Freshwater bivalves are one kind of freshwater mollusc

Freshwater mollusc

Freshwater molluscs are those members of the Phylum Mollusca which live in freshwater habitats, both lotic such as rivers, streams, canals, springs, and underground cave streams and lentic such as lakes, ponds , and ditches.This article is about freshwater Mollusca in general; for information on...

s. They are bivalves which live in freshwater, as opposed to saltwater. Although the majority of species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of bivalve molluscs live in the sea, a number of different families of bivalves live in freshwater (and in some cases also in brackish water). These families belong to two different evolutionary lineages (freshwater mussels and freshwater clams), and the two groups are not closely related.

The two groups of bivalves live in many types of freshwater habitat, ranging from small ditches and ponds, to lakes, canals, and rivers.

Species in the two groups vary greatly in size.