286 BIOLOGY: GENERAL AND MEDICAL 



Class I. Asteroidea star-fishes. 

 Class II. Ophiuroidea brittle sea- 

 stars. 

 Class III. Echinoidea sea-urchins 



and sand-dollars. 

 Class IV. Crinoidea sea-lilies and 



feather-stars. 



Class V. Holothuroidea sea - cu- 

 cumbers. 



C. With a true codomic cavity bilaterally symmet- 

 rical. 



Phylum Platyhelminthes. 



The unsegmented worms, etc. 

 Class I. Cestoda. 

 Class II. Trematoda. 

 Class III. Turbellaria. 

 Phylum Nemathelminthes. 



Round worms, threadworms, etc. 

 Phylum Molluscoidea. 



Mollusk-like animals. 

 Phylum Trochelminthes. 



The wheel animalcules or rotifers. 

 Class I. Polyzoa. 

 Class II. Brachiopoda. 

 Phylum Annulata. 



The segmented worms. 



Class I. Chaetopoda, bristle-footed 



worms. 



Sub-class A. Polychseta (with 

 numerous bristles). 

 Sub-class B. Oligochaeta (with 

 few bristles) . 



Class II. Discophora sucker-bear- 

 ing worms. 



Class III. Archiannelida. 

 Class IV. Siphunculoidae. 

 Class V. Chaetognatha. 



