6o 



The Ltv'mg Things of the Earth unit i 



Fig. 86 Organ-pipe coral. The tiny animal within each tube can extend brightly 

 colored tentacles. (American museum of natural history) 



outside their bodies. There are many spe- 

 cies of coral animals. Each species con- 

 structs of shell of a particular kind. 



Most corals inhabit the warm waters 

 of tropical seas in vast colonies contain- 

 ing thousands upon thousands of indi- 

 viduals. When each animal dies its skel- 

 eton remains behind; thus slowly but 

 steadily a mass of shells piles up. This 

 turns to stone — limestone. After long 

 ages so much rock gathers that a reef or 

 coral island may rise out of the water. 

 Reefs are sometimes a thousand miles or 

 more in length. The Bermudas are a 

 group of coral islands. 



A third class — the jellyfish. Grownup 

 coral animals and sea anemones spend 

 most of their lives sittin<r down but in 

 their vounger stages thev can move 

 about. There are other forms, such as 

 the jellyfish, that never settle down. The 

 animal is realh' jcllvlike; clear, trans- 



parent, and soft. The body of the jellv- 

 fish is more than 95 per cent water. 

 When washed up on the dry beach the 

 water soon evaporates away until just 

 a shriveled shadow remains. 



Jellyfish look like inverted saucers 

 floating in .the water. See Figure 87. 

 They vary in size from about one inch in 

 diameter to several feet. The jellyfish 

 moves throuijh the water by wavintj its 

 tentacles or by contracting its body. The 

 contraction squeezes w^ater out of the 

 central cavity; this gives the jellyfish a 

 little push in the opposite direction. 



Characteristics of the coclenterates. 

 The coclenterates are all water-dwelling 

 animals. Like the starfish thev have ra- 

 dial symmetry, but thc\^ are far simpler 

 in make-up. Each animal is much like a 

 simjilc sac. The sac has one opening 

 called the mouth which is surrounded 

 b\^ tentacles with stinging hairs. 



