An echinoderm is a type of sea animal with a body built around a pattern of five parts, like a five-pointed star. The most familiar echinoderms are starfish (also called sea stars), but the group also includes sea urchins, sand dollars, and sea cucumbers.

The name comes from Greek words meaning “spiny skin,” which makes sense when you look at a sea urchin covered in sharp spines or feel the bumpy texture of a starfish. These animals have no front or back the way fish do. Instead, their bodies radiate outward from a central point in five directions, giving them radial symmetry.

Echinoderms have another remarkable feature: tiny tube feet powered by water pressure that help them move, grip surfaces, and even pry open clam shells. A starfish can use hundreds of these tube feet working together to slowly pull apart a mussel's shell, then push its own stomach out through its mouth to digest the soft animal inside.

All echinoderms live in the ocean, from shallow tide pools to the deepest parts of the sea. If you've ever picked up a starfish at the beach, you've met an echinoderm up close.