39i 



CHAPTER XXIV. 



ASTEROIDEA, OPHIUROIBEA, AND HOLOTHUROIDEA. 



Class II. Asteroidea. 



The class Asteroidea comprises the ordinary Star-fishes, and is 

 defined by the following characters : The body (fig. 269) is star- 

 shaped or pentagonal, and consists of a central body or "disc" sur- 



Fig. 269. — Astropecten irregularis, viewed from the upper surface ; m Madreporite. Recent. 



rounded by five or more lobes {"arms" or "rays"), which radiate 

 from the body, are hollow, and contain prolongations of the viscera. 

 The body is not enclosed in an immovable box, as in the Echinoidea, 

 but the integument ("perisome ") is coriaceous, and is stre7igthe7ied by 



