PART II 



THE ANARTHROPODA : INVERTEBRATES 

 WITHOUT JOINTED LEGS 



10. MOLLUSCA 



THE members of this phylum differ from the preceding 

 in not having segmented bodies or jointed feet. Most of 

 the twenty thousand species are included in the three 

 important classes, Pelecypoda, Gastropoda, and Cepha- 

 lopoda. 



Pelecypoda: Bivalved Shellfish 



The name bivalve is derived from the two shells which 

 hinged together form the protecting case for the soft- 

 bodied animal within. All bivalves are aquatic. Certain 

 species form a leading item of food in many parts of the 

 world. 



The soft-shelled clam (My a arenaria), abundant north of 

 Cape Cod, occurs in large numbers in the mud flats, from 

 which they are dug at low tide. They usually lie in the 

 mud at a depth of from two inches to a foot, and have a 

 very long siphon consisting of two tubes, of which the 

 ventral one is used for taking in water and food, while the 

 excretory products pass out through the dorsal one. 



The hard-shelled clam (Venus mercenaria), or quahog, is 

 the common edible species south of Cape Cod. 



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