spherical, encrusting or branching grow on the bottom 

 in less close association with the coral. The microscopic 

 silica spicules contained in the tissues of many of these 

 eventually are released by death and contribute to the 

 building of the reef rock. 



Living independently of the coral are also the small 

 red starfish Echinaster sentus, the six armed starfish, 

 Dnckia guildingii and the giant starfish Oreaster recti- 

 culata. These possess limestone skeletons. The dark col- 

 ored, leathery skinned sea cucumber, Tlotothuria jlori- 

 dana moves like a giant slug over the bottom and 

 extracts nutrient by running the sand through its body. 

 If interfered with it may eject its entire set of internal 

 organs and crawl away to grow them anew. Some of 

 its relatives have very delicate transparent skin and may 

 live in the interstices of the rocks. Euapta lappa, one of 

 these, may be crammed full of coarse sand but yet is 

 so delicate that it falls apart on handling. 



Close relatives of the sea urchins are the potato ur- 

 chin, Clypeaster rosaceus, which lives among weeds or 

 burrows in the sand. Greatly flattened versions of these 

 are the sand dollars, which are also found in the sand 

 between masses of coral. 



Many of the coral reef animals which are not closely 

 associated with the coral itself, live among the so called 

 sea grasses which grow in the quieter shallower waters 

 behind the outer reef. These grasses are not seaweeds 

 but are really flowering plants which have become 

 adapted to life under the ocean. Commonest is the flat 

 bladed turtle grass, Jhaltassia. 



Certain marine algae or seaweeds living on the reef 

 and in the shallow lagoons have the property of deposit- 

 ing limestone in their living tissues so that they also 



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