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| The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels) |
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; rising-spiral (but only slightly raised in Vallonia); 3–3.25 whorled (Vallonia), or 4 whorled (Acanthinula), or 5.5–6 whorled (Spermodea); typically dextral; 2–2.7 mm in its maximum dimension; about as high as wide (Acanthinula), or about as high as wide to wider than high (Spermodea), or wider than high (Vallonia); 2 mm high (Acanthinula), or 2–2.7 mm high (Spermodea, Vallonia); 2 mm wide (Acanthinula, Spermodea), or 1.25–1.4 mm wide (Vallonia); height about 0.5–0.55 x the width (Vallonia), or 0.81 x the width (Spermodea), or 1.13 x the width (Acanthinula); with the body whorl predominating and the spire small and short (in Vallonia), or high-spired and tapered gradually from the body whorl. The height of the spire about 0.14–1.18 x that of the shell (Vallonia), or 0.33 x that of the shell (Acanthinula and Spermodea). The spire when raised, obtuse. The shell when wider than high, discoid, or cochleate (in Vallonia), or cochleate to globose (in Spermodea); when higher than wide, broadly inverted-pyriform (in Acanthinula). The body whorl very strongly convex. The whorls neither shouldered nor keeled to shouldered, or keeled (in Acanthinula); exhibiting a median whorl of spines (in Acanthinula only, the spines derived via prolongations from the transverse ridges, along the keel), or without spines; conspicuously and regularly transversely ridged across the whorls (V. costata, Spermodea lamellata, and Acanthinula), or not conspicuously transversely ridged. The aperture round; with neither teeth nor calluses. The shell with an umbilicus. The umbilicus large and wide (open). The shell thick-lipped (the mouth edge more or less expanded to form a flat lip); thin and translucent, or opaque; greyish white or translucent (Vallonia), pale golden brown (Spermodea), or brown (unweathered Acanthinula); plain.
General biology, ecology. Terrestrial. In diverse habitats.
Hermaphrodite. Courtship involving exchanges of ‘love darts’ prior to mating (the Vallonia species being equipped with a dart sac secreting a straight, simple dart: cf. Ellis), or not involving ‘love darts’.
Classification. Gastropoda; Pulmonata.
Representation in Britain and Ireland. Acanthinula (1, “Prickly snail”), Spermodea (1, “Plated snail”), Vallonia (3, “Grass snails”).
Illustrations. • Vallonia costata, V. excentrica, V. pulchella (Ellis). VALLONIIDAE. 1–3. Vallonia costata (Müller), "Ribbed Grass Snail", 2.0–2.7 mm.; 4–6, Vallonia excentrica Sterki, "Eccentric Grass Snail", 2.0–2.2 mm.; 7–9, Vallonia pulchella (Müller), "Smooth Grass Snail" or "Beautiful Grass Snail", 2.0–2.5 mm. From Ellis (1926). • Acanthinula aculeata, Spermodea lamellata (Ellis). VALLONIIDAE. 1–2, Spermodea lamellata (Jeffreys), "Plated Snail"), 2.0–2.2 mm.; 3, Acanthinula aculeata (Müller), "Prickly Snail", 2.0–2.2 mm. From Ellis (1926). • Acanthinula aculeata, Spermodea lamellata, Vallonia pulchella, with Discidae, Euconulidae, Punctidae, Pyramidulidae, Vitrinidae (Adams). PYRAMIDULIDAE. 1, Pyramidula rupestris (Draparnaud), "Rock Snail". PUNCTIDAE. 2, Punctum pygmaeum (Draparnaud), "Dwarf Snail". VALLONIIDAE. 3, Vallonia pulchella (Müller), "Smooth Grass Snail, Beautiful Grass Snail"; 4, Acanthinula aculeata (Müller), "Prickly Snail"; 5, Spermodea lamellata (Jeffreys), "Plated Snail"). DISCIDAE. 6, Discus rotundatus (Müller), "Rounded Snail, or Radiated Snail"). VITRINIDAE. 7, Vitrina pellucida (Müller), "Pellucid Glass Snail". EUCONULIDAE. 8, Euconulus fulvus agg., probably E. fulvus (Müller), "Tawny Glass Snail". From Adams (1896).
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’.
