The dinoflagellates are a large group of flagellateprotists. About half are photosynthetic, the rest are mostly heterotrophpredators of other protists. The ones which are photosynthetic are sometimes loosely called 'algae'; the one which are predators are sometimes loosely called 'protozoa'.
They have been classified as an order, a class and a phylum by different authors. Research is being done on their relationships.