122 



ELEMENTARY ZOOLOGY 



three feet; in color they are yellow or red or brown or 

 purple. 



Brittle-stars (Ophiuroidea) . The brittle-stars, or ser- 



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" : ^r5-^ r > 



pent-stars (fig. 22) as 

 they are also called, 

 resemble the starfishes 

 in external appearance, 

 that is, they are flat and 



FIG. 22. A group of Echinoderms; the composed of a Central 



upper one. a starfish, Asterina mineata , . , ,. 



the one at -the right a starfish, Asterias dlSC Wltn radiating arms 

 ocracia, at the left a brittle-star, spe- 



(always five in number, 

 although each arm 



, - 

 cies unknown, and at bottom two sea- 

 urch ins, Strongylocentrotn*. franciscanus. 

 (From living specimens in a tide-pool on 

 the Bay of Monterey, California.) 



branched). The central 



disc is always sharply distinguished from the arms, and 

 the arms are usually slender and more or less cylin- 



