ECHINODERMATA — SEA CUCUMBERS 171 



1. Sketch (a) side view, (b) ventral view, (<:) dorsal view. 

 Label ambulacra, interambulacra, mouth, anus, teeth if 

 present, openings for tube-feet, madreporite, ocular and genital 

 plates. 



2. Compare it with a starfish. 



3. How and what does Strongylocentrotus eat ? 



4. Describe its respiration. 



5. How does the animal move? 



6. How does it increase in size ? 



7. Of what use are the spines? Make a sketch illustrating 

 how they are moved. 



8. In what directions may a spine be moved? 



9. Can Strongylocentrotus chmb ? 



10. Give the geologic range of Echinoidea. 



Melonechinus multiporus (Fig, 68). Mississippian. 



Test very large, spheroidal, marked vertically by elevated, 

 melon-like ribs, which are due to the thickening of the plates 

 and are hence hardly recognizable in internal molds. Ambu- 

 lacra broad with ten columns of plates at widest part ; inter- 

 ambulacral areas with eight or nine columns of plates. Tubercles 

 small, numerous ; spines minute, needle-like. This species 

 was very abundant in the St. Louis (Mississippian) seas of Mis- 

 souri. 



The earliest species of Melonechinus had fewer columns of 

 plates than the later ones. (This genus was formerly called 

 Melonites.) 



1. Sketch side view, noting ambulacra, interambulacra. 



2. Was the living animal attached or free ? 



CLASS G, HOLOTHURIOIDEA (SEA CUCUMBERS) 



Free, with elongated, more or less cylindrical body. Mouth 

 and anal opening at opposite ends. The body differs from that 

 of the starfish in being greatly drawn out in the direction 

 of the line joining mouth and anus ; this line is likewise the direc- 

 tion of movement. The ventral surface is parallel with the 

 axis joining mouth and anus, not at right angles to it as in the 



