278 



SUBPHYLUM VERTEBRATA: 



dorsal fin 



operculum 



ACIPENSER 



homboid scales 



caudal fin 



anal fin 



pectoral fin 



Figure 16.14 External features of Polyodon, a paddlefish, and Acc/penser, a sturgeon. Order 

 Acipenseroidei, Superorder Chondrostei. (From Malcolm Jollle, Chordate Morphology, Reinhold 

 Publishing Corp., New York, 1962.) 



Sturgeons are fresh-water species, but there is a ma- 

 rine form in the Atlantic. 



Paddlefish can usually be recognized by their pad- 

 dle-shaped snouts and their almost complete lack of 

 scales. They attain a length of 6 feet and feed upon 

 small bottom invertebrates which are strained by the 

 gill apparatus. 



Sturgeons are shark-like in form but are unique 

 in having five rows of bony plates along the body. 

 They reach a length of about 10 feet. Their diet is 

 varied; food items include aquatic plants, inverte- 

 brates, and smaller fishes. Despite their size and 

 palatability, sturgeons often are considered of little 

 food value; however, their eggs are the source of 

 caviar. 



to survive in small amounts of water. This animal 

 is a voracious, pugnacious carnivore that feeds upon 

 moUusks, crustaceans, insects, and other fish. 



The other family is represented by a single genus, 

 containing about eight species of beaked fish, the 

 gars. Gars are found east of the Rockies in the 

 greater Mississippi drainage, but are also found in the 

 West Indies and well down into Central America. 

 Gars are long, slender fishes that are protected by a 

 heavy covering of overlapping plates and by long, 

 thin teeth. In general, they are fish predators that 

 quietly stalk their prey and swallow it whole. The 

 fact that they stalk their prey may seem surprising, 

 because they have been known to grow to over one 

 hundred pounds. 



Superorder Holostei (Intermediate Ray-finned Fishes) 



Diagnosis: backbone deflected upward into upper 

 lobe of tail; tail fin rounded; mouth terminal and 

 bearing strong teeth; skeleton bony; fresh-water 

 (Figure 16.1.5). 



The intermediate ray-finned fishes are represented 

 by two living families. One family includes a single 

 species, the bowfin or fresh-water dogfish found in 

 North America from Texas east and southern Can- 

 ada south. The bowfin does not have its snout drawn 

 into a beak as does the other family. The bowfin is 

 an inhabitant of quiet waters, generally living in 

 weeds and mud of lakes, rivers, and swamps. It is 

 well known for its nest-building habits and ability 



Superorder Teleostel (Modern Fishes) 



Diagnosis: backbone not deflected upward, fuses 

 into a more or less symmetrical plate; tail usually 

 symmetrical and forked; fresh-water and marine 

 (Figure 16.15). 



Modern fishes present an almost insurmountable 

 problem insofar as identification is concerned. Be- 

 cause any attempt at meaningful identification would 

 necessitate very technical consideration of structures, 

 this taxon is beyond the scope of this book. In the 

 UnitedStates there are approximately 600 fresh-water 

 species alone. The Superorder Teleostei, containing 

 over 20,000 species, includes the fishes most familiar 

 to us. For example, teleosts include herring, salmon. 



