Orientation directs circular swimming of rolling sperm and tethered spinning for sperm that do not roll. (A, B) Right cheek (RCh) orientation maintained during a counterclockwise (CCW) circular swimming track. Duration 4.4 s, medium HSB, green dot marks starting point. Scale bar 50 μm. (C, D) Left cheek (LCh) orientation and associated clockwise (CW) swimming track. Duration 3 s, medium HSB0Ca. (E) Oscillation of centroid region-of-interest (ROI) intensities reports abortive rolling during the circular swimming of cells in A, B (red) and C, D (blue). Rising baseline for cell A results from uneven illumination. (F) Sparse rolling abruptly changes swimming trajectories. Tracking of a cell initially in LCh orientation that transiently assumes RCh orientation. Yellow arrows indicate CW and CCW trajectories. Duration 3 s, medium HSB0Ca, scale bar 50 μm. (G) RCh (left panel) or LCh (right panel) orientation also determines direction of spinning of tethered sperm in medium HSB0Ca. Central panel shows a tethered sperm (in medium HSBE) that does not spin. Overlaid flagellar traces are offset slightly. Initial (green) and final (black) traces. (H, I) Time courses of ROI centroid intensities (black) and best-fit sine functions (green) in upper panels align with flagellar displacements during each beat cycle (lower panels). Data from tethered, spinning cells in left and right subpanels of panel G.