Shellfish (noun)

1. Edible aquatic animals, such as clams, oysters, mussels, scallops, and lobsters, that have a shell or shell-like exoskeleton.
2. Any aquatic animal, such as a crab or a shrimp, that has a shell or exoskeleton.

Origin:

Middle english shel-fissh, from old english sc(e)l-fisc "fish that lives in a shell".

Examples:

1. Shellfish is a rich source of zinc, iron, and vitamin B12.
2. He went to the beach to collect some shellfish for dinner.
3. She was allergic to shellfish, so she couldn't eat shrimp or crab.
4. The shellfish platter at the restaurant was a delicacy.
5. Some people avoid eating shellfish during the summer months.