Flagellar apparatus and nuclear chambers of the green dinoflagellate Gymnodinium chlorophorum

The green dinoflagellate Gymnodinium chlorophorum (BAH ME 100, the type culture) was reexamined with emphasis on the structure of the flagellar apparatus and nuclear envelope. Like other Gymnodinium species, G. chlorophorum possessed a nuclear fibrous connective linking the flagellar apparatus and the nucleus, albeit in a very reduced and unique form. Microtubules nucleated from the R3 flagellar root associated with the nuclear fibrous connective and terminated at the nucleus, a novel arrangement not known in any other dinoflagellate. Although overlooked by previous researchers, nuclear chambers were present in G. chlorophorum similar to those reported in Gymnodinium aureolum and Gymnodinium nolleri. In contrast to the type species of Gymnodinium, Gymnodinium fuscum, only one nuclear pore was present per chamber. The presence of a feeding tube (peduncle) suggests that G. chlorophorum is mixotrophic. Although the fine structure of G. chlorophorum revealed its affiliation to the Gymnodinium group the above discrepancies set it apart, indicating that it might belong in a different genus.