Oysters, clams, snails, and certain other kinds of mollusks make seashells. The shells help protect these animals’ soft bodies from dangers such as parasites, sharp objects, heavy-footed animals, and especially from animals that would try to eat them. A shell grows as the surface of the mollusk’s body secretes a chemical that contains calcium, the same element that makes bones hard. The calcium helps form the hard shell, and when the mollusk dies, the shell is left behind.
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