Answer: Jellyfish

For years, swimming efficiency estimates were based on a ratio of the size of the marine animal, the amount of food it consumed, and the distance it traveled. In such measures where the emphasis is on how much energy it takes to move mass, it was common for large whales such as the Blue Whale to dominate the charts, because pound for pound, the whale could move itself vast distances with ease. In alternative, but closely related measures focused on speed and energy efficiency, the zippy Bluefin Tuna typically comes in first.

Research led by mechanical engineering professor Neelesh Patankar, however, paints a much different picture of efficiency. Using equations typically reserved for aeronautical engineering, he established that the efficiency of marine creature movement was essentially equivalent: given their size and shape, each animal is equally energy efficient. The degree of efficiency stayed constant across all creatures except in the case of the jellyfish.

The contract-and-relax motion that jellyfish use to propel themselves through the water actually allows them to recapture some of their expended energy (somewhat like a biological flywheel) and use that energy for the next burst of propulsion. Thanks to the already efficient movement and the reclamation of energy in each push of water, the jellyfish breaks free from the mass/energy constant that applies to other marine life and ends up more efficient than any other swimming creature on Earth.