Cyanobacteria: 

Cyanobacteria: 

Cyanobacteria:  A lso known as blue-green algae , these phytoplankton are a form of bacteria. Especially in freshwater, cyanobacteria can cause toxic blooms. Diatom: Single-celled microalgae. One of the most abundant and diverse phytoplankton groups. ​ Dinoflagellate: Have two flagella (hair-like organelles). Many are mixoplankton , and some are toxic and responsible for 'harmful algal blooms'. Coccolithophore: Composed of individual plates or scales made of calcium carbonate and play an important role in the global carbon cycle.​ Many are mixoplankton . Green algae: Green due to the absence of the brown and red pigments in many microalgae. They are mostly found in the coastal waters of the tropics and subtropics. Some are mixoplankton . Microalgal plankton (phytoplankton and m ixoplankton ) (Image source: NASA. Collage adapted from drawings and micrographs by Sally Bensusen , NASA EOS Project Science Office.)