196 



PHYLUM CCELENTERA 



ZOANTHARIA 



The Zoantharia include many orders, e.g. the primi- 

 tive Cerianthidea {Cerianthus, etc.) and Edwardsiidea 

 (Edwardsta), the Actiniidea (including the typical sea- 

 anemones and the Madreporaria), and the divergent Anti- 

 pathidea. 



Making of a typical coral. — Although the term 



Fig. 102. — The formation of a coral shell {Astroides). — 

 After Pfurtscheller. 



St., StomodiBum ; ms., mesentery ; s., calcareous septum ; B., basal plate. 



" coral " is applied to many different Coelenterate types 

 with substantial calcareous skeletons, e.g. to Millepores 

 which are Hydrozoa, and to " blue corals " and " red 

 corals " which are Alcyonarians, the corals par excellence 

 are the Aladreporarians. They form the coral rock and 

 " coral islands " found in many parts of the globe, but 

 rarely north or south of a belt extending 30° on each side 

 of the equator, and rarely below the 40-fathom line. 



In a general way a Madrepore polyp is like a sea-anemone 

 in structure, and the " coral " it forms is its external shell 



