ACTINOZOA. 231 



Order 2. ALCYONARIA = OCTACTINIA. 



Polyps and polyp slocks witli eight plumed tentacles and the same 

 number of uncalcijied mesenteric folds. 



The calcareous secretions of the so-called cutis lead to the forma- 

 tion of fle hy polyparia or of friable crusts surrounding an axial 

 skeleton, which is sometimes horny, sometimes calcareous and stony, 

 or of rigid calcareous tubes (Tubipora). In all cases definite cal- 

 careous bodies, the sclerodermites, form the foundation of the 

 skeleton. The embryos are mostly born as ciliated larvae, without 

 mesenteries or tentacles. The separation of the sexes in diiferent 

 individuals is the rule (fig. 172). 



1. Fam. Alcyonidae. Fixed polyp stocks without axial skeleton, usually 

 with a fleshy, leathery polypariuni, with only a slight deposition of calcareous 

 matter in the cutis. The colonies arise either through lateral gemmation, 

 when they form lobcd and ramified masses, e.g. Alcyonium palmatum, Pall., 

 digitatum L., or the individual animals are connected by basal buds and root- 

 like processes, e.g., Cornularia crassa Edw. 



2. Fam. Pennatulidae (Sea feathers). Polyp stocks, the naked free basis of 

 which is embedded in sand and mud, usually with horny, easily bent axial 

 skeleton. There are small sterile polyps as well as the sexual animals. The 

 presence of an opening in the stem for the ejection and reception of water is 

 worthy of remark. The animals sometimes are placed on the side twigs of the 

 stem, and the polyparium is feather-like, e.g., Penuatula rubra Ellis ; some- 

 times they are distributed on all sides of the simple stem, e.g., the dioecious 

 Veretillum eynomorium Pall. In other cases the polyparium appears flat and 

 shaped like a kidney, with a bulbous root without an axis, Renilla tlolacea 

 Quoy. Gaim., or a kind of umbel is formed by the aggregation of the polyps at 

 the upper end of a long stem, Umliclhda Thomsonii Kb'll. 



3. Fam. Gorgenidae. The fixed colonies possess a horny or calcareous tree- 

 like branched axial skeleton, which is surrounded by a friable crust, or by a 

 softer parenchyma containing calcareous particles. The body cavities of the 

 individual animals communicate by branched vessel-like tubes which contain 

 the common nutritive fluid. The axis is either horny, flexible, and unjointed, 

 as, e.g., Gorgonia verrucosa Pall., {Rliipidogorgia) ftabellum L., or composed 

 of alternating horny and calcareous segments, as, e.g., Isis hij'puris Lam., 

 JJclithcea ocliracca Lam., or stony and formed of calcareous matter. The red 

 coral, Corallium rulrum Lam., falls under the last head, and yields the coral 

 stone which is used in jewellery. This species is found in the Mediterranean, 

 on the rocky coasts of Algiers and Tunis, and there forms an important object 

 of industry. 



4. Fam. Tubiporidae, organ coral. The polyparia resembling the pipes of an 

 organ. The animals are placed in parallel calcareous tubes connected by hori- 

 zontal plates. Tublpora Hempriclitii Ehrbg. 



Order 3. ZOAXTHARIA = HEXACTIXIA. 



Polyps and polyp stocks, whose tentacles usually alternate in several 

 circles, and are either six or some multiple of six in number. 



