What type of exoskeleton do some molluscs present?
Some molluscs, like bivalves and gastropods, secrete an external calcareous carapace (the shell). Calcium carbonate is secreted by the mantle, a fold in the epidermis, forming the shell. In pelecypods, the shell is made of two valves that articulate and contain the individual body within. In gastropods the shell contains only part of the body, the visceral mass.
