PHYLUM ECHINODERMATA 



225 



and are lactile and slightly respiratory in function. Gonads are 

 borne on the arms. The skeleton is well developed in all crinoids 

 and for that reason many of the ancient forms are preserved as fos- 





Fig. 121. 



^TALKZD CKIWOID 



-Distal portion of a stalked crinoid. (Courtesy of General Biological 



Supply House.) 



sils in widely distributed limestone layers of the earth's surface. The 

 nervous and circulatory structures parallel the ambulacral grooves 

 and encircle the mouth. Neocomatella, Pentacrimis, Rhizocrinns, 

 Metacrinus and Antedon are representative genera. 



