Dinoflagellate. Coloured scanning electron micrograph (SEM) of the dinoflagellate, Prorocentrum micans. Prorocentrum species produce okadaic acid, which is associated with diarrheic shellfish poisoning (DSP). Dinoflagellates are unicellular protozoans. About 90% are found in marine environments as plankton. They are characterised by the presence of two flagella (not visible). One flagellum beats back and forth, while the other is flat and ribbon- like, and works as a rudder to steer and rotate the organsim. Magnification: x1800 when printed at 10 centimetres wide. Specimen courtesy of Mike Allen, Plymouth Marine Laboratory.