Crustacea

Definition of Crustacea, crustaceans: subphylum of arthropods, considered as a class in older classifications. They are mainly aquatic, gill-breathing animals, such as crabs, lobsters and shrimps. The body is divided into a head bearing five pairs of appendages (two pairs of pre-oral sensory feelers and three pairs of post-oral feeding appendages) and a trunk and abdomen bearing a variable number of often biramous appendages wich serve as walking legs and gills. Crustacea often have a hard carapace of shell. This is the common definition for Crustacea, crustaceans, other definitions can be discussed in the article