GROUPS OF ANIMALS 



269 



Coelenterates. The members of this group are very 

 simple in structure being tubular in shape with but one 

 opening to the body. Frequently thread-like , arms aiv 

 present around this opening. Sometimes these animals 

 reproduce by a process called budding. A small knob- 

 like structure grows out at the side of the body and 

 gradually becomes larger finally forming an adult 

 animal. This bud may break off, or with many others 

 like it, it may remain attached and form colonies. Here 

 belong the jelly-fishes, 

 sea - anemones, corals, 

 and hydras. They are 

 all found in water and 

 most of them only in 

 salt water. 



The coral has long 

 been of interest because 

 of the islands, reefs, 

 which are formed by the 

 gradual accumulation of 

 coral shells, and also 



because of the use of one 



kind of coral for ornaments. 



Porifera. The skeletons of some of the representa- 

 tives of this group form our commercial sponges. 

 Sponges live in colonies. Each of the largest holes in 

 a commercial sponge represents the central body cavity 

 of a single animal. Sponges are very simple in struc- 

 ture; each animal consists of a cup-like structure the 



126 - A sea-anemone. 



