CHAPTER IV 



ECHINODERMS 



THE Echinoderms include the Sea Cucumbers, Sea 

 Lilies, Sea Urchins and Starfishes, and are without 

 exception confined to salt water. The name is 

 derived from the Greek " hedgehog skin " or " spiny- 

 skin " and applies aptly to most members of the group, 

 since their skins are covered with spines of carbonate of 

 lime. 



Sometimes the internal skeleton is scattered as in all 

 sponges and many soft corals, but frequently the spines 

 and plates unite as in the Sea Urchins to form a shelly 

 " test " or box enclosing the entire animal. Although 

 Echinoderms vary enormously in outward form all are 

 built upon a radial pentagonal star pattern, though this 

 is not apparent in the larval stages through which most 

 forms pass before reaching maturity. 



The internal structure is much more complex than in 

 the Coelenterates. There is a well-defined intestine and 

 a complex system of canals which fill hollow muscular 

 tubes with water, by means of which the animals progress. 

 Echinoderms live at all depths and in all climes, some 

 of the giants of the race emanating from the tropics and 

 arctic circle, and from the shallows to the uttermost 

 depths. The larvae are hatched from eggs and progress 



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