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.

The animal with two pairs of tentacles. Eyes at the tips of the posterior tentacles.

The shell inoperculate; planispiral (Helicodonta), or rising-spiral (the rest, but some discoid, with the spire scarcely raised); (4–)5–7 whorled (mostly), or 8–10 whorled; typically dextral; (5–)6–40(–50) mm in its maximum dimension (wide), or 10–25(–40) mm in its maximum dimension (high); higher than wide (conspicuously so only in Cochlicella), or about as high as wide (more or less,in Trochoidea elegans, Helix aspersa, H. pomatia and Arianta arbustorum), or wider than high (mostly, at least somewhat); 3.5–50 mm high; 5–50 mm wide (the measurements and proportions reflecting great variation in sizes and shapes among, and sometimes within, the genera); height about 0.45 x the width (Helicodonta), or 0.59–1 x the width (mostly), or 1.8–2 x the width (Cochlicella); with the body whorl predominating and the spire small and short, or high-spired and tapered gradually from the body whorl. The height of the spire about 0.09–0.32 x that of the shell (mostly), or 0.57–0.66 x that of the shell (Cochlicella), or inapplicable to the planispiral in Helicodonta. The spire acute (in Cochlicella), or obtuse (mostly). The shell when not or scarcely higher than wide, discoid (in Helicella, and more or less so in Helicogona lapicida), or conical (in Trochoidea elegans and Cochlicalla barbara), or cochleate (most commonly), or subglobose to globose (in Helix aspersa and H. pomatia); when markedly higher than wide, i.e. in Cochlicella, tear-shaped, or turretiform; shallowly sutured, or deeply sutured, or shallowly sutured to deeply sutured. The whorls neither shouldered nor keeled (mostly), or shouldered (Perforatella subrufescens), or keeled (Trochoidea, Hygromia, Helicogona); conspicuously and regularly transversely ridged across the whorls, or not conspicuously transversely ridged. The aperture with neither teeth nor calluses. The shell with an umbilicus. The shell thick-lipped; opaque; variously white, yellow, pink, horn-coloured, or brown; conspicuously colour-patterned (often strikingly banded along or occasionally across the whorls), or plain.

General biology, ecology. Terrestrial. Mostly in dry, sunny, open, especially calcareous places, in quarries, stone walls, hedgerows, waste ground, gardens, etc.; but a few confined to moist and sheltered or marshy places, or woodland.

Hermaphrodite. The stalk of the bursa copulatrix with a diverticulum. Courtship involving exchanges of ‘love darts’ prior to mating; the darts calcareous (the darts exhibit characteristic shapes and sculpting, for example providing ready means of distinguishing C. hortensis from C. nemoralis - see illustrations).

Classification. Gastropoda; Pulmonata.

British representation. Arianta (1, “Copse snail”), Ashfordia (1, “Silky snail”), Candidula (2, “Wrinkled snail”), Cepaea (2, “Grove snail and White-lipped snail”), Cernuella (1, “Striped snail, Zoned snail”), Cochlicella (2, “Pointed snails”), Helicodonta (1, “Cheese snail”), Helicella (1, “Heath snail”), Helicogona (1, “Lapidary snail”), Helix (including Cantareus) (2, “Garden snail”, and “Edible” or “Roman snail”), Hygromia (2, “Girdled snail and Hedge snail”), Monacha (2, “Carthusian snail and Kentish snail”), Perforatella (2, “Brown snail”), Ponentina (1), Trichia (3, including “Strawberry snail“ and “Hairy snail”), Theba (1, “White snail, Sandhill snail”), Trochoidea (2, “Top snails”).

Illustrations. • Arianta arbustorum: shell variation (Taylor). • Arianta arbustorum: shells (L.W.). • Cepaea hortensis: shell variation (Taylor). • Cepaea hortensis: diverse shells from one locality (L.W.). • Cepaea nemoralis: shell variation (Taylor). • Cepaea nemoralis: shell variation from one locality (L.W.). • Cernuella virgata: shell variation (Taylor). • Cochlicella acuta: live animal (Reeve). • Helicella itala, shells (L.W.). • Helicogona lapicida: shell varieties (Taylor). • Helicigona lapicida (L.W.). • Helix aspersa: shell varieties (Taylor). • Helix aspersa: live animal (Reeve). • Helix pomatia shells (Taylor). • Monacha cartusiana shells (L.W.). • Theba pisana: shell variation (Taylor). • Theba pisana (L.W.). • Trichia striolata, shells (L.W.). • Candidula, Cernuella, Helicella, Helicodonta, Hygromia, Trochoidea (Ellis). • Ashfordia, Perforatella, Ponentina, Trichia (Ellis). • Helix sens. lat., exemplifying 16 genera (Adams). • Courtship in Helix aspersa (Shaw and Nodder, 1790). • Love darts of Arantia, Cepaea, Cernuella, Helicigona, Helix, Theba (Taylor).

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.’.