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Phylum Chordata
FISH!
SP Vertebrata
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
SP Vertebrata: the amniotic egg
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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)
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Fish Diversity - 1 -
28-32,000 species: more than any other group of vertebrates
39% Freshwater species
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)
Class Agnatha – the jawless fish
•   Evolved during the
Cambrian ~530 MYA
•   Many, including ostracoderms
(armoured plates), became extinct during the devonian - about
370 MYA
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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 ʼ t osmoregulate
•   Lampreys have a larval stage
•   Neither has a stomach!
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
Lampreys
They can tie themselves in knots!
About 40 species
Osmoregulate - found in freshwater and ocean - parasitic
Larval stage called ammocoete
Ammocoetes undergo metamorphosis
Ammocoetes are filter feeds
Keratinized ‘teeth’
Lampreys
Hematophagus feeders as adults – suck blood and fluids – anticoagulant in their saliva
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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
Figure 34.8 The evolution of vertebrate jaws
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Cl. Chondrichthyes: sharks, rays and chimeras
•   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
Buoyancy: oils and fats – often concentrated in the liver
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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 - ʻ live birth ʼ from eggs
Vivipary - placental - live birth
Ovipary - lay eggs
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
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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
•   swim bladder in many
•   Mucus to reduce drag and protect
•   Diversity of form and size!
Dorsal Fin
1 or 2
External anatomy of a fish
Caudal Fin
Gill cover:
Operculum
Anal Fin
Pectoral Fin
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
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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
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Filter feeders
Filter feeders
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Biters: pursuit
Feeding
Suction Feeding
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Protrusible jaw
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Pickers Ambush!
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Grazers – key to many healthy ecosystems!
Color: disruptive, camoflauge, advertise, countershading
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Surfperch
Reproduction – live bearing viviparous
Live birth from eggs inside the female – ovovivipary
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Brooding – nesting
‘on the body’
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Seahorses and pipefish are brooders
Usually in this group it’s the males…
Fish respire with a complex arrangement of gills to increase surface area, along with counter current blood flow
Respiration
Aerial respiration
Broadcasting – sending eggs and sperm into the water column
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Buoyancy
Oils
Air/gas
Hydrofoil lift
Sensory:
•   Sight
•   Pressure (lateral line)
•   Electromagnetic fields (ampulae of lorenzini)
•   Chemosensory –
‘smell’
•   Otolith – ear bones - balance schooling
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
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Figure 34.13 The Devonian radiation of fishes
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•   Fleshy fins
•   Primitive lungs
•   Aestivate
Lungfish Coelocanth: Latimeria
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Figure 34.14 The origin of tetrapods Figure 34.21x Turtle
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