The families of British non-marine molluscs (slugs, snails and mussels)
Morphology. Slugs, with no external shell.
15–50 mm long when fully extended. With a small, totally internal, asymmetrical shell. Contracting protectively when molested, but not assuming the hemispherical or sub-globular form characteristic of Arionidae. The body very variable in colour and markings: buff, cream, pale yellow, light to chestnut or dark brown, grey or black, often flecked, sometimes rather translucent. The mucous colourless, or milky. The mantle anterior and large; with a fingerprint-like pattern of fine, concentric rings; with the concentric rings centred to the right of the mid-line, above the respiratory pore. The animal with two pairs of tentacles (the anterior pair short). Eyes at the tips of the posterior tentacles. The jaw arcuate, with a vertical central keel ending in a median projection on the lower edge (cf. Zonitidae). The respiratory pore towards the posterior right of the mantle. The tail dorsally bluntly keeled, but the keel falling short of the mantle.
General biology, ecology. Terrestrial, or terrestrial to freshwater aquatic (D. laeve). D. laeve occurs in very wet places - fens, river banks, water meadows, etc., where it can survive submerged. The other species are found in gardens, parks, waste ground, hedges, fields, meadows, pastures, etc., and D. reticulatum is a major agricultural and horticultural pest in lowland areas, where it is perhaps the commonest British slug. Feeding mainly on living green plants.
Classification. Gastropoda; Pulmonata.
British representation. Deroceras (4, Marsh, Field, and Milky slugs).
Illustrations. • Deroceras laeve and Deroceras reticulatum: assorted varieties (Taylor). • Deroceras reticulatum and D. laeve, with Limacidae (Ellis). • Deroceras reticulatum and Deroceras laeve, with Arionidae, Limacidae and Milacidae (Adams). • Deroceras reticulatum (Reeve).
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’.