ECHINODERMATA 



221 



3. The echinoderms may be divided into three sub- Divisions of 

 phyla, called Pelmatozoa, Asterowa, and Echinozoa. dermata 

 The Pelmatozoa in- 

 clude the cystoids, 

 blastoids, and cri- 

 noids, but only the 

 last of these divisions 

 is living today. The 

 other two disappeared 

 before the end of Pa- 

 Iseozoic time, but were 

 important groups in 

 their day. The Pel- 

 matozoa are fixed, 

 usually with a distinct 

 stalk, on the aboral 

 surface, and conse- 

 quently the mouth 

 is directed upward. 

 Exceptions to this 

 statement are found, 

 however, in the adults 

 of many crinoids, IG ' SI ' 



which are wholly free, and might easily be confused 

 with starfishes. The word crinoid means "like a lily" 

 and has been given because of the long-stalked forms, 

 with the so-called calyx and feathery arms at the sum- 

 mit, resembling flowering plants. ' The crinoids were 

 dominant during the Palaeozoic, producing innumerable 

 genera and species, often of large size and complex form. 

 A wonderful slab of fossil crinoids (Scyphocrinites) may 

 be seen in the United States National Museum. These 

 existed during a period when much of the interior of 

 North America, east of the Rocky Mountains, was cov- 



From Perrier's "Traite de Zoologie" 

 Isocrinus (or Pentacrinus) asteria. 



Crinoids or 

 sea lilies 



