ECHINODERMATA 



221 



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

 phyla, called Pelmatozoa, Asterozoa, 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- 

 laeozoic 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, 

 which are wholly free, and might easily be confused 

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

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

 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 "Traitf de Zoologie' 

 FIG. 51. Isocrinus (or Pentacrinus) asteria. 



