and aquatic habitats, often on emergent vegetation or tolerant of seasonal dessication. L. truncatula, living in wet places but mostly out of water, is notorious as the intermediate host of Fasciola hepatica, the sheep liver fluke.
Hermaphrodite (but individuals acting as either male or female when mating).
Classification. Gastropoda; Pulmonata.
British representation. Lymnaea (6, Pond snails), Myxas (1).
Illustrations. • Lymnaea auricularia, L. glabra, L. palustris, L. peregra, L. stagnalis, L. truncatula, Myxas glutinosa (Reeve). • Lymnaea auricularia, L. glabra, L. palustris, L. peregra, L. stagnalis, L. truncatula, Myxas glutinosa (Ellis). • Lymnaea species and Myxas glutinosa, with Ancylidae (Adams). • Lymnaea peregra (L.W.).
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’.