ONTOGENY REVERSAL. “All stages of the medusa Turritopsis nutricula, from newly liberated to fully mature individuals, can transform back into colonial hydroids, either directly or through a resting period, thus escaping death and achieving potential immortality. This is the first metazoan known to revert to colonial hydroids, either directly or through a resting period, thus escaping death and achieving potential immortality.”
http://www.biolbull.org/content/190/3/302.full.pdf