MALACOSTRACA (Gr. m,alakos soft, ostraken, shell), Aristotle's name for crusts ,cinns. The malacostraca are now classified as a sub-class of crustacea, which comprises two divisions, edriophthalmata, and podophthalmata. In the first division the eyes are sessile, and the body not generally protected by a carapace. It comprises two orders, Amphiopoda and isopoda. The e) es are generally compound, but are sometimes simple, and placed on the sides of the head, which is nearly always distinct from the body. The typical number of feet is seven pairs. The amphiopoda include the whale-louse (q.v.) And the sand-hopper (q.v.). A section of this order, lamidopoda, has been regarded as a distinct order, but the pretension has been withdrawn. In isopoda the respiratory organs Are not thoracic as they are in amphiopoda, but are attached to the inferior surface of the abdomen. There are two eyes formed of a collection of simple eyes, or are some thnes really compound. The young isopod is developed within a larval membrane with out appendages, which after a time bursts and sets free the young, which resemble the adult in most respects, but have only six pairs of limbs instead of seven. Like the
ampidopoda, some are aquatic, and some terrestrial. Milne-Edwards divides the isopoda into three sections, 1, natatory, 2, sedentary, and 3, eursorial. In the first sec tion some of the animals are parasitic, and some are not. In the second section they sre all parasitic, generally within the gill chambers or upon the ventral surfaces of decapod crustaceans, as shrimps and others. The third section, the cursorial, includes the wood-louse (q.v.) and limnoria (q.v.). The second division of malacostraca, podoph lhalmata, have compound eyes, supported upon movable stalks, and a body completely protected by a carapace. There are two orders, stomapoda (q.v.) and decapoda (q.v.). see also INVERTEBRATE ANIMALS, LOBSTER, CRAB, and SHRIMP.