Carapace: the hard outer covering or case of certain organisms such as arthropods and turtles. As in, "Fubsy the snail could always rely on his trusty carapace to protect him from the neighborhood bullies who tried to beat him up."
Fun fact: a snail is not an arthropod (it's a mollusk) but it does indeed have a carapace. If you want to get less specific, there's the word "scute," which is the bony plate on animals like armadillos and turtles. Animal kingdom lesson plus new vocabulary word. I better be careful of setting my standards so high.