Is a starfish a fish?

No.Starfish are not fish. They're sea stars, a kind of echinoderm related to sea urchins, sand dollars and sea cucumbers. They have no backbone, fins or gills, which is why scientists prefer the name sea star.

What's actually true

Starfish aren't fish at all. Despite the name, sea stars have no backbone, fins or gills. NOAA puts it plainly: sea stars, commonly called starfish, are not fish. They're echinoderms, the same group as sea urchins, sand dollars and sea cucumbers. That's why scientists prefer the name sea star.

Takeaway: 'Starfish' are sea stars: echinoderms, related to sea urchins and sand dollars, not fish.

Why people believe it

The name does all the work. Old common names lumped many sea creatures together as 'fish': jellyfish, shellfish, cuttlefish and starfish among them. Most people meet sea stars in tide pools or aquariums, next to real fish, so nothing contradicts the label. 'Sea star' is the more accurate name, but 'starfish' has centuries of head start.

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