OphiurioideaO`phi*u`ri*oi"de*a\, Ophiuroidea \O`phi*u*roi"de*a\, n. pl. [NL., fr. Gr. ? serpent + ? tail + ? form.] (Zo["o]l.) A class of star-shaped echinoderms having a disklike body, with slender, articulated arms, which are not grooved beneath and are often very fragile; -- called also Ophiuroida and Ophiuridea. See Illust. under Brittle star.