548 The Animal Kingdom 



(Fig. 181,^). This larva then changes by the elongation and cilia- 

 tion of the lobes to form the brachiolaria. After several weeks (six 

 or seven) the larva settles on the bottom, the posterior end enlarges, 

 bends to the left, and five lobes form. These form on the right side 

 and become the aboral surface of the adult starfish while the left side 

 becomes the oral surface. 



The Biology of A. forbesi. — This species is found along the 



entire eastern seashore, ranging from Maine to the Gulf of Mexico, 



from shallow areas to a depth of some 50 meters. They are most 

 commonly found in rocky areas. 



Economically this form may be considered of some importance 

 due to its destruction of oysters. When this starfish attacks a mollusc, 

 it arches its body over the shell and by the concerted action of the tube 

 feet forces the clam to open. The tube feet may be aided in this action 

 by paralyzing secretions. The starfish is able to evert the cardiac por- 

 tion of its stomach when feeding. 



The starfish can move in any direction and can reverse its direc- 

 tion without the necessity of turning around. The small suction discs 

 of the tube feet attach the animal to a substrate and pull it forward. 

 They work synchronously, with some relaxing while others contract. 

 If turned over, the starfish can right itself by attaching the tube feet 

 at the tip of one or two arms and gradually pulling itself over. 



Possibly the tube feet at the ends of the arms also perform some 

 sensory functions. If small portions of clam meat are placed in an 

 aquarium with the starfish, it will quickly move toward them and con- 

 sume them. 



Some starfish exert rather startling effects on their would-be prey. 

 If Asterias is placed near a scallop, the scallop will flap away rapidly 

 in a hasty retreat. One species that feeds on sand dollars will cause 

 the immediate burrowing of these latter forms simply by passing near 

 them. 



The powers of regeneration of the starfish are very remarkable for 

 such a highly developed animal. A single arm may regenerate a 

 complete animal. Some species actually seem to separate and by re- 

 generation supplement their sexual reproduction by asexual means. 

 At one time, the oyster fishermen hired men to go along on oyster 

 fishing expeditions. These men had the task of "destroying" starfish 

 by chopping them into small pieces which were then thrown over- 



