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CHAPTER VI 



MOLLUSCS 



THE general term of Mollusc (Mollusca) is employed 

 to embrace many varied soft forms and includes 

 the slugs, snails, oysters, squids, octopuses, etc. 

 The group is represented in every quarter of the globe 

 and, so far as marine species are concerned, have even 

 penetrated within the arctic and antarctic circles. 



Molluscs are believed to have had their origin in forms 

 nearly related to the Annelids or segmented worms and 

 although many appear to have little in common they 

 nevertheless agree in certain particulars. All have soft 

 unsegmented bodies and there may be an external or internal 

 shell present either in the adult or immature form and often 

 in both. Molluscs have a heart, blood vessels and a com- 

 plex nervous system. Often there is a fleshy organ which 

 can be used for locomotion and a rasping organ or tongue 

 with which the creature eats. 



The great majority of Molluscs carry external shells, 

 and of such over 60,000 species have been identified to 

 date. A large number of these are widely used for food 

 and the shells of many have played an important part in 

 human economics from the earliest times. The mollusc 

 shells supplied man with his first plates, spoons, and 

 currency. Shells are still put to endless purposes of 



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