BORING LIFE 147 



wide in its distribution. Since it is rarely, if ever, found 

 apart from the Gribble it seems as though it needs the 

 pioneer assistance of that highly competent animal before 

 it can itself attack the wood with any success. In the 

 warmer seas in particular there is a common crustacean 

 borer called Sphaeroma which is rather like a large Gribble, 

 to which it is fairly closely related. It often measures 

 almost half an inch in length and constructs burrows about a 

 fifth of an inch wide. It has the habit, when disturbed, 

 of rolling itself up into a round ball. It does not do so 

 much damage as the other two crustaceans but can work, 

 as they cannot, in water that is almost, or entirely, fresh. 



Stone Borers 



In spite of its greater hardness, stone is bored into by a 

 greater variety of animals than is wood, although none of 

 the stone borers can compare with the Shipworm in 

 efficiency. Amongst the animals which bore into stone 

 are Sponges, Worms, Molluscs, and Crustaceans, while it 

 is also attacked, strange though it may sound, by plants. 

 Limestone rock and especially oyster shells (made of the 

 same calcareous material) are dften eaten into by a boring 

 sponge called Clione (Plate 55). The surface of the rock 

 or shell is found covered with many minute holes which 

 lead into branching passages within which the sponge 

 lives. Oyster shells may be completely destroyed in this 

 manner and on some oyster beds the boring sponge is a 

 serious pest ; it seldom penetrates far into rock, two inches 

 at the most. How the sponge bores is not known, probably 

 by chemical means for it can hardly do so mechanically. 



Several worms spend their lives within tubes which they 

 have hollowed out in rock. Though very small they often 

 occur in great numbers. The tubes are often U-shaped 

 but may be oval or in the form of a figure of 8. Though 



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