Any of numerous one-celled, aquatic organisms that have two dissimilar flagella and characteristics of both plants ( algae ) and animals ( protozoan s).
Most are microscopic and marine. The group is an important component of phytoplankton in all but the colder seas, and it is an important link in the food chain. Dinoflagellates also produce part of the luminescence sometimes seen in the sea. Under favourable conditions, dinoflagellate populations may reach 60 million organisms per litre of water. Such rapid growths, called blooms, result in the red tide s that discolour the sea and poison fish and other marine animals. See also Ceratium .