Chapter Eight 



ECHINODERMATA 



1. ASTEROIDEA Starfis' 



2. OPHIUROIDEA Brit 4 or Serpent Stars 



3. ECHINOIDEA and Sand Dollars 



4. HOLOTHUROIDEA di . rs 



5. CRINOIDEA foiSs or Sea Lilies and Feather-s'ars 



ASTEROIDEA 



(Starfish) 



Starfish are perhaps the most distinctive ani- 

 mals of the sea and their star-like shape makes them 

 an object of curiosity to even the most casual visitor 

 to the seashore. 



While the common starfish (Asterias) normally 

 has five arms, some species have more; some of the 

 Sun Stars (Heliaster) of the southern Pacific coast 

 have forty or more. 



Starfish are carniverous and are especially de- 

 structive to mollusks. The common Asterias feeds on 

 oysters and its unusual method of procuring its food 

 is described on page 



The mouth of the starfish is at the center of the 

 under side. This leads into the stomach which 

 occupies the center of the disc with projections 

 (caeca) into the various arms. 



Extending from the mouth to the tips of the 

 various arms are grooves known as ambulacral 

 grooves, one on each arm. In these grooves are 

 situated a great number of small tube-like processes 



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