160 THE OCEAN 



of insects is represented by only a few species 

 of Halobates. 



The protozoa (foraminifera and radiolaria) 

 form a most important item in the plankton, 

 for though of microscopic dimensions they 

 swarm in countless myriads in tropical and 

 temperate regions (see Plate VII. for radio- 

 laria, and Plate IX. for foraminifera), and 

 deposits largely composed of their dead shells 

 and skeletons cover extensive areas of the 

 sea-floor in different parts of the world. 



The Crustacea are probably the most 

 abundant of all pelagic animals, and especially 

 the smaller forms, like the copepoda and 

 amphipoda, the small size of which is 

 counterbalanced by the enormous number 

 of individuals. 



The pelagic molluscs (pteropods and hetero- 

 pods) are specially characteristic of the 

 warmer regions of the ocean (see Plate VIII.), 

 where their shells fall to the bottom in such 

 numbers as to form in moderate depths a 

 large part of the deposit called pteropod ooze. 



The pelagic tunicates (Salpa, Doliolum, 

 Pyrosoma, Appendicularia) are important 

 members of the plankton, and many species 

 of fishes and cephalopods, being powerful 

 swimmers, are included among the nekton. 



Pelagic larvae of benthonic animals are 

 abundant near shore in shallow water, but 



