442 The Animal Kingdom 



than a millimeter in length, which are in part covered with elongated 

 spines. The body is divided into thirteen or fourteen segments and 

 there is a retractile head. The excretory system is of the protoneph- 

 ridial type with flame cells; there is a well-developed pseudocoel and 

 a pharynx similar to that of the nematodes. The sexes are separate, 

 but are identical in appearance. The eggs develop into larval forms 

 quite different in appearance from the adult. By a series of molts, the 

 adult form is gradually attained. 



Fig. 143. — Representatives of some minor phyla related to the nematodes. A, 

 Chaetonotus, a gastrotrich; B, Priapulus, a priapulid; C, a member of the phylum 

 Kinorhyncha. DG, Paragordius, a member of the phylum Nematomorpha : D, 

 entire worm; E, larva; F, posterior end of male; G, posterior end of female. H, 

 Pedicellina, an entoproct. 



The exact relationships of this phylum are quite obscure, but due 

 to the possession of a pseudocoel it is probable that their relationships 

 are with these phyla. 



The Phylum Nematomorpha. — The members of this phylum 

 are commonly known as "horsehair worms" or gordiaceans (Figs. 

 143,D-G). These two names are based on the apparent resemblance 

 of these worms, first to horsehairs, and second to the Gordian knot 

 of mythological fame. They are extremely long, slender forms which 

 at times become entangled in complex masses. While most of the 

 species are fresh-water forms, there are a few marine representatives. 

 The adult is free-living, but the larva is parasitic in arthropods. 



