Figure 1.

An observed free-swimming behaviour of an Euchaeta rimana female. The results were obtained through frame-by-frame analysis of a video clip of 650 frames in total at 30 frames per second so that the time duration was approximately 21.67 s. A trajectory of an entrained algal particle is also shown with respect to a frame of reference fixed on the copepod's body (data points were shown every 10 frames). (a) Frame 0–130, the copepod sank obliquely at a time-varying velocity and simultaneously rotated around its anterior–posterior body axis. The rotation started from the body position in orange and ended at the body position in dashed lines. (b) Frame 130–650, the copepod sank obliquely at a time-varying velocity without body rotation. Note that the algal trajectory was a spiral-like unclosed curve.