228 



HOW DO WE CLASSIFY ANIMALS? 



of the starfish envelops it and covers it with the secretions of di- 

 gestive glands, and it is rapidly digested and changed to a fluid. 



Hundreds of thousands of dollars' damage is done annually to 

 the oysters in Connecticut alone by the ravages of starfish. 



Practical Exercise 5. What echinoderms, if any, exist in your community? 

 What would you consider the chief characteristics of the echinoderms ? 



Platyhelminthes (Gr. platys, flat; helminthos, worm), or flat- 

 worms. These are usually small, ribbon- or leaf-like, and flat. 

 They live in water. Most flatworms are parasitic. The most 

 commonly known ones are the tapeworm and the liver fluke. 

 There are about 5000 known species. 



PLATYhELMINTHK 1 



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Nemathelminthes (Gr. nematos, a thread), or roundworms. 

 These three-layered, elongated threadlike animals are often par- 

 asitic. Vinegar eels, the horsehair worm, the pork worm or trichina, j 

 and the dread hookworm are examples. About 15,000 species are 

 known. Examples of these worms will be discussed later in the unit 

 ''How Does Man Control His Environment for Health?" 



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