THE SPONGES AND THE TWO-LAYERED ANIMALS 



157 



Fig. 8-20. A typical coral reef with the abouncJing life associated with it. The fish are strikingly colored to match 

 the background of corals, sponges, and other marine life. The tentacles of a large sea anemone can be seen in 

 the lower left. The corals are numerous and highly varied in size, shape, and color. 



Sea. Our overseas forces in the past war 

 became familiar with the corals around the 

 Philippines and Australia. 



Perhaps the most interesting thing about 

 coral is its ability to form reefs, some of 

 which reach many miles in length, like the 

 Great Barrier Reef of Australia, for exam- 

 ple, which extends over 1,100 miles in 

 length. There are three kinds of coral reefs, 

 depending on how they were formed ( Fig. 

 8-21). The fringing reef lies along the 

 shoreline of an island or mainland and 

 usually extends up to a quarter of a mile 



out into the sea. Boats approaching such 

 shores are in great danger, particularly in 

 rough weather. Sometimes, as the result of 

 a shifting shoreline, a lagoon appears be- 

 tween the main reef and the shore; this type 

 is called a barrier reef. The atoll is perhaps 

 the most unique of the three kinds of reefs. 

 It is a rim of coral taking on varying shapes, 

 usually a completely enclosed circle. These 

 have always fascinated biologists. One of 

 the greatest among them was Charles Dar- 

 win who gave an explanation of how tiiey 

 formed, a theory which is still considered 



Fig. 8-21. Various types of coral reefs. 



