Marine organisms can be classified according to where they live and how they move. They can be classified as either plankton (floaters) or nekton (swimmers). Among planktons, the algae that undergo photosynthesis are called phytoplanktons. Most phytoplanktons, such as diatoms, are microscopic. Animal planktons are called zooplankton. Nekton includes all animals capable of moving independently of the ocean currents, by swimming or other means of propulsion. Nekton is able to determine its position within the ocean and in many cases complete long migrations. Nekton includes most adult fish and squid, marine mammals, and marine reptiles.