As they mature, echinoderms become radially symmetrical. Ophiuroideas are brittle stars and basket stars. The differences between the two sub-types lies in how the arms connect to the central disk. Ophiuroids have arms that do not connect with each other. There is a distinct boundary between arm and central disk.
Asteroids have arms that are connected to each other.
Also, it is harder to tell with asteroids where the central disk ends and the arms begin. If you look very closely you will notice that there are different types of growths on the surface. Some bumps are used to absorb oxygen, they are called Dermal Branchiae. Pedicellaria are pincher-like organs used to clean the surface of the skin. Barnacle larvae could land on a sea star and start growing if it were not for these organs.