Sphaerium nucleus is a freshwater bivalve of the family Sphaeriidae.

[1] Sphaerium nucleus is a very small bivalve which may grow up to 8mm in width and length.

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.

[3] S. nucleus occurs widely in Europe, from Spain to Ukraine.

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