Plankton (including jellyfish, algae, krill) is named from Greek 'planktos', which refers to its defining feature?
Plankton a wide range of sizes, including large organisms such as jellyfish. Technically the term does not include organisms on the surface of the water, which are called "pleuston"—or those that swim actively in the water, which are called "nekton". The name "plankton" is derived from the Greek adjective πλαγκτός ("planktos"), meaning "errant", and by extension, "wanderer" or "drifter", and was coined by Victor Hensen in 1887. While some forms are capable of independent movement and can swim hundreds of meters vertically in a single day (a behavior called diel vertical migration), their horizontal position is primarily determined by the surrounding
Plankton water movement, and plankton typically flow with ocean currents. This is in contrast to nekton organisms, such as fish, squid and marine mammals, which can swim against the ambient flow and control their position in the environment. Within the plankton, holoplankton spend their entire life cycle as plankton (e.g. most algae, copepods, salps, and some jellyfish). By contrast, meroplankton are only planktic for part of their lives (usually the larval stage), and then graduate to either a nektic (swimming) or benthic (sea floor) existence. Examples of meroplankton include the larvae of sea urchins, starfish, crustaceans, marine worms, and most fish.