THE BEXTHAL 



215 



of the reef are supplied by the massive corals — the balls and pillars of 

 Porites, the rounded walls of Maeandrina, and the great group of 

 Astraeas." 76 



Animals associated with coral reefs. — The coral reef forms the 

 background and basis for a wealth of animal life unequaled elsewhere 

 even in tropical seas. Griffin reports from the coral reefs of Port Galera, 

 Mindoro, 111 species of Alcyonaria, few starfish and sea urchins, but 

 numerous brittle stars, crinoids, and holothurians; 70 species of 

 chaetopod worms, 3 echiurids, and 10 sipunculids; and 200 to 250 

 species of crustaceans, among them 25 to 30 hermit crabs. Mobius 

 estimates the number of molluscan species (without nudibranchs) on 



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Fig. 44. — Outlines of the habitat forms of Madrepora muricata. a, forma palmata; 

 b, forma prolifera; c, forma cervicornis. After Vaughan. 



the reefs of Mahebourg, Mauritius, at 336. In general character this 

 fauna associates it with the fauna of the rock bottom. The condi- 

 tions which permit of such a rich development, in addition to the 

 generally favorable tropical environment, are the abundance of food 

 and adequate protection. 



The reef corals with their symbiotic algae are to be reckoned 

 among the food producers, and are fed upon to some extent by the 

 reef inhabitants. The colorful mixture of green, brown, and red algae 

 supports another series of animals. The surf produces and brings 

 detritus and plankton, which serve as food for others, and predators 

 follow the herbivores, as everywhere. 



The coral reef habitat offers much better protection and conceal- 

 ment than solid rock. It is permeated with pores and hollows like a 

 sponge; broad caves, well-like hollows, connected with each other and 

 with the sea; cracks and interspaces, all afford retreats and hiding- 

 places to the animal population. Even the individual coral heads are 

 porous, and when one is broken up, a crowd of varied inhabitants 



