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Cover: Experiments have shown that anguilliform swimmers generate laterally split wakes with two rows of vortices whereas carangiform swimmers generate wakes with a single row of connected vortex loops. I. Borazjani and F. Sotiropoulos (pp. 576−592) carried out three-dimensional numerical simulations and showed that this striking difference is not due to body shape and/or kinematics but rather a Strouhal number effect. The figure visualizes the calculated wake structure of a tethered lamprey at Reynolds number Re_4000 and Strouhal number St=0.2. The numerical results suggest that anguilliform swimmers would also generate a single row wake if they could swim at Strouhal numbers in the same range as carangiform swimmers.