Bivalves consist of 5 subclasses. They are: Protobranchia, Taxodonta, Anisomyaria, Eulamellibranchia and Septibranchia.

Subclass Protobranchia consists of Mollusks. They have unfolded gills that aren’t used for breathing and capturing food.

Subclass Taxodonta consists of Ark Shells and blood clams. Each valve has teeth and sockets that are similar to other bivalves. The gills are used for breathing and catching food.

Subclass Anisomyaria consists of mussels, oysters and scallops. They have posterior muscles which is the largest muscle in the body that helps the bivalves to open and close their shells. It is harder to find the Anterior Adductor muscles because of their small size. They also have gills for breathing and catching food.

Subclass Eulamellibranchia consists of clams. They have anterior and posterior adductor muscles that are the same size. They have gills used for breathing and catching food.

Subclass Septibranchia consist of marine bivalves that have a muscular septum for breathing instead of gills.