Cabe, so you mean the basic physics definition. I still think that the usefulness of the robot's motion in the particular application is just as important as the physics in the abstract. This has become especially clear as I've been working on a nautical robots slideshow, where designs can be wildly different depending on end-usage--or wildly different to achieve the same basic purposes.
CLMcDade, I agree about the project being inspiring as well as the article. The field of Biomimicry has no boundaries and limits to creating magnificent machines. I'm really impressed with the waterproof material protecting the electronics and the graceful movement of Cyro's legs. Nice work as usual Ann!
Cabe, "most efficient" defined how? I've written about several different swimming robots, modeled after tuna, sea turtles and jellyfish. Each of these was described as highly efficient and/or with an optimum size or function(s) for the tasks it was designed for--and they weren't all the same set of tasks. Most robotics R&D is past the stage of fundamental research and is now applied to a specific end-use. OTOH, there are also some competing designs for similar uses.
Clinton, thanks for your comments (and for using the correct plural of a Greek word: nemesis, pl. nemeses). You bring up an interesting point that some other commenters have mentioned: what about predators thinking that a realistic robot is potential food? This jellyfish is bigger than most, if not all, sea turtles, but a killer shark could be a problem.
What a great piece of engineering, it certainly mimicks a real jellyfish in motion. My question is about directional control and how does it steer, which are not so very obvious. But I can see that it could run for quite a while, since it does not need to run to stay afloat.