66 A NATURAL HISTORY OF THE SEAS 



form — are hatched from eggs that are either cast adrift 

 or anchored to some stable object. 



The intake of some of our Common Starfish — (Asterias 

 rubens and A. glacialis, both abundant off our shores) — is 

 prodigious. Specimens only six inches across the arm 

 will stretch themselves about a whelk and then, extending 

 their stomachs, devour the victim. It attacks oysters and 

 scallops by applying the suckers of three arms to one valve 

 and of two to the other, and then " pulling against itself." 

 At the same time the stomach is everted and the digestive 

 juice is brought to bear on the slowly widening gap 

 between the valves. 



Our largest native species of Starfish {Asterias auran- 

 tiacd) from deep water measures nearly 30 inches across. 

 One species of Starfish (Luidia) is cannibalistic, and by 

 preying on the Common Starfish keeps some check upon 

 the pest. 



Starfishes present a wonderful range of colour, some, 

 such as the Twelve -rayed Sun Star (Solaster papposus), 

 being as gorgeous as any dahlia or carnation. The so- 

 called Cushion Stars (Vorania pulvillus) are legion both as 

 regards numbers of individuals and species, and range in 

 size from an inch to two feet or more in diameter. 



Most of the forms mentioned above are rock dwellers, 

 but the attenuated Brittle Stars affect a sandy or gravelly 

 bottom. 



The Sand Stars {Ophiura ciliaris) have an almost circular 

 body with jointed arms sharply defined. Instead of creep- 

 ing steadily forward on tube feet, they stride over the 

 sea floor by throwing the arms forward and then thrusting 

 vigorously backwards. 



