Fine Structure of the Dinoflagellate Transverse Flagellum

Abstract

THE dinoflagellates have for some time been known to possess two flagella which differ from one another in their movements and in the orientation of the beating portions. One, called the posterior or longitudinal flagellum, has a relatively slow movement which has been shown to be in the form of a planar wave1,2. Electron microscopy shows that this flagellum is constructed of the normal axoneme plus organized packing material in the proximal two-thirds, all surrounded by a membrane. The transverse flagellum, often situated in a groove around the cell, has a completely different type of motion. With the light microscope it appears ribbon-like3 and has a rapid undulatory motion which recent investigations have shown to be in the form of a circular or elliptical helical wave1 (in Ceratium). In an early electron microscopical study of Gyrodinium4, it was found that this flagellum had an expanded sheath much wider than the axoneme, with an array of fine hairs along one side. Our observations have confirmed these findings and have revealed other structures which account for the unusual behaviour of this flagellum.