An Electron Microscope Study of Dinoflagellate Flagella

SUMMARY The two flagella of the dinoflagellates examined possess the normal axoneme structure with 9+2 filaments, the nine outer doublets forming triplets in the basal region. Unlike other flagella which possess one basal disc, the dinoflagellates have two basal discs and two diaphragms in the transition region. The two flagella differ from each other in their external morphology and extra-axonemal structures. The longitudinal flagellum contains much packing material in its proximal two-thirds, whereas the distal third contains only the axoneme. This flagellum bears short fine hairs. The transverse flagellum differs from any other type which has been described. It has a helical ribbon-like form due to the presence of a striated strand, which is shorter than the axoneme, and an expanded sheath. It also bears long fine hairs in a unilateral array. The distal end of this flagellum is attached to the cell in the region of the flagellar bases. The structure of the two flagella appears to be compatible with their respective forms of movement.