Fig. 1. Visualizations of medusa flow currents. (A) Jet propulsion in juvenile Aequorea victoria. A vortex ring (CV) is formed in the water during the bell contraction phase, whereas no vortex is formed in the water during the bell relaxation phase. (B) Jet-paddling in Aurelia aurita. Vortex rings of opposing rotational orientation are formed in the water during bell contraction (CV) and relaxation (RV), respectively. The stopping vortex can be observed forming near the bell margin (RV). This vortex will interact with the subsequent contraction phase vortex, affecting swimming thrust and efficiency (see text).