Phototactic Orientation by the Marine Dinoflagellate Gyrodinium dorsum Kofoid.

SYNOPSIS. The phototactic orientation of the dinoflagellate Gyrodinium dorsum was examined using photomicrographic, cinematographic, and closed‐circuit television technics. Particular emphasis was placed on examining the movements and possible roles of the flagella during orientation. The data suggest that the longitudinal flagellum is primarily responsible for phototactic orientation, while the lateral flagellum is involved in forward propulsion and cell rotation. A possible receptor mechanism is proposed by which light direction sensing is accomplished.