‘Cheat’ answer: the biologically immortal Turritopsis dohrnii . It can cycle from a mature adult stage to an immature polyp stage and back again under stress, such as starvation or sudden temperature changes or damage to its bell, meaning no natural limit to its lifespan is known.
Unfortunately we’ve never observed any single specimen for any extended period, and we have no idea how to estimate a specimen’s age. In practice they still die from predation and disease.
"Limitless regenerative capacityIf we restrict ourselves to animals that age, the sea still has lost of surprises in store for us. For instance, in 1986 researchers dredged up the skeleton of a specimen of the glass sponge Monorhaphis chuni from a depth of 1,100 meters in the East China Sea.
You can see the skeleton below, over two meters long and looking like a fiberglass rod, in the hands of sponge expert Xiaohong Wang. It consists of silicon dioxide and is made up of hundreds of fine lamellae which have grown annually like the rings of a tree from the inside outwards. When it was alive one end of it was attached to the seabed and the other was free to grow. They determined its age to be over 11,000 years when it finally died.
"The longest-lived vertebrate known is the Greenland shark https://en.wikipedia.org/wiki/Greenland_shark . One specimen was found to be 392 ± 120 years old, so anywhere between ages 272–512 (you have to admit that’s a pretty big range…).
I feel somehow obliged to mention the story of Hanako https://en.wikipedia.org/wiki/Hanako_(fish) , the scarlet koi fish, who was reportedly 226 when she died in July 7, 1977. ‘Hanako’ means ‘flower girl’ or ‘flower maid’; the name was chosen by her first caretakers, the Koshihara clan of the Tokugawa era, all the way back in the monsoon season of the first year of Horeki (c. 1751).
Her last and final owner, Dr. Komei Koshihara, said in an interview that she spent most of her life in a quiet pond at the foot of Mt. Ontake in a locality near Oppara, Higashi-Shirakawa Village, Kamo County. The pond was apparently carefully constructed by his ancestors with only Hanako’s well-being in mind.
How did they determine her age? In 1966, Dr. Koshihara got in touch with his friend and colleague Prof. Masayoshi Hiro to examine the scales that were extracted from Hanako’s body. Apparently it took Hiro about two months to precisely determine her age. That year, together with Koshihara, he concluded that Hanako koi was 215 years old. She died 11 years later, which is where the ‘226’ figure comes from.
Hanako a few years before she diedThe oldest known land animal still alive today is a giant Seychelles tortoise named Jonathan https://en.wikipedia.org/wiki/Jonathan_(tortoise) , who lives on the island of Saint Helena https://en.wikipedia.org/wiki/Saint_Helena . He’s reportedly 187 years old. Jonathan still has excellent hearing, but is otherwise blind from cataracts and has lost his sense of smell, so he can’t detect his food.
That’s him back in 2014:
"I'm not sure if chickens necessarily take first place for longest living decapitated animal on average, but here are some notable mentions:
Cockroaches can live days to weeks without a head.
A male praying mantis may have their head eaten by the female before mating, and then complete the act without a head!
Snakes will continue to bite after they are dead. In 2018, a man was bitten by a rattlesnake head minutes after he decapitated it.
Flies can keep living for days/weeks without their heads. Here's a video of a headless fly. [url=https://m.youtube.com/watch?v=IlHvSRy2HdQ\\"}}}], \\"indent\\": 0, \\"quoted\\": false, \\"type\\": \\"unordered-list\\", \\"is_rtl\\": false},
The axolotl can regenerate entire limbs, tail, jaw, portions of its head, brain, portions of its spine, perfectly.