THE FIRST VERTEBRATES
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Oldest and simplest vertebrates
Most abundant vertebrates
Three groups of fishes
◦ Jawless fishes
◦ Cartilaginous fishes (Chondrichthyes)
◦ Bony fishes (Osteichthyes)
◦ Yes, it is FISHES- the rule is fish is for a single
individual or more than one individual of the same
species
◦ FISHES- refers to more than one species
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Class Agnatha
Around 30 known species
Includes hagfish & lampreys
Feed by suction with aid from teeth
No fins, & lack true vertebrae; no scales
Body is elongated and cylindrical
Most primitive fishes
Class Chondrichthyes
Skeleton made of cartilage
Movable jaws
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Mouth ventral
Underneath the head
Paired lateral fins
Sandpaper-like skin because of Placoid
Scales
Includes sharks, rays, skates, and ratfishes
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~350 living species
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Caudal Fin is Heterocercal
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Powerful jaws with rows of teeth that are
Continuously replaced
Upper lobe longer than lower lobe
Fusiform, or spindle-shaped bodies
Five to seven gill slits
Carnivores & Filter Feeders
Found most often in warm
coastal water
Most only live in marine env.
Some travel upstream
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~450-500 known species
Dorsoventrally flattened
Demersal: fish that live on the bottom
Five ventral gill slits
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Stingrays
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Electric Rays
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Whip-like tail with stinging spines
Electric organs on each side of head
Skates lack the stinging tail
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Ratfish: AKA Chimaeras
~30 known species
Only one pair of gill slits covered by a flap of skin
Long, rat-like tail
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www.itsallaboutfish.co.uk/ratfish.htm
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Class Osteichthyes
~23,000 known species
Skeleton made of bone
Cycloid or Ctenoid Scales
Operculum: Gill Cover
Upper & lower tail fin same size:
Homocercal
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Homocercal tail
Cycloid scales
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Fin Rays: thin membranes supported by
bony spine
Anterior, terminal mouth
More flexible jaws with teeth attached to
jawbone
Swim Bladder: gas-filled sac above stomach
& intestines that helps in buoyancy
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ICHTHYOLOGY- study of fish
Body shape varies with habitat and lifestyle
◦ Fast swimmers are streamlined- like tuna, marlins,
mackerels, sharks
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Dorsoventrally flat- skates, rays and sea
moths- demersal fish (live near bottom)
Dragon sea moth
Image from
Liveaquaria.com
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Laterally flattened
bottom dweller fish
such as flounder,
halibut and sole
Born with eyes on both
sides of body but as
they mature, one eye
migrates to the
dominant side
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Elongated bodies such as eels- live in narrow
places amongst rock and coral reef
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Laterally compressed bodies live around coral
reefs, kelp beds etc.
Butterfly fish
snappers
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CHROMATOPHORES-skin cells that contain
pigments; irregular in shape with branches
radiating out from the center of the cell
STRUCTURAL COLORS-Colors that result
when light is reflected by a particular surface
◦ Many times caused by IRIDOPHORESchromatophores with light-reflecting crystals
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Colors reflect mood
◦ warning coloration- coloration that allows
organisms to escape from predators by advertising
something harmful or distasteful video
◦ cryptic coloration-color pattern that allows an
organism to blend in its surroundings- video
◦ Disruptive coloration- a color pattern that helps
break the outline of an organism
Ornate cowfish
Disruptive coloration
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COUNTERSHADING- a color pattern that
results in a dark back and a light belly- most
common in epipelagic fishes (surface to 200
m)