Genus Gyrodinium Kofoid and Swezy, 1921
Cells unarmoured. Cells small to large-sized. Cells fusiform, biconical, ovoid or tear-shaped. Sometimes cells compressed dorso-ventrally or laterally. Cingulum displaced more than 1/5 body length in a descending left spiral, with or without overhang. Many species with cingulum displaced more than 1/3 body length. Sulcus often invading epitheca. Some species with apical groove. Chloroplasts present or absent. Pigmentation and nutrition vary. Some species form cysts.
Planktonic species with world-wide distribution. Some are red tide bloom formers; some are toxic.
Remarks: Species of this genus are differentiated based on the following characteristics: 1) shape and contours; 2) size; 3) presence and shape of apical groove; 4) presence of striae, ribs or furrows; 5) total displacement of cingulum; 6) sulcus extending into epitheca; 7) torsion of sulcus; 8) presence of chloroplasts; 9) lateral compression of body; and 10) color.
Species included from this genus:
Gyrodinium galatheanum (Braarud) Taylor, 1992