Gastropoda. 



'35 



A Drilling Sea Snail. Natica (see Fig. 88) is common on the New 

 England coast. It is one of the largest of the snails found along the 

 northern shores, sometimes reaching a length of five inches. Natica is 

 carnivorous, and lives mostly on clams and other bivalves. It burrows 

 in the mud or sand ; and when it finds a clam, it uses the lingual riobon 

 and bores a hole through the shell, rotating its own body meanwhile. 



Tentacles 



Gills 



FIG. 89. A SEA SNAIL (NATICA) CRAWLING. 



Showing the very large foot "(surrounding the shell). 



It produces as neat a countersunk hole as any made by a drill for the 

 head of a screw such as may be seen in any door hinge. After the hole 

 is made through the shell, the soft body of the clam is eaten. 



Sea Slugs. Sea slugs are found near shore, on rocks or among 

 seaweeds. Many of them are devoid of shells when adult, but all. have 

 shells in their earlier stages. Many of them are symmetrical externally, 

 but few are so in their internal structure, the intestine, for example, 

 usually ending on the right side. In some the gills are covered, in others 

 exposed. The gills often project 

 as leaflike appendages on the 

 posterior part of the dorsal sur- 

 face ; and the whole animal, in 

 form and color, has such a close 

 resemblance to the seaweeds, on 

 which it crawls and feeds, that it 

 escapes the enemies to which, in 

 its defenseless condition, it would 

 be an easy prey. Some of the 



sea slugs can swim, and usually do so inverted, with the flat surface of 

 the foot at the surface of the water. When the adult has a shell, it 

 sometimes has its edges covered by the overlapping mantle, and some- 

 times is completely inclosed by a sac like mantle. 



FIG. 90. NAKED MOLLUSK. 



From Kingsley's Comparative Zoology. 



