Plankton, from the ancient Greek word plagtós (" wandering "), are minuscule species that move in the water and flow with the current. Often invisible to the naked eye, their size varies from 0.2 micrometres (0.002 millimetres) to 0.2 millimetres. Types of plankton include phytoplankton, which are plants, and zooplankton, which are animals.
Plant plankton are mainly diatoms (unicellular siliceous algae).
Animal plankton includes microcrustaceans (copepods, water fleas), insect larvae (mosquito…), protozoans (unicellular organisms).
Planktonic larvae of a cold water fish (zooplankton). ©