Which mollusc group can be described as having several calcium carbonate plates along their dorsal side?

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Chitons are often described as having a coat-of-mail appearance due to their eight overlapping plates made of calcium carbonate that run along their dorsal side. Bivalves have two shells that hinge together, gastropods have a single, coiled shell or no shell at all, and cephalopods have no shell or a reduced internal shell.

Which Mollusc Group Can Be Described as Having Several Calcium