CHAPTEE X 



COELENTERATA 



INTRODUCTION CLASSIFICATION HYDROZOA ELEUTHEROBLASTEA 



MILLEPORINA GYMNOBLASTEA CALYPTOBLASTEA GRAP- 



TOLITOIDEA STYLASTERINA 



The great division of the animal kingdom called Coelen- 

 terata was constituted in 1847 by E. Leuckart for those 

 animals which are commonly known as polyps and jelly-fishes. 

 Cuvier had previously included these forms in his division 

 Eadiata or Zoophyta, when they were associated with the Star- 

 fishes, Brittle-stars, and the other Echinodermata. 



The splitting up of the Cuvierian division was rendered 

 necessary by the progress of anatomical discovery, for whereas 

 the Echinodermata possess an alimentary canal distinct from the 

 other cavities of the body, in the polyps and jelly-fishes there is 

 only one cavity to serve the purposes of digestion and the cir- 

 culation of fluids. The name Coelenterata (ko2\os = hollow, 

 evTpov = the alimentary canal) was therefore introduced, and it 

 may be taken to signify the important anatomical feature that 

 the body-cavity (or coelom) and the cavity of the alimentary 

 canal (or enteron) of these animals are not separate and distinct 

 as they are in Echinoderms and most other animals. 



Many Coelenterata have a pronounced radial symmetry, the 

 body being star-like, with the organs arranged symmetrically on 

 lines radiating from a common centre. In this respect they have a 

 superficial resemblance to many of the Echinodermata, which are 

 also radially symmetrical in the adult stage. But it cannot be 

 insisted upon too strongly that this superficial resemblance of 

 the Coelenterata and Echinodermata has no genetic significance. 



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