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SOFT-BODIED ANIMALS— THE MOLLUSKS 



mother and must find a fish in order to continue their existence. If a fish 

 comes near, these larvae immediately clamp onto its skin or gills and live 

 there as parasites until they have developed into small clams. These are 

 commonly called "blackheads" when seen on fish. This seems to be 

 an adaptation for distribution as well as for protection and nourish- 

 ment. A fish may travel a great distance carrying these little parasites 

 and they will drop off far from their place of origin. Since the clams 

 are so sluggish in their movements this is probably the only way that 

 they could be well distributed, especially upstream in a river. 



stomach 



digestive gland heart 



esophagus 



pericardia! cavity 



excretory organ 



Animals Without Backbones, Buchsbaum, The University of Chicago Press 



Fig. 19.5. Internal organs of the clam. This diagram shows the digestive tract and 



various surrounding internal organs. 



Certainly there is no one that has not heard of the renowned "clam 

 bakes" and "clam chowder" of the New England states which testify to 

 the good eating qualities of the marine clams. There are many varieties 

 of edible clams in the ocean ranging from tiny ones no bigger than the 

 end of your finger, which make delicious cocktails, to huge ones from 

 which you can get a good sized steak. The New England long-necked 

 clam buries itself in the sand of the beach when the tide is out and keeps 

 just the tip of its neck above the sand. This neck is really an extension 

 of the siphons. If a person comes too close and inquisitively looks down 



