178 THE OCEAN 



the mud-line of the continental slopes. In 

 the cold waters of the deep sea decomposition 

 and putrefaction are slow processes, so that 

 in the dead bodies of organisms there is still 

 food for the scavengers, like holothurians, 

 which eat the mud and in turn provide nour- 

 ishment for the deep-sea carnivores. 



Many characteristic deep-sea forms have 

 long stalks lifting the bodies of the animals 

 out of the mud, like some crinoids, pennatulids, 

 alcyonarians, hydroids and bryozoans ; others, 

 like the pycnogonids and crustaceans, have 

 long legs ; others have well-developed tactile 

 organs, like some crustaceans and fishes. 

 Most of these forms are delicate in structure 

 but of gigantic size when compared with their 

 shallow-water allies. Those species which 

 require calcium carbonate to form their 

 skeletons — like the molluscs and corals — 

 are feebly developed in the abyssal region. 

 A selection of benthonic calcareous foramini- 

 fera is shown on Plate X. 



Phosphorescent light evidently plays an 

 important role in deep-sea life ; coelenterates 

 like the alcyonarians have frequently been 

 brought up from great depths in a light-giving 

 condition. The colouring of deep-sea animals, 

 mostly red and brown monotones without any 

 patches of vivid colours, is doubtless corre- 

 lated with the faint gleams of phosphorescent 



