字幕表 動画を再生する 英語字幕をプリント All alone, in a vast emptiness. A baby sea urchin. A pleuteus Blind and deaf, its sole purpose is to find the right place to land. Here's what it will become, an adult sea urchin. Basically a rugged ball of spines, built to survive in some of the harshest environments in the ocean. Like their cousins the sea stars and sand dollars, sea urchins have little tube feet. They use them to move around... and pull kelp into their mouths. And between their spines are pincers called pedicellariae that they use to groom themselves. Each spring males release clouds of sperm and females release huge numbers of eggs. A tiny percentage of them find each other in the open ocean. The fertilized egg grows and eventually hatches. An embryo swims for its life. As it grows, it takes on the shape of a little lunar lander. It can swim for weeks or months like this, covering huge distances, feeding on algae along the way. Meanwhile, a microscopic adult urchin is growing inside its own teenage self. The pluteus needs to land somewhere before the adult inside it grows too big. The ocean currents drag it towards shore and into the pounding surf. That turbulence plus the smell of tasty kelp lets the pluteus know, it's time. It stops swimming. It falls to the seafloor. Then something really weird happens. From inside, tube feet reach out It pulls itself inside out, like a sock. Here's a sand dollar doing the same thing. A miniature adult emerges And then, after so much change and tumult, time kind of … stands still. Unless an urchin is eaten or gets sick, it can grow for centuries. Having survived the long odds of youth... it's now practically immortal. Hey, this is Amy! Check out more of our ocean stories. Like this one, about how pygmy seahorses make themselves nearly invisible. Or this one, about how sea otters' fur keeps them warm in frigid water. Thanks for watching!