Gymnodinium chlorophorum (Dinophyceae) in the Adriatic Sea: electron microscopical observations

The micromorphology and fine structure of a chlorophyll b-containing green dinoflagellate commonly found along the coasts of the Northern Adriatic Sea (Mediterranean Sea) were re-examined by scanning and transmission electron microscopy. It was identified as Gymnodinium chlorophorum Elbrächter et Schnepf based on ultra-structural features. New details are given about the amphiesmal structure, the flagellar apparatus and mucocysts. The amphiesma consists of two outer membranes, ‘plate’ material, pellicular layer, and inner membrane. The cell surface appears to be formed by polygonal amphiesmal vesicles arranged into a honeycomb pattern, and shows a well-marked apical groove describing a counterclockwise elliptic path in the epicone. The flagella emerge from two distinct pores, with the basal bodies lying at an angle of about 120-130°. The longitudinal microtubular root, the transverse striated root and the striated fibrous root connective are present in the arrangement found in other Gymnodinium species. A great number of mucocysts, formed by regularly arranged fibrillar material, fill most of the cell volume. Different stages of mucocyst formation and extrusion are shown.