ZOANTHARIA. 183 



Verr. ; Menella Gray ; Ads Duch. and Mich.; Thesea Duch. and Mich.; Bebryce 

 Philippi. 



Fam. 9. Plexauridae. Colony branched, axis horny ; polyps occur fty. over 

 the thick coenerichyma ; spicules large ; cortical club-shaped and deeper spindle- 

 shaped spicules. Eunicea Lamouroux ; Plexaura Lamotiroux ; Psammogorgia 

 Verr. ; Platygorgia Studer. 



Fam. 10. Gorgonidae. Colonies upright and branched usually in one plane ; 

 axis horny, rarely horny and calcareous ; polyps arise from stem and twigs in a 

 bilateral and biradiate manner. Coenenchyma smooth, spicules small. Platy- 

 caulos "Wr. and St.; Loplwgorgia M.-Edw. ; Leptogorgia- M. -Edw. ; Stenogorgia 

 Verr.; Callistephanus Wr. and St.; Swiftia Duch. and Mich.; Gorgonia L. ; 

 Eugorgia Verr. 



Fam. 11. Gorgonellidae. 



Order 3. ZOANTHARIA = HEXACTINIA. 



Polyps and polyp-colonies, usually with simple unbranched tentacles. 

 There are usually incomplete as tcell as complete mesenteries, and the 

 tentacles usually alternate in several circles. 



This order includes the Sea-Anemones and Corals. The order 

 owes its name Hexactinia to the fact that in some of the best- 

 known forms the mesenteries and tentacles are arranged in some 

 multiple of the number six. There is, however, the greatest variation 

 in this respect, and with the progress of research it has become clear 

 that the number six is by no means universally characteristic; indeed 

 we may go further, and say that it is not even typical; and it appears 

 probable that, when this matter has been more fully looked into, the 

 hexactinian arrangement will be found tq be only one of many 

 mesenterial arrangements found in the group. In some cases the 

 number of mesenteries increases with the growth of the animal. 



Development. Our knowledge is not very complete. An in- 

 vaginate gastrula has been observed, with a blastopore persisting as 

 mouth. A ciliated, free-swimming larva is usually formed. 



There are three sub-orders. 



Sub-order 1. ACTINIARIA.* MALACODERMATA. 



Solitary, rarely colonial polyps with mesenteries, the number of which is 

 usually a multiple of six ; without skeleton. Body moving freely, or adherent 

 by means of the pedal disc ; rarely firmly fixed. 



* P. H. Gosse, A History of the British Sea-Anemones and Corals, London, 

 1860. R. Hertwig, "Report on the Actiniaria," Challenger Reports, Pt. 15, 

 1882. R. Hertwig, Supplement to the above, Challenger Reports, Pt. 73, 1888. 

 A. Andres, " Le Attinie," Fauna and Flora des Golfes von Neapel, 1884. A. C. 

 Haddon, "A Revision of the British Actiniae," Pts. 1 and 2, Sci. Trans. Roy. 

 Dublin Soc. (2), 4, 1889-91. J. Playfair McMurrich, "Report on the Actiniae 

 collected by the United States Fish Commission Steamer Albatross," Proc. U. S. 

 National Museum, vol. xvi. p. 119, 1893. 



