CHAPTER XVIII 



THE CLAM AND OTHER BIVALVES: ACEPHALA 



And I then engaged myself, with the other merchants, in a pearl fishery in 

 which I employed many divers on my own account. 



Sindbad the Sailor, in the Arabian Nights 



The Long-Neck Clam 



Habitat and Distribution. The animal which is described 

 first in this chapter is commonly known as the long-neck 

 clam or the soft-shell clam. It is more accurately designated 

 by its scientific name, My' a arena 'ria (Fig. 101). As the 

 specific name implies, the animal lives in the sand. It is 

 found in great abundance along our Atlantic coast, even as 

 far north as the Arctic regions. 



External Structure. The shell of the clam has the same 

 general use as the carapace of the crayfish. In both ani- 

 mals these hard, external parts protect the organs within 

 from injury and also afford surface for the attachment of 

 muscles. The clam's shell, however, is never molted. It 

 grows continuously from the time it begins existence at the 

 little rounded prominence called the umbo (pi., umbones), 

 or beak (Fig. 101). 



Anyone who examines a dry shell of this kind can tell 

 which is the youngest portion of the shell. Probably he will 

 observe at the same time the little spoon-shaped piece ex- 

 tending horizontally inward from one of the valves of the 

 shell. This projection is always on the left valve. It meets 

 a brown, rubber-like pad beneath the umbo of the right 

 valve, and is joined with it. As long as the two valves hold 



together at this point, the pad, which is called the hinge 



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