The families of British non-marine molluscs (slugs, snails and mussels)

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L. Watson and M. J. Dallwitz

Arionidae

Morphology. Slugs, with no external shell.

25–130 mm long when fully extended. With a degenerate internal shell (this sometimes represented by a few calcareous granules). Contracting protectively into into a hemispherical or (Geomaculus) sub-globular form when molested (this readily distinguishing Arionidae from the other slug families). The body variable in colour and often with much infra-specific variation, as exemplified by the big, ubiquitous Arion ater, which is often black but may be brick-red, orange or grey; but spotted only in Geomalacus. The mucous colourless, or milky, or yellow or orange. The mantle anterior and large; shagreened, but with neither a dorsal island demarcated by a groove, nor a fingerprint-like pattern of folds. The animal with two pairs of tentacles. Eyes at the tips of the posterior tentacles. The respiratory pore towards the anterior right of the mantle. The tail not dorsally keeled.

General biology, ecology. Terrestrial. Species of diverse, moderately damp, usually sheltered habitats.

Hermaphrodite.

Classification. Gastropoda; Pulmonata.

British representation. Arion (3, “Large Black, Dusky, Durham, etc., slugs”), Geomalacus (1, “Kerry slug”).

Illustrations. • Arion ater: assorted varieties (Taylor). • Arion circumscriptus, A. hortensis, A. intermedius, A. subfuscus, Geomalacus maculosus: assorted varieties (Taylor). • Arion ater, A. circumscriptus, A. hortensis, A. intermedius, A. subfuscus, Geomalacus maculosus (Ellis). • Arion and Geomalacus, with Agriolimacidae, Limacidae and Milacidae (Adams). • Arion ater, Arion hortensis, Geomalacus maculosus (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’.

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