140 



THE ANIMALS AND MAN 



Starfishes and sea-urchins.— Among the most easily found 

 and most readily recognized seashore invertebrates are the 

 starfishes and sea-urchins, which belong to the animal branch 

 called Echinodermata. Although these animals do not 

 look at all alike, the starfishes having a body composed of 



Fig. 57. Starfishes of various kinds in a tide-pool on the Bay of Monterey, 

 California; note two with five rays, three pentagonal, and two with 

 many rays. (Photograph by the author, from living specimens in 

 situ.) 



central disk and long rays or radiating arms, and the sea- 

 urchins looking like spiny flattened balls, they are really 

 closely related. In each the body, with its various organs, 

 is built on a radiate plan of structure, the mouth being in 

 the center of the under side and all the body parts radiating 

 out from this center. 



