Genus Dinophysis Ehrenberg, 1839
Species are laterally compressed with a small, cap-like epitheca and a much larger hypotheca (dorso-ventral depth of epitheca is 1/3 to 1/2 of hypotheca). In most species, epitheca is not readily visible, the shape and height of which can be species specific. The shape of the cell in lateral view is one important criterion used for identification. However, size and shape varies considerably within species.
Cells armoured. Theca divided into 2 lateral halves, separated by a suture. Unique genus with sulcal list elaborations and ornamentations. Epitheca with 2 large and 2 small plates. Cingulum with 4 plates; dorsal plates larger than ventral. Sulcus with 4 plates surrounding 1 large flagellar pore through which both flagella emerge. Hypotheca with 2 large and 2 small plates. Left and right sulcal lists present and well developed. Left sulcal list larger, more elaborate with 3 supporting ribs, and is often a diagnostic feature.
Species widely distributed. Some species toxic causing DSP (diarrhetic shellfish poisoning) outbreaks.
Remarks: Species are differentiated by the following features: 1) dorsal and ventral cell curvature; 2) relative length of cell; 3) length and shape of left and right sulcal lists; 4) position of the three supporting ribs of the left sulcal list; 5) presence or absence of chloroplasts; 6) thecal ornamentation; and 7) dorsal-ventral depth of epitheca.
Species included from this genus:
Dinophysis acuminata
Dinophysis acuta
Dinophysis caudata
Dinophysis fortii
Dinophysis mitra
Dinophysis norvegica
Dinophysis rotundata
Dinophysis sacculus
Dinophysis tripos