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| The families of non-marine molluscs of Britain and Ireland (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.
Hermaphrodite.
Classification. Gastropoda; Pulmonata.
Representation in Britain and Ireland. Deroceras (4, “Marsh, Field, and Milky slugs”).
Illustrations. • Deroceras laeve and Deroceras reticulatum: assorted varieties (Taylor). AGRIOLIMACIDAE. 1–4, Deroceras reticulatum (Müller), "Field or Milky Slug", animals 35–50 mm long when extended. 5–8, Deroceras laeve (Müller), "Marsh Slug", 15–25 mm. From Taylor (1906). • Deroceras reticulatum and D. laeve, with Limacidae (Ellis). AGRIOLIMACIDAE: 6, Deroceras reticulatum (Muller), 35–50 mm.; 7, Deroceras laeve (Müller), "Marsh Slug", 15–25 mm. LIMACIDAE. 1, Limax maximus; 2, Limax cinereoniger Wolf, "Ash-black Slug", 100–200 mm.; 3, Limax flavus L., "Yellow Slug", 80–130 mm.; 4, Lehmannia marginata (Müller), "Tree Slug", 70–80 mm.; 5, Malacolimax tenellus (Müller), "Slender Slug" or "Tender Slug", 35–50 mm. From Ellis (1926). • Deroceras reticulatum and Deroceras laeve, with Arionidae, 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). • Deroceras reticulatum (Reeve). AGRIOLIMACIDAE. Deroceras reticulatum (Müller): "Field Slug", "Milky 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’.
