32 



The Living Things of the Earth unit i 



Fig. 44 Sharks belong to a group lower than fishes. They have neither true scales nor 

 bones. Gill covers are lacking. This shark has two shark suckers attached to its lower 

 side, (new york zoological society) 



mals, to the simpler ones, you met first 

 the birds, then the reptiles, then the 

 amphibians. There are other cold- 

 blooded vertebrates even less complex; 

 these are the fishes. Their distinguishing 

 characteristics are slimy scales, fins, and 



r' 



gills. Of course they have a backbone 

 just as other vertebrates do. They are 

 water dwellers, obtaining the oxygen 

 they need from the air dissolved in the 

 water. Out of water, fish die quickly 

 because their gills cannot take oxygen 

 from the atmosphere. Most fish have 

 paired fins, usually two pairs, and other 

 fins which occur singly. Make your own 

 observations of fish by doing Exercises 

 lo, 1 1, and 12. 



"Fish" that are not fish. The animals 

 of this group are closely related to fish 



Dorsal fin 



Left nostril 



Gill cover Left pectoral fin 



Left pelvic fin 



but have skeletons made of a softer sub- 

 stance called cartilage (car'til-aj). You 

 may know cartilage by the name of 

 gristle (griss'l). One of the commonest 

 is the dogfish that destroys large num- 

 bers of food fishes along the coast. 

 Sharks are its larger cousins, with repu- 

 tations often much worse than they de- 

 serve. Most species of sharks do not 

 attack man but eat only fish and other 

 animals of the sea. 



Fish are numerous and varied. There 

 is three times as much sea as land. You 

 can see that there is plenty of room for 

 fish. Great numbers live in both \yarm 

 and cold waters; even in the arctic seas 

 there are fish. Some kinds swim near 

 the surface, others far below. It is es- 

 timated that at present there are about 



Tail fin 



Fig. 45 Which characteris- 

 tics of fishes does this gold- 

 fish have';' Where are the 

 gills? How many fins has the 

 goldfish? 



Anal fin 



