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| The families of non-marine molluscs of Britain and Ireland (slugs, snails and mussels) |
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.
Representation in Britain and Ireland. “Orb mussels, Pea Shells”: Musculium (2), Pisidium (17), Sphaerium (3).
Illustrations. • Bivalvia: Margaritifera, Musculium, Pisidium, Sphaerium, Unio (Adams). SPHAERIIDAE. 1, Sphaerium corneum (Linn.), "Horny Orb Mussel"; 2, Sphaerium rivicola (Lamarck), "Nut Orb Mussel, River Orb Mussel". 3, Musculium transversum (Say), "Oblong Orb Mussel"; 4, Musculium lacustre (Müller), "Lake Orb Mussel, Capped Orb Mussel". 5, Pisidium amnicum (Müller), "River Pea Shell, Giant Pea Shell"; 6, Pisidium pulchellum Jenyns; 7, Pisidium obtusale (Lamarck); 8, Pisidium nitidum Jenyns; 9, Pisidium milium Held, "Rosy Pea Shell". UNIONIDAE. 10, Unio tumidus Philipsson, "Swollen River Mussel:; 11, Unio pictorum (Linn.), "Painter's Mussel". MARGARITIFERIDAE. 12, Margaritifera margaritifera (Linn.), "Freshwater Pearl Mussel, Scottish Pearl Mussel". From Adams (1896). • Pisidium nitidum, P. obtusale, P. pulchellum, and P. pusillum (Adams). 1, Pisidium pulchellum Jenyns; 2, Pisidium nitidum Jenyns; 3, Pisidium milium Held, "Rosy Pea Shell"; 4, Pisidium obtusale (Lamarck). 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’.
