Sea Urchin Facts: Lesson for Kids

Instructor: Lauren Scott

Lauren has a Master's degree in special education and has taught for more than 10 years.

This lesson will introduce you to the sea urchin. You will learn how these round, spiny animals eat and move, and you'll also learn how other animals (and people!) eat them.

What Is a Sea Urchin?

Sea urchins are covered in spines that help protect them.
sea urchin

It may look like a prickly pom-pom, but a sea urchin is really an animal. It doesn't have any bones supporting its body. Instead, it has a tough shell called a test. Its closest relatives, sea stars and sand dollars, have tests, too. That hard shell protects them, but sea urchins have another mode of defense--sharp spines! Some sea urchins have sharper spines than others, but all of them are pretty tough to eat. As if getting poked by a sea urchin spine wasn't bad enough, some of them are poisonous.

This image shows a sea urchin test without spines.
urchin test

Sea urchins move around on hundreds of sticky tube feet that allow them to crawl on rocks and sand. They move water in and out of their bodies to control their feet. They move their spines using a layer of muscle under the test. The spines help them to walk, too. They have a beak-like mouth on the underside of their bodies, which they use to scrape food off of rocks and other surfaces.

Sea urchins don't have brains or eyes, but they can detect light and sense nearby predators, or other animals that might harm them. Scientists think they have light sensors all over their bodies and along their pointy spines.

Sea Urchin Habitat and Diet

If you ever see a tide pool on a rocky beach, look closely. You just might spot a sea urchin! Sea urchins live in oceans all over the world. They are found along the coasts, but also live deeper waters.

Sea urchins are scavengers, meaning they eat whatever they find. They will eat algae, dead animals, and leftovers from other animals' meals. Kelp, or seaweed, is one of their favorite foods. Large groups of sea urchins can destroy a kelp forest!

Who Eats Sea Urchins?

In spite of their sharp spines and hard tests, some animals do eat sea urchins. Birds and sea stars break through their hard shells. Land animals, like foxes, sometimes grab them out of tide pools. Perhaps the most well-known sea urchin eater is the sea otter. These small, furry animals occupy the same kelp forests as sea urchins. They smash sea urchins open on rocks and eat the insides. With a little work, they can get a good meal!

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