20 CORALS 



I. Animal Corals. 



A. Polyp-bearing corals. 



1. Coelenterate corals. 



(a) Madreporarian corals. 



(b) Alcyonarian corals. 



(c) Antipatharian corals. 



(d) Hydrozoan corals. 



2. Polyzoan corals. 



B. Corals that do not bear polyps. 



1. Foraminiferan corals. 



2. Poriferan corals. 



II. Plant Corals. 



A. Red Seaweed corals. 



B. Green Seaweed corals. 



Additional Note on the Nutrition of Corals 



Although there can be no doubt that the polyp-bearing 

 corals can catch and digest living organisms for food as 

 described above, it seems to be highly probable that, in 

 many cases, this food is not the only source of their nutrition. 



The canal system and often the polyps themselves of 

 many Coelenterate corals that live in shallow water are 

 crowded with little spherical cells {circa -oi mm. in diameter) 

 surrounded by a well-defined cell wall and bearing the char- 

 acteristic coloured vegetable substance Chlorophyll. 



These cells are not coelenterate cells belonging to the 

 polyps but unicellular organisms, living under the protection 

 of their hosts, with their own independent reproduction and 

 nutrition. They should not be called parasites, for it is 

 evident that they do not irritate or injure the polyps. They 

 are of the nature rather of associates who live with the corals 

 for mutual help and protection. 



This kind of association is called symbiosis, and the 

 unicellular organisms that take part in this symbiosis of 

 corals are called the Zooxanthellae. 



The great importance of these organisms in the general 



