HIGHER CHORDATES 



279 



dorsal fin 

 spinous soft ray 



nasal tube^ 



caudal fin 



pectoral fin 



AMIA 



pelvic fin 



Figure 16.15 Holostean {Amia, o bowfin, and iepisosteus, a gar) and teleostean fishes. {From 

 Malcolm Jollie, Chordate Morphology, Reinhotd Publishing Corp., New York, 1962.) 



trout, flying fish, eel, codfish, catfish, minnow, perch, 

 mackerel, flounder, and the "weird" deep sea fishes. 

 They are animals that can be found in almost any 

 fresh or salt waters of the world at almost any depths. 

 Because of their number and diversity of aquatic 

 habitats, they might be called the rulers of earth's 

 waters. 



We shall content ourselves with a brief and very 

 general mention of their life cycle. Most fishes gather 

 in breeding swarms, and sperm and eggs are shed 

 simultaneously. Characteristically, many eggs are 

 laid. The eggs hatch into a larva that is barely remi- 

 niscent of the adult, and after a variable period the 

 larva assumes the adult form. 



Some modern fishes display interesting modifica- 

 tions of the general reproductive pattern. Female 

 surfperches retain the eggs within their bodies and 

 bear the young alive, a phenomenon also found in the 

 guppies and their allies. Although many teleosts 

 merely shed their eggs in water, some build nests. 

 The sticklebacks, for example, have elaborate court- 

 ships, build nests of varying complexity, and often 

 remain to protect the nest and eggs. 



The salmon are of particular interest because many 

 spend most of their lives in the sea, but at the time 

 of breeding return to their "hatching stream." In 

 the headwaters of these streams a simple nest is 



scooped out of the bottom of the stream, the female 

 lays her eggs in the nest, and the male fertilizes the 

 eggs. In the Atlantic salmon most males die shortly 

 after fertilizing the eggs, although many of the seem- 

 ingly exhausted females drift down the breeding 

 stream, regain the ocean, and survive. Both sexes of 

 Pacific salmon die after reproducing. 



A truly remarkable breeding pattern is found in the 

 fresh-water eels. The American eel breeds in the 

 vicinity of Bermuda, and the eggs develop into larvae 

 which take one year to reach the United States. 

 After metamorphosis, the young eels migrate up our 

 eastern fresh-water streams. However, the really 

 remarkable eel is the European form. It breeds in 

 much the same area as ours but the young take two 

 years to reach the European coast. However, ap- 

 proximately another year is taken before the comple- 

 tion of metamorphosis and reentry into the fresh- 

 water streams. 



LAND VERTEBRATES: SUPERCLASS 

 TETRAPODA 



Although most of Tetrapoda occur on land and are 

 four-legged, we are hard pressed to provide a com- 

 mon name that truly describes all of them. "Land 



