Immortal Jellyfish

Forever is a long time, especially towards the end.

The ‘Immortal Jellyfish’ Can Age in Reverse And Possibly Live Forever : ScienceAlert

Tardigrade

Tardigrades have been on Earth for about 600 million years, about 400 million years before dinosaurs.

You can boil them, bake them, deep-freeze them, crush them, dehydrate them, or even blast them into space. It doesn’t matter—tardigrades can survive practically anything. These eight-legged aquatic animals may be small, but they’re nearly indestructible.

Tardigrade (nationalgeographic.com)