Chapter 26 



ECONOMIC IMPORTANCE OF ANIMALS 



Naturally, not all the animals of economic importance, nor the eco- 

 nomic importance of all the animals listed, can be given in a short chap- 

 ter. Economic importance is considered from the beneficial as well as 

 the detrimental standpoints. Additional information along these lines 

 may be found in the chapter on Applied Biology. The following exam- 

 ples are representative, but more detailed accounts should be read if 

 these are not sufficient for the particular needs of the reader. 



PHYLUM 1— PROTOZOA (SINGLE-CELLED ANIMALS) 



Certain Protozoa which bear shells (class Sarcodina, order Foraminif- 

 era) leave a deposit of chalk after their death. The limestone pyramids 

 of Egypt contain numerous, large Foraminifera. Other Foraminifera 

 are useful in determining the proper places to drill oil wells. Foraminif- 

 era (Fig. 257) are of great geologic importance because they are common 

 fossils from the Silurian rocks (395 million years ago) down to the pres- 

 ent (Figs. 320 to 322). 



Certain marine, fossilized types of Protozoa (class Sarcodina, order 

 Radiolaria) are found in chalk, flint, slate, and deep-sea deposits. The 

 siliceous skeletons of certain Radiolarians aid in the formation of flint. 



Protozoa of various kinds may impart unpleasant odors, tastes, and 

 colors to waters. For example, Bursaria (class Infusoria) produces a 

 ''salt marsh" odor in water (Fig. 258) ; Uroglena (class Mastigophora) 

 produces a yellow color and a "codfishy" odor (Fig. 259) ; Peridinium 

 (class Mastigophora) turns the sea water along the coasts of California 

 and Australia a reddish color; Dinohryon (class Mastigophora), a colonial 

 form, produces a "fishy," seaweed odor (Fig. 260) ; Synura uvella (class, 

 Mastigophora) produces a bitter, spicy taste (like ripe cucumbers) and 

 an "oily" odor in water (Fig. 261) ; Noctiluca (class Mastigophora) may 

 be quite common in sea water, giving a reddish-brown color or a green- 

 ish-blue phosphoroscence at night. 



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