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