An order of dinophysiphyte dinoflagellates, cell laterally compressed; cingulum close to cell apex of cell; cingulum and sulcus often elaborate; with and without plastids and/or photosynthetic endosymbionts, some phagotrophs; motile cell with a theca divded longitudinally by sagittal suture; relatively few thecal plates - 6-7 on the episome, 4 cingular, 4 sulcal and 4 on the hyposome, 2 large lateral epithecal plates and 2 large lateral hypothecal plates. The flagella insert ventrally and emerge from a single flagellar pore.