PHYLUM PLATYHELMINTHES. SIMPLE ORGAN-SYSTEM ANIMALS 



147 



SOME COMMON CESTODES OF M.\N 



SCIENTIFIC NAME 



DEVELOPMENTAL 

 STAGES 



GEOGRAPHIC 



DISTRIBUTION 



HOSTS 



CLASSIFICATION OF THE 

 PLATYHELMINTHES 



{For reference purposes only) 



The Platyhelminthes are animals character- 

 ized as being unsegmented, triploblastic, and 

 bilaterally symmetrical. The body is flattened 

 dorsoventrally. No anus (usually) or coelom is 

 present. They have no skeletal, circulatory, or 

 respiratory systems; but they have an excretory 

 system with many flame cells. They have a 

 head, sense organs, and a central nervous sys- 

 tem which consists of a brain and two longitu- 

 dinal nerve cords. Most flatworms are herma- 

 phroditic. 



The principle classes, subclasses, and orders 

 are as follows: 



Class 1. Turbellaria. Mostly free-living; epi- 

 dermis at least partly covered with 

 cilia, with rodlike rhabdites and many 

 mucous glands. No suckers. 

 Order 1. Acoela. Marine; no intestine. 



Ex. Polychoerus caudatus. 

 Order 2. Rhabdocoela. Intestine simple, 

 unbranched. Ex. Stenostomum 

 leucops. 

 Order 3. AUoeocoela. Usually cylindroid; 

 intestine straight or with short 



Figure 77. Facing page, upper part of illustra- 

 tion, life cycle of the dog tapeworm, Echinococcus 

 granulosus. Lower part of illustration, life cycle of 

 the broad tapeworm of man, Dibothriocephalus 

 latus (formerly Diphyllobothrium latum). 



branches; mostly marine. Ex. 

 Prorhynchus. 

 Order 4. Tricladida. Intestine of three 

 main trunks, each with many 

 lateral branches. Ex. Dugesia 

 tigrina (Fig. 68). 

 Order 5. Polycladida. Marine; central di- 

 gestive ca\ity with many irreg- 

 ular branches. Ex. Stylochus 

 ellipticus. 

 Class 2. Trematoda. Parasitic; intestine pres- 

 ent; no cilia on adult; cuticle present; 

 suckers on ventral surface. 

 Order 1. Monogenea. External or semiex- 

 ternal parasites; direct de- 

 velopment with no asexual 

 multiplication. Ex. Benedenia 

 (Epibdella) melleni. 

 Order 2. Digenea. Internal parasites; an 

 asexual generation in life cycle. 

 Two or more hosts required, 

 with alternation of hosts. Exs. 

 Fasciola hepatica (Fig. 73); 

 CloTiorchis sinensis (Fig. 74). 

 Class 3. Cestoda. Endoparasites; no intestine; 

 no cilia on adult; cuticle present; usu- 

 ally proglottids. Ex. Taenia solium 

 (Fig. 76). 



SELECTED COLLATERAL 

 READINGS 



Chandler, A.C. Introduction to Parasitology. 

 Wiley, New York, 1955. 



