CLASSIFICATION 137 



3. Class Annelida . 



I. Subclass Chaetopoda.— Metamerism usually well marked; with 

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



I. Order Polychaeta. — Marine forms; with the setae usually 

 upon lateral lobes of the body (parapodia). 



1. Suborder Aechiannelida. — Without parapodia. 



2. Suborder Errantia. — Elongated swimming or creeping 

 forms ; metameres more or less similar Nereis. 



3. Suborder Sedentaria. — Usually tubicolous; anterior meta- 

 meres more or less different from the rest Serpula. 



II. Order Oligochaeta. — Aquatic or terrestrial forms; with setae, 

 but without parapodia; hermaphroditic. 



I. Suborder Naidomorpha. — For the most part aquatic; fre- 

 quently reproducing nonsexually; nephridia serve as repro- 

 ductive ducts Nais. 



2. Suborder Lumbricomorpha. — For the most part terres- 

 trial ; not reproducing nonsexually ; special reproductive ducts. 



Earthworm. 



II. Subclass Hirudinea. — Metamerism well marked ; without setae ; 

 with anterior and posterior suckers. 



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

 developed teeth; pharynx not protrusible Leech. 



2. Order Rhynchobdellidae. — Without teeth and with protusible 

 pharynx Clepsine. 



III. Subclass Gephyeea. — Metamerism indistinct; without para- 

 podia. 



1. Order Echiureae. — ^With setae Echruls. 



2. Order Sipunculaceae. — Without setae Phascolosotna. 



