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A large group of Arthropods is known as Crustacean. They include crabs, shrimps, lobsters, crayfish, krill, copepods and mantis shrimps. They have wide habitat mostly freshwater living, some are marine animals, some of them are terrestrial and some are parasitic. Crustaceans have 50,000 species. They are divided into major groups the Branchiopods, the Ostracods, the Malacostraca and the Maxillopodes. Their body is divided into three segments the head, the thorax and the abdomen. They are having hard exoskeleton called “carapace”. Their body is bilaterally symmetrical, having open circulatory system and jointed appendages. Their digestive system is consisting of straight tube which has pair of digestive glands. For respiration gills are present and for excretion green glands are present.