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 the backward pointing apex).

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

The shell vestigially rising-spiral, or . The animal sinistral, with the genital orifice and anus opening on its left side, although the vestigial spire of the shell is slightly twisted to the right. The shell wider than high; 4–8 mm wide (somewhat less than this across, but much more broadly ovate than those of Acroloxus lacustris). 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; greyish horn-coloured, with strong radiating striae and fine growth lines; 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). A. fluviatilis lives in quick-flowing, soft or hard water, attached firmly to stones and grazing on algae and mosses. F. wautieri, by contrast, usually attaches to submerged plants in stagnant or slowly moving water.

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

Classification. Gastropoda; Pulmonata.

British representation. “Limpets”: Ancylus, Ferrissia.

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

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.’.