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KINGDOM ANIMALIA
Phylum Chordata
Subphylum Vertebrata
Superclass Osteichthyes
Vertebrate Classes
Class Actinopterygii
Ray-finned fishes
Most bony fishes and largest single
group of chordates (24,000 species)
Well-adapted; successful in marine and
freshwater
Carnivores, herbivores, parasites, and
scavengers
Features
Well-developed
lateral fins
Fins contain
delicate bony rays
extending from
internal skeleton
Provide support and
articulation
Caudal fin provides
thrust and other fins
stabilize
Features
Scales = 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
Features
Acrodin-covered teeth
Circulation
– 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
Examples
Primitive: heavy scales,
use swim bladder for
respiration in stagnant
waters
–
–
–
–
–
Bichir - freshwater Africa
Gar - Kansas
Paddlefish - N. Am.
Sturgeon - N. Am.
Bowfin - N. Am.
Examples
Derived: 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 Actinistia
Only one marine species remains
in this ancient lineage
Lobe-finned fish called a
coelacanth
Only living chordate with a
movable intracranial joint
– divides skull into anterior and
posterior halves
– may allow upper jaw to elevate
Fatty swim bladder (some
buoyancy)
Predator
Enamel-covered teeth
Coelacanth
Thought to have been extinct until
discovery in Indian Ocean in 1938
Since then, recovered 70+
Live in underwater lava caves at depths of
200-300 meters
Compared to fossil evidence, not many
changes-habitat stable (molecular level
unknown)
Class Dipnoi
Lobe-finned fishes
Reduced skeleton
Teeth modified into
plates (enamel)
Intracranial joint is
immobile
Swim bladder highly
vascularized and used as
a lung
Lungfishes
6 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