GYMNODINIUM

genus of marine or freshwater organisms called dinoflagellates. Members of the genus are bilaterally symmetrical with a delicate pellicle (or envelope) and disk-shaped chromatophores, which, when present, contain yellow, brown, green, or blue pigments. The genus is claimed by both botanists and zoologists, for, like all dinoflagellates, it has both plantlike and animal-like species. Some species are photosynthetic; others seek out food. Gymnodinium, which may be bioluminescent, undergoes periodic blooms, or population increases, and may colour water bright yellow or red. It also produces a toxin similar to that of the dinoflagellate Gonyaulax; both toxins are fatal to fish and irritate the nose and throat of human beings.