Phylum Chordata, subphylum Vertebrata
• Share the 4 chordate
characters with lancelets
and sea squirts
• Backbone, vertebral
column, spine
– Series of hollow vertebrae
– Protects nerve cord
(spinal cord)
• Bilateral symmetry
• endoskeleton
Agnatha (jawless fishes)
• Lack: paired fins, scales,
& well developed
vertebrae
• Hagfish (slime eels)
– Mucus for protection
– Feed on decaying flesh
• Lampreys
– Parasitic
– Anadromous
• Marine adults, breed in
freshwater
Chondrichthyes (cartilagenous fishes)
• Sharks, rays, skates,
& ratfishes
• Movable jaws of
ventral mouth
• Paired fins
• Placoid scales
– Dentricles (same
composition as teeth)
Sharks
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Heterocercal caudal fin
Two dorsal fins
Paired pectorals
5-7 gill slits
Many rows of teeth
Oily liver
Diverse examples:
hammerhead, sawfish,
thresher, whale sharks
Rays, Skates, & Ratfishes
• Flattened
• Demersal
• 5 prd ventral gill slits
• Expanded pectorals
Rays vs. skates
rays: reduced or no dorsal fin
– Stingrays
• Venomous defensive spine
– Electric rays
• Upto 200 volts for defense
and predation
– Ratfishes (chimaeras)
• Deep, bottoms, long skinny
tail
• Paired (pelvic) & unpaired
(forehead) male claspers for
copulation & holding female
--seen in rabbitfish
Osteichthyes (bony fishes)
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Swim bladder
Operculum (gill cover)
Homocercal tail
Scales of bony origin
– Smooth cycloid
– Spiny ctenoid
• Diverse morphologies,
habits, & behaviors
•
Tear flesh; most swallow whole
by: snout; protrusible; beak-like;
large filtering mouths
•
Undulating entire body; muscular
caudal flex; fins only; caudal fin
only
Digestive systems
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Mouth
Esophagus
Stomach
Intestine w/ increased SA
– spiral valve
– pyloric caeca
• Pancreas
– Digestive enzymes
• Liver
– Bile to breakdown fats
• cloaca or anus
Circulatory system: 2 chambered heart (“one way
flow”) …atrial chamber to gills, “fresh” blood to
tissues, back to ventricle chamber
a.) Water across gills through mouth and
spiracles in cartilagenous fishes
– Why are spiracles significant?
b.) Opercula of bony fishes opens and
closes with mouth; greater suction; more
efficient
Gill function and diffusion of gas
• High surface area
from many folds or
lamellae of gill
filaments
• The water : blood
relationship is in a
counter-current
orientation -enhances diffusion
– higher [Oxygen] in
water than blood
Osmosis
a.) concentrated urea
prevents dehydration
to deal with excess
salts; excrete via
rectal gland
b.) to compensate for
tissue water loss:
drink sea water,
conserved by
kidneys, excrete urine
Fish reproduction & development
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Internal fertilization
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w/specialized copulatory structures
External fertilization
–
Broadcast spawning
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Some fishes deposit eggs on bottoms
Some bury in sandy shores
Unique examples:
–
Male carriers
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Eggs released, fertilized, developed
externally, lots of yolk
Viviparous
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e.g. At Birch aquarium
Oviparous
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•
Millions of eggs released as part of
plankton
Internal development, direct
nourishment; birth live young
Ovoviviparous
–
Internal egg development; yolk; birth
live young