Starfish, or sea stars, range in size from 5 inches to over 9 inches. Starfish may weigh over 10 pounds. There are 2,000 species of starfish, with most having five arms, but some species having as many as 40 arms.
Starfish have a hard exterior that keeps them safe from predators. However, in the event that a starfish is harmed, it can grow back much of its body. Starfish are unique invertebrates that have no brain or blood. Ocean water serves the role of blood in starfish. Starfish live in all of the oceans, but there is no species in freshwater environments.