496 



ECHINODERMATA — OPHIUROIDEA 



in tlie disc, or (expressing the same fact in another way) tlie 

 interradial lobes out of which the disc is composed are not com- 

 pletely united. Radial shields and dorsal plates naked. Arm- 

 spines smooth and inserted on tlie posterior border of the lateral 

 arm-plates. 



This family includes all the Brittle Stars of smooth porcel- 

 anous aspect and provided with only short spines. Forbes ^ 



Fig. 218.— Oral view of Ophioglyplw {Ophiura) buUnfa. 



(From Wyville Thomson.) 



called them Sand-stars, since their short spines render these 

 animals incapable of burrowing or of climbing well, and hence 

 they appear to move comparatively rapidly over firm ground, 

 sand, gravel, or muddy sand, and tliey are active enough to be 

 able to capture small worms and Crustacea. The prey is seized 

 by coiling one of the arms around it. 



One genus, Ophiura, is fairly common round the British coast, 



^ Forbes, "A History of British Starfishes and other animals of the class 

 Echinodermata," 1841, j). 23. 



