18 GUIDE TO THE STUDY 



Key to the Chief Groups of Cercariae 



Adapted from Liihe, 1909 



A. Body of the cercariae with strong longitudinal projections 



along the side Lophocercarice 



AA. Body without such longitudinal projections. 



B. Two long, symmetrical projections from the end of, 

 and several times exceeding the length of the body. 

 Mouth opening in the middle of the ventral surface. 



Intestine simple, sac-like Gasterostome cercarice 



BB- Tail variously formed but never split to the base. 

 Mouth at anterior end. Intestine forked. 



C. Ventral sucker lacking Monostome cercarice 



CC. Ventral sucker present. 



D. Ventral sucker at the very end of the body 

 directly before the base of the slender 



tail Amphistome cercarice 



DD. Ventral sucker in front of the 

 caudal end of the body. 



Distome cercarice 



Key to the Major Genera of Fresh-water Snails 



A. Shell spiral, dextral (i.e., with aperture to right of the axis 



when held apex uppermost with aperture facing you) 

 Spire more or less elongate Genus Lymncea 



B. Shell discoidal, usually sinistral Genus Planorbis 



C. Shell spiral, sinistral Genus Physa 



References 



Cort, W. W., 1915. Some North American larval trematodes. Illinois 



Biol. Monographs, 1 : 447-532. 

 Faust, E. C, 1917. Life history studies on Montana trematodes. Illinois 



Biol. Monographs, 4 (1): 120. 

 Faust, E. C, 1919. A biological survey of described cercariae in the 



United States. Am. Naturalist, 53: 85-92. 

 Luhe, M., 1909. " Parasitische Plattwurmer. I. Trematodes. Siiss- 



wasserfauna Deutschlands." Heft 17, 217 pp. 

 Miller, H. M., 1925. The larval trematode infestation of the fresh-water 



mollusks of San Juan Island, Puget Sound. Washington Univ. Studies, 



13 (Science series 1): 9-22. 

 Ward, H. B., 1918. Key to North American fresh-water Trematoda. In 



Ward and Whipple, "Fresh-water Biology," pp. 374-424 



