VERMES 



1. 1 1 



For the sake of completeness we may mention here two 

 classes of Annelida which are probably somewhat closely re- 

 lated to the Cha^topoda. The Myzostomida (Fig. 133) are 

 minute marine worms, parasitic on some Echinodermata, par- 

 ticularly the Crinoidea. The form of the body is generally 



FIG. 133. Myzostoma. m, mouth; ft, parapodium ; s, sucker; I-X, marginal cirri. (After 

 von Graff, from Parker and Haswell's Text-book.) 



discoidal. There is no trace of external segmentation, but they 

 have five pairs of parapodia, each provided with a single bristle 

 or seta. The Archi-Annelida (Fig. 134) are likewise marine 

 worms, slender, about three centimeters long, and some live 

 freely in the sand, others as external parasites on such ani- 

 mals as the lobster. They are segmented, but without para- 

 podia or setae, and develop by means of a typical trochosphere 

 larva. 



