STARFISHES, URCHINS AND SEA-CUCUMBERS 55 



The Mud Starfish, fCtenodiscus crisiMtus, Fig. 27), is abund- 

 ant upon muddy bottoms at depths greater than 100 feet from Cape 

 Cod to the Arctic Ocean. The upper surface is covered with a 

 flexible skin beset with niimerous regularly arranged granulations. 

 The sides of the arms are straight and vertical, giving the starfish 

 the appearance of a five-rayed cake cut out of a thick sheet of 

 dough. 



At the centre of the upper surface of the disk there is a pro- 

 jecting papilla. In this connection it is interesting to observe that 

 starfishes are probably descended from forms which were attached 

 to the bottom by means of a stalk that extended downward from 

 the middle of the aboral side, and it is possible that the little blunt 



Fig. 27; ML'D-STAR. From a Deptli of 120 Feet Off Cape Ann, Mass. 



papilla seen in the mud star is the remnant of the base of such a 

 stalk that has long since ceased to serve as an organ of attachment. 



The feet of this starfish have no terminal suckers, and serve 

 merely to push the animal along as it glides over the mud. The 

 arms are sharp-pointed although short and blunt, and the creature 

 is about two and three-quarters of an inch in diamter. 



The starfish is dull ochre-yellow or slightly greenish in hue. 

 It swallows large quantities of mud, and probably subsists upon 

 minute organisms contained therein. 



The Giant Starfish, (Pentaceros reticulatus, Fig. 28 J, is found 

 on sandy bottoms, usually at depths greater than ten feet, off the 

 Florida coast and West Indies. It is the largest of our starfishes, 



