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Sea Urchin

December 6, 2021

Sea urchins are the most interesting animals found on the bottom of the ocean floor. You may have seen what these little guys look like when scuba diving or at an aquarium with your family. For those of you that haven’t seen them, they look like little porcupines because they have a common interest. Sea urchins are spiky as well. Here are some interesting facts about sea urchins, including what they eat and what they do.

What They Eat

  • Sea urchins have sharp teeth, so they can eat just about anything.
  • Their favorite thing to eat is algae because they can use their sharp teeth to scrape it off for food.
  • They eat lots of other things such as mussels, periwinkle and kelp.
  • Fish is also a popular thing for sea urchins to eat.

What They Do

  • They help our environment by eating dead organisms.
  • Sea urchins stay on the coral reef.
  • They are sensitive to light, which is why they stay at the bottom of the ocean and don’t move that much.
  • They will protect themselves if something tries to poke them. Their spiky needles will go in that direction, so don’t get too close to one!

There are other interesting facts about the sea urchin. For example, they are very small. An adult can be as big as 4.7 in. They are located all over the world, and there are lots of them. Another interesting fact is that they are considered the ocean’s oldest animals.


  1. Judy

    Poor report!
    They don’t “look like” something because of what they”do”
    Your question “Do sea urchins have eyes?” Is never answered.
    Is the picture his bottom or his top?
    Try again please.

  2. Ann Beamer

    Where is the answer to the question at the top of your email? Do sea urchins have eyes?

  3. Ann Beamer

    Where is the answer to the question at the top of your email? Do sea urchins have eyes?

  4. Johnathan

    Still did not say if they had eyes or not!!???

    • Anna CLARK

      I was waiting for that answer, too. Not highly developed eyes, but they must have something that is sensitive to light. They avoid sunlight and stay in the shadows.

    • Thomas P Redick

      Sea Urchins don’t have eyes, but they do have mouths. Although they have no eyes, they can also feel light. This is because they have eyespots and photoreceptor cells in their aboral epidermis. Eye spots and photoreceptor cells help them sense light.

      • Phyllis Arrowood

        Thank you!

    • Christine

      That disappointed me, too.

    • Meghan

      I looked it up. They don’t have eyes, just photoreceptor cells.

  5. Leslie

    I was able to quickly Google this to help you out 🙂
    Sea urchins, like their close relatives the sea stars (starfish), don’t technically have eyes. Instead, the ball-like invertebrates detect light striking their spines and compare the beams intensities to get a sense of their surroundings.

  6. GbG

    Well, if they are sensitive to light– they must have SOME way to detect it. I guess?

  7. dennis

    .Do They have Eyes???..and how can they move around, fins or ..?

  8. Barbara A Fickes

    Because they are sensitive to light, I assume that they have at least one eye. ?

  9. Mary

    The Japanese harvest them for their eggs or Roe ; called as it’s pronounced: Ooo-nee. Succulent and delicious as a sushi compliment. Far more costly than salmon roe. Please try it at your finer Japanese establishment.

    • Eve Molyneux

      Uni is an acquired taste. I’m a foodie, but was rather put off by it.

  10. FrankM

    Available at your sushi bar. At one time, they were plentiful at any tide pool for the picking. Like everything else, not so much anymore.

  11. Jo

    What is a compound eye?

  12. William B Seek

    you forgot to say people eat them

  13. Candice Holman

    Yeah…eyes or not!?

  14. Cube Toronto

    Hi there great blog! Does running a blog like this require a lot of work? I’ve virtually no knowledge of computer programming but I was hoping to start my own blog in the near future. Anyway, if you have any ideas or tips for new blog owners please share. I understand this is off topic but I just had to ask. Kudos!


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