A beautifully simple mechanism; this is a lot of fun to watch.
Here's Festo's Aqua Jelly:
Design News has details.
The US Navy is funding a RoboTuna
In other news on robotic creatures, the University of Washington has created Robofish!>
Sometimes, people wonder if robotic lifeforms will take over the world. There are limits to what a robot can do which you can read about here. That begs the question what is a lifeform, and how would you recognize it if you saw one? Here's a definition for life that works better than what the biology text books present.
Ever want your own mobile robot suit? Sakakibara Machineworks has created one!
There are a lot of virtual lifeforms out there as well. Enjoy!
Finally, if you're interested in how the artificial intelligence of artificial creatures can be created, here are some technical details and theory, and here's an example of some artificial children playing ball.