CHAPTER V 

 PHYLUM CCELENTERATA 



THE Phylum CCELENTERATA (Gr. koilos, hollow; enter on, 

 intestine) includes a great number of aquatic animals, mostly 

 marine, very few of which ever come to the notice of persons 

 who do not visit the sea-shore or are not especially interested in 

 natural history. As in the case of the sponges, many species 

 of ccelenterates, the corals, are known because of the beautiful 

 skeletons they construct. 



The three classes of ccelenterates are as follows : - 



CLASS I. HYDROZOA (Gr. hudra, a water serpent; zo'on, an 

 animal), fresh- water polyps, hydroid zoophytes, many of the 

 small medusae or jelly fishes, and a few stony corals; 



CLASS II. SCYPHOZOA (Gr. skuphos, cup; zo'on, animal), most 

 of the large jelly fishes; and 



CLASS III. ANTHOZOA (Gr. anthos, a flower; zo'on, animal), 

 (Actinozoa), sea-anemones, most stony corals, sea-fans, sea-pens, 

 and precious corals. 



A simple member of the CCELENTERATA and one that is com- 

 mon in fresh water is the polyp known as Hydra. A study 

 of this little animal will serve to illustrate ccelenterate charac- 

 teristics and will enable one to understand the more complex 

 species belonging to this phylum. 



i. THE FRESH-WATER POLYP HYDRA 



Hydra fusca is abundant in ponds and streams, where it may 

 be found attached by one end to aquatic vegetation. Hydras 

 are easily seen with the naked eye, being from 2 to 20 mm. in 

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