Starfish Aren't Actually Fish

Starfish — now more correctly called sea stars — are not fish at all. They have no backbone, no brain, no blood, and they can eat prey larger than their own mouths. These echinoderms are among the most fascinating animals on the ocean floor.

Why Are They Called Sea Stars, Not Starfish?

Scientists now prefer "sea star" because starfish are not fish. Fish are vertebrates with backbones and gills. Sea stars are echinoderms — invertebrates related to sea urchins, sand dollars, and sea cucumbers. They breathe through tiny structures on their skin, not gills.

How Do Sea Stars Move?

Sea stars move using thousands of tiny tube feet on the underside of their arms — each tipped with a small sucker. A hydraulic water vascular system pumps fluid in and out of the tube feet, allowing the sea star to walk, grip, and pry open clam shells. A single sea star has up to 15,000 tube feet.

Can Starfish Regenerate?

Yes! Sea stars can regrow lost arms — and some species can even regrow an entire body from a single arm (as long as the arm contains a piece of the central disc). This incredible ability is called autotomy and is used as a defense against predators.

How Do Sea Stars Eat?

Sea stars have a bizarre feeding method: they push their stomach outside their body, wrap it around their prey (like a clam or mussel), digest it externally, then pull the stomach back in. This allows them to eat prey that is too large to fit in their mouths.

Amazing Sea Star Facts

• There are over 2,000 species of sea stars found in every ocean on Earth.
• Sea stars have no brain and no blood — seawater filtered through their body carries nutrients.
• Some sea stars have up to 40 arms!
• Sea stars are important predators — without them, mussels can take over and crowd out other species.
• The sunflower sea star is the world's largest, spanning up to 3 feet across.