88 



BRANCH MOLLUSCA 



and many zoologists place them above the Arthropoda. They 

 have a well-defined circulatory system and nervous system and 

 especially highly developed eyes. They usually have a metamor- 

 phosis, some of the stages of which show indications of affinity 

 with "worms." 

 Classification. — 



Class. 

 Pel'ecyp'oda. 



Gas'terop'oda. 

 Ceph'alop'oda. 



Examples. 

 Sea-mussel, Oysters, Scallop, 



Fresh-water mussel. 

 Limpets, Periwinkle, Snails. 

 Cuttlefish, Octopus, Nautilus. 



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42. 



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