ROLL CALL ^^. 



PHYLUM V — PLATYHELMLXTHES — Flatworms. 



Characteristics : Dorso-ventrally flattened, soft bodies, bilaterally sym- 

 metrical, animals lacking true segmentation and blood vascular system; 

 no anus; excretory system of flame-cell type; only Class I free-living, all 

 others parasitic ; 4600 species. 



Class I — Turbellaria — Free-living flatworms {Planaria, Microstomum, 

 Bdelloura). 



Characteristics: Typically free-living, possessing a ciliated ectoderm; 

 some ectodermal cells secrete mucus, or produce rodlike bodies (rhnMite.s) ; 

 classification into orders depends upon nature of intestine. 



Cl.\ss II — Trematoda — Flukes (Polystoma, Pneumonoeces, Clonorchis). 



Characteristics: Parasitic flatworms with non-ciliated ectoderm in the 

 adult, possessing one or more suckers; highly specialized for parasitic 

 existence; many are internal parasites having complicated life cycle, 

 occupying as many as four hosts during development ; digestive system 

 present. 



Class III — Cestoda — Tapeworms {Taenia, Diphyllobothrium). 



Characteristics : Members of this group are completely parasitic, living 

 as adults in the alimentary canal of vertebrates; digestive tract absent; 

 body typically divided into a chain of segments (proglottids), except for 

 Cestodaria, budded from neck, gradually increasing in diameter towards 

 posterior end; the head (scolex) typically bearing organs of adhesion in 

 the form of hooks and suckers. 



Class IV — Nemertinea — Nemertines (Micrura, Cephalothrix, Cerebralidus). 

 Characteristics : Members of this gnnij) because of uncertain systematic 

 position not always placed with the flatworms ; characteristically found in 

 moist earth or fresh water, most forms being marine; characterized by 

 possessing alimentary canal with mouth and anus, definite blood-va.scular 

 system, and a long proboscis enclosed in a proboscis sheath. 



