Antarctic phytoplankton, Fragilaria kerguelensis (large group), Nitzschia sp. (single small cell on the left) and partial cell of Thalassiosira sp.
Plankton are microscopic organisms that drift in either saltwater or freshwater. Phytoplankton range in size from extremely small – less than 0.001 mm – to substantially bigger (on a phytoplankton scale) – about 0.5 mm in length.
Image: National Institute of Water and Atmospheric Research (NIWA)