| | 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 present, or absent (Helicodiscus singleyanus being subterranean and blind); when present, at the tips of the posterior tentacles. The jaw not as in Zonitidae and Limacidae; of a single piece.
The shell inoperculate; rising-spiral; 3.5–4 whorled (Helicodiscus), or 4–6 whorled (Discus); typically dextral; 1.8–2.5 mm in its maximum dimension (Helicodiscus), or 5.5–7 mm in its maximum dimension (Discus); wider than high; 1.8–2.5 mm wide (Helicodiscus), or 5.5–7 mm wide (Discus); height about 0.43–0.65 x the width; with the body whorl predominating and the spire small and short to high-spired and tapered gradually from the body whorl. The height of the spire about 0.15–0.29 x that of the shell. The spire obtuse. The shell discoid, or cochleate; deeply sutured. The body whorl moderately convex to very strongly convex. The whorls neither shouldered nor keeled, or shouldered. The aperture with neither teeth nor calluses. The shell with an umbilicus. The umbilicus large and wide. The shell thin-lipped (the mouth edge simple, not deflected); thin and translucent to opaque; yellowish- or greenish-brown; conspicuously colour-patterned (that of D. rotundatus with regularly spaced reddish-brown transverse stripes across the whorls), or plain (in the rest).
General biology, ecology. Terrestrial.
Hermaphrodite.
Classification. Gastropoda; Pulmonata.
Representation in Britain and Ireland. Discus (2), Helicodiscus (1).
Illustrations. • Discus rotundatus (Taylor). DISCIDAE. 6, Discus rotundatus (Müller), "Rounded Snail", "Radiated Snail", maturew shells 5.5–7.0 mm. From Taylor (1914). • Discus rotundatus, with Euconulidae, Punctidae, Pyramidulidae, Valloniidae, Vitrinidae (Adams). DISCIDAE. 6, Discus rotundatus (Müller), "Rounded Snail, or Radiated Snail"). 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"). 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’.
