From start to finish, a sea urchin’s life involves an incredible and lengthy journey. From the moment a wandering sperm meets an egg somewhere in the ocean’s current, a sea urchin will endure continuous motion until it’s finally an adult and ready to settle down somewhere discreet.
After the embryo develops, an adult sea urchin follows the ocean’s current in a small lunar lander-shaped body until it finds a place to settle down. The critter survives on the small bits of algae it collects along the way. Upon finding itself somewhere ideal to settle down, the sea urchin flips inside-out and feeds some more on the algae around it.
While the aforementioned sea urchin is technically considered an adult, it’s still incredibly small. As it flips inside out upon finding a place to crash, the sea urchin’s tiny bodily tubes and feet emerge, and it will continue to feed on algae until it grows big and strong like the plethora of other sea urchins around it.
Notably, the journey from youth to adulthood is a long one for sea urchins, and survival isn’t always guaranteed. For the small percentage of young sea urchins that actually do make it to their destination at just the right time, they’ll live on for centuries, feasting on tasty algae and growing larger over time. Once they're large enough, they can tackle just about any terrain on their own.