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.[3]
Distribution
S. nucleus occurs widely in Europe, from Spain to Ukraine. It appears to be absent from Russia.[1]
This species lives in standing freshwater habitats, specifically in swampy conditions in drainage ditches and occasionally in lake margins, including temporary lakes.[1]
^Studer, S. 1820. Kurzes Verzeichniss der bis jetzt in unserm Vaterlande entdeckten Conchylien. - Naturwissenschaftlicher Anzeiger der Allgemeinen Schweizerischen Gesellschaft für die Gesammten Naturwissenschaften 3 (11): 83-90, 91-94. Bern.
^Korniushin, A.V. 2001: Taxonomic revision of the genus Sphaerium s. l. in the Palaearctic region, with some notes on the North American species. Arch. Molluskenk. 129: 77–122.
^Anderson, R. 2005, An Annotated List of the Non-Marine Mollusca of Britain and Ireland, Journal of Conchology, London, 38: 607-638.
^Killeen, I.J., Aldridge, D.C. & Oliver, P.G.,
2004. Freshwater bivalves of Britain and Ireland. Field Studies Occasional Publication 82. FSC Publications,
Shrewsbury. 114pp.
^(in Czech) Horsák M., Juřičková L., Beran L., Čejka T. & Dvořák L. (2010). "Komentovaný seznam měkkýšů zjištěných ve volné přírodě České a Slovenské republiky. [Annotated list of mollusc species recorded outdoors in the Czech and Slovak Republics]". Malacologica Bohemoslovaca, Suppl. 1: 1-37. PDF.
^Kořínková T., 2006: The first reliable records of Sphaerium nucleus (Mollusca: Bivalvia: Sphaeriidae) in the Czech Republic. Acta Soc. Zool. Bohem. 69: 293-297. ISSN 1211-376X pdf
^Glöer P. & Meier-Brook C., 2003: Süsswassermollusken. DJN, pp. 134, page 109, ISBN3-923376-02-2