9 6 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



globular, usually more or less flattened at the poles. It 

 is covered with many movable spines which may be small 

 and light or long and heavy. When the spines are removed 

 the calcareous plates that constitute the firm part of the body- 

 wall are plainly distinguished. Sea-urchins are found mostly 

 in tide pools near the shore, but some occur at great depths. 



FIG. 36. A sea-lily, Pentacriims sp. (About 5 natural size.) 



The sand-dollars or cake-urchins belong to the same class. 

 Their bodies are very much flattened and often brightly 

 colored. They are common in the sand on both the Atlantic 

 and Pacific coasts. 



The sea-cucumbers, class Holothuroidea (Gr. holos, whole; 

 thouros, rushing; eidos, likeness), look even less like starfish. 



