What types of animals are crustaceans?

Crustaceans can be broken down into a few main groups: decapods, which include crabs, shrimps, lobsters, hermit crabs, and crayfish; isopods, which includes pill bugs and other similar terrestrial crustaceans; amphipods, which includes beach hoppers; as well as copepods, barnacles, krill, and more.  There are more than 50,000 species of crustaceans known to exist.