Aging

The immortal jellyfish, Turritopsis dohrnii, can revert from an adult medusa to a young polyp when stressed or injured. That means it can avoid death by aging, not that it is invincible: predators and disease can still kill it.

The Greenland shark is the longest-living vertebrate. In 2016, radiocarbon dating aged one female at ~400 years; the species may reach 272–512. The secret is a metabolism crawling in the cold, deep Arctic. It takes ~150 years to mature — so one maturing today was born in the 1600s.

Lobsters produce telomerase, preventing their telomeres from shortening—so they theoretically never age. They grow stronger over time, but their shells become so hard to molt that they eventually die from exhaustion during molting or from predators.