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 PTiorowjs 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 ia 

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

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

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

 Annelida. 



SUBKINGDOM METAZOA. 

 TYPE ANNELIDA. 



I. Class OH.ETOPODA. — Metamerism usually well marked ; with dorsal 

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

 I. Subclass PoLYCH^TA. — Marine forms ; with the setse usually borne 

 upon lateral lobes of the body (parapodia). 

 1. Order Archiannelida.- — Without parapodia. Polygordius. 

 3. Older Errantia. — Elongated swimming or creeping forms; 

 metameres more or less similar. Nereis, Lepidonotus, 

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

 Polyophthalmus, Arenicola, Aricia. 

 3. Order Sedentaria.^-'Usaally tubicolous ; anterior metameres 

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

 Sabella, Terebella. 

 II. Subclass OuaocaMTA. — 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, Chcetohranchus, .Molo- 

 soma, Chwtogaster, Ctenodrilus, Tubifex. 



2. Order Lumbricomorpha. — For the most part terrestrial ; 



not reproducing non-sexually ; special reproductive ducts. 

 Lumbricus, PericJiceta, Anachata. 

 II. Class HiEUDiNEA. — Metamerism well marked ; without setae ; with 

 anterior and posterior suckers. 

 1. Order Qnafhobdellidce. — Mouth with three more or less well 

 developed teeth ; pharynx not protrusible. Hirudo, Ma- 

 crobdella, NepheKs. 



