Genus Gymnodinium Stein, 1878
Cells unarmoured. Small to large cells with varied morphology from spherical to biconical and lobed to pyriform. Single cell or chain-forming species. Theca with or without longitudinal ridges or ribs. Cingulum usually equatorial or premedian, with or without descending displacement (left-handed). Displaced cingulum less than 1/5 body length. Sulcus often invading epitheca. Apical groove present or absent. Chloroplasts present or absent. Color can be green, yellow, brown, blue or pink.
Planktonic species. Some are red-tide bloom forming species; some are toxin producing species.
Remarks: Species of this genus are differentiated based on the following characteristics: 1) shape and contours; 2) size; 3) chain formation; 4) presence and shape of apical groove; 5) cingulum placement (pre-, post- or median) and/or displacement; 6) sulcus extending into epitheca; 7) sulcal-apical groove juncture; 8) shape of ventral ridge; 9) presence of striae, ribs or furrows; 10) presence of chloroplasts; 11) placement of nucleus; and 12) color.
Species included from this genus:
Gymnodinium breve Davis, 1948
Gymnodinium catenatum Graham, 1943
Gymnodinium mikimotoi Miyake et Kominami ex Oda, 1935
Gymnodinium pulchellum Larsen, 1994
Gymnodinium sanguineum Hirasaka, 1922
Gymnodinium veneficum Ballantine, 1956