DescriptionUnarmoured cells, sometimes compressed. Cingulum displaced by at least 20-35% of the cell length (cf. Gymnodinium) in a descending left spiral. Individual species are differentiated by size, shape and contours, the presence and shape of the apical groove, the presence of striae, ribs or furrows, total displacement of the cingulum, torsion of the sulcus, the presence of chloroplasts, lateral compression of the body and colour (Steidinger & Tangen, 1997). See Larsen (1994, 1996) for a discussion of the separation of Gymnodinium and Gyrodinium.