22 



ECONOMIC ZOOLOGY 



IV. Ophiuroidea, Fig. 17. These are the brittle-stars or serpent- 

 stars; the first name is appropriate because of the brittle, delicate 

 character of the rays; the latter name comes, as the class name indicates, 

 from the snake-like character of the rays. The distinct central disk 

 and snake-like arms are sufficient to identify the members of the class, 

 Fig. 17. In some species the rays are much branched, making the 



FIG. 14. Sea-urchin. xM- 



animal very complex in appearance, as in the basket fish or Venus' 

 basket. 



V. Crinoidea, Fig. 18. These are the feather-stars, sea-lilies, or 

 stone-lilies, named from their feather or plant-like appearance. They 

 have five arms which often branch repeatedly and give the feathery 

 appearance. They are generally attached by the aboral apex, either 

 during their developmental stages or throughout life, sometimes by a 



