PHYLUM ECHINODERMATA 



209 



possible enemy may become entangled. These structures, however, are 

 soon regenerated. 



240. Crinoidea. — The sea lilies, which were exceedingly abundant in 

 the seas ages ago, are echinoderms which, typically, are attached by the 

 aboral surface to a stalk that rises from the bottom and frequently 

 possesses many rootlike branches (Fig. 123). The oral surface is upper- 

 most and the disc is surrounded by more or less complexly branched rays 



O/'a/ feni-ac/es 



P/n^ cai/7a/ 



Pc>//fT/7 



ves/c/es 



Gen/-^/ o, 



Ampu/Zae 







lOf7^/'-/-ac///-?ar/ 

 musc/e banc/ 



Cov/'e-/'/crr7 



^«V7//^ 



rl ~'\^i\/^^^^^por/'-^e 



Gonard 



;7~ ~\\^/n-/-esf/ne 



— b/ooof vessel 



Venfrenf 

 b/ooo/ vessef 



^^^^ - Pesp/'ra-Z-ory 

 tree 



Paef/'a/ musc/es 



Fig. 121. Fig. 122. 



Fig. 121. — A sea cucumber, Cucumaria planci Brandt, from the Mediterranean. 

 From a preserved specimen. X /s- 



Fig. 122. — Diagram of the internal anatomy of a sea cucumber representing the animal 

 laid open and the wall of the body turned to each side. 



bearing smaller pinnules arranged like the barbs on a feather. The 

 tube feet are tentacle-like and without ampullae. Crinoids are found 

 mostly at moderate depths, but a few belong to the deep-sea fauna. 

 They may be free-swimming, when they are known as feather stars 

 (Fig. 124). 



241. Reproduction. — The reproduction of all echinoderms is similar 

 to that of the starfish. They all develop a bilaterally symmetrical 

 swimming larva, and all undergo metamorphosis. The larvae of the 



