INVERTEBRATE ZOOLOGY. ^^ 



Sub-t}-pe II. Metanephridozoa {Ajwscolecida). 



Cladus III. Articulata. 



Sub-cladus I. Annelida. 



Class I. Archiannelides Small marine forms of very simple or- 

 ganization. No external segmentation. 

 Metameres all alike : bristles, cilia and 

 parapodia fail. Development with a 

 metomorphosis. in which occurs the most 

 typical trochophore. -^ Polygordius. 



Class II. Chaetopoda Typical Annelids, with well marked ex- 

 ternal segments, corresponding to the in- 

 ternal metamerism — segments furnished 

 wdth paired groups of chitinous bristles. 



Order 1 . Polychaeta Bristles conspicuous, situated on raised 



l&teral portions, parapodia. Head gen- 

 erall}^ present. Development by a meta- 

 morphosis, iisually with a Trochophore 

 larva. 



Sub-order 1. P. errant i<i Free-swimming, active, predaceotis. 



^ Nereis. 



Sub-order 2. P. sedentaria Live in tubes built of sand, mud, bits of 



shell, etc., subsist upon vegetable sub- 

 stances. -^ Aiiiphitrite, Serpula. 



Order 2. Oligochaeta Bristles very small, sunk in hollows along 



the sides : no parapodia : no distinct head : 

 hermai)hroditic. development direct. 



Sub-order 1. O. liiiiicohi Aquatic, in miul of swamps. -^ Nais. 



Si;b-order 2. O. terricola In damp earth. -^ Lumbricus. 



Class III. HiRUDiNEA .Aquatic hermaphroditic ecto-parasites ; 



segments withoxit bristles ; move by ter- 

 minal, adhesive suckers. External and 

 internal segments do not correspond. 



Order 1. Rhynchobdellidae Pharynx extensile, forming a sort of pro- 

 boscis. -^ Clepsine. 



