The river mussel has a round-bodied, egg-shaped, bivalved shell, with a colour range from yellow-green over brown-green to dirty brown.
The mussel reaches a length of up to 10cm. The shell may grow to a thickness of 2.5cm and a height of 5cm. On the inside of the shell are two strong constrictor muscles that open and close the valves.
A pair of gills, located inside the shell, functions as the respiration and ingestion organ as it filters the surrounding water. The brood pouch (marsupium), in which the mussel’s larvae grow, is located inside the female’s gills. The river mussel’s muscular foot is generally of a white-yellowish colour, less frequently it is orange.
The mussel uses its foot to anchor itself on the river bed, the foot also functions as the mussel’s locomotion organ.