(n)largest subclass of Crustacea including most of the well-known marine, freshwater, and terrestrial crustaceans: crabs; lobsters; shrimps; sow bugs; beach flies, Syn.subclass Malacostraca
‖prop. n. pl. [ NL., from Gr. malako`s soft + &unr_; shell of a testacean. ] (Zool.) A subclass of Crustacea, including Arthrostraca and Thoracostraca, or all those higher than the Entomostraca. [ 1913 Webster ]