How to Watch a Sea Urchin

It can be fun to visit Pacific Science Center on a busy day or to watch something thrilling in the Boeing Imax theater.

But there is a whole other experience to be had on a quiet day. There is time to stroll from one exhibit to the next. In the butterfly house, there is time to smell the flowers. At the tide pool there is time to stop and watch the sea urchins. These mostly vegetarian creatures live to amazing ages – some may be as old as 200 years. Isn’t it worth a little time out of our days to check them out?



Like sea stars, urchins are echinoderms, a group of animals with tube feet, a five-sided body plan and a bumpy skeleton, or test, just under their skin. As their name suggests, the sea stars sometimes hog the limelight, but the urchins are well worth a second look.

The first thing you notice about a sea urchin is its long spines. These are hard and rigid, and are used for movement, defense and to snare bits of seaweed, which the urchins eat. But look more closely and you will see little long, flexible strands called tube feet or pedicellarines, moving about between each of the stiff spines. Their tube feet can grab and hold food and can also help the animal cling to surfaces and sense where it is going. If an urchin loses spines or tube feet, it can eventually grow them back, but this takes months and is stressful to the animal. Instead of touching an urchin, hold a finger between its spines and it will move them to softly squeeze your finger.



If you see an urchin against the glass of the tide pool, there is a good chance you can see its mouth, which is on the underside. The mouth is five sided, beak-like, and has the unusual name of Aristotle’s lantern. When an urchin eats, it passes seaweed to the mouth using its tube feet, like a conveyer belt. This is very exciting to watch, if you can accept that it will take a while. If you see an urchin in the process of eating, plan on spending the next half hour watching in fascination.

Urchins do not have a central nervous system. Information from their many spines and tube feet is passed into a net of neurons, which processes information and helps them go toward food and away from danger. Watch an urchin walk. They may walk slowly, but they are a bundle of moving parts as they go, tube feet waving, spines tapping. The urchin probes the area ahead of it with its spines, much as a blind person might use a cane to test the ground. Then the spines and tube feet convey the animal forward. Urchins almost always keep their mouth side against a surface. But they do not have a forward and backward. If they change direction, they do not need to turn and “face” a new way, as we would, but simply start going that way.



Right now, Pacific Science Center’s two urchins are on the move. Normally they have staked out a small territory in the deep end, but in recent weeks they might be found anywhere in the tide pool. Not only that, but they are usually in motion, racing along at nearly an inch per minute! Over time, urchins will excavate small areas in a stone outcropping, which become their homes.

Come take a look, and expect to leave with a better appreciation of a very different life form. Although we encourage you to take your time and watch these animals, the time frame for this process is years, so do not plan on observing it in a single visit. Better yet, check in on the urchins whenever you like. Consider a Pacific Science Center membership plan!