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4. Phylogeny I Chordate Origins

4. Phylogeny I Chordate Origins. Protochordates. Vertebrae. All four chordate characteristics retained throughout lifetime. Notochord. Tadpole like larvae with post-anal tail. Dorsal Hollow Nerve Chord. Gill Slits . Chordate characters:. 1- gill slits in pharynx. pharynx. gill bars.

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4. Phylogeny I Chordate Origins

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  1. 4. Phylogeny I Chordate Origins

  2. Protochordates Vertebrae All four chordate characteristics retained throughout lifetime Notochord Tadpole like larvae with post-anal tail Dorsal Hollow Nerve Chord Gill Slits

  3. Chordate characters: 1- gill slits in pharynx pharynx gill bars gill basket or pharyngeal basket gill slits gill bars The pharynx is housed inside an atrium.

  4. 1- gill slits in pharynx Pharyngeal basket is primitively a feeding structure Used in filter feeding Water enters mouth Flows between gill bars Food catches on gill bars Water exits from pharynx via atriopore Food is moved dorsally and ventrally by cilia, then posteriorly to esophagus gill basket or pharyngeal basket gill slits atriopore gill bars

  5. 1- gill slits in pharynx Pharyngeal basket also used for filter feeding in adult tunicate Water and food enter incurrent siphon Water is expelled through excurrent siphon Food is trapped within pharynx and enters stomach

  6. Chordate characters: 2- dorsal hollow nerve chord Central part of nervous system A hollow tube made up of neurons Extends entire length of amphioxus and jawless fishes Always dorsal to notochord dorsal hollow nerve chord notochord

  7. notochord notochord

  8. Dorsal hollow nerve chord -notochord

  9. Chordate characters: 3- post-anal tail It works with muscles and notochord To aid in mobility Post- anal tail anus

  10. Chordate characters: 4- notochord Central part of axial skeleton A solid, stiff cartilage rod Extend entire length of amphioxus and jawless fishes Always ventral to dorsal hollow nerve chord dorsal hollow nerve chord notochord

  11. gill arches Myomeres (muscle segments) and Myosepta (the connective tissue between segments

  12. Classification of Deuterstomes Phylum Chaetognatha Phylum Echinodermata Phylum Hemichordata Phylum Chordata Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata

  13. Classification of Deuterstomes Phylum Chaetognatha Phylum Echinodermata Phylum Hemichordata THE PROTO- CHORDATES Phylum Chordata Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata

  14. Phylum Hemichordata Acorn worm Have half of chordate characters: Gill slits in pharynx Dorsal Hollow Nerve Chord

  15. Detail of collar region Phylum Hemichordata Gill slits in pharynx Live in marine sediments Dorsal Hollow Nerve Chord Process sediment like an earth worm

  16. Subphylum Urochordata “tail chordates” Larvae have notochord restricted to tail Also called Tunicates tunic For the tunic or jacket that covers the adult

  17. 1) gill slits in pharynx 2) dorsal hollow nerve chord Subphylum Urochordata 3) notochord Free-swimming larva showing four chordate characteristics 4) post-anal tail

  18. Two of four chordate characteristics lost in tunicates during metamorphosis

  19. 1500 species Subphylum Urochordata marine Solitary tunicates colonial tunicates

  20. But a variant (mutation) could have occured Reproduction normally does not occur in larvae That caused a timing change HETEROCHRONY Such that a larval form would be able to reproduce Reproduction occurs here What’s the evolutionary advantage?

  21. HETEROCHRONY “Different time” Changes in timing of events during embryology. These are a major contributor to evolution. Paedomorphosis “Child-like morphology” Child-like morphology in an otherwise adult organism Paedomorphosis can occur by two mechanisms: Neoteny “new retaining” Organisms hold on to morphologies that they had when they were new, but remaning systems become adult. Progenesis “early production” Organisms produce adult features in an otherwise larval form.

  22. Subphylum Cephalochordata -named for extension of notochord into the anterior (head) end -NOT because it has a head -cephalization is weakly developed -no brain, -no skull -minimal sense organs This group retains chordate characters throughout lifetime.

  23. Subphylum Cephalochordata Dorsal hollow nerve chord Post anal tail notochord myomeres gonad Midgut caecum atriopore intestine anus Pharynx with gill bars and gill slits

  24. Phylum Chordata a monophyletic group Vertebrae All four chordate characteristics retained throughout lifetime Notochord Tadpole like larvae with post-anal tail Dorsal Hollow Nerve Chord Gill Slits

  25. Subphylum Vertebrata Larvae of the most primitive vertebrates, the Agnatha or jawless fishes, do not differ in basic body plan from Amphioxus or tunicate larvae. This is the “ammocoetes” larva of the lamprey

  26. Subphylum Vertebrata -otic vesicle hearing Agnathan Larva -eye sight The most significant differences are: -median nostril smell 1) anterior swelling of DHNC 2) development of sense organs

  27. Subphylum Vertebrata Adult Agnathan (Lamprey) -has an obvious head -with additional sense organs a pineal organ senses light a lateral line system senses pressure and/or movement Significant development of the head (Cephalization) suggests alternate to the name Vertebrata: Craniata

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