74 



THE STARFISH FAMILY 



Figure 74. — Purple Sea Urchin. 



62. Respiration. — Oxy. 

 gen is taken from the 

 water and carbon dioxide 

 given off through little 

 thin-walled, gill-like 

 processes which cover 

 the upper surface of the 

 disk and arms. These 

 gill-like processes pro- 

 ject through holes in 

 the exoskeleton. 



63= Other Echinoderms. 

 — The sea urchins are 



thickly covered with spines and have tube feet which, in 



many cases, may be greatly extended. When the spines are 



removed, an exoskeleton is revealed, which readily shows the 



radial arrangement characteristic of the echinoderm group. 

 64. Economic Importance of the Group. — Of echinoderms 



the starfish alone has an eco- 

 nomic bearing. It is harmful. 



Living as it does in the region 



of the oyster and clam beds 



and feeding almost exclusively 



on them, the starfish annually 



destroys thousands of dollars' 



worth of clams and oysters. 



By removing the seaweed where 



the immature starfish gather and 



by dragging the oyster and clam 



beds great numbers of starfish 



are destroyedc 



In former times the fishermen 



used to break starfish to pieces 



on the side of the boat and throw Figure 75. — Sea Lily. 



