(gyre-o-din-ee-um), a typical dinoflagellate. Most dinoflagellates have two flagella and they lie in grooves in the cell surface. There is an circumferential groove (the girdle or cingulum) which wraps around the cell, and a longitudinal groove which extends from the point of flagellar insertion towards the back of the cell. The two ends of the circumferential groove are offset, and this is said to define the genus. This image is focussed on the surface of the cell and shows the undulating flagellum within the circumferential groove. This is a heterotrophic dinoflagellate Differential interference contrast.