Chapter Six 



COELENTERATA 



1. HYDROZOA Hydroids and small jellyfish 



2. SCYPHOZOA Larger jellyfish 



3. ACTINOZOA Sea Anemones and Corals 



HYDROZOA 



Hydroids at first glance resemble plants rather 

 than animals for they appear to have a stem, root, 

 branches and even flowers. In fact, they are very 

 often collected and preserved as sea-weeds. Never- 

 theless, they are really animals, or more strictly 

 speaking, groups or colonies of associated animals. 

 A true hydroid colony is made np of two, or in some 

 cases three, kinds of individuals or polyps, each- 

 performing different functions for the benefit of the 

 entire colony. Some individuals have months and 

 tentacles and obtain the food for the colony: these 

 are the nutritive polyps. Other individuals serve a 

 reproductive function and produce the young of the 

 next generation. Some species possess a third type 

 of individual, serving a protective function. These 

 may be armed with thousands of small stinging cells 

 which serve the double purpose of protecting the 

 colony from enemies and in paralyzing the prey 

 which is to be used as food. 



Many of the species of Hydrozoa pass through 

 what is known as Alternation of Generations; in 

 other words, they have two distinct forms, (1) the 



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