Head to head
Starfish vs Jellyfish
A starfish and a jellyfish are both simple, brainless, boneless sea creatures, and both are radially symmetrical rather than having a left and right side. That is about where the resemblance ends: they belong to different phyla and live in completely different ways.
| Starfish | Jellyfish | |
|---|---|---|
| Group | Echinoderm (with urchins, sea cucumbers) | Cnidarian (with corals, anemones) |
| Body | Firm, spiny-skinned, five arms | About 95% water, soft bell |
| Where it lives | On the sea floor | Drifting in open water |
| Movement | Crawls on hundreds of tube feet | Pulses the bell; mostly drifts |
| How it feeds | Hunts slow prey; everts its stomach | Stings whatever touches the tentacles |
| Stinging cells | None | Yes, on the tentacles |
| Regeneration | Regrows arms; some regrow from one arm | Limited; one species can revert to a polyp |
| Brain | None (nerve ring) | None (nerve net) |
Starfish vs Jellyfish: common questions
Are starfish and jellyfish related?
Only very distantly. They sit in different animal phyla that split near the base of the animal family tree, more than 550 million years ago. Jellyfish are cnidarians, whose closest relatives are corals, sea anemones, and hydroids, and whose bodies are built around a single opening that serves as both mouth and anus. Starfish are echinoderms, a group whose closest relatives are actually the chordates, the phylum that includes vertebrates, which makes a starfish a closer cousin to a human than to a jellyfish. Their shared brainlessness and radial symmetry are not signs of kinship; the jellyfish is radial from ancient ancestry, while the starfish's five-part symmetry evolved later from a bilaterally symmetrical ancestor.
Do starfish sting like jellyfish?
No. Starfish have no stinging cells at all. Stinging cells, called cnidocytes, are the defining feature of the cnidarians, the group that contains jellyfish, and they are not found in echinoderms. A starfish defends itself instead with a tough, often spiny or knobbly skin, and the crown-of-thorns starfish adds long venomous spines that deliver a painful wound if trodden on or handled, but that is a puncture from a venom-coated spine, not a sting from firing cells. Most starfish are completely harmless to touch, though it is still best to leave them in the water, since handling and air exposure can hurt them.
Which is older, starfish or jellyfish?
Jellyfish-like animals are older in the fossil record. Soft-bodied impressions interpreted as early cnidarians appear more than 550 to 600 million years ago, in the Ediacaran period, before the major explosion of animal diversity. Recognisable starfish, with the distinctive five-armed echinoderm body and skeletal plates, appear later, around 480 million years ago in the Ordovician, though the echinoderm lineage itself goes back further. Both groups are far older than fish, land plants, or backbones, and both have survived every mass extinction since, which is part of why their simple, robust body plans are still so widespread today.