THE IMPENETRABLE SEA 



sea-urchins and other relatives they are known as 

 echinoderms, meaning spiny skin. 



Other Hfe on and in the Reef are: hermit-crabs, 

 which borrow the shells of other creatures for their 

 houses ; sea-wasps (a venomous kind of jelly-fish, the 

 sting of which can be fatal to humans) ; cowries, with 

 their brilliantly coloured mantles ; and all kinds of crus- 

 taceans. Sting-rays lurk in the shallows, as obscure, 

 ominous patches. Wedge-tailed shearwaters, called mut- 

 tonbirds locally, burrow and build their nests under- 

 ground — to mention only one of the extraordinary birds 

 which fly in myriads over the Reef. Enormous crowds of 

 soldier crabs — as large as a shilling — may suddenly in- 

 vade a particular beach : only to vanish, if frightened, as 

 suddenly as they appeared. 



The warm waters of the world's coral reefs encourage 

 the prolific breeding of all kinds of creatures, and 

 numbers of these — like the giant Crocodilus porosus — reach 

 dimensions far exceeding those of their normal relatives 

 in colder waters. There are, for instance, the moray eels, 

 which lurk in the coral crevices of many reefs, resenting 

 the intrusions of divers and often snapping at them with 

 their slit-like mouths, which are armed with long needle- 

 sharp teeth. These have small heads and bead-like eyes, 

 and are sometimes six feet in length. Clams weighing up 

 to fifteen ounces are considered large specimens among 

 the long (or soft-shelled) varieties, and the gaper {My a 

 arenaria) is among the moderately large British bivalves, 

 although it is usually no more than four inches long and 

 two and a half inches broad.* But the clams of the coral 

 reefs are commonly ten, twenty or even a hundred times 

 larger, while one species, Tridacna gigantea, may weigh as 

 much as several men. One specimen, taken in Australia 

 and now exhibited at the American Museum of Natural 



♦The largest British bivalve is the fan-shell, Pinna fragilis; specimens up to 

 fifteen inches long and eight inches wide have been found. 



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