Journal reprints of scholarly writings by leading marine biologists regarding crustaceans. A very large group of invertebrates, comprising of almost 52,000 described species, crustaceans include various familiar animals, such as crabs, lobsters, crayfish, shrimp, krill and barnacles. The majority of them are aquatic, living in either marine or freshwater environments, but a few groups have adapted to life on land, such as terrestrial crabs, terrestrial hermit crabs and woodlice.