"Morphologically, we've built a jellyfish. Functionally, we've built a jellyfish. Genetically, this thing is a rat."

Bioengineers have made an artificial jellyfish using silicone and muscle cells from a rat's heart. The synthetic creature, dubbed a medusoid, looks like a flower with eight petals. When placed in an electric field, it pulses and swims exactly like its living counterpart.

"I grabbed him and said, `John, I think I can build a jellyfish.' He didn't know who I was, but I was pretty excited and waving my arms, and I think he was afraid to say no."

Nawroth created a structure with the same properties by growing a single layer of rat heart muscle on a patterned sheet of polydimethylsiloxane. When an electric field is applied across the structure, the muscle contracts rapidly, compressing the medusoid and mimicking a jellyfish's power stroke. The elastic silicone then pulls the medusoid back to its original flat shape, ready for the next stroke.

Parker says his team is taking synthetic biology to a new level. "Usually when we talk about synthetic life forms, somebody will take a living cell and put new genes in. We built an animal. It's not just about genes, but about morphology and function."

They also hope to reverse-engineer other marine life forms, says Parker. "We've got a whole tank of stuff in there, and an octopus on order."