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(also Sphaeriidae), a genus of bivalve mollusks. (Some classifications treat the mollusks as a group of genera, a subfamily, or a family.) The oval or spherical shell is 1–3 cm long; there is a beak in the center of the mantle. The mollusks are viviparous, with the newly born young acting the same as adults.
The Sphaerium are distributed mainly in northern temperate regions. There are some species in the tropics (East Africa), and some in southern temperate regions (South America and Australia). The mollusks inhabit freshwaters, burrowing to a shallow depth in the silty or sandy bottom.