Ultrastructure of the flagellar apparatus of Oxyrrhis marina

Oxyrrhis marina, like all dinoflagellates, possesses one transverse and ene longitudinal flagellum, which show structural differences. The transverse flagellum contains a small fibre, 20 nm in diameter, associated with doublet no.7, whereas the longitudinal flagellum is sustained by a large (200-300 rim) hollow structure closely resembling the paraflagellar rod described by several authors in kinetoplastidae and in euglenoids. This structure is made up of a hemlcylindrical network of filaments which are often linked on one side to the outer doublet no. 4, and on the other side to a dense plate. Another thinner filamentous network closes this hemicyclinder. In cross-section, the wall of this structure is made up of 8 filaments 2 4 nm in diameter that show a thicker periodic structure. In longitudinal section the same filaments appear arranged in periodic rhombus meshes or a helicoidal pattern, depending on the orientation of the section relative to the axoneme.