TIL that Hydra are small freshwater invertebrates whose stem cells exist in a continuous state of renewal. Kept safe and in isolation, these organisms show no signs of aging.

https://biology.ucdavis.edu/news/hydra-and-quest-understand-immortality

https://www.reddit.com/r/todayilearned/comments/14ywpzv/til_that_hydra_are_small_freshwater_invertebrates/