malacostracan

noun

mal·​a·​cos·​tra·​can ˌma-lə-ˈkä-stri-kən 

: any of a large subclass (Malacostraca) of crustaceans having a thorax consisting of eight segments usually covered by a carapace and including the decapods and isopods

malacostracan adjective

Word History

Etymology

ultimately from Greek malakostrakos soft-shelled, from malakos soft + ostrakon shell — more at mollify, oyster

First Known Use

1835, in the meaning defined above