malacostracan

adjective

of a large class (Malacostraca) of highly evolved crustaceans typically consisting of 19 segments, including the decapods, krill, and isopods

Etymology: < ModL Malacostraca < Gr malakostrakos, soft-shelled < malakos, soft (see malaco-) + ostrakon, shell + -an

noun

such a crustacean