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10/22/13
Phylum Chordata
FISH!
SP Vertebrata
SP Vertebrata: the amniotic egg
Largest subphylum: ~42000 species in 7 classes.
Larger size and activity led to more highly developed
nervous system and other characteristics.
Major characteristics:
• Notochord is replaced with vertebrae
• All have a cartilaginous or bony skeleton
(endoskeleton)
• High degree of cephalization
• Brain is protected by a cranium
• Well developed 2-4 chambered heart
• Closed circulatory system
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Figure 34.6 One hypothesis for the evolutionary relationships among the chordates
The age of Fishes: Devonian period
420-360 Million Years Ago (MYA)
Fish Diversity - 1 -
28-32,000 species: more than any other
group of vertebrates Freshwater species 39%
Temperature range -2 to +44
Fish Diversity - 2 -
Number of families 445
Seven largest families
Represent 30% of all species
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4 classes, 1 of which is extinct:
•  Agnatha (jawless) ~60 species
•  Placoderms (extinct)
•  Chondrichthyes (sharks, rays and
chimeras)
•  Osteichthyes (bony fish)
Cl. Agnatha: jawless vertebrates
• About 55 species extant today: hagfish and
lampreys. Have a cartilaginous skeleton, no
paired fins, 2 chambered heart • Hagfish are the only marine vertebrates that
don t osmoregulate
• Lampreys have a larval stage
• Neither has a stomach!
Class Agnatha – the jawless fish
• Evolved during the
Cambrian ~530 MYA
• Many, including
ostracoderms
(armoured plates),
became extinct during
the devonian - about
370 MYA
Hagfishes - Mixini
30-35 species
Live deep – scavengers
No real stomach
Slime!
No scales
Young develop directly from
eggs
Only marine - isoosmotic - no
osmoregulation
They have a skull but no
vertebral column (but a
notochord)
http://www.youtube.com/watch?v=pmaal7Hf0WA
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Hagfish eat
rotting and
decaying
animals in the
deep sea
They can tie
themselves in
knots!
Lampreys About 40 species
Osmoregulate - found in freshwater and ocean - parasitic
Larval stage called ammocoete
Ammocoetes undergo metamorphosis Ammocoetes are filter feeds
Lampreys
Hematophagus feeders as
adults – suck blood and
fluids – anticoagulant in
their saliva
Keratinized ‘teeth’
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Figure 34.8 The evolution of vertebrate jaws
Cl. Placoderma: armored fishes
Evolved during the Silurian: ~440 MYA
Extinct. 410-350 MYA
Major innovations: diversification of lifestyle and
nutrients:
• Hinged jaws – allowed active predation. • Paired fins – enhanced swimming ability
Cl. Chondrichthyes: sharks, rays
and chimeras
Buoyancy: oils and fats – often
concentrated in the liver
• Appeared about 400 MYA
• 12 orders, 45 families, 800 species,
half are rays, ~ 350 sp sharks
• They have paired fins and biting
jaws.
• Cartilaginous skeletons: means they
have to be big and most are.
•Many use fat (not air) for buoyancy
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Cl. Chondrichthyes: sharks, rays
and chimeras
Other adaptations:
• Body shapes-stiff fins
• Ventilation of gills
• Feeding
• Sensory systems - lateral line and ampulae of
lorenzini
• Osmoregulation - salty! urea
• Reproduction
Ovovivipary - live birth from eggs
Vivipary - placental - live birth
Ovipary - lay eggs Cl. Osteichthyes: bony fishes
• 19 orders, 206 families (25,000 species)
• gill cover = operculum
• fin rays – bony spines that are connected
by a membrane = flexible, for swimming
• teeth fused to jawbone
Cl. Osteichthyes: bony fishes
• Bony fish and Cartilaginous fish
probably both arose from the
placoderms – but took very
different trajectories. Osteichthyes arose about 415
MYA:
Lobe-finned fishes (lungfish and
ceolocanths) – these gave rise to
the tetrapods (amphibians etc…)
Ray-finned fishes
External anatomy of a fish
Caudal Fin
Dorsal Fin
1 or 2
Gill cover:
Operculum
• swim bladder in many
Anal Fin
Pectoral Fin
• Mucus to reduce drag and protect
• Diversity of form and size!
Pelvic Fin
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Modified fins
Dorsal fin
Pelvic fins
Pelvic fin
Modified fins
Anal fin
Modified fins
Caudal fin
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Other modifications
Fish body form
Fish body form
Laterally compressed
Dorso-ventrally compressed
‘other’
Fish body form
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Laterally compressed
Dorso-ventrally compressed (rays)
Laterally compressed!
Fusiform: speedy
Shapes
Eel-shaped
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Odd shapes
Feeding: suck, pick, bite, slurp, filter feed, grind,
graze. No chewing…wrong teeth
•  Generalists
•  Specialists
Filter feeders
Filter feeders
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Biters: pursuit
Feeding
Suction Feeding
Protrusible jaw
slurpers
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Pickers
Grazers – key to many healthy
ecosystems!
Ambush!
Color: disruptive, camoflauge, advertise,
countershading
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Surfperch
Reproduction – live bearing
viviparous
nests
Live birth from eggs inside the
female – ovovivipary
Brooding – nesting
‘on the body’
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Seahorses and pipefish are brooders
Broadcasting –
sending eggs and
sperm into the water
column
Usually in this group it’s the males…
Respiration
Aerial respiration
Fish respire with a
complex arrangement
of gills to increase
surface area, along
with counter current
blood flow
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Sensory:
•  Sight
•  Pressure (lateral
line)
schooling
•  Electromagnetic
fields (ampulae
of lorenzini)
•  Chemosensory –
‘smell’
•  Otolith – ear
bones - balance
Buoyancy
Oils
Air/gas
Hydrofoil lift
Symbiosis:
mutualism – both benefit
parasitism – only one benefits and one is
compromised
Commensalism – one benefits and the
other is neutral
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Cleaning stations
Thermal regulation
Figure 34.13 The Devonian radiation of fishes
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Lungfish
Coelocanth: Latimeria
• Fleshy fins
• Primitive lungs
• Aestivate
Figure 34.14 The origin of tetrapods
Figure 34.21x Turtle
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