Shellfish are distinguished from fin fish by their hard outer shells and their lack of backbone or internal skeleton.
There are two classifications of shellfish:
Mollusks are soft sea animals that fall into three main categories:
- Bivalves, which have a pair of hinged shells (such as clams and oysters).
- Univalves, which have a single shell (such as abalone and conch).
- Cephalopods (such as octopus, squid, and cuttlefish).
From the scientist’s point of view, there are other mollusks as well, but they do not concern us here.
- Crustaceans are animals with segmented shells and jointed legs.