The key to determining if a starfish is alive or dead is to look for movement. However, because starfish are not the most mobile organisms on the planet, it can be difficult to tell if they are alive or dead. If you cannot observe any movement at all, the starfish is probably dead.
Bodily movements made by a living starfish may include the subtle pulsing of its body cavity or the moving of an arm. If such movements cannot be detected, turn the starfish onto its "back." On the bottom of the starfish’s arms are numerous small, tubular feet. These are the structures on which the starfish moves. Additionally, these tubular feet allow the starfish to learn about its surroundings. Generally, some movement can be observed in a living starfish. If the legs are not moving, consider touching them to see if they respond.
Starfish are a type of animal called an echinoderm. They are very different than humans, fish and other vertebrates and lead a very different lifestyle. Unlike fish and humans who search widely for their food, starfish tend to live right next to their food sources and move very little. Typically, starfish consume coral, mollusks and vegetation.