Diagnose_Genus: Gymnodinium F. Stein emend. G. Hansen & Moestrup: Unarmoured unicellular or colony-forming dinoflagellates with horseshoe-shaped apical groove running in an anticlockwise direction. Nuclear envelope with vesicular chambers. Cingulum displacement one or more cingulum widths. Nuclear or dorsal fibrous connective present. microreticulate cyst.
Diagnose_Species: Gymnodinium nolleri: Epicone conical. Hypocone rounded and almost cylindrical. A polygonal pattern in the amphiesma. Cingulum descends with a displacement of one to three widths. Sulcus reaches the apex and an acrobase surrounds the apex. Pyrenoid multistalked, not penetrated by thylakoids. Cells often in pairs, never forming longer chains. Cyst spherical, 28-38 µm in diameter. Surface covered with a fine reticulate pattern of four- to seven-sided polygons, each measuring 0.3-1.9 µm in maximal dimension. Parastructures marked by rows of finer polygons, which are more regular in size and shape. Paracingulum demarcated by two double rows of vesicules, parasulcus, and paraacrobase by one row. Three (2-4) uneven rows of vesicles of 0.45-2.3 µm maximal dimension present within the paracingulum.

Body_length: 30-43 µm
Body_Width: 23-30 µm 

Cyst_length: 28-38 µm