TWO-LAYERED ANIMALS— PHYLUM COELENTERATA 



127 



that come off as digestion causes the fish's body to begin to disintegrate. 

 While such a relationship may seem marvelous, especially to those 

 with a limited knowledge of the animal kingdom, it is only one of many 

 such cases which could be mentioned. The word symbiosis is used to 

 describe this condition where two organisms live together in a mutually 



gastrovascular cavity 



adial canal 



tentacular swellings 



tentacle 



medusa bud 



Animals Without Backbones, Buchsbaum, The University of Chicago Press 



Fig. 9.7. Gonionemus, medusa on the top with part of the bell removed to show 



internal structures ; polyp on the bottom. 



