ANIMALS WITH SPINY SKINS— THE ECHINODERMS 



295 



generate a new one. Brittle stars are not so aggressive in their feeding 

 habits as the starfish and are usually content to crawl around and eat 

 mud on the sea bottom, deriving their nourishment from whatever or- 

 ganic matter the mud might contain. 



Sea Urchins and Sand Dollars — Echinoidea 



This class includes the sea urchins and sand dollars. The sea urchins 

 are globe-shaped echinoderms with very long spines projecting out from 

 their bodies which are a very effective protection. Some species of these 

 have poison on their spines, so it pays to be careful where you wade in 



Photo by Winchester 



Fig. 20.5. A living sea urchin. The long, sharp spines afford a very good protection 



to this echinoderm. 



regions where these may be found. When the brittle skeleton is cracked 

 the yellow gonads may be seen almost filling the interior, and these are 

 sometimes used as food. They are especially popular in regions around 

 the Mediterranean Sea and are even sold in large quantities from the 

 push carts of the lower east side district of New York around Christmas 

 time each year. Many of the customers are probably emigrants from 

 the Mediterranean countries who developed the taste before coming to 

 the United States. 



