Palaeos		Echinodermata
Echinodermata		Asteroidea

Class Asteroidea

The asteroids or true starfish usually have five arms, although some species have more. Unlike the ophiuroids, there is no sharp distinction between the arm structure and the central body structure, and the internal body parts extend into the arms.

Starfish move along the sea-floor or climb rocks using the numerous small tube feet which are present on the underside of their bodies. These tube feet are also used for burrowing and manipulating prey.

Most starfish are voracious hunters, preying on other animals, particularly clams, corals, other echinoderms, or anything else unlucky enough to cross their path. Some asteroids can extrude their stomach through their mouth, killing and partially digesting their prey outside their body. Asteroids are among the most active echinoderms.