 A 2018 study found that species "O. quadratus" could be three separate morphospecies based on inferences from modern imaging techniques of morphology.The genus is not as diverse as other dinoflagellate genera such as "Dinophysis" but does have at least 24 recognized species.It has been extensively studied around the world, with species found to inhabit waters including the North Arabian Sea, Eastern Tropical Pacific, Indian Ocean, Red Sea, Vitiaz Strait, Caribbean Sea, Gulf of Aden, Southern Ocean, Boeton Str, California Current, Gulf of Mexico, Panamic Area, Peruvian Current Galapagos Eddy, and the coast of the Korean Peninsula.