98 



STARFISH, SEA URCHIN, BRITTLE STARS 



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

 some there is a distinct ventral side, and in others tliere 

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

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



L 



1 



Fig. 51. — Scu cuciiiubLT. Nod' the branched tcntack'S about the mouth. 



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

 retain a cylindrical shape owing to many very small, loosely 

 connected calcareous plates imbedded in the integument, 

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

 body walls, notwithstanding, are leathery and flexible. 



