What external and internal features indicate that the starfish is organized in a pattern of fives?

The sea stars or starfish are the Echinoderms and belongs to the class Asteroidea. The species thrives in the ocean's seafloor. Various starfishes thrives in deep water, while some are also witnessed in shallow water. Though starfish are invertebrates, however, they do exhibit a certain type of skeleton. The bodies of starfish are formed of the plates of calcium carbonate called ossicles. The external and internal characteristics suggest that the starfish are arranged in the pattern of fives, that is, starfish exhibit five organs, which forms the water vascular system, and they function as an organ system, these organs are sieve plate, radial canal, ring canal, ampullae, and tube feet.