Carapace

Carapace, a term applied to the shield on the back of such crustaceans as Crab and Lobster, of the unique King Crab or Limulus, or of chelonians like Tortoise and Turtle. In the former cases it is a horny and limy modification of the outer portion of the skin, in the last it is mainly due to backbone and ribs. It is obviously therefore a term of no precise significance. For its exact nature, see CRAB and TORTOISE.