232 THE EVOLUTION OF THE META20A 



end of Hexacorallia, because of their aberrant septal apparatus; 

 more rarely, however (for example, Beklemischcw, 1958)^ they 

 are considered as a category equal to that of Hexacorallia. It is 

 certain that the Ceriantharia had evolved as a side branch from 

 a root which has remained unknown so far (we cannot expect 

 that we will ever be able to find the corresponding fossil mate- 

 rial since we have here animals that possess no skeletons whose 

 development goes far back into geological past). It may be 

 better, however, to place them immediately after the Actiniaria 

 because they have remained, like Actiniaria, primarily solitary 

 animals. They should be followed by the remaining orders: 

 Madreporaria (it is possible that among these there still exist 

 primarily solitary and now already completely immobile 

 species), Antipatharia, and finally Zoantharia. The last two 

 orders are highly specialized, each in its own direction. 



Fortunately enough, the subdivision of Octocorallia (Oc- 

 tactiniaria) has already been well made. The most important 

 difference between various systems that have been proposed 

 can be found in the number of subgroups. Some zoologists are 

 satisfied with three orders (Alcyonaria, Gorgonaria, andPenna- 

 tularia) while it is believed by others that five orders must be 

 distinguished (Stolonifera, Telestacea, Alcyonacea, Coenothe- 

 calia, Gorgonacea, and Pennatulacea). This difference, how- 

 ever, is not important in connection with the present study. 



At present, we are hardly able to determine with certainty 

 where and when Scyphozoa had branched off from the Antho- 

 zoa. Those Anthozoa which stand closest to the present day 

 Stolonifera among Octocorallia, represent in all probability the 

 starting point for the evolution of Scyphozoa (Fig. 42). This 

 development had probably taken place at a time when their 

 ancestors did not yet of necessity possess branched tentacles 

 and when their polyps, w^hich were protected by a periderm 

 that extended high over the body of the animal, formed the 

 "creeping" (stolonate) cormi. Medusae began to be developed 

 from some intermediate forms w^hich have now become extinct. 

 Viewed from our standpoint we must put into the first 



