PHYLUM ANNULATA 



525 



The following diagram will serve to illustrate this view of the 

 relationships of the various groups referred to : — 



Poly c hael-a 



Myzosfotnida 



Cephyrea 



Oligochaefa 



Hirudinea 



Archi-Annelida 



DInofihllea Roh'fcra 



-Gastrofricha 



Troch onshore 



Fig. 419. — Diagram illustrating the relationships of the Aiinulata and the Truchelminthes. 



It should, be added, however, that it is not likely that the 

 trochophore actually represents the ancestral form, since, to some 

 e.xtentat least, its special features, such as the special arrangement 

 of the cilia, may be adaptations to a pelagic mode of life. 



