Starfish have sharp spines that serve to deter possible predators and make a starfish look like a rock, helping it blend into the background. Some species of starfish have a chemical coating on their bodies that gives them a bitter taste. Others produce poisons in their outer body walls.

Starfish have five arms that form a distinctive star shape radiating out from a central disk. Some starfish have more than five arms. The sun star has 40 arms. Each arm has an eye spot at the end that can sense light and dark.

Starfish have a water vascular system, with the water providing structure and a method of propulsion. Their feet fill up with sea water and can be retracted or used as suctions to create movement.

The diet of the starfish consists of clams, mussels, small fish, barnacles, oysters, snails and limpets. They use their arms to grab their prey and push their stomach out through their mouth to digest it. The stomach then slides back into the body.

Though commonly known as starfish, these animals are not technically fish. Their scientific name is the sea star. Most live in tide pools, with a few species living in deeper water.