PHYLUM ANNUL AT A 



525 



The following diagram will serve to illustrate this view of the 

 relationships of the various groups referred to :- 



Polychaeha 



Myzosl'omida 



Gephyrea 



Oligochaefa 



Hirudinea 



Arch i -Annelida 



Dinofihilea RoHfera 



-Gastrotricha 



Troch ojahore 



FIG. 419. Diagram illustrating the relationships of the Annulata and the Trochelminthes. 



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

 trochophore actually represents the ancestral form, since, to some 

 extent at least, its special features, such as the special arrangement 

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



