54 



The Living Things of the Earth unit t 



Fig. 75 (above) The octopjis is a iiiollusk irhich 

 has 710 shell. Its eight ivaving tentacles {or feet) 

 hear sucking cups. With feet and beak it tears 

 its prey to pieces, (new york aquarium) 



Fig. 76 (right) This zebra snail is creeping on 

 its foot. (I)AVIS) 



Clams, oysters, and mussels. These 

 mollusks have a shell in two parts. Often 

 the shell is left open and the hatchet 

 foot, a thick muscle, may stick out. 

 Oysters and mussels, which spend their 

 lives attached to rocks or other shells, 

 have so small a foot that they can hardly 

 be said to have one. Clams use their foot 

 for locomotion. Exercise 8 is interesting 

 althouoh difficult. 



Snails with and without shells. Snails 

 live in water and on land. Land-living 



forms especially have a well-developed 

 foot. They have a well-developed head 

 too, with a real mouth, and eyes carried 

 on long stalks. Many species carry a 

 spiral shell from which the head and 

 foot protrude. When danger threatens, 

 both head and foot arc drawn into the 

 shell and the tough, slimy foot seals 

 the mouth of the shell so \\ell that it is 

 difficult to extract the animal. Snails that 

 lack a shell are called slugs. They may 

 do much damage in the vegetable garden. 



