98 



STARFISH, sp:a xtrchin, brittle stars 



rows of tube feet, and some of them Iiave none. In 

 some there is a (hstinct ventral side, and in others there 

 is not. They do not have large and closely connected cal- 

 careous plates in the body walls to form a continuous skele- 



FlG. 51. — Sea cucumber. Note the branched tentacles about the mouth. 



ton like that of the starfish and sea urchin, yet their bodies 

 retain a cyhndrical shape owing to many very small, loosely 

 connected calcareous plates imbedded in the integument, 

 somewhat like the spicules in the walls of a sponge. The 

 body walls, notwitlistanding, are leathery and flexible. 



