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CHAPTER 13 



OJI 



Phylum 

 Nemathelminthes, 



Phylum 

 Nematomorpha, and 



Phylum 



Acanthocephala. 



Roundworms 



Iematodes are one of man's worst ene- 

 mies. Their activities are less spectacular 

 than those of insects, but they are nearly as 

 detrimental. They are universally present in 

 the sea, in the fresh water, and in the soil. 

 They occur also as parasites of plants and 

 animals, including man. It is estimated that 

 roundworms cause millions of dollars of 

 crop damage every year. On the other hand, 

 some of the many free-living species are 

 known to be beneficial. Together, the para- 

 sitic and free-living roundworms form a 

 subdivision of the animal kingdom which is 

 of the utmost importance to man because 

 it affects his well-being and economy. 



Formerly, three different groups of round- 

 worms were placed together in a single phy- 

 lum. However, this arrangement was un- 

 satisfactory to most zoologists, who preferred 

 to classify them separately as the phylum 

 Nemathelminthes, phylum Nematomorpha, 

 and the phylum Acanthocephala. These 

 three groups will be considered in the same 

 chapter, even though divided into three 

 separate phyla, for they do have some char- 

 acteristics in common. 



PHYLUM NEMATHELMINTHES 



The Nemathelminthes are called unseg- 

 mented roundworms to distinguish them 

 from the flatvvorms and segmented annelids. 

 They are, typically, long slender animals, 

 usually with a smooth glistening surface, and 

 tapering at one or both ends. In size, they 

 range from ^4 2 5 oi an inch to 4 feet in 

 length. 



Many of them are so important economi- 

 cally and undergo such amazingly complex 

 life histories that a knowledge of some of 

 the parasitic species of animals is of great 

 interest to everyone. For this reason, a brief 

 description of Ascaris is presented, as well 

 as an account of a number of the more im- 

 portant parasitic species. These include the 

 hookworm, trichina worm, pinworm, whip- 

 worm, filaria, eye worm, and guinea worm. 



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