Sea Urchins and Their Tiny (Indestructible) Teeth

As I’m sure everyone will agree, the weather on Thursday was not exactly the best kind for being near the windy waters of South Lido beach, but the trip was a nice experience and the landscape was lovely as the sunset neared. The sea shells looked especially pretty, being scattered across the shoreline like a little mosaic, and I was surprised to see so many different textures and colors of seaweed and sea sponge in there as well.

But I was most surprised by the sea urchin that was found somewhere along the shore, broken in half. I’ve seen sea urchins before, and have even come close to stepping on a few, but I’m not very familiar with sea life in general and I’m reluctant to admit that I had no idea sea urchins were living, mobile, mouth-having things (sea urchins have mouths! what!). So because this mouth structure was so fascinating a discovery to me, I decided to do a little research on the subject.

sea-urchins08-sea-urchin_17935_600x450Photo: National Geographic

As it turns out, sea urchins, despite being the abstract, seemingly faceless creatures they are, have a physiology exactly as any other animal would. Within that tiny, spiky sphere is an entire functioning system complete with a digestive system, nervous system, circulation, respiration, and feet. They have tiny little tube feet that allow them to filter and pump water to help push them along the bottom of the ocean. These feet are softer than the spines of the sea urchin, which are long and sharp in many of the adults in certain species, and even poisonous in a few others.

The mouths on sea urchins are as weird as you might expect them to be. They have five teeth that are hollow, and in the hollowed part of each tooth is a fleshy, tongue-like organ. What’s especially interesting about their teeth is that despite grinding through rock and stone, the teeth don’t dull and instead remain sharp. Scientists have discovered that the teeth are mosaics of two kinds of calcium crystals: fibers and curved plates. The crystal shapes are arranged crosswise to each other and are bound together with a cement of nanoparticles. These particles are organic and tear away easily, but this means the teeth, which grow continuously, can regularly shed damaged areas to keep a sharp edge.

This discovery isn’t just interesting, but scientists and engineers have been working to apply a similar, artificial self-sharpening features to tools and blades. Pupa Gilbert, a biophysicist at the University of Wisconsin-Madison said, “[We are] inspired by these discoveries, and we can use them to think of super-robust and fracture-resistant nanocements, or layered nanotips to do nanogrinding that rarely need replacing.” Much remains uncertain, though, such as the exact composition of the organic layers or the separate functions of the crystalline plates and fibers, so it’s unclear when technology like this will really be available to us.

So even though I was a bit slow to discover that urchins even had a mouth in the first place, I think I’m rightfully amazed by all the strange and interesting functions that their mouths have.


One thought on “Sea Urchins and Their Tiny (Indestructible) Teeth

  1. I really enjoyed your post and learning more about sea urchins. Mrs. Karla actually picked up a piece of one that had the mouth still attached on the inside so I got to see how the creature absorbed its nutrients and what not!

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