| | The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels) |
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.
Representation in Britain and Ireland. Arion (3, “Large Black, Dusky, Durham, etc., slugs”), Geomalacus (1, “Kerry slug”).
Illustrations. • Arion ater: assorted varieties (Taylor). ARIONIDAE. 1–10, Arion ater (Linn.), "Large Black Slug", animals when extended 60–130 mm long. From Taylor (1907). • Arion circumscriptus, A. hortensis, A. intermedius, A. subfuscus, Geomalacus maculosus: assorted varieties (Taylor). ARIONIDAE. 1–6, Arion subfuscus Draparnaud, "Dusky Slug", animals when extended 50–70 mm long. 7–11, Arion hortensis agg., "Garden Slug", 25–35 mm; 12–17, Arion circumscriptus agg., "Bourguignat's Slug", 30–40 mm. 18–23, Arion intermedius Normand, "Hedgehog Slug", 15–20 mm.; 24–27, Geomalacus maculosus Allman, "Kerry Slug", 60–90 mm. From Taylor (1907). • Arion ater, A. circumscriptus, A. hortensis, A. intermedius, A. subfuscus, Geomalacus maculosus (Ellis). ARIONIDAE. 3, Geomalacus maculosus Allman, "Kerry Slug", extending to 60–90 mm. 4, Arion subfuscus Draparnaud, "Dusky Slug", 50–70 mm.; 5, Arion circumscriptus agg., "Bourguignat's Slug", 30–40 mm.; 6, Arion ater (Linn.) var. livida, "Large Black Slug", 60–130 mm.; 7 and 8, Arion intermedius Normand, "Hedgehog Slug", extending to 15–20 mm.; 9, Arion hortensis agg., "Garden Slug", 25–35 mm. TESTACELLIDAE. 10, Testacella haliotidea Draparnaud, "Shelled Slug", 70–100 mm. MILACIDAE. 1, Milax gagates (Draparnaud), "Jet Slug", 45–55 mm.; 2, Tandonia sowerbyi (Férussac), "Sowerby's Keeled Slug", 60–75 mm. From Ellis (1926). • Arion and Geomalacus, with Agriolimacidae, Limacidae and Milacidae (Adams). ARIONIDAE. 1, Arion ater (Linn.), "Large Black Slug"; 2, Arion intermedius Normand, "Hedgehog Slug"; 3, Arion hortensis agg., "Garden Slug"; 5, Geomalacus maculosus Allman, "Kerry Slug". LIMACIDAE. 6, Limax maximus Linn., "Great Grey Slug"; 7, Limax flavus Linn., "Yellow Slug"; 8, Lehmannia marginata (Müller), "Tree Slug". AGRIOLIMACIDAE: 4, Deroceras laeve (Müller), "Marsh Slug"; 9, Deroceras reticulatum (Müller), "Field or Milky Slug". MILACIDAE: 10, probably Tandonia sowerbyi (Férussac), "Sowerby's Keeled Slug". From Adams (1896). • Arion ater, Arion hortensis, Geomalacus maculosus (Reeve). ARIONIDAE. 1, Arion hortensis agg., "Garden Slug". 2, Geomalacus maculosus Allman, "Kerry Slug". 3, Arion ater (L.), "Large Black Slug". From Reeve (1863, with 1cm scale added).
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’.
