162 



ANALYSIS OF THE ENVIRONMENT 



the 2000 meter line. On the other hand, 

 organic matter is often mixed in with sand 

 and mud even close to shore (Johnstone, 

 1923). 



Character is given to the organic oozes of 

 the deeper ocean bottom by the skeletal 

 matter that accumulates on the bottom. 

 These skeletons originate mainly from 

 waters in or just below the lighted, surface 



deeper than the others. The calcareous 

 oozes cover the major part of the bottom 

 in the Atlantic and Indian oceans. 



The important features of these sub- 

 strates for bottom-dwelling animals are their 

 consistency and the organic matter they 

 contain. The consistency is about that of 

 unchilled butter in summer, and animals 

 living on such a semisolid medium require 



Fig. 34. An intertidal oyster bank in South Carolina. (Photograph by Dean; loaned by Fish 

 and Wildlife Service, U. S. Department of Agriculture.) 



zone. Bottom oozes are of two kinds: cal- 

 careous, characterized by Globigerina (Pro- 

 tozoa) and by Pteropod (Gasteropoda) 

 shells; and siliceous oozes, characterized by 

 diatom or radiolarian remains. Red clay, 

 when typically developed, lacks more than 

 a trace of these skeletal remains. It appears 

 to be richer in organic matter than are the 

 calcareous oozes, but not so rich as the 

 diatomaceous ones. Red clay covers some 

 38 per cent of the ocean bottom beyond the 

 Hmit of terrigenous deposits, as compared 

 with 14 per cent for the siliceous, and 48 

 per cent for the calcareous oozes. Red clay 

 is poor in calcareous remains. It occurs in 

 the three main oceans and is most extensive 

 in the Pacific, an ocean that is somewhat 



speciaUzed support if they are not to be- 

 come engulfed. Motile animals of the deep 

 benthos have an enlarged ventral surface- 

 several echinoderms, for example— or long 

 legs with terminal segments expanded by 

 bristles that increase their supporting sur- 

 face, as in deep-sea crustaceans. Sessile 

 forms are raised above the soft ooze by a 

 stalk with rootlike outgrowths or by brushes 

 or collars of spines. Such structures are typi- 

 cal of deep-sea sponges, hydroid polyps, 

 and a variety of other animals of this exten- 

 sive community (Hesse, Alice, and Schmidt, 

 1937). 



Marine animals are best known from the 

 littoral region. Benthic littoral animals are 

 abimdant on rocky surfaces and on fairly 



