CHAPTER IX 



PHYLUM CCELENTERA 



Class I. Hydrozoa. 



Hydroids and 

 Medusoids. 

 Class 2. ScYPHOMEDUSvE or 



ACRASPEDA. 



Jelly-fishes. 



Class 3. Anthozoa or 



ACTINOZOA. 



Sea-anemones, 

 Madrepore-corals, 

 Alcyonarians, etc. 

 Class 4. Ctenophora. 



The Coelentera — including zoophytes, swimming-bells, 

 jelly-fish, sea-anemones, Alcyonarians, corals, and the like 

 — form a very large series of Acoelomate Metazoa, i.e. 

 multicellular animals without a body cavity. Their 

 simplest forms are not much above the level of the simplest 

 sponges, but the series has been more progressive. Thus 

 many illustrate the beginnings of definite organs. In their 

 variety they seem almost to exhaust the possibilities of 

 radial symmetry, and some types {e.g. Ctenophora) may be 

 regarded as pioneers of the yet more progressive bilateral 

 " worms." Many are very vegetative, deserving the old 

 name of zoophytes (which should rather be read back- 

 wards — Phytozoa), and in their budded colonies afltord 

 interesting illustrations of co-operation and division of 

 labour. With the exception of three or four fresh-water 

 forms like Hydra, all are marine. 



General Characters 



The Coelentera are almost always radially symmetrical 

 animals in which the primary long axis of the gastriila 

 becomes the long axis of the adult. There is no body cavity, 

 or coelom, distinct from the digestive cavity {enteron) and its 



outgrowths. In the lower members of the phylum, the 



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