204 ZOOLOGY 



c 2 . Body without arms ; more or less spheri- 

 cal or cake-shaped .... Echinoidea 



(Sea-urchins) 



5 2 . Body elongated; skin soft, leathery, contain- 

 ing microscopic calcareous bodies ; madre- 

 poric plate absent ; mouth surrounded by 

 tentacles Holothuroidea 



(Sea-cucumbers) 



