shellfish means: A water-based animal such as clams and oysters, mussels or crabs. (in Cooking Dictionary)

What else does shellfish mean?

All aquatic invertebrates that have shells or carapaces. They can be found worldwide in freshwater and saltwater environments. Most shellfish are edible. (in Cooking Dictionary)

Any one of many edible aquatic invertebrate animal shells. (in Merlin Dictionary)

A edible mollusk is different to a crustacean. (in Merlin Dictionary)

These animals’ edible flesh. (in Merlin Dictionary)