Our Privacy/Cookie Policy contains detailed information about the types of cookies & related technology on our site, and some ways to opt out. By using the site, you agree to the uses of cookies and other technology as outlined in our Policy, and to our Terms of Use.


Sea Urchin Information for Kids

| Updated October 19, 2017

Sea urchins, the round and spiky creatures that hang out on the bottom of the ocean floor, can be found in both shallow and deep waters. Sometimes sea urchins' spikes are soft and chalklike, while other times, they are hard and covered by a shell-like structure. With more than 200 types of sea urchins, there are many different sizes and shapes of sea urchin species. The shape and spikes of the sea urchin help it to move about the ocean floor while defending itself from predators and gathering food.

Food for the Sea Urchin

As a sea urchin moves moves about the ocean floor, he may be gathering up things to eat. Sea urchins commonly enjoy eating algae, which may be sticking to the rocks the sea urchin travel against. They also eat seaweed, plankton and dead fish that may be found floating on the bottom of the ocean floor. The spikes of the sea urchin allow it to grab food. After grabbing the food found on the bottom of the ocean floor, the sea urchin eats with his mouth, which contains teeth, and is located on the underside of its belly.

Appearance of the Sea Urchin

With an almost porcupinelike structure and spine, the sea urchin is a unique an interesting looking sea creature. Its round, globelike shape adds its spectacular appearance. Sea urchins come in a range of sizes, while some are tiny, at only 1.2 inches around. Others may be 3.9 inches in diameter. There are different species of sea urchins and they come in various colors including black, brown, red, green and purple. The five rows of feet that also serve as "suckers" are located on the underside of the sea urchin. The rows of feet are important because they allow sea urchin to move around the ocean floor while also gathering up food.

Protection and Self-Defense

Sea urchins, like many other animals, must defend themselves against other animals in their environment. To do this, sea urchins can use their "claws," which are located on their body and close to their spine. These "claws" are called pedicellariae and along with protection from other animals, they also help the sea urchin to collect bits of food in the ocean and remove things that may try to stick themselves onto the sea urchin. The sea urchin has many predators it must protect itself against, such as sea otters, sea birds, crabs, fish, sunflower stars and human predators. The purple sea urchin is at risk for becoming endangered due to overharvesting.

Fun Facts

  • Many types of sea urchins can live 30 years.
  • Sea urchins mate in the spring.
  • The mouth of the sea urchin contains five teeth that are so sharp they can actually make a hole in a rock.
  • A type of sea urchin called the flower urchin has venom within its spikes.
  • Sea urchins commonly live in warm water from 20 feet to 5,000 feet deep.


  • Helping to keep beaches clean and remove waste that may get into the ocean can help to protect sea urchins and other marine life. Do your part to throw away litter on the beach before it becomes waste in the ocean.