260 



SUBKIN^GDOM ECHINODERMATA. 



CLASS II. ECHINOIDEA. 



General Characteristics. — The Echin 

 like) are covered with spines, raoved by the 



Fig. 14,5. 



EcKirms sp/itera. Sea Urchin. Spines remoyed from left half. 



to move over the rocks 

 (pediciUanm), each 

 ending in forceps, 

 apparently for pre- 

 hension and for rid- 

 ding the animal of 

 parasites. The 

 mouth is armed 

 with fi V e sharp 

 teeth, which con- 

 tinually wear upon 

 one another, but, 



* A fnll-sfTown Urchin 

 may have five hundred 

 plates, four thousand 

 spines, and perhaps two 

 thousand suckers. 



Mingled with the 



oids (hedgehog- 

 general envelop- 

 ing membrane. 

 Their shell is 

 composed of reg- 

 ularly-shaped 

 plates, arranged 

 in radiating 

 zones, every al- 

 ternate plate per- 

 forated for the 

 passage of suck- 

 ers {(tnibiddcrd), 

 which can be ex- 

 tended beyond 

 the spines,* and 

 by adhesion en- 

 able the animal 

 spines are stems 



MelRta quinquefSra, Key -hole Urchin. 



