At the top of our immortal animals list is a tiny variety of jellyfish known as Turritopsis doohmii, or more commonly, the immortal jellyfish. It has found a way to cheat death by actually reversing its aging process, according to National Geographic. If the jellyfish is injured or sick, it returns to its polyp stage over a three-day period, transforming its cells into a younger state that will eventually grow into adulthood all over again. (Here's how to properly treat a jellyfish sting.)
There is a debate among the scientific community whether these red ocean dwellers are biologically immortal animals; a common cause of death is disease, not old age, and unlike other animals, lobsters grow and reproduce until they die. One lobster captured off the coast of Newfoundland was estimated to be 140 years old, but most males survive into their early 30s while females live an average of 54 years, according to Smithsonian. Fun fact: The bigger the lobster, the older it is.
Slow and steady really does win the race. Turtles have been known to live for centuries, and researches have found that their organs don’t seem to break down over time. The New York Times reports that turtles might even be able to live indefinitely if they are able to avoid predators and disease. In other words, they definitely have a potential to be immortal animals. (Don't miss the 8 smartest animals that learn faster than humans.)
These creepy crawlers, also known as planarian worms, are famous for their regeneration abilities, where a worm cut across or lengthwise can form two separate worms. This apparently limitless regeneration also applies to aging and damaged tissue, allowing the worms to cheat death indefinitely, according to a study at the University of Nottingham.
Though not technically immortal animals, the bowhead whale is the oldest living mammal. According to Popular Science, several species of whales have been known to live for more than 70 years, though in the 1990s scientists discovered scars on the massive animals that had been made by weapons from the 1800s. The oldest known bowhead lived to be 211 years old. (Whales are also very smart. This particular one even thanked the scientists who rescued him from a fishing net.)