Peridinium Ehrenberg emend. Stein
	From Greek peridineo, "to whirl around"
	Peridinium is a dinoflagellate with thick, armored plates that are often lobed and ornamented. The sutures are quite noticeable, and the cingulum is nearly at the cell median. The cells may be generally round to oval-shaped or flattened, with a convex dorsal surface and a concave ventral surface. Some species (such as Peridinium limbatum) have distinctive horns. The genus has over 30 species, most of which are photosynthetic.
Most researchers agree that Peridinium should be separated into two genera. The first group would include large cells (as much as 65 µm in diameter) with three intercalary plates. The second group would have significantly smaller cells less than half that size, with only two intercalary plates.