CLASSES OF NEMATOHELMINTHES 243 



Class Nematomorpha 



The Gordiidae (e.g. Gordius aquaiicus — the horse-hair worm) are so 

 different from true Nematodes that they must be ranked in a separate 

 class. There are no lateral lines. Three nerve-strands lie close 

 together in the mid-ventral line. In the adult Gordius the mouth is 

 shut and the food canal is partly degenerate. The adult Gordiidae 

 usually live freely in fresh water ; larval forms occur in aquatic 

 molluscs, young insects, etc. ; later stages usually occur in carnivorous 

 insects, whence they emerge to become adult in the water. One form, 

 Nectonema agile, is marine. 



Class Acanthocephala 



For a few genera, of which the best known is' Echinorhynchus, 

 whose larvae live in Arthropods, and the adults in Vertebrates, a 

 special class, Acanthocephala, has been established. They may be 

 placed beside Nematodes, but the relationship does not seem to be 

 very close. Mouth and gut are absent. The anterior end bears a 

 protrusible hooked proboscis used in boring in the intestinal wall of the 

 host. In the minute swellings at the ends of the two much-branched 

 excretory organs of E. gigas, there are ciliated cells — the only case 

 known among Nematohelminthes. 



Echinorhynchus proteiis of pike, minnow, trout, etc., larva in the 

 Amphipod Gammarus pulex. 

 „ angustafus of perch, larva in the Isopod Asellus 



aquaticus. 

 „ moniliformis of rat, etc., larva in larval beetles 



{Blaps). 

 „ gigas of pig, larva in grubs of cockchafer, etc. 



Desiccation 



Many of the smaller Nematohelminthes are able to 

 survive prolonged drying up or desiccation. The body 

 may become quite brittle, and yet replacement in water 

 brings about revivification — even after years. This state 

 of latent life is of great theoretical interest, for the living 

 matter loses most of its water-content and passes out of 

 the colloid state. 



