272 



THE MOLLUSKS 



in the arts, while they form a money basis still in parts of the world. 

 Sepia comes from the cuttlefish. 

 /The Starfish. — By aU means the most important enemy of the oyster 

 ,'&nd other salt-water moUusks is the starfish. The common starfish, as the 

 name indicates, is shaped like a five-pointed star. A limy skeleton which is 

 made up of thousands of tiny plates gives shape to the body and arms. 



Slow movement is effected 

 by means of tiny suckers, 

 called tube feet. Breathing 

 takes place through the skin. 

 The mouth is on the under 

 surface of the animal, and, 

 when feeding, the stomach is 

 protruded and wrapped around 

 its prey. The body of the 

 starfish, as well as that of the 

 sea urchin and others of this 

 group, is spiny ; hence the 

 name Echinoderm (spiny- 

 skinned) is given to the 

 group. 



Food of the Starfish.— 

 Starfish are enormously de- 

 structive of young clams and 

 oysters, as the following evi- 

 dence, collected by Professor 

 A. D. Mead of Brown Uni- 

 versity, shows. A single star- 

 fish was confined in an aqua- 

 rium with fifty-six young 

 clams. The largest clam was 

 about the length of one arm 

 of the starfish, the smallest about ten miUimeters in length. In six 

 days every clam in the aquarium was devoured. The method of 

 capturing and killing their prey shows that they wrap themselves around 

 the valves of the moUusk and actually puU apart the valves by means 

 of their tube feet, some of which are attached to one valve and some 

 to the other of their victim. Once the soft part of the moUusk is 

 exposed, the stomach envelops it, and it is rapidly digested and changed 

 to a fluid. This it can do because of the five large digestive glands 

 which occupy a large part of each ray, and which pour their digestive 

 fluids into five pouehlike extensions of the stomach extending into 

 each ray. 



Hundreds of thousands of dollars' damage is done annually to the 

 oysters in Connecticut alone by the ravages of starfish. During the 



Ventral or under surface of the starfish. The 

 dark circle in the middle is the mouth, from 

 which radiate the five ambulacral grooves, 

 each filled with four rows of tube feet. Photo- 

 graph half natural size, by Davison. 



