THE PHYLA COELENTERATA AND CTENOPHORA 



197 



glea is packed with supportive elastic fibers. The gonads develop in the 

 endoderm along the iree edges ot the partitions. In general, the structure 

 o£ these polyps is closer to that oi the Scyphozoa than that of the Hy- 

 drozoa. The anthozoan polyp also has a stomodeum, an inturned mouth 

 lined with ectoderm. 



The larger members ot this class are the solitary sea anemones, 

 which are liower-like in appearance when their tentacles are spread in 

 search of prey. Many of them are brightly colored and feed voraciously 

 on fish. 



The Anthozoa include the colonial true corals which contribute 

 greatly to the bulk of coral reefs along some tropical shores. The in- 

 dividual polyp is only half an inch across, but the colony secretes an 

 external supporting framework of calcium carbonate that may be of 

 considerable size. This skeleton may be encrusting, arborescent or mas- 

 sive (Fig. 10.15). 



Coral reefs are formed by large populations of many species of coral 

 and other limestone-secreting organisms. They develop only in warm 

 shallow water exposed to the ocean waves. At present the two major 

 regions that offer these conditions and support reefs are: (1) the Carib- 

 bean area, including Florida, Bermuda, the Bahamas and the West 

 Indies, and (2) the Indo-Pacific area known as the Coral Sea, extending 

 from Australia to Hawaii and the IMiilippines. 



The precious coral of commerce is not a true coral but a member 

 of the third order of Anthozoa, the alcyonarians. These have an internal 

 skeleton formed by the secretion of calcium carbonate and protein horny 

 material into the mesoglea. In some species these secretions fuse into a 

 rigid framework hard enough to resist wear. Precious corals form irregu- 

 lar branching colonies in the Mediterranean Sea and near Japan. 

 Wooden frames with rope tangle mops are dragged over the sea bottom 



Figure 10.16. Sea fan. (Courtesy of the American Museum of Natural History.) 



