This is pretty interesting.
Once it reaches sexual maturity, Turritopsis looks like a tiny, transparent, many-tentacled parachute (only about 5mm in diameter) that floats freely in warm ocean waters. But when times get tough, Turritopsis can turn into a blob, anchor itself to a surface, and undergo a sort of reverse methamorphosis back to its youthful form as a stalk-like polyp. That’s like a butterfly turning back into a caterpillar. Scientists, who first described this phenomenon [pdf] in the 1990s, believe Turritopsis can repeat its life cycle indefinitely.