LOWER COASTAL ANIMALS 



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Sea-urchins (Echinometra) in the lower edge of the tidal zone. St. Thomas. 



wooden statues. In California, where they go under the name abalone, 

 interest in them is mainly gastronomic, and they are a delicacy considered 

 well worth diving for. 



But it is the Tropics which hold the record for fauna. Where the water 

 temperature all the year round is more than 20° C we find, in shallow 

 water, the kind of epifauna called coral reefs. Take such a coral reef 

 on a day when the water is crystal clear and there is just enough move- 

 ment to bring a steady flow of fresh food to the many sedentary animals 

 there. Even hardened zoologists are caught in a fever of excitement when 

 let loose in such a spot. Often the reef lies with its top just under the 

 surface, so that one wades knee-deep in water with the risk of suddenly 

 sinking up to the middle. Here we found large brown blocks which re- 

 sembled boulders, but which were labyrinth corals (Poritis). In the white, 

 decayed central portion we would often find a strange blue, broad and 

 zigzag stripe which, when we stooped down, would shrink and vanish. 

 This was the giant clam (Tridacna) ; and it was its vividly coloured soft 

 parts which attracted attention when the shells were open. Erect, roughly 

 branched corals (Acropora) shone with a brownish luminescence, and 

 everywhere ^ve trod on a confusion of finely branched coral stems, which 

 all the time would crack and break, and threaten to send us sprawling. 



