There is a type of jellyfish that is immortal - Apparently.
The Turritopsis dohrnii, also known as the "immortal jellyfish," is a species of jellyfish that can transform its body into a younger state through a process called transdifferentiation. This process allows the jellyfish to essentially revert back to its polyp stage, which is the juvenile form of a jellyfish, and then grow back into an adult again. This means that Turritopsis dohrnii can theoretically live indefinitely, making it the only known immortal animal in the world.