ECHINODERMS 



227 



gives shape to the body and arms. Slow movement is effected 

 by means of tiny suckers, called tube feet. The mouth is on the 

 undersurface of the animal, and, when feeding, the stomach is 

 protruded and wrapped around its prey. The body covering of 

 the starfish, as well as that of the sea urchin and others of this 

 group, is spiny ; hence the name echinoderm, which means spiny- 

 skinned, is given to the group. 



Starfish are enormously destructive of young clams and oysters, 

 as is shown by the evidence, collected by Professor A. D. Mead 

 of Brown University. A single starfish was confined in an 

 aquarium with fifty-six young clams. The largest clam was 

 about the length of one arm of the starfish, the smallest about 

 ten millimeters in length. In six days every clam in the aquarium 

 was devoured. 



In order to capture and kill mollusks, the starfish wraps itself 

 around the valves of the shell and actually pulls them apart by 

 means of its tube feet, some of which are attached to one valve 

 and some to the other of its victim. The mollusk can withstand 



AsteroicCea 



-.OphiuroicCea 



/ -brittle 



Ifchmoidea-' ttolothuroidea x Crir2oi<£ea 



urchi 



c c~c. - 



fioe** 



Sect feather 



Class I. Asteroi'dea, or starfishes. 



Class II. Ophiuroi'dea, the brittle stars or snake stars. 

 Class III. Echinoi'dea, or sea urchins. 

 Class IV. Holothuroi'dea, including the sea cucumbers. 



Class V. Crinoi'dea, or stonelike, deep-sea forms, now almost extinct; sea lilies and 

 feathers. 



a strong pull, but not a long one, and so it eventually gives 

 way. Once the soft part of the mollusk is exposed, the stomach 



