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. 



