What is the oldest living marine animal?

The title of "oldest living marine animal" is a bit tricky, as it depends on how you define "oldest."

Here are a few contenders:

* Ming the clam: This ocean quahog clam, found in 2006, was estimated to be 507 years old at the time of its death. While it died in the lab, Ming holds the record for the oldest known individual animal with a lifespan verified by scientists.

* The Greenland shark: These massive sharks are thought to be capable of living for hundreds of years, potentially reaching ages of 400 years or more. However, their longevity is harder to confirm due to their elusive nature and lack of accurate age-dating methods.

* Immortal jellyfish: Technically, Turritopsis dohrnii is capable of reverting to its polyp stage after reaching sexual maturity, effectively resetting its lifespan and potentially living forever. However, this process is not truly "immortal" as they can still die from predators or disease.

Therefore, while Ming the clam holds the record for the oldest known individual animal with a verified lifespan, the Greenland shark might be the oldest living animal, although we don't have conclusive evidence. The immortal jellyfish's ability to rejuvenate is fascinating, but not a true form of immortality.