An electron microscope study of the excystment and early development of the dinoflagellateCeratium hirundinella

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Abstract
The excystment and development of cells of C. hirundinella (O. F. Mull.) Bergh. was studied in the laboratory using transmission and scanning electron microscopy. The occurrence of an exit slit through which excystment takes place was confirmed. The emergent cell, or gymnoceratium, lacks thecal plates but has thecal vesicles with extensive microtubules lying beneath. Thecal plates rapidly form within the vesicles except in the ventral region adjacent to the chamber. The flagellar apparatus is present at the gymnoceratium stage prior to excystment, but the more extensive chamber develops with cell growth. Starch and lipid reserves are present in the gymnoceratium and throughout the cell''s development, and they have distinct locations within the cell. The occurrence of a pusule was confirmed. This opens near the base of the longitudinal flagellum. The ultrastructure of the orange pigmented bodies, observed with the light microscope, is described and these are compared with the food vacuoles reported for this species.