Chapter 23

Chapter 23 - Chapter 23: Animal Diversity II, Vertebrates...

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Chapter 23: Animal Diversity II, Vertebrates
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Vertebrate animal evolutionary tree Primitive ancestral vertebrate
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Key Features of Chordates All chordates possess four features at some stage of their lives… 1. Notochord (stiff flexible rod extending in the length of the body) 2. Dorsal, hollow nerve chord (expands anteriorly to form brain) 3. Pharyngeal gill slits (may form respiratory organs or may appear as grooves 4. Post-anal tail (extends past the anus)
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Are Humans Chordates? Only one chordate characteristics, the nerve cord, is present in adult humans; however, human embryos exhibit all four. Tail will disappear completely. Notochord is replaced by the backbone. Gill slits (grooves) contribute the formation of the lower jaw. As an example, observe a 5-week-old human embryo picture…
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eye heart liver tail limb bud (future leg) limb bud (future arm) gill slit
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Invertebrate Chordates Lack a backbone Include lancelets and the tunicates Lancelets are fishlike filter-feeders Adults and larvae exhibit all key chordate features (4) Tunicates (sea squirts) Larvae are mobile and exhibit all key chordate features Adults are sessile filter-feeders that have lost their tail and notochord.
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Lancelet mouth gill slits notochord gut tail anus (b) mouth gill slits gut larva anus notochord tail water enters (mouth) water exits gill slits gut adult 0 Tunicate
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Vertebrate Chordates Have a backbone ( vertebral column ) composed of bone or cartilage (resembles bone, but is more flexible) Provides attachment sites for muscles. Provides attachment sites for muscles Protects nerve cord and brain.
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Vertebrate Adaptations Several adaptations have allowed vertebrates to successfully invade most habitats. Endoskeleton that can grow and repair itself Paired appendages (fins, legs, wings) Increased size and complexity of the brain and sensory structures.
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Major Vertebrate Groups Earliest vertebrate fossils were found in 530-million-year-old-rocks Resembled lancelets with a brain, skull, and eyes. Present day vertebrates include jawless fishes, cartilaginous fishes, bony fishes, amphibians, reptiles, birds, and mammals.
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Jawless Fishes Jawless Have eel-shaped bodies and smooth scale-less skin Include hagfishes and lampreys
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Hagfishes Exclusively marine (live near ocean floor). Feed primarily on worms
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Chapter 23 - Chapter 23: Animal Diversity II, Vertebrates...

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