Fig. 3. Particle imaging velocimetry images of currents generated by a male crab, with and without courtship stationary paddling. (A) Side view of the crab when it is not performing courtship stationary paddling. The gill current generates flow upwards toward the water surface. (B) Side view of the crab performing courtship stationary paddling, which generates a forward current. (C) View from above of the crab performing courtship stationary paddling, which generates a forward current. The mean velocity for current generated by the paddling was 3.1 cm s^–1.