Category Archives: intertidal

Sea urchins

Time for some sea urchin love. These different urchins were all found during the last minus tide. While it’s fun to find them in the rocky intertidal zone, I also like watching them underwater bc only then do you get to see them extend their tube feet! Yes, urchins have tube feet. They are echinoderms, as are seastars, sea cucumbers, and sand dollars. All of them have radial symmetry and tube feet. If you look at a test (empty skeleton of an urchin), you will see bumps on the outside where the spines attach. If you look from the inside, you will see pinholes of light—that’s where the tube feet extend from. On a sand dollar the tube feet only extend from the petal-shaped design on the “top” of their bodies.