Also known as starfish, these echinoderms are found on the sea floors of all the world’s oceans from the equatorial tropics to frigid polar zones. There are around 1500 species of sea stars, some being able to survive at abyssal depths of 20,000 feet below the surface of the ocean. They usually have a central disc with five arms, though some exceptions have more. Their tube feet, which help them move, maneuver food, breathe, and also attach themselves firmly to rocks and other underwater structures, are operated by their “water vascular system,” a hydraulic system of interconnected fluid-filled canals. Their digestive system or “gut” occupies most of their central disc and also extend into their arms.