| | 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 one pair of tentacles only (these broad-based, triangular, and flattened). Eyes at the bases of the tentacles.
The shell inoperculate; rising-spiral; 3–8 whorled; typically dextral, or sinistral (exemplified in particular by aberrant populations of Lymnaea peregra); (7–)10–45(–50) mm in its maximum dimension; higher than wide (mostly), or higher than wide to about as high as wide; (7–)10–45(–50) mm high; height about 1.2–2.8 x the width. The height of the spire about 0.05–0.48 x that of the shell. The spire acute (even when very short). The shell very asymmetric about the vertical axis, with the spire much displaced to one side (notably in Lymnaea auricularia, Myxas glutinosa and forms of L. peregra), or more or less symmetrical about its vertical axis (mostly). The shell when wider than high, very asymmetic about its vertical axis, with a large body whorl and a small, displaced spire; when higher than wide, fusiform (broadly), or ovoid-asymmetric, or inverted-pyriform, or tear-shaped, or turretiform; deeply sutured (especially so at the base of the spire). The whorls neither shouldered nor keeled. The aperture with neither teeth nor calluses. The columella folded, or twisted. The shell thick-lipped (the aperture often strengthened by a thickened rib), or thin-lipped; thin and translucent to opaque; mostly more or less horn-coloured, sometimes brown-, purplish- or greyish-tinged, but sometimes rendered blackish by extraneous matter; plain.
General biology, ecology. Terrestrial to freshwater aquatic, or freshwater aquatic. Breathing air directly via the lung-like mantle cavity (and via the skin in general). Species of diverse wet and aquatic habitats, often on emergent vegetation or tolerant of seasonal dessication. L. truncatula, living in wet places but mostly out of water, is notorious as the intermediate host of Fasciola hepatica, the sheep liver fluke.
Hermaphrodite (but individuals acting as either male or female when mating).
Classification. Gastropoda; Pulmonata.
Representation in Britain and Ireland. Lymnaea (6, “Pond snails”), Myxas (1).
Illustrations. • Lymnaea auricularia, L. glabra, L. palustris, L. peregra, L. stagnalis, L. truncatula, Myxas glutinosa (Reeve). LYMNAEIDAE. 1, Lymnaea peregra (Müller), "Common Pond Snail", "Wandering Pond Snail". 2, Lymnaea involuta Thomson (confined to Co. Cork and Co. Kerry, probably a form of L. peregra). 3, Lymnaea palustris (Müller), "Marsh Pond Snail". 4, Lymnaea glabra (Müller), "Mud Pond Snail". 5, Lymnaea truncatula (Müller), "Dwarf Pond Snail". 6, Lymnaea auricularia (L.), "Ear Pond Snail". 7, Lymnaea stagnalis (L.), "Great Pond Snail". 8, From Reeve (1863), with shell lengths added. • Lymnaea auricularia, L. glabra, L. palustris, L. peregra, L. stagnalis, L. truncatula, Myxas glutinosa (Ellis). LYMNAEIDAE. 1–2, Lymnaea peregra (Müller), "Common Pond Snail", "Wandering Pond Snail". 3–6, varieties of L. peregra: 3, var. ovata; 4, var. burnetti; 5, var. praetenuis; 6, var. involuta. 7, Lymnaea glabra (Müller), "Mud Pond Snail". 8–9, Lymnaea truncatula (Müller), "Dwarf Pond Snail". 10, Lymnaea palustris (Müller), "Marsh Pond Snail". 11 and 12, Lymnaea auricularia (L.), "Ear Pond Snail". 13, Lymnaea stagnalis (L.), "Great Pond Snail". 14 and 15, Myxas glutinosa (Müller), "Mucilaginous Snail". From Ellis (1926), with approximate shell lengths added. • Lymnaea species and Myxas glutinosa, with Ancylidae (Adams). LYMNAEIDAE. 1, Myxas glutinosa (Müller), "Glutinous Snail". 2, Lymnaea involuta Thomson, probably a form of L. peregra. 3b, Lymnaea peregra (Müller), "Common Pond Snail, Wandering Pond Snail". 3a and 3e, Lymnaea ovata (Draparnaud), probably also a form of L. peregra. 4, Lymnaea auricularia (Linn.), "Ear Pond Snail". 5, Lymnaea stagnalis (Linn.), "Great Pond Snail". 6, Lymnaea palustris (Müller), "Marsh Pond Snail". 7, Lymnaea truncatula (Müller), "Dwarf Pond Snail". 8, Lymnaea glabra (Müller), "Mud Pond Snail". ANCYLIDAE. 9, Ancylus fluviatilis Müller, "River Limpet". 10, Acroloxus lacustris (Linn.), "Lake Limpet". From Adams (1896). • Lymnaea peregra (L.W.). Limnaea peregra. Canal, Leek, Staffs. November 1949.
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’.
