254 CLASSIFICATION OF ANIMALS 



oral surface of the arms are also important. The digestive 

 tract opens by a vent on the oral surface in an eccentric 

 position. 



552. Class II. Asteroidea. The starfishes lie on the sea bot- 

 tom with the mouth or oral side down. The ambulacral feet 



FIG. 145. A starfish, Astropecten. X 3/4. 



serve for locomotion. The oral-aboral axis is shorter than a 

 radius and the five radii are longer than the inter-radii so that 

 the body assumes the form of a five-rayed star. The skeleton 



