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Ophiurida
:''Not to be confused with Ophiuroidea, the class that contains Ophiurida.''
The Ophiurida are an order of echinoderms within the class Ophiuroidea. It includes the vast majority of living brittle stars.
==Characteristics==
The upper surface of the disk of Ophiurida is covered with scales.〔Grzimek's Animal Life Encyclopedia, vol 1, Gale Cengage 2003〕
They 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. Most are five-armed, some with 4 or 6 arms as an abnormality, but others properly bear six or seven arms. The madreporite is on the oral surface. The digestive glands are entirely within the central disc.〔R.C.Brusca, G.J.Brusca. Invertebrates. Sinauer Associates, 2 ed.(2003)〕 They move their arms side to side by means of ball-and-socket joints. Tropical species tend to contrast color from the environment, but most others prefer to blend in. These biochromes do not include echinochromes. Some species exhibit luminescence, but only for short periods when stimulated, generally on the bases of the arm spines.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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