Fish and Their Fabulous Neighbors [191 



THE CLAM'S PEARLY LINING 



One of the best-known mollusks, the clam, has a shell 

 made up of three layers a thin one on the outside, a thick strong 

 middle layer, and a smooth pearly lining. When a bit of sand or 

 other foreign matter gets lodged within the shells, it becomes 

 coated like the lining and in time may become a true pearl. 



SQUATTERS' RIGHTS 



We find mollusks not only in the sea, but in fresh-water 

 lakes and streams and on land as well. Some of them the peri- 

 winkle, for example have a single shell; others, such as clams 

 and oysters, have two shells hinged along the back. Shellfish give 

 the deceptive appearance of leading a peaceful existence, though 

 the fact is that life is a constant struggle for them. They are de- 

 voured by a variety of animals, and they often vie with each other 

 for living space. 



Oysters settle as a rule in fairly deep water, though sometimes a 

 colony is located on a mud flat that is exposed to the air during 

 low tide. In such a situation you may see an invasion take place. 

 Mussels, which multiply with a great rapidity, may move in and 

 smother the oysters out of existence by sheer weight of numbers. 

 But, once the mussel colony is established, it may in turn be 

 invaded by a host of barnacles which soon take over the territory 

 for their own. 



One of the mollusks' worst enemies is an innocent-looking snail 

 with the sinister name of oyster drill. It plays great havoc in 

 oyster beds boring holes through the oyster shell and feeding 

 on the soft underlying flesh. 



THE SELF-EFFACING CRABS 



You have to keep a sharp lookout to catch a glimpse of 

 these notable creatures of the seashore. Some are expert at dis- 

 guising themselves by putting seaweed or bits of sponge on their 

 back; some hide themselves almost completely in the sand as they 

 lie in wait for prey; and some are very small. 



The Rock Crab: It should not be too difficult to discover the 

 rock crab, which is common on most rocky shores. Full grown. 



