Analysis of the mechanism of dinoflagellate flagella contraction‐relaxation cycle

Summary— Dinoflagellates possess two flagella. One of them, the longitudinal flagellum, retracts from time to time in some species, such as Ceratium and Peridinium . Additional structures which run along the axoneme seem to be responsible for this particular behaviour. The retraction which is rapid (less than 60 ms) may be subdivided into several steps: i) the undulating movement stops; ii) the flagellum appears then as a jagged line during 20 ms; iii) finally a rapid retraction (20 ms) takes place, the flagellum being folded 20 times inside the cylindrical flagellar pocket. The measurements on video‐records suggest that the R‐fibre shortens to 30% of its original length. The contraction and relaxation mechanism of nanofilaments is proposed to be through coiling and uncoiling dependent on Ca 2+ concentration.