Page:American Seashells (1954).djvu/40

22 frequently see the three-inch-long, tubular proboscis being withdrawn into the snail’s head.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.

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 Busycon 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, Busycon 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 1), the cones and Terebra 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 limpets, 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