A sea urchin is like a tiny, spiky coconut that decided to live underwater. Its body is a round, hard ball covered in sharp, pokey things that look like they’re always ready for a party. Instead of legs, it has little tube feet that help it crawl around like a slow-motion ninja, and it mostly just hangs out on the ocean floor, munching on seaweed and pretending to be a rock. When it feels threatened, it curls up into an impenetrable fortress, kind of like a medieval castle but much smellier and wetter. And yes, it’s not exactly the cuddliest pet option out there!