Biologically Immortal

Basicly creatures that do not age or die due to old age. Not that they can't die. It's just that if nothing interferes with their existence, they will live forever. So there is a jellyfish that has figured it out. The secret for immortal life is not just to live for a really long time but to never mature. Turns out that after this jellyfish has reproduced they shrink back to infant from and grow again. This jellyfish is called Turritopsis Dohrnii. It kinda reminds me of the phoenix life regeneration system. Though the existence of phoenix's are said to be myth.... and their regeneration is by bursting into flame and bring born from the ashes. This jellyfish refuses to die in any form. Pretty cool huh? Guess nature does many miraculous things outside the view of humans.