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.

 “Morphologically, we’ve built a jellyfish. Functionally, we’ve built a jellyfish. Genetically, this thing is a rat,” says Kit Parker, a biophysicist at Harvard University in Cambridge, Massachusetts, who led the work. The project is described today in Nature Biotechnology.

Parker’s lab works on creating artificial models of human heart tissues for regenerating organs and testing drugs, and the team built the medusoid as a way of understanding the “fundamental laws of muscular pumps”. It is an engineer’s approach to basic science: prove that you have identified the right principles by building something with them.