Starfish are not actually a fish, but are animals belonging to the Phylum Echinodermata. Starfish feed mostly on mollusks and other echinoderms. There are about 2,000 species of sea star living in all the worlds oceans. The five arm varieties are the most common. They have bony skin, which protects from most predators, and many wear striking colors that camouflage them or scare off potential attackers.