THREADWORMS, HAIRWORMS, BRISTLEWORMS 



in addition to the swarms which inhabit the bottom mud, 

 the surfaces of plants, and everything else in the water. 

 They are constantly moving through its lower levels and even 

 city tap water sometimes contains them. Although many 

 of them are parasites and their ranks include the well-known 

 hookworm, there are also great numbers of them which are 

 harmless and free-living. 



Nematodes are very active, constantly lashing their bodies 

 to and fro ; this habit and their smoothness and small size will 

 usually identify them (Fig. 109, i). The mouth is at the 

 blunt end of the body; the other end is pointed. Aquatic 

 members of this group are uniformly minute and difficult to 

 distinguish, except the allied "hair-snakes" or Gordiacea 

 which may be a foot or more long. 



Hairworms — Gordiacea 



Form and habits of hairworms. — Although hairworms are 

 generally classed as allies of the nematodes they are in many 

 ways so different from them that they cannot be considered as 

 very closely related. 



Hairsnakes or wireworms lie like twisted roots or loose- 

 coiled wire, on the bottom of brooks, springs, ponds, troughs, 

 and rain-barrels. They look like coarse horse-hairs, and 

 about them clings the well-known story that a hair will "turn 

 to life" if you leave it in water over night. Their bodies are 

 entirely covered with a thin layer of hortiy brown chitin, 

 which stiffens them so that in their slow coiling and uncoiling 

 they seem to be so much living wire. The front end of the 

 body tapers to a point but the rear end is split into two or three 

 parts, the number varying in the two sexes and in different 

 species (Fig. no). 



The adult hairworms that live in the water are a foot or 

 two long (Fig. no). They lie on the brook bottom, often 

 singly but sometimes a half dozen are twisted together like a 

 snarl of twine. They lay their eggs in long strings hung upon 



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