Copied from geekologie.com!
"So apparently there's this little jellyfish creature (Turritopsis nutricula, a form of hydrozoa) that doesn't ever die. Biology is beyond me, so I'll let somebody else do the talking while I make a sandwich have a sandwich made for me.
What these little folks do is they revert completely to a sexually immature, colonial stage after they reach sexual maturity. They're even cooler than that. When they're young they've got only several tentacles, but at a mature stage, they get to 80-90 of them.
They're able to return to polyp stage due to a cell change in the external screen (Exumbrella), which allows them to bypass death. As far as scientists have been able to find out, this change renders the hydrozoa virtually immortal.
Did that make any sense? I didnt' bother reading it, but I think it had something to do with being able to regenerate your arm like a starfish. *sawing through bone*
UPDATE: Um, so does anybody have the number for Luke Skywalker's doctor?
Meet the world's only immortal animal [zmescience]
Thanks to Emile, who only wants to live long enough to see a hovercar."