Peridinium is a large genus of small to medium sized
dinoflagellates, some but not all of which are photosynthetic.
Nonphotosynthetic species are phagotrophic or osmotrophic.
Species occur in freshwater and marine planktonic habitats
worldwide. At least a few photosynthetic species may form
significant blooms ("red tides"). Some of these blooms are
associated with nuisance odors and fish kills, although the most
devastating "red tide" dinoflagellates belong to other genera.
Photosynthetic species in the genus Peridinium, and species in
closely-related genera that are still treated as species of
Peridinium by many workers, are frequently used as experimental
organisms in cell biology research, especially in the areas of
nuclear structure and function, circadian rhythms, and
endosymbiosis. The unique structural and molecular features of
Peridinium and its relatives have prompted much speculation on
the evolutionary history of dinoflagellates. Not long ago, this
group was believed to be among the most ancient of