Lecture 9 - Class Osteichthyes

Lecture 9 - Class Osteichthyes

1. Advantages (over Chondrichthyes)

   • 1. Skeleton of endochondral bone (replaces cartilage in juveniles)
     • 2. Webbing between bony (dermal) fin rays
       • 3. Operculum covering gill arches
         • 4. Enlarged, protrusible maxillae (allows gape and suck feeding)
           • 5. Reduce dermal armor
             • 6. Swim bladder as evagination from gut
               • (part of the stomach)
             • becomes typical fish scales
           • maxilla - the jaw or jawbone, specifically the upper jaw in most vertebrates

2. Subclass Actinopterygii

   • Superorder Acipenseriformes
     • Suborder Neoptergii
       • Bowfins, gars, all other bony fish
         • Many have Weberian apparatus (combines use of swim bladder and inner ear to increase sensitivity to vibration)
           • Weberian apparatus - connects the swim bladder to the auditory system; swim bladder & inner ear linkage & serve to enhance hearing by conducting pressure changes produced by externally originating sound waves from the swim bladder to ear
     • Sturgeons & Paddlefish
       • Cartilaginous skeleton
         • Freshwater or Anadromous
           • Desirable for caviar
   • ray-finned fishes, aprox. 24,000 sp.
     • 1. Bony rays (more or less parallel) supporting fin membrane, increased fin flexibility and therefore mobility
       • 2. Hypural bones articulate with tip of upturned vertebral column = homocercal tail
         • 3. Flexible skull & cheek increased orobranchial chamber volume, thus increased predatory & respiratory ability
           • orobranchial - inside of the mouth
         • homocercal tail - a tail in which the last vertebra adjoins modified bony elements (the urostyle & hypurals) which support the fin rays in such a manner that the tail fin outwardly appears symmetrical
         • causes increased mobility

3. Subclass Sarecopterygii

   • Suborder Actinistii
     • Superorder Dipnoi
       • Lungfish
         • Freshwater with poor gill function
           • Evagination from gut (former swim bladder) modified into single or pair lungs
             • Aestivate to escape drought conditions
               • aestivate - spend a hot or dry period in a prolonged state of torpor or dormancy EX- African lungfish
     • Latimeria (coeleachanth, a "living fossil"
       • Marine
         • Carnivorous with internal fertilization
   • 1. Fleshy fins with bony central axis
     • 2. Two dorsal fins
       • 3. Enlarged head musculature