This is another of the shell-bearing molluscs which live in burrows in the sandy mud, and it is called the “gaper” because the shells are always open at the top, just as if the animal were yawning, or gaping. Through this opening the siphon tubes project. These tubes are used in breathing, just like those of the cuttle, and are enclosed in a kind of leathery case, which the animal can stretch out or draw back at will; so that when it is lying at the bottom of its burrow it can keep the tips of the siphon tubes just above the surface of the mud, and so draw water down to its gills quite easily.
1. INSIDE OF SUNSET SHELL.2. THE SUNSET SHELL.
3. THE GAPER.
On some parts of the coast gapers are used as food. But if you want to buy some you must not call them “gapers.” You must call them “old maids”; for by that name they are always called by the fishermen. Some of the sea-birds are very fond of them too, and dig them out of their burrows with their long beaks. And in the far North millions and millions of them are devoured by walruses, and also by Arctic foxes, which prowl about the shore in search of them every day when the tide goes down.
PLATE XVII
THE PIDDOCK (1)
Now we come to one of the most wonderful of all the creatures which live in the sea; namely, the Piddock. You can find its empty shells lying about in numbers on almost any part of the shore where the cliffs are made of chalk or limestone. And if you look at the rocks which are left dry when the tide goes down you will see the entrances to its burrows—large, oval holes, several of which you may often find quite close together. For the piddock is a boring shell, which drives its tunnels through and through the rocks, until very often they are quite honeycombed by its tunnels. Sometimes you may meet with a big block of chalk which only weighs about half as much as it should, because all the rest has been cut away by piddocks. And if you could split it open you would find several of these creatures lying in their burrows.
But how they manage to cut their way through the hard chalk, or the still harder limestone, nobody quite knows. Most likely, however, they do so partly by means of the soft part of the body which we call the “foot,” and partly by means of the shell, which they turn first a little bit to one side, and then a little bit to the other side, just like a man who is using a bradawl. Every now and then, of course, the burrow gets choked up with the material which has been scraped away. But the piddock knows quite well what to do in order to clear it. It just squirts out a jet of water from the siphon tubes, by means of which it breathes, and so washes the burrow out!