What sea creatures have an outside skeleton?

Sea creatures with an external skeleton, known as exoskeletons, include crustaceans like crabs, lobsters, and shrimp, which have a hard shell that provides protection and support. Additionally, some species of mollusks, such as oysters and clams, possess external shells made of calcium carbonate. Other examples include sea urchins and certain types of jellyfish, which have a more rigid outer structure. These exoskeletons serve crucial roles in defense and maintaining the organism's shape.