CCELENTERATA : ALCYONARIA. 



139 



FAMILY IV. GORGONID*:. In the Gorgonida, or "Sea- 

 shrubs," there is an arborescent ccenosarc permanently rooted 



Fig. 48. Pennatula phosphorea 

 (after Johnston). 



b 



Fig. 49. Pennatulidse. 

 Virgularia mirabilis. 

 a A portion of the 

 stem in the living con- 

 dition, enlarged ; b 

 Portion of the stem in 

 its dead condition. 



and provided with a grooved, or silicate, branched sclerobasis, 

 which is sometimes associated with true tissue-secretions, 

 termed " dermo-sclerites." 



The sclerobasis of the Gorgonidcz varies a good deal in its 

 composition. In some it is corneous, and these have often 

 been confounded with the AntipathidcR^ amongst the Zoantharia. 

 The distinction, however, between them is easy, when it is 

 remembered that the polypes in the Gorgonidcz have tentacles 

 in multiples oifour, whilst in the Antipathidce they are in sixes. 

 The sclerobasis, too, in the former is always marked by grooves, 

 whereas in the latter it is always either smooth or spinulous. 

 In Isis (fig. 44, b) and Mopsea the sclerobasis consists of alter- 

 nate calcareous and horny segments, branches being developed 

 in the former from the calcareous, and in the latter from the 

 horny segments. 



In Corallium rubrum, the "red coral" of commerce, the 

 sclerobasis is unarticulate, or unjointed, and is entirely cal- 



