THE STARFISH AND ITS ALLIES 



201 



The Holothurians 1 may be likened to soft-skinned sea- 

 urchins, with the body drawn out to the form of a cucum- 



FIG. 187. Echinarachnius paruia, 

 the sand dollar. Spines removed 

 from left side. Nat. size. Photo, 

 by W. H. C. P. 



FIG. 188. Clypeaster, a bi- 

 lateral sea-urchin from the 

 West Indies. Spines partially 

 removed and surface rubbed 

 in patches. Reduced photo. 



ber, or even of a worm. The calcareous skeleton is reduced 

 to small plates embedded in the skin. The mouth is sur- 

 rounded by a circle of tentacles. 

 The ambulacral feet are sometimes 

 absent. The Holothurians live in 

 sand and mud, often deeply buried, 

 and feed on small marine animals 

 or the decaying particles mingled 

 with the mud which they devour. 

 They are of considerable economic 

 importance. The members of one genus (Holothuria) is 

 taken in great numbers on the coral reefs of the Pacific 



, a sort of water-polyp. 



FIG. 189. Caudina, the 

 tailed Holothurian. a, 

 mouth; b, anus. After 

 Selenka. 



