The families of British non-marine molluscs (slugs, snails and mussels)


L. Watson and M. J. Dallwitz


Morphology. Limpets, with a conspicuous, protective patelliform shell bearing only a vestigial spire (the latter represented by a small, rearwardly-directed apical point).

The animal with one pair of tentacles only. Eyes at the bases of the tentacles.

The shell vestigially rising-spiral, or . The animal dextral, with the genital orifice and anus on its right side, although the vestigial spire of the shell inclines to the left. The shell wider than high; 4–7 mm wide (more or less ovoid, and about half this across). The shell very asymmetric about the vertical axis, with the spire much displaced to one side (i.e., taking account of the displaced vestige of the spire). The shell opaque; plain.

General biology, ecology. Freshwater aquatic. The mantle cavity obliterated, and a lobe of the mantle functioning as a gill (and gas exchange also occurring via the skin in general). In clean, still or slow moving water, attaching to plants, submerged timber, or the shells of larger molluscs.

Hermaphrodite (but individuals acting as either male or female when mating).

Classification. Gastropoda; Pulmonata.

British representation. Acroloxus (1, “Lake limpet”).

Illustrations. • Acroloxus lacustris, with Ancylidae and Lymnaeidae (Adams). • Acroloxus lacustris, with Ancylus fluviatilis (Reeve).

To view the illustrations with detailed captions, go to the interactive key. This also offers 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.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2005 onwards. The families of British non-marine molluscs (slugs, snails and mussels). Version: 4th January 2012.’.