Beastfile · Marine Life

Immortal Jellyfish

Turritopsis dohrnii

It can run its own life cycle backwards, which is not the same as not dying.

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Overview

A jellyfish normally goes one way: polyp fixed to the seabed, then free-swimming medusa, then death. Turritopsis dohrnii can reverse it. Injured, starved or simply stressed, an adult medusa can settle, reabsorb its own tentacles and revert to a polyp colony, its cells converting from one type directly into another. In principle it can do this indefinitely, which is where the name came from. In practice it is a four millimeter animal that gets eaten, infected and killed constantly. Biologically open-ended is not the same as immortal, and the distinction is the whole story.

A translucent jellyfish drifting in dark water with tentacles trailing

Origin

Originally described from the Mediterranean and now recorded worldwide in warm and temperate coastal water, apparently spread in ships’ ballast.

Habitat

Ocean

Notable Traits

•Reverts from adult medusa back to polyp under stress
•Cells convert directly from one type to another
•About four millimeters across, smaller than a fingernail
•Still dies easily to predators and disease
•Now found worldwide, likely carried in ballast water

Conservation

Not assessed. It is small, widespread and apparently spreading, so it is not a conservation concern; the interest in it is medical rather than protective.