SOFT-BODIED ANIMALS— THE MOLLUSKS 



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collapses like a mass of jelly. Also, it has only eight arms instead of 

 ten. 



The chambered nautilus is another member of the class Cephalopoda. 

 Unlike the squid and octopus, its mantle secretes a shell, which is laid 

 down in a series of spiral chambers to form a very beautiful, coiled shell. 

 A new chamber is formed as the animal outgrows the older one, so each 



Photo by Winchester 



Fig. 19.13. Chiton, a primitive mollusk. Note the row of articulating plates that 

 take the place of less flexible shell as found in other mollusks. 



new chamber is larger than the preceding one. Upon learning of the 

 characteristics of this animal, Oliver Wendell Holmes wrote the well- 

 known poem, "The Chambered Nautilus." The poem ends with a moral 

 which is memorized by most grade school children : 



"Build thee more stately mansions, O my soul, 

 As the swift seasons roll, 



