PLATYHELMINTHES 



Body elongated, flattened and unsegmented. Anus gener- 

 ally absent. 



Class 1. Turbellaria. 



Outer surface ciliated. Free living. 



Order 1. Polycladida. 



Intestine complexly branched. No separate 

 vitellaria. (Planocera, Leptoplana, Stylochus.) 



Order 2. Tricladida. 



Intestine with anterior median, and two poste- 

 rior lateral limbs. Vitellaria numerous. 

 (Planaria, Bdelloura, Syncoelidium.) 



Order 3. Rhabdocoelida. 



Simple, saclike intestine. Body usually elon- 

 gated. (Polychoerus, Microstomum.) 

 Class 2. Trematoda. 



Parasitic. Generally with sucking disks. Well- 

 developed digestive system. 



Order 1. Monogenetica. 



Ectoparasitic. Direct development. Three or 

 more suckers. (Polystomum.) 



Order 2. Digenetica. 



Endoparasitic. Complicated development. 

 Never more than two suckers. (Distomum.) 



Class 3. Cestoda. 



Endoparasitic. Without digestive cavity. Usu- 

 ally having a scolex, bearing clinging organs 

 (suckers or hooks). 



Order 1. Monozoa. 



Body not divided into proglottids. (Caryophyl- 

 laeus.) 



Order 2. Polyzoa. 



Body consisting of scolex and proglottids. 

 (Taenia, Crossobothrium.) 



Class 4. Nemertinea. 



Elongated, ciliated, with eversible proboscis 

 not directly connected with the alimentary 

 canal. Intestine usually with lateral divertic- 

 ula. Anus present. (Tetrastemma, Cere- 

 bratulus.) 



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