What is an adult grows a hard shell?

An adult that grows a hard shell is typically a mollusk, such as a snail or a clam, or a crustacean like a crab. These hard shells serve as protective exoskeletons, safeguarding the animal from predators and environmental hazards. In some cases, the shell also plays a role in the animal's buoyancy and mobility. The process of shell formation involves the secretion of calcium carbonate or chitin, depending on the species.