A Freshwater Mollusk is a type of aquatic invertebrate that lives in freshwater habitats. The most common type of Freshwater Mollusk is the MUSSEL, which is a bivalve mollusk with a shell composed of two hinged parts. Mussels are filter feeders, meaning they feed on plankton and other small organisms suspended in the water. They are an important part of the food chain and provide food for many species of fish and birds.