Unionidae is a family of freshwater mussels, the largest in the order Unionoida, the bivalve mollusks sometimes known as river mussels, naiads, 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 recognized 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. Life habits Unionidae burrow into the substrate,… (More on Unionidae)