^68 



THE RISE OF ANIMAL LIFE 



Fig. 12-20. The common starfish {Asterias), Mice most starfish, is found along rocky shores crawling over the hard 

 surfaces in search of mollusks, particularly clams, which constitute its main food. This one is crawling over the 

 shells of clams, many of which are empty because their soft bodies were sacrificed to satisfy the hunger of this 

 and several other starfish. 



swim, but it more commonly crawls over 

 rocks on the bottom of the ocean. 



are the luminescent organs, the value of 

 which is not entirely known. It may be to 

 attract food to the animal or to keep 

 enemies away. 



Stories of the dangers of the devilfish, or 

 octopus (Fig. 12-19), may be considered 

 practically fictional, at least in respect to 

 the grasp of its tentacles being deadly 

 to man. Actually the octopus is harmless to 

 man, with the possible exception of the 

 giant devilfish, which reaches a length of 

 28 feet. The bulbous and flexible body of 

 the octopus possesses muscular tentacles 

 "that are well armed with suckers. The ani- 

 mal usually lurks in shady underwater cav- 

 erns awaiting its prey, which it seizes by 

 extending the tentacles. A siphon, similar 

 to that of the squid, enables the octopus to 



PHYLUM ECHINODERMATA 



The second group of higher invertebrate 

 animals that possess remarkable and unique 

 characteristics is the phylum Echinoder- 

 mata. Members of this group deviate from 

 the direct line of ascent to higher forms 

 even more than the mollusks and occupy 

 their own isolated position in the animal 

 kingdom. Although they have acquired the 

 complex organs of the higher types, they 

 have reverted to radial symmetry, a pre- 

 dominant characteristic of the coelenter- 

 ates. For this reason they were once classi- 

 fied with the coelenterates but, because of 



