POND SNAIL 



Classification : — Phylum Mollusca, Class Gastropoda, Order 

 Pulmonata, 



1. Phvsa and Planorbis are two of the most common genera 

 of pond snails found in this region. The two genera are 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 filled 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 hody 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 mouth 

 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 sitle of the shell in a series of small, pointed projections, 



4. Both Physa and Planorbis breathe by lungs. Conse- 

 quently 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. 



6. Observe the method of feeding by looking through the 

 side of the aquarium at the ventral side of the animal. Can you 

 determine the nature of the food ? Notes required. 



