The Ophiurida are an order of echinoderms within the class Ophiuroidea.
It includes the vast majority of living brittle stars.
Ophiurida have bursae for respiration and excretion, and dorsal and ventral arm shields are present and usually well developed.
Arms are unbranched and incapable of coiling vertically.
Tropical species tend to contrast color from the environment, but most others prefer to blend in.