Starfish and brittle stars are both free-moving marine echinoderms (belonging to the phylum Echinodermata). Starfish belong to the class Asteroidea. Most starfish have five broad arms that radiate from a central disc and a centrally placed mouth and muscular tube-feet on their underside. Brittle Stars belong to the class Ophiuroidea. Brittle stars generally have five long, slender. very flexible whip-like arms formed of a central column of “vertebrae” and a flat , nearly circular central disc.