We know there are a few species that don't die of old age, like the giant tortoise and naked mole rat. But those species aren't truly immortal — as they still eventually die. These tiny worms might be a different story... one which could have major implications for humans trying to live longer.
Negligible senescence is the term for species where the death rate doesn't increase as individuals get older, and the animals don't experience the lost reproductive capability and diminished functions seen in all other species. That in itself is a plenty impressive biological feat — and figuring out why species like giant tortoise, naked mole rats, lobsters, and rockfish have beaten aging, in a way that all other species haven't, is a major topic of longevity research.