Unionidae

The Unionidae are a family of freshwater mussels, the largest in the order Unionoida, the bivalve mollusks sometimes known as river mussels, or simply as unionids.

The range of distribution for this family is world-wide. It is at its most diverse in North America, with about 297 recognised taxa, but China and Southeast Asia also support very diverse faunas.

Freshwater mussels occupy a wide range of habitats, but most often occupy lotic waters, i.e. flowing water such as rivers, streams and creeks.

Life history

Unionidae burrow into the substrate, with their posterior margins exposed. They pump water through the incurrent aperture, obtaining oxygen and food.

Unionoids remove phytoplankton and zooplankton, as well as suspended bacteria, fungal spores, and dissolved organic matter. Despite extensive laboratory studies, it remains uncertain as to which of these filtrates unionoids actually process. In high densities, they have the ability to influence water clarity but filtration rates are dependent on water temperature, current velocity, and particle size and concentration. In addition, gill morphology can determine particle size filtered, as well as the rate.