62 The Under-Water World 



largely used in the manufacture of an 

 indelible ink. 



The Starfishes have the rays free, in- 

 stead of united, as in the urchins, and 

 so enjoy much greater freedom of move- 

 ment. Very large specimens may travel 

 at the rate of a quarter of a mile on the 

 flat, and are capable of squeezing into 

 the narrowest rock fissures and crevices. 

 They have yet another great advantage 

 over the urchin. The free rays can be 

 used as arms, and are employed to hug 

 the oyster or other bivalve mollusc in a 

 deadly embrace that ends in forcing the 

 valves asunder. The common starfish, 

 indeed, has cost the oyster farmer count- 

 less millions of pounds. Some starfish 

 reach a very large size, a form common 

 on our west coast attaining a span of 

 two feet, whilst a Papuan species exceeds 

 a yard across the arms. Whereas a 

 fairly heavy blow ends the sea urchin's 

 career for good, the starfish is almost 



