The turritopsis nutricula, an immortal species of jellyfish: Since it is capable of cycling from a mature adult stage to an immature polyp stage and back again, there may be no natural limit to its life span. Scientists say the hydrozoan jellyfish is the only known animal that can repeatedly turn back the hands of time and revert to its polyp state (its first stage of life).
Related to the jellyfish and corals, Siphonophore is a continuous chain of specialized polyps - individual animals that grow from one another in an organized colony. Some in the colony are devoted to feeding, armed with stinging cells to snag fish or invertebrates. Others are devoted to locomotion, propelling the whole group with a continuous pumping motion while some exist only to reproduce.