A starfish has a spiny skin. It belongs to a group of spiny skinned animals which includes the sea urchin and the sea cucumber. This group of animals is known as the echinoderms.

The spiny skin protects the starfish from predators. On the underside of each arm are lines of tube feet. Each tube foot is a small cylinder with a sucker on the end. The starfish controls the movements of its tube feed so that it can glide along over the surface of a rock. The common starfish feeds on mussels but other species feed on worms, and crustaceans.