Dinoflagellates "whirling" and flagellum "whip, scourge" are single-celled eukaryotes constituting the phylum Dinoflagellata.

Usually considered algae, dinoflagellates are mostly marine plankton, but they also are common in freshwater habitats. Their populations are distributed depending on sea surface temperature, salinity, or depth.

Many dinoflagellates are known to be photosynthetic, but a large fraction of these are in fact mixotrophic, combining photosynthesis with ingestion of prey: phagotrophy and myzocytosis.

Noctiluca scintillans, commonly known as the sea sparkle, and also published as Noctiluca miliaris, is a free-living, marine-dwelling species of dinoflagellatethat exhibits bioluminescencewhen disturbed. Its bioluminescence is produced throughout the cytoplasm of this single-celled protist, by a luciferin-luciferasereaction in thousands of spherically shaped organelles, called scintillons.

Karenia is a genus that consists of unicellular, photosynthetic, planktonic organisms found in marine environments. The genus currently consists of 12 described species. They are best known for their dense toxic algal blooms and red tides that cause considerable ecological and economical damage.