476 RADIATA : POLYPI. 



like beautiful flowering shrubs. All secrete a solid cen- 

 tral axis, which is either horn-like, or calcareous. 



The stems and branches of the Gorgonacea are covered 

 with a layer of united polyps, whose tissues are more or 

 less filled with calcareous particles called spicules (Fig. 

 713) ; and it is to these spicules that the Gorgonias owe 

 their various and beautiful colors. 



Spicules occur in the other alcyonarians, and they are 

 very important guides in classification. 



The Sea-fans are Gorgonias which are broadly fan- 

 shaped, branching in one plane, the branchlets coalescing 

 so as to form a net-work (Figs. 709, 716). 



The shrub-like precious coral of the Mediterranean 

 Coralliumrubrum, or Bed Coral (Figs. 715, 717) is allied 

 to the Gorgonians. It has a solid calcareous axis of a 

 beautiful crimson or rose color. 



Another type of alcyonarians is seen in the Alcyonacea, 

 which occur in the form of arborescent clusters which 

 are more or less fleshy or coriaceous in their texture, but 

 filled with calcareous spicules ; or, as in one family the 

 Organ-pipe coral family, they form beautiful red calca- 

 reous tubes (Fig. 719). 



SUB-SECTION III. 

 THE ORDER OF ACTINARIA OR SEA-ANEMONES. 



THE Sea-anemones and their immediate allies have the 

 abactinal region largely developed, and the tentacles con- 

 ical, or cylindrical. 



The Sea-anemones or Actinia group have from ten to 

 hundreds of tentacles, and the mouth furnished with folds 



