KINGDOM ANIMALIAPhylum Chordata

Subphylum VertebrataSuperclass Osteichthyes

Vertebrate Classes

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

Tetrapod Ancestors

Skeletal bones in fins similar to bones of primitive tetrapods

Limbs thought to have developed in the water, not on land