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 (Buccinwm undatum). 
This molluse 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. Radule 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 
