The Crustacea are a subphylum of arthropods with 67,000 described species. They are part of the phylum Arthropoda. Crustaceans include crabs, lobsters, crayfish, shrimp, krill and barnacles. They are relatives of insects. If the Arthropods are regarded as a superphylum, then the insects and crustacea would be phyla (see List of animal phyla). The group has an extensive fossil record, reaching back to the Cambrian.