CCELENTERATA 



8l 



forms by the slow sinking of the bottom of the ocean, 

 or by the death, decay, and disintegration of the corals 

 on the landward side of the reef, where the food supply 

 is necessarily restricted. 



FIG. 35. Sea Fan {Gorgonia} and Sea Pen (Pennatula}. 



(2) Sclerobasic Corals. Corallium rubrum, the precious 

 coral of commerce, is shrublike, about a foot high, solid 

 throughout, taking a high polish, 

 finely grooved on the surface, and 

 of a crimson or rose-red color. 

 In the living state the branches 

 are covered with a red ccenosarc 

 studded with white polyps (Fig. 

 34). 



CLASS 4. Ctenophora 



The CtenopJiora (as the Pleuro- 

 brachia, Cestum, and Beroe) are 

 transparent and gelatinous, swim- 

 ming on the ocean by means of FIG. 3 6. A ctenophore 



, .. robrachia pileus); natural 



eight comblike, ciliated bands, size. 

 DODGE'S GEN. ZOOL. 6 



