Approximately 30,000 species make up this Subphylum. Members of the Subphylum include lobsters, crabs, crayfish, shrimp, copepods, barnacles, and several other groups of organisms. Crustaceans respire via gills. Like other arthropods, all have a hard but flexible exoskeleton.
Most crustaceans are free-living, but some are sessile and a few are even parasitic.
Most use their maxillae and mandibles to take in food. The walking legs, including specialized chelipeds, may be used to help capture prey. Most crustaceans are dioecious. The actual mechanisms by which fertilization is achieved vary greatly. Many species, including lobsters, crayfish, barnacles, and crabs are important to human economies, some very much so.