POND SNAIL 

 PHYSA OR PLANORBIS 



Classification : Phylum Mollusca, Class Gasteropoda, Order 

 Pulmonata. 



1. Physa and Planorbis are two of the most common 

 genera of pond snails found in this region. The two genera arc 

 readily distinguishable one from the other by the general shape 

 of the shell, that of Physa being more or less cone shape while 

 that of Planorbis is a practically flat coil. Indicate by labels 

 which kind is being studied. 



2. Place a snail in a Mason jar lid rilled with water. Allow 

 the snail to crawl onto the under side of a glass slide, one end 

 of which is placed in the water. Notice that the body protrudes 

 from a single opening in the shell. Examine a fully extended 

 body and on its ventral surface note a crosswise fold which sep- 

 arates it into a small anterior region, the head, and a larger tri- 

 angular posterior region, the foot. The head bears the month 

 on its ventral surface and a pair of tentacles on the dorsal sur- 

 face. 



3. The mantle is a membrane which lines the shell. In 

 fact the shell is formed by secretion from the mantle. In Physa 

 the mantle may be seen best on the right side where it folds back 

 upon the side of the shell in a series of small, pointed projections. 



4. Both Physa and Planorbis breathe by lungs. Consequently 

 they must come to the surface of the water occasionally for air. 

 The lung opening is a small circular opening into the side of the 

 body between the foot and the shell. It can be seen only when the 

 snail is at the surface of the water taking air. 



5. Draw X4 a side view of a fully extended snail, from 

 the right side. Label all of the parts. Draw a ventral view X4. 



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