What You Didn't Know About Sea Stars

By Scuba Diver Life

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  Sea Stars are Echinoderms

  Though commonly called starfish, sea stars are not fish at all. They're Echinoderms, the same phylum as sea urchins, sea cucumbers, and sand dollars. There are over 1500 different species.

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  They have eyes on their arms

  While not technically eyes, sea stars do have eyespots on each arm that can sense degrees of light and dark. Their tube feet can also sense chemicals in the water, food, and temperature.

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  One arm can take control

  Though it doesn't have a brain and can't plan, it does have a nervous system. If the sensors on one arm detect food, it becomes the dominant arm and essentially takes control of the rest of the body.

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  They have a hydraulic system

  Instead of blood, they have a water vascular system that provides nutrient transport, gas exchange, and locomotion using the surrounding water. Out of water they can't move far and won't survive long.

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  They don't use suction to stick

  It seems as though all of the tubular feet use suction to pull and move, but it's actually a chemical that provides adhesion. The feet move in a wave, with one attaching as the previous releases.

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  They are predators

  Mostly carnivores, sea stars can be voracious, sometimes even consuming each other.  Some, like the Crown-of-thorns, are considered dangerous pests since they eat coral polyps and can destroy reefs.

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  They can turn their stomach inside out

  To eat bivalves, they open the shells a bit and push their stomach inside the shell, digesting the contents.  This is how they can also consume animals much larger than themselves. 

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  They have a range of sizes

  The largest sea star- the Sunflower Star - can grow over 3 feet wide.  It has up to 24 arms and is the fastest moving sea star with a top speed of nearly 9 feet a minute.

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  They have cool defenses

  While the cushion star emits a noxious slime when threatened, the most interesting means of defense is the sea star's ability to detach an arm in order to escape. But it's okay, they grow back.

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  They have a wide range

  Sea stars can be found in tidal pools and even as deep as 20,000 feet. They come in countless shapes and sizes.  Regardless of which ones you see, we hope you'll look at them a little differently now.