Dinoflagellate protozoan. Coloured scanning electron micrograph (SEM) of a Ceratium dinoflagellate. Ceratium species are easily identifiable because of their unique shape. They are covered with an armor-like cell wall, made out of polysaccharidel. The most distinguishing characteristic are the arms (also known as horns), the shape and size of which vary from species to species. Dinoflagellates are unicellular protozoans. About 90% are found in marine environments as plankton. They range in size from 2 millimetres to less than a hundredth of a milimetre across. Magnification: x800 when printed at 10 centimetres wide.