PHYLUM ECHINODERMATA 



r6 9 



2. THE OPHIUROIDEA 



The Brittle-stars bear many resemblances to the true Star- 

 fishes, but have a number of special features of sufficient 

 importance to justify their being regarded as constituting a 

 separate class (Ophiuroidea). Like Asterias, the Brittle- 



FIG. 87. Ophioglypha lacertosa. A, outline, of the natural size. B, central disc, 

 dorsal view. C, the disc, ventral view showing the mouth and genital fissures. 

 (From Nicholson and Lydekker's Paleontology.} 



star (Fig. 87) has a star-shaped body with a central disc 

 and five radiating arms. But the arms, instead of appearing 

 merely as radiating prolongations of the central disc, are 

 sharply marked off from it, and have rather the appearance 

 of appendages. They are solid, long, slender and tapering, 



