Sphaerium nucleus

Sphaerium nucleus is a freshwater bivalve of the family Sphaeriidae. It has been often confused with Sphaerium corneum and is consequently quite poorly known.

Description
Sphaerium nucleus is a very small bivalve which may grow up to 8mm in width and length. It differs from Sphaerium corneum only in details. Like almost all bivalves, it is a filter-feeder.

Taxonomy
Sphaerium nucleus was described by Studer 1820, who placed it in the genus Cyclas. It was later thought to be a subspecies of Sphaerium corneum. Subsequently it was raised to a full species again as Sphaerium nucleus (Studer, 1820) due to its having a different form of kidney, and the shell having a broad hinge plate, dense porosity and more tumid shells with broad umbones. Unlike S. corneum it has a preference for temporary habitats.

Distribution
S. nucleus occurs widely in Europe, from Spain to Ukraine. It appears to be absent from Russia.


 * Austria
 * Britain and Ireland (but see )
 * Czech Republic – in Bohemia, in Moravia
 * Germany
 * Kyrgyzstan (but see )
 * Slovakia
 * Ukraine

Ecology
This species lives in standing freshwater habitats, specifically in swampy conditions in drainage ditches and occasionally in lake margins, including temporary lakes.