Starfish, also known as sea stars, belong to the phylum Echinodermata, which includes organisms with radial symmetry, a water vascular system, and a unique endoskeleton made of calcium carbonate plates. Starfish are marine invertebrates and are found in all oceans, from the shallows to the deep sea. They come in various shapes, sizes, and colors and are predators, feeding primarily on mollusks, crustaceans, and other small marine organisms.