If the valves are similar, the shell is said to be equivalve (clams, mussels).
The outer surface may be striated or ribbed.
The two valves are held together by an elastic ligament which leaves a scar on the hinge.
The bivalves are identified mainly based on the shell morphology. The shell comprises of two valve. The two valves are held together by an elastic ligament which leaves a scar on the hinge.