SHALLOW-WATER FAUNA. 



43 



Boring-molluscs. The Rock-borers belong to 

 many different species. Some of them, such as 

 the Pholases, make long cylindrical holes in 

 chalk, and even in harder rocks. The Teredo 

 is the borer, commonly known as the Ship- 

 worm, on account of its powers of penetrating 

 into timber. The long calcareous tube which 

 it forms as it works its way into the wood, 

 gives it a superficial resemblance to a large 



FIG. 13. Sea-urchin with large thick spines, 



sedentary worm, but it is in reality a bivalve 

 Mollusc, specially modified in structure for its 

 peculiar habits. 



The next group of animals we have to consider 

 in the Fauna of the rocks includes all those that 

 slowly creep or crawl, without possessing any 

 powers of rapid locomotion. Amongst these 

 may be mentioned the Sea-urchins and Star- 



