SOME COMMON FISHES OF NORTH AMERICA , 279 



occurs off the coast of Florida. Its name is derived from the 

 sting inflicted by a spine at the base of its whiplike tail. The 

 sawfish (Fig. 161, B) is a' ray with its head extending forward 

 as a long, sawlike projection. 

 The saw of a fifteen-foot fish 

 is about five feet long; it is 

 used to defend the fish or to 

 capture its food. The tor- 

 pedo ray possesses electric 

 organs on either side of its 

 head which can give a shock 

 strong enough to stop rather 

 large animals. 



Subclass 3. Teleostomi 



The true fishes or Teleos- 

 tomi have a skeleton con- 

 sisting entirely or partly of 

 bone and an operculum 

 covering the gills. About 

 twelve thousand species are 

 known from the entire world 

 and over three thousand 

 species occur in North 

 America. 



The sturgeon (Fig. 163, A) 

 is a rather primitive fish that 

 resembles a shark in the shape of the body. Its tail fin is larger 

 above and its mouth is on the ventral surface. It feeds on the 

 bottom, using its snout for stirring up the mud and the sensitive 

 filaments (barbels) near the mouth for finding food. Sturgeons 

 are economically important; their flesh is excellent for food; 

 their eggs are made into a much-prized table delicacy called 

 caviar; and their air bladders are used as isinglass. 



A near relative of the sturgeon is the paddlefish (Fig. 163, B) 



Fig. 162. — Sting ray. (From Jordan 

 and Evermann.) 



