The main characteristics of class Crustacea and Insecta are as follows. (1) Class Crustacea : Mostly aquatic with gills, two pairs of antennal, and atleast three pairs of Jaws, Appendages mostly biramous and always more than four in the trunk region. Example : Prawn, Crab, Loboster, etc. (2) Class Insect a : Hexapod arthropods with a pair of antennae and three pairs of Jaws Examples: Cockroach, Grasshopper, Bees housefly etc.