9 Fascinating Facts About Starfish

Starfish are brilliantly colored creatures that inhabit oceanic habitats. There are approximately 2,000 species of starfish, all unique in shape, size, and color—from blue and purple to pink and orange. These star-shaped sea creatures are covered in all sorts of interesting patterns like speckles, stripes, and even some fancy swirls and flower-like designs.

These intriguing stars of the sea can be found in tidal pools and coral reefs, as well as among kelp beds and seagrass. Starfish can only live in saltwater, so you won't be finding them in freshwater environments. They also can't survive out of water for more than a matter of minutes.

Here are 9 more facts you may not know about starfish.

1. Starfish Are Not Actual Fish

That's right—starfish as a name is misleading. Like sand dollars and sea urchins, starfish do not have backbones, which means they’re invertebrates. Fish have backbones, which makes them vertebrates and in a different class altogether from starfish.

The more accurate name for starfish is sea stars, a tribute to the five limbs that many of the species commonly have.

2. Not All Starfish Are Star-Shaped

While the starfish that most people are familiar with have five arms, some species can have many more. The crown of thorns starfish (Acanthaster planci), for example, is reported to have up to 21 arms.

Likewise, sunstars—starfish aptly named for their resemblance to the sun—have about 12 arms. This subspecies may have vivid shades of orange or sport concentric bands of pink, orange, white, and yellow.

3. Starfish Have Tube Feet

Hundreds of little feet-like suction cups help starfish move from place to place. Another bonus of their feet? They contain a glue-like substance that helps them stick to surfaces like rocks, so they don’t fall off or get washed away with the waves.

4. They Can Regenerate Lost Limbs

Starfish have the ability to regenerate lost limbs in cases of injury—for example, if they are hit by a rock from crashing tides. In fact, starfish are able to regrow an entire body from just one arm and at least one-fifth of their central disk. This is a slow process that can take up to a year. Starfish are also able to regenerate their neurons, something very few animals can do.

5. They Don't Have Any Blood

Rather than blood coursing through their veins, starfish have a water vascular system. This system—common in echinoderms like starfish and sea cucumbers—is composed of canals connecting tube feet that pump seawater throughout the starfish’s body. The filtered seawater sends nutrients through its nervous system.

6. Starfish Are Carnivores

These innocent-looking creatures don’t just feast on algae and plants. Starfish are known to feed on creatures like injured fish, oysters, mussels, clams, and sand dollars. In some instances, starfish can even aggressive cannibals. Juvenile starfish, in particular, have been documented eating one another.

7. They Use Their Feet to Eat

Speaking of eating, starfish eat their meals in a rather unique way. Their feet—or rather, the tiny suction cups on the backs of their legs—help them hold onto their food. These feet also help them open up shellfish like clams and mussels.

8. Starfish Digest Outside Their Bodies

The unique eating style of starfish doesn’t stop with them using their tube feet—starfish also digest outside of their bodies. Once they have opened their food, they extend their stomach outside of their mouth and envelop their prey with their stomach. After their prey is partially digested, they draw the prey back into their digestive glands to complete consumption.

9. Starfish Have Eyespots on Their Arms

Have you ever noticed a starfish's eyes? While they aren't eyes like ours, starfish have eyespots on the tips of each of their arms. Each of these eyespots creates one pixel of the image that the animals see. When combined with all of the other eyespots on their legs, starfish can see all of their surroundings at once. While studies have shown that their viewing capabilities are still somewhat limited by low resolution, they're at least able to detect shapes as they navigate through the sea.