Crustaceans are primarily aquatic arthropods that are often covered with a shell or “crust.” Though most crustaceans are aquatic, some are terrestrial (like the sandhopper and woodlice), some are sessile (meaning they don’t move, like barnacles), and some are even parasitic (like tongue worms, fish lice, and rhizocephala). 

About 8 million tons of crustaceans are harvested each year often for human consumption. There are more than 50,000 species of crustaceans and are divided into the following 4 groups: Malacostraca, Ostracods, Branchiopods, and Maxillopods. 

Common crustaceans include lobsters, wood lice, shrimp, crabs, krill, barnacles, and crawfish.