ECHINODERMA. 295 



CLASS V. CRINOIDEA (SEA-LILIES). 



While all other echinoderms are free throughout their 

 lives, the crinoids are characterized by being fixed to some 

 firm support by a long stalk arising from the aboral surface 

 of the body. In most the stalk persists throughout life, 

 but in a few, after the adult condition is reached, the body 

 separates from the stalk and thereafter follows a free life. 

 From the central disc or calyx radiate the five (usually) 

 branching arms, and these arms and their branches bear 

 small branchlets, so that as these animals rest in their 

 ordinary position, the whole forms a funnel-like net with 

 the mouth at the small end. On the upper (oral) side of 

 all these branches run grooves converging at the mouth, 

 and so any object which falls anywhere on the funnel is 

 brought to the animal as food. The alimentary canal runs 

 spirally through the calyx, and the vent is on the oral 

 surface. The stalk, like the calyx, is strengthened by 

 calcareous plates, those of the stalk being disc-like and 

 piled one on another. 



Crinoids, with the exception of the free forms (Comatuld), 

 are among the rarities of museums, as they are found only 

 in the deeper seas. In past time, however, they were very 

 abundant, and whole layers of rock in certain localities are 

 made up of their remains. The fossil forms present a 

 greater variety of shape than do the living representatives. 



