KINGDOM ANIMALIA Phylum Chordata Subphylum Vertebrata Superclass Osteichthyes
Dec 18, 2015
Class ActinopterygiiRay-finned fishesMost bony fishes and largest single group of chordates (24,000 species)Well-adapted; successful in marine and freshwaterCarnivores, herbivores, parasites, and scavengers
Features
Well-developed lateral fins Fins contain
delicate bony rays extending from internal skeleton Provide support
and articulationCaudal fin provides
thrust and other fins stabilize
FeaturesScales = light bone (small or
absent in fast swimmers)Swim bladder (lung) – saclike extension of digestive
tract during development– used to retain gases to provide
fish with buoyancy (don’t sink, energy saving)
– may also be used for atmospheric respiration
Gills to maximize area for gas exchange– Covered by bony operculum– Force water over gills when not
moving
FeaturesAcrodin-covered teethCirculation– 2-chambered heart– Blood flow under low pressure– Blood flows in opposite
direction as water in gills, which maximizes oxygen saturation
Brain– Sensory and to some extent
motor coordinating centers well developed
– Overall coordinating and reasoning centers are primitive
ExamplesPrimitive: heavy scales,
use swim bladder for respiration in stagnant waters– Bichir - freshwater Africa– Gar - Kansas– Paddlefish - N. Am.– Sturgeon - N. Am. – Bowfin - N. Am.
ExamplesDerived: Dominant fishes today;
extremely diverse (morphology); upper jaw protrusible, thin/flexible scales, swim bladder for buoyancy– Herring (predator)– Coral reef fish (lateral compression)– Flounder (very laterally compressed,
swim on side, eyes on upper body)– Moray eel (tubular, sacrifice speed for
agility)
Class ActinistiaOnly one marine species remains
in this ancient lineageLobe-finned fish called a
coelacanthOnly living chordate with a
movable intracranial joint – divides skull into anterior and posterior
halves– may allow upper jaw to elevateFatty swim bladder (some
buoyancy)PredatorEnamel-covered teeth
CoelacanthThought to have been extinct until
discovery in Indian Ocean in 1938Since then, recovered 70+ Live in underwater lava caves at depths
of 200-300 metersCompared to fossil evidence, not many
changes-habitat stable (molecular level unknown)
Class DipnoiLobe-finned fishesReduced skeletonTeeth modified into plates
(enamel)Intracranial joint is immobileSwim bladder highly
vascularized and used as a lung
Lungfishes6 species of freshwater
lungfishes found in tropical regions of Africa, Australia, and S. America
Areas subject to drought– Some use lungs when
conditions unfavorable, use gills otherwise
– In others, gills reduced and dependent on lungs
African Lungfish
Burrows in mud when water dries up
Secretes a mucous cocoon around its body with air hole at tip
Can survive up to 4 years
Tetrapod Ancestors
Response to periodic drying or to avoid predation/competition in aquatic habitat
Limbs further developed as stayed on land
Few competitors, no predators—selective pressure in favor of the land move
2 features:– Functional lungs (as well as gills)– Fleshy lateral fins containing muscle to
support body and provide mobility