TYPE ANNELIDA. 251 



rence of a closed blood vascular system. The lophophore of Phoronis, and 

 the epistome, are on the other hand characteristic Polyzoan features, and it 

 seems not at all improbable that Phoronis occupies an intermediate posi- 

 tion between the Gephyrea and the Polyzoa. There is this at all events to 

 be noted concerning the Prosopygia (see following chapter), and that is 

 that they are certainly closely related to the Annelida. If the supposition 

 advanced on p. 243 to the effect that the Sipunculacea are to be regarded 

 as Annelida which have secondarily lost their metamerism be correct, and 

 if Phoronis really indicates a derivation of the Prosopygia from Gephyrean- 

 like ancestors, then the Prosopygia too must be regarded as Annelida in 

 which all traces of metamerism have been lost. This view seems preferable 

 to that which would refer the Polyzoa, for instance, back to unsegmeuted 

 ancestors back, that is to say, to the non-segmented ancestors of the 

 Annelida. 



SUBKINGDOM METAZOA. 



TYPE ANNELIDA. 



I. Class CHjETOPODA. Metamerism usually well marked ; with dorsal 



and ventral rows of setae along the sides of the body. 

 I. Subclass POLYCILETA. Marine forms ; with the setae usually borne 

 upon lateral lobes of the body (parapodia). 



1. Order Archiannelida. Without parapodia. Poly gor dins. 



2. Order Errantia. Elongated swimming or creeping forms; 



metauieres more or less similar. Nereis, Lepidonotus, 

 Diopatra, Autolytus, Hesione, Syllis, Alciope, Capitella, 

 Polyophtlialmus, Arenicola, Aricia. 



3. Order Sedentaria. Usually tubicolous ; anterior metameres 



more or less different from the rest. Amphitrite, Serpula, 

 ISabella, Terebella. 



II. Subclass OLIGOCH.ETA. Aquatic or terrestrial forms ; with setae, 

 but without parapodia. 



1. Order Naidomorpha. For the most part aquatic ; fre- 



quently reproducing non-sexually ; nephridia serve as re- 

 productive ducts. Nais, Dero, Chcetobranchus, *3?olo- 

 soma, dialog aster, Ctenodrilus, Tubifex. 



2. Order Lumbricomorpha. For the most part terrestrial ; 



not reproducing non-sexually ; special reproductive ducts. 

 Lumbricus, PericTiceta, Anachceta. 

 II. Class HIRUDINEA. Metamerism well marked ; without setae ; with 



anterior and posterior suckers. 



1. Order Gfnathobdellidce. Mouth with three more or less well 

 developed teeth ; pharynx not protrusible. Hirudo, Ma- 

 crobdella, Nephelis. 



