Hallo.
Im not pretty sure about but i guess you mean Turtles/Tortoises cause of their high age and far travvelroutes. Or Whales cause of there size and intellect or you mean Jellyfishes in special this one:(turritopsis nutricula jellyfish). He is practically immortal and use ‘transdifferentiation’ after sexual intercourse in order to rejuvenate all of their cells in their body so that they can start life again as ‘polyps’.
So maybe im right but if not im very eager to learn something new :D