There are many species of Freshwater Mussels and they make interesting aquarium subjects.
They are protected by two shells (Bivalves) hinged by a tough, elastic membrane. They move about by protruding a broad, tongue-shaped muscle (the foot) into the sand, then pulling themselves slowly forward. This process may dislodge plants in newly set up aquariums.
They are best known in the aquarium hobby for their role in protecting and incubating eggs of the popular Bitterling, which lay their eggs in the breathing opening of the mussel.