ANTHOZOA 133 



the gonads, and also nematocysts ; at its lower end also, in many species, 

 are long threads called acontia charged with nematocysts which can be 

 protruded from the mouth and also, in some cases, through pores (cin- 

 clides) in the body wall. The mesenteries bear the retractor muscles, each 

 of which appears as a prominent ridge on one side of it. At the upper end 

 of the body is usually a strong sphincter muscle which draws this end 

 together and closes the mouth. The body wall consists of the two main 

 cell layers and the mesoglea, which contains nuclei. The mesenteries are 

 composed of mesoglea and entoderm; the important retractor muscles and 

 the gonads being thus of entodermal origin, the latter migrating later 

 into the mesoglea of the mesenteries where they are found. 



Very characteristic is the skeleton, which most Anthozoa possess. This 

 is composed either of calcium carbonate or a horn-like substance called 

 ceratine, both of which are secreted by the ectoderm and serve to elevate 

 the colony in the water, bringing it into a favorable position for main- 

 taining itself. 



The Anthozoa are in most cases unisexual. Tlie ova and sperm are 

 thrown into the gastrovascular space, where in many cases a portion of 

 the development may be carried on. In some sea anemones, the young are 

 carried awhile in pits on the side of the body. After a short free life, the 

 young animal settles to the bottom, and in most cases becoming fixed, 

 develops into the adult animal. Asexual reproduction by budding is very 

 general and leads to the fonnation of the colonies which are so character- 

 istic of the group. All of the Anthozoa are marine animals and are espe- 

 cially numerous in the warmer parts of the world. Corals are of impor- 

 tance to man because of the coral reefs, banks, and islands they help to 

 form. The only species which have commercial importance are the red 

 corals of the Mediterranean and Japan which are used in the manufacture 

 of jewelry. The name of the class originated with Ehrenberg, who in 

 1831 divided the polyps as then known into two groups, the Anthozoa or 

 flower animals and the Bryozoa or moss animals. The class contains 

 over 2,000 living and many fossil species, which are grouped in two 

 orders. 



Key to the orders of Anthozoa: 



a, Eight pinnate tentacles present 1. Alcyonaria 



(li Tentacles simple and usually numerous 2. Zoantiiaria 



Order 1. ALCYONARIA.* 



Colonial Anthozoa with 8 pinnate tentacles and 8 mesenteries (Eig. 

 222, B). A siphonoglyph is present on but one side of the polyp, or not 

 at all. The retractor muscles are all on the same side of the mesen- 



* See "Alcyonaria of Porto Rico," by C. W. Hargitt and C. R. Rogers, Bull. U. 

 S. Fish. Com., Vol. 20, p. 267, 1900. 



