Computational Fluid Dynamics to Investigate the Possible Behavior of Ercaicunia multinodosa While Swimming Inverted on the Water Surface.

Inverted swimming behavior has been documented in marine arthropods from the Cambrian to modern oceans. It was previously theorized that this behavior contributed to bringing the center of gravity to a lower position, thereby enhancing balance and stability, and preventing clogging of the mouth in deposit and suspension feeders. In this study, by using the computational fluid dynamics analysis method and wave impact experiments, we evaluate the hydrodynamics of inverted swimming behavior in the early Cambrian Ercaicunia multinodosa when it was at the water surface. The results show that when Ercaicunia multinodosa swam at the water surface, the inverted swimming was more stable than the normal posture regardless of the direction from which the waves came. Moreover, as the wave amplitude increased (within the tested and validated range of 0.33 to 1.0 times the body height), the rate at which the flipping occurred in the normal posture was accelerated and then remained stable in the inverted posture. Finally, we used a stereolithography apparatus to create a physical model of Ercaicunia multinodosa and performed wave impact experiments to verify the research results. Our findings support the hypothesis that the inverted swimming behavior of Ercaicunia multinodosa helps increase balance and stability.