HABITS OF MARINE ANIMALS 151 



the oyster soon sickens and his valves gape open, then 

 the star-fish sucks out the contents and rejects the 

 shell. Occasionally the star-fish arches itself over the 

 oyster, and grasping the two valves with its tube-feet, 

 by a steady pull forces it open. 



Constant war is waged against the star-fish, and 

 any brought up in the dredge are thrown into a bucket 

 or other receptacle on board and taken ashore. Here 

 they are collected in a heap and sold as manure. If a 

 star-fish is merely broken up and thrown back into the 

 sea, it does not necessarily follow that he will die, for 

 these creatures are very tenacious of life, and are able 

 to renew parts that have been destroyed. 



Another enemy is the whelk (Buccinum undatum). 

 This mollusc holds the oyster with his fleshy foot, drills 

 a neat hole right through the hard shell, and then sucks 

 out the contents. This hole is made with a rasp-like 

 band, known as a radula. Radulae are to be found 

 in the floor of the mouth of many molluscs. In the 

 whelk the radula is armed with about two hundred 

 and fifty teeth. I once saw a whelk surround the end 

 of a dead crayfish with its foot, of which an illustration 

 is shown ; later, when the crayfish was picked up, the 

 whelk dropped off, but not before he had partially 

 sawn through the shell. Mussels sometimes do great 

 damage on a bed, not only by harbouring dirt all around 

 them, but by actually growing over and smothering the 

 oyster. The mussel is a favourite food of the star-fish, 

 and so though the star-fish devours oysters, it also helps 



