STAKFISH, SEA URCHIN, BRITTLE STARS 97 



Fig. 49. — Shell of a sea urx'hin after spines have been removed. 



Certain sea urchins, such as the sand dollars, or sea 

 biscuits (Fig. 50), have flat bodies, instead of globular ones. 

 The bodies of others are soft and flexible, wholly unlike 

 that of the common 

 sea urchin. 



Sea cucumbers. — 

 Superficially, these 

 echuioderms show 

 little resemblance to 

 a starfish or sea 

 urchin. They are 

 more or less cylindri- 

 cal in shape and some 

 of them roughly re- 

 semble cucumbers in 

 appearance. Some of 

 them have five double 



herdick's zool. 



Fig. 50. — Sand dollar, or sea biscuit. 



