The limbs of a starfish assist escape because they can be shed.
"Starfishes, which have hard spiny skeletons and five (or more) arms or limbs in a star-like arrangement, are also adept at autotomy when caught by predators. Their subsequent regeneration, however, can be particularly dramatic. As long as the shed limb is not devoured by the predator and still contains a section of the central body disc of the starfish that shed it, this limb has the ability to regenerate into a complete starfish." (Shuker 2001:132)
Learn more about this functional adaptation.