9_Vertebrates - The Evolution of Vertebrates Home Page...

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1 The Evolution of Vertebrates © 2006: D. Julian Home Page Clades of extant deuterostomes Figure 34.1 © 2006: D. Julian Chordate characteristics All chordates possess four trademarks: 1. Notochord (future “backbone”) 2. Dorsal, hollow nerve cord 3. Pharyngeal slits 4. Postanal tail © 2006: D. Julian
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2 Urochordates Figure 34.1 © 2006: D. Julian Urochordates © 2006: D. Julian Urochordates Adult tunicates are sessile, but juveniles are free-swimming and nonfeeding, and their chordate characteristics are more evident. The notochord and dorsal hollow nerve cord are lost in adults. © 2006: D. Julian Adult Juvenile
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3 Cephalochordates Figure 34.1 © 2006: D. Julian Cephalochordates Campbel Lancelets (e.g., amphioxus) have all four chordate characteristics, but lack a cranium. © 2006: D. Julian Identical developmental genes Many genes that control development of the central nervous system in lancelets are conserved in vertebrates (including humans). © 2006: D. Julian
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4 Craniates Figure 34.1 Cranium (skull) Elaboration of brain Paired sensory organs on head Neural crest cells during development © 2006: D. Julian Neural crest cells in craniates Fig: 34.7 © 2006: D. Julian Myxini (hagfishes) Figure 34.1 © 2006: D. Julian Most primitive extant craniates. Hagfish lack bones, true teeth, paired fins, or even vertebrae . They look like eels, but true eels are bony fish.
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5 Hagfishes Hagfishes make lots of “slime” and have faces that only their mothers could love © 2006: D. Julian The Vertebrates • True tissues • Bilateral symmetry • Deuterostome • Notochord • Cranium • Vertebrae Campbel Fig. 34.7 Lampreys
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9_Vertebrates - The Evolution of Vertebrates Home Page...

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