CCELENTERATA 



77 



waves against the shore. They are 

 also very important geologically and 

 constitute the extensive formations 

 known as the coral limestones. 



Order i. Octocorallia 



The Octocorallia (Gr. oktco, eight, 

 and KopaWiov, coral), sometimes 

 called the Alcyonaria (Lat. alcyo- 

 nium, sea foam), include man}- of 

 the animals commonly known as 

 corals, as well as some others. They 

 all possess eight mesenteries, and 

 eight tentacles ; the latter are pin- 

 nate or feathery in appearance. 

 The valuable red coral (Fig. 62) 



belongs to this group, as well as the organ-pipe coral (Fig. 63), 

 the sea fans (Fig. 64), and the beautiful sea pens (Fig. 65). 



FIG. 62. Corallium 7-ubrum. Portion 

 of a colony, enlargt d two dianjetels. 

 (After Lacaze-Duthiers, from Parkei 



and Haswell's Mam 



Fn;. 63. Tubipora musica. Nat- 

 ural size; from the Indian 

 Ocean. //, platform. (After 

 Cuvier, from Parker and Has- 

 well's Manual.) 



Order 2. Hexacorallia 



The Hexacorallia (Gr. ef, six, and 

 KopaWiov, coral), also known as the 

 Zonatharia (Gr. t,wov, animal, and avdos, 

 a flower), consist of the sea anemones 

 (Figs. 61 and 66), and some of the corals. 

 Their mesenteries are usually some mul- 

 tiple of six, and are arranged for the 

 most part in pairs, with the longitudinal 

 muscle bands facing one another. The 

 tentacles are generally simple, hollow 

 tubes, unbranched. The sea anemones 

 ha\ e no skeleton, but the so-called stony 

 corals (Figs. 59 and 60) belong for the 

 most part to this order, and have a 

 calcareous skeleton ; the black corals 

 secrete a supporting substance resem- 

 bling horn. 



