Nekton refers to actively swimming marine organisms capable of moving independently of water currents (as opposed to plankton, which drift passively, or benthos, which live on or in the seafloor); nekton is typically composed of fish, along with some actively swimming crustaceans, cephalopods, and marine mammals/reptiles, and does not include sessile or benthic organisms such as tube worms, crabs, or limpets, nor planktonic organisms such as copepods or larval crustacean stages.