The Immortal Jellyfish

Recently I watched a great TED talk by Rachel Sussman, in which she details her journey to photograph the world's oldest living organisms. As an aside, she mentioned the Immortal Jellyfish, the only species known to revert from a sexually mature individual back to the polyp stage. From Wikipedia--

"This ability to reverse the life cycle (in response to adverse conditions) is probably unique in the animal kingdom, and allows the jellyfish to bypass death, renderingTurritopsis nutricula potentially biologically immortal."

Image from:
http://www.fieldandstream.com/blogs/fishing/2010/06/chad-love-thoughts-immortal-jellyfish