Naiad molluscs are bivalve molluscs, three species of which are endemic to Banyoles Lake. They live in the mud at the bottom of the lake and in irrigation channels, in shady areas with silt. They are filter feeders, which usually live in clean, good-quality water, half-buried in the mud. They can grow to more than four inches in length, and they have a life expectancy of over thirty years. The larvae live as parasites on certain species of fish before they reach the adult stage.