22 American Seashells 



frequently see the three-inch-long, tubular proboscis being withdrawn into 

 the snail's head. This indicates that a clam or worm, upon which the snail 

 was feeding, is located at that spot one or two inches below the surface of 

 the mud. 



Figure 6. The open mouth of the Moon Snail, Natica, showing the radula ribbon 

 and its teeth. X3. (Redrawn from Ankel 1936.) 



In the Natica Moon Shells, there is a muscular disk on the under surface 

 near the end of this extensible proboscis, which serves as a suction disk while 

 the radula is at work on the clam shell. No evidence of the presence of acid 

 has been presented so far. Once the clam is perforated, the long proboscis is 

 wiggled down into the flesh of the clam and the moon shell is able to remove 

 most of the flesh without opening up the valves of the clam. Some Murex 

 Snails and the Busy con Whelks open their clam victims by applying suction 

 with the sole of the foot and by prying apart the valves with the edge of the 

 outer lip of the shell. 



The large group of rachiglossate snails (those having three large teeth 

 in each radular row) are for the most part predators. The Tun Shells and 

 Cassis Helmet Shells feed upon live sea urchins. The Xancus Chanks, Busy con 

 Whelks and others feed upon live clams. The Nassa Mud Snails, however, 

 are purely scavengers, and their ability to detect the odor or taste of spoiled 

 meat in the water is highly developed. Among the toxoglossate snails (those 

 with tiny, needle-like, harpoon-shaped teeth as shown in figure i), the cones 

 and Terehra shells have a highly developed poison gland and duct which are 

 presumably used in quieting their prey. 



Vegetarians are found among the more primitive gastropods. All of the 

 Hmpets, nerites, trochids and turban snails graze on seaweeds. However, many 

 of the "middle-class" snails, among them the ceriths, Modulus, and some 

 periwinkles, limit their feeding to swallowing mud detritus on the bottom 



