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What is Meant by ‘Chordate’?
- Chordate does not = vertebrate
- Chordate includes vertebrates and groups with similar evolutionary development
- All chordates share several structural features
- Chordates do not necessarily have a backbone or bony skeleton!
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Features
of Chordates
- All chordates have four distinct
- structures
- Notochord a stiff flexible rod extending the length of the body
- dorsal, hollow nerve cord lies above the digestive tract and expands to form the brain
- Pharyngeal gill slits may form respiratory organs or may appear as grooves
- post-anal tail which extends past the anus
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Humans
as Chordates
- Humans are members of Chordate clade
- In humans, the chordate features are best seen during embryonic development later, we lose our notochord, gill slits, and tails
- Only the dorsal nerve cord is retained in post embryonic human development
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Lancelets
- Marine filter-feeders
- Small, fishlike, invertebrate chordates
- Retain all the four chordate features as adults
- Live half-buried in the sand
- Food particles are drawn into the mouth by pharyngeal cilia and are then transported to the digestive tract
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Tunicates:
Urochordates
- Tunicates include sea squirts and salps
- Marine
- Larvae are motile and exhibit all
- key chordate features
- Adult sea squirts are sessile filter-feeders that have lost their tail and notochord
- Salps are not sessile
- Live in the open ocean
- Can be colonial
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Craniates
- Craniates have a skull or braincase that encloses a brain
- Includes hagfish (jawless fishes)
- Includes vertebrates the embryonic notochord is replaced
- during development by a backbone, or
vertebral- column
, composed of bone or cartilage
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Hagfish
- Lack jaws exclusively marine, and live near the ocean floor
- They feed primarily on worms
- They secrete massive quantities of slime as a defense against predators
- Ectotherms
- Lack a true vertebral column
- Cartilage braincase (no bony skull)
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Vertebrates
- Lampreys
- Cartilaginous fishes (sharks, rays)
- Ray-finned fishes
- Coelacanths
- Lungfishes
- Amphibians
- Reptiles
- Mammals
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Characteristics
of Vertebrates
- Internal skeleton grow and repair itself
- allowed for greater size and mobility, enabling vertebrates to occupy most habitats
- Jaws allow vertebrates to exploit a much wider range of food sources
- Paired appendages (fins, legs, wings) helped to stabilize movement
- Complexity of the brain and sensory ability
- Permits better perception of environment
- Rapid response to stimuli
- I <3 PB + J
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Vertebrate
Development
- Patterns of embryonic development are very similar for all vertebrates
- All vertebrates are deuterostomes
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Vertebrates:
Lampreys
- Some lampreys parasitize fish
- Like hagfishes, lampreys are jawless
- Have a large rounded sucker that surrounds the mouth
- Spinal cord is protected b y cartilaginous segments
- They live in both fresh and salt waters
- Marine forms must return to fresh water to spawn
- Invasive in Great Lakes
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Vertebrates:
Cartilaginous Fishes
- Chondrichthyes includes sharks, skates, and rays
- Most are marine
- Possess jaws and a cartilaginous skeleton
- Body protected by a leathery skin embedded with tiny scales
- They respire using gills
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Cartilaginous
Fishes
- Internal fertilization- male deposits sperm directly into a female’s reproductive tract (unlike other fish)
- They tend to sink when they stop swimming because they lack a swim bladder
- Many are filter feeders, most predators
- Specialized sensory organs
- Can be benthic (seafloor living) or pelagic (open
- ocean)
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Vertebrates:
Ray-finned Fishes
- Diverse clade
- Freshwater and marine
- Bony skeletons
- Interlocking scales on skin
- Gills
- Swim bladder
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Vertebrates:
Lobe-finned fishes
- Lungfish and coelacanths
- Share common ancestor with tetrapods (Tiktaalik)
- Lungfish have lungs and gills
- Freshwater, can survive low oxygen
- and without water!
- Coelacanths
- Thought to be extinct until 1938
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