The Collaborative International Dictionary of English v.0.48:

Carapace \Car"a*pace\ (k[a^]r"[.a]*p[=a]s), n. [F.] (Zool.)
   The thick shell or shield which covers the back of the
   tortoise, or turtle, the crab, and other crustaceous animals.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

18 Moby Thesaurus words for "carapace":
   armor, chitin, cortex, elytron, episperm, lorica, lorication, mail,
   pericarp, plate, protective covering, scute, scutum, shell, shield,
   test, testa, thick skin