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Pisidium

noun
Pi·​sid·​i·​um | \-ēəm\

Definition of Pisidium 

: a genus of nearly cosmopolitan minute freshwater bivalves (family Sphaeriidae) usually somewhat smaller than those of the genus Sphaerium and having the siphons united at their ends

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History and Etymology for Pisidium

New Latin, diminutive of Latin pisum pea

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