Bivalve oyster shell
This is a very large example of a Gryphaea oyster shell. Worm tubes and smaller oyster shells, Nebeculinella, are attached to the shell, suggesting it was used as a hard surface by other animals on the soft clay sea floor.
As the name suggests, bivalves consist of two shells. ‘Bi’ means two and ‘valve’ means shell. The shells are held together by a strong muscle, and hinged at the pointed end.
Find out more about bivalves on the molluscs pages.