Starfish, or sea stars, of the echinoderm family, are characterized by a radial disk with radiating arms, usually in a "star"shape, although some sea stars, like the basket star, can have dozens of arms. Each arm contains rows of tube feet with suction cups that enable the sea star to move along most surfaces. If the arm is lost to a predator, it will regrow. A sea star’s mouth is located on its underside, in the middle of its central disk. If the sea star’s food is large, it will flip its stomach out and secrete a digestive enzyme that breaks down the food. Many sea stars have an "eye" in the center, which can detect light. There are about 1,800 species of sea stars in a large variety of colors, shapes, and textures.
Sea urchins, in the same echinoderm family, are shaped like a sphere, with spines and tube feet. They also come in many different colors and shapes.