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Dinophyta A division of algae which are sometimes alternatively regarded as protozoa (class Phytomastigophora). They are mainly unicellular. The cell typically has a transverse furrow (the girdle) and a longitudinal furrow (the sulcus); the girdle divides the cell into 2 halves called the epicone and hypocone. Some members are ‘armoured’, i.e. they have thick cellulose plates which lie in vesicles beneath the plasmalemma; others have empty vesicles or only thin plates. Typically, 2 flagella are present. Species are photosynthetic and/or heterotrophic. Many species are capable of emitting light, and members of this class are main contributors to bioluminescence in the sea. Most are planktonic in marine and freshwater environments; some occur in symbiotic association with animals, e.g. the flatworm Amphiscolops, marine anemones, and corals, the symbiosis being based on the exchange of nutrients between symbionts. Genera include Amphidinium, Gonyaulax, Noctiluca, Oodinium, Oxyrrhis, and Pyrodinum.