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


L. Watson and M. J. Dallwitz


Morphology. Mussels, enclosed by a hinged, bivalve shell.

Eyes absent (the animals with no developed head). Without a byssus.

The shell 1.5–11 mm in its maximum dimension (Pisidium), or 7–22 mm in its maximum dimension; 1.5–11 mm wide (Pisidium), or 7–22 mm wide (and usually about two thirds as long from the hinge to the front). The shell not bent, the margin opposite the hinge outwardly curved. The shell thin and translucent, or opaque (but thin relative to that of other British mussels); greyish-, creamy-, yellowish or greenish horn-coloured, glossy.

General biology, ecology. Freshwater aquatic. Breathing via complex gills. In diverse aquatic habitats, some species tolerating seasonal drying up.

Classification. Bivalvia.

British representation. “Orb mussels, Pea Shells”: Musculium (2), Pisidium (17), Sphaerium (3).

Illustrations. • Bivalvia: Margaritifera, Musculium, Pisidium, Sphaerium, Unio (Adams). • Pisidium nitidum, P. obtusale, P. pulchellum, and P. pusillum (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.’.