It has a pair of hinged shells.

These are animals with segmented shells and jointed legs.

It has fins and internal skeletons

A market forms of fish that completely intact, as caught.

A market forms of fish where both sides of a fish still joined, but with bones removed.

A market forms of fish where cross-section slices of fillets.

A market forms of fish where cross-section slices, each containing a section of backbone.

Theses are fish that high in fat

These are fish that low in fat