272 



SOFT-BODIED ANIMALS— THE MOLLUSKS 



CHITON 



CLAM 



SNAIL SQUID 



Animals Without Backbones, Buchsbaum, The University of Chicago Press 



Fig. 19.1. The mollusks show a great variation in their plan of body organization, 

 but all have the same body parts which have been modified in various ways to suit the 

 needs of the animal. The digestive system is shaded, the foot is stippled, and the shell 



is shown by the heavy black line. 



A fresh- water clam, or mussel, will serve as a good type animal for 

 the phylum and an example of this class. Clams are found widely dis- 

 tributed in the rivers and lakes of the United States wherever there is 

 sufficient lime dissolved in the water to enable them to produce their 

 shells. They are very abundant in the Mississippi Valley where much 



