An order of the class Phytamastigophorea, also known as the Dinoflagellata. Many botanists consider this group to be a member of the class Dinophyceae. Noctiluca scintillans, one of the largest species, may measure 0.06 in. (1.5 mm), whereas the flagellate state of some species may be as small as 10 micrometers. Although primarily marine, some dinoflagellates occur in fresh water. Some possess brown chromatophores, some are variously colored, and others are colorless. Masking pigments are frequent, occurring in the cytoplasm or in chromatophores. All types of nutrition exist, and some species are parasitic. Two flagella emerge laterally from a longitudinal depression or sulcus. An encircling flagellum in a groove or girdle divides the body into epicone and hypocone; the other, extending backward, propels the organism forward. The nucleus is very large.