THE SEA BOTTOM 71 



strange shapes like the whitened bones of some prehistoric 

 monster ! 



Abyssal Zone 



Owing to the remarkable conditions there prevailing, the 

 inhabitants of the Abyssal zone are quite unlike those of the 

 Continental Shelf, far fewer in numbers and quite different 

 in appearance. The Continental Slope which connects these 

 two regions is seldom traversed by animals passing from the 

 one zone to the other for the conditions in the great depths 

 are such that its inhabitants have to be very specially 

 equipped for life and are unable to adapt themselves to 

 existence in shallower water. Conditions are more uniform 

 in the abyss than on any other part of the earth's surface. 

 There is absolute darkness, an unchanging temperature 

 only slightly above zero and an enormous pressure amount- 

 ing, at depths of three thousand fathoms, to about three 

 tons per square inch. There is no vegetation and no exposed 

 rocks, everything being covered with a layer of soft ooze. 

 The place of attached animals is taken by creatures with 

 long stalks, which lift their bodies clear above the mud. 

 Examples are provided by the sea lilies (Plate 25), closely 

 related to the feather-stars of shallower water but with a 

 long stalk in place of the short root-like outgrowths, and 

 also by the sea pens, here at their most abundant, some 

 alcyonarian corals, sponges, sea squirts and sea mats. 

 Many of the crustaceans have long legs for lifting their 

 bodies above the mud, and so have the sea spiders which 

 may have limbs two feet long (Plate 25). There are 

 relatively few animals with calcareous skeletons, molluscs, 

 especially bivalves, being particularly rare, though some 

 interesting examples of the latter which, unlike their shallow 

 water relatives, have become carnivorous, are found in the 

 greatest depths. The total darkness has resulted, para- 



