A sea urchin is a small, spiny ocean animal that looks like a living pincushion. These round creatures are covered in sharp spines that protect them from predators like sea otters and fish. Sea urchins crawl slowly along the ocean floor using tiny tube feet hidden beneath their spines, scraping algae off rocks with their five sharp teeth.

Despite their prickly appearance, sea urchins are considered a delicacy in many coastal countries, especially Japan, where the soft, orange insides (called uni) are prized for sushi. The shell of a sea urchin, called a test, is surprisingly beautiful when the spines fall off. It reveals an intricate pattern of bumps and holes arranged in perfect geometric designs.

Sea urchins play an important role in ocean ecosystems. They graze on kelp and algae like underwater lawnmowers, helping to keep these plants from growing out of control. However, when sea urchins become too numerous, they can create urchin barrens by eating so much kelp that they destroy entire underwater forests. Scientists study these patterns to understand how ocean ecosystems stay balanced.