200 INVERTEBRATE ZOOLOGY 



Class 2. Chaetopoda. With setae, segmentally arranged. 



Order 1. Polychaeta. Mostly marine chaetopods with parapodia 

 on which are numerous setae. Ex. Nereis. 



Order 2. Oligochaeta. Earthworms. Mostly freshwater or land 

 chaetopods without parapodia and with few setae. Ex. Lumbricus. 



Class 3. Hirudinea. Leeches. Annelids with a sucker at each end 

 and no appendages or setae. Ex. Hirudo. 



Class 4. Myzostomida. Disk-shaped parasites of echinoderms with 

 five pairs of parapodia. Ex. Myzostoma. 



PHYLUM V. ARTHROPODA 



Externally segmented animals with segmented appendages. 



Class 1. Crustacea. Aquatic, gill-bearing arthropods ; two pairs of 

 antennae present. 



Division 1. Entomostraca. Small, simply constructed crustaceans 

 with a variable number of body-segments and without abdominal 

 appendages. 



Order 1. Phyllopoda. Entomostracans with flat, leaf-like append- 

 ages. 



Suborder 1. Branchiopoda. Elongated phyllopods with segmented 

 body. Ex. Branchipus. 



Suborder 2. Cladocera. Laterally compressed phyllopods, the body 

 of which is not distinctly segmented and is enclosed in a bivalve 

 shell; second pair of antennae are swimming organs and project 

 from the shell. Ex. Daphnia. 



Order 2. Copepoda. Elongated entomostracans with distinctly 

 segmented body and without gills ; the female often carries one or 

 two egg-sacs. Ex. Cyclops. 



Order 3. Ostracoda. Minute, laterally compressed entomostracans 

 with entire body enclosed in a bivalve shell. Ex. Cypris. 



Order 4. Cirripedia. Sessile, hermaphroditic entomostracans with 

 body enclosed in a calcareous shell ; barnacles. Ex. Lepas. 



Division 2. Malacostraca. Crustaceans with a constant number 

 (20) of body-segments and nineteen pairs of appendages ; abdominal 

 appendages present. 



Subdivision 1. Phyllocarida. Primitive malacostracans with cara- 

 pace and with leaf-like thoracic feet. Ex. Nebalia. 



