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Echinoderms & Early Chordates

Echinoderms & Early Chordates. Second major branch of animal evolution Present in Cambrian period Crinoids (sea lilies) dominant at end of Paleozoic Deuterostomes During development, mouth develops second Coelomate. Protostome – blastopore becomes mouth

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Echinoderms & Early Chordates

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  1. Echinoderms &Early Chordates • Second major branch of animal evolution • Present in Cambrian period • Crinoids (sea lilies) dominant at end of Paleozoic • Deuterostomes • During development, mouth develops second • Coelomate

  2. Protostome – blastopore becomes mouth Deuterostome – blastopore becomes anus Embryological development gastrulation in sea urchin

  3. Echinoderm “pluteus” larvae brittle star sea cucumber sea lily sea urchin sea star

  4. Echinoderm diversity (also sea cucumbers)

  5. Echinoderm characteristics • adults have secondary radial symmetry • spiny “skin” (calcium plates below skin) • water vascular system • movement • circulation • complete gut • entirely marine • only phylum

  6. Lower Chordates • Phylum Chordata includes us • Several subphyla are invertebrate (i.e. lack a skeleton) • Urochordates • Cephalochordates

  7. Chordate characteristics • notochord – at least in embryo • dorsal, hollow nerve cord • pharynx (feeding “basket”) - at least in embryo • segmented musculature • post-anal tail - at least in embryo

  8. Nervous system development

  9. Urochordates • “tail chordates” • notochord only in tail • sea squirts • larval stage has chordate characteristics • adult loses them and becomes a sessil, filter feeder adult larva

  10. Cephalochordates • “head chordates” • notochord extends into head • lancelets • adults have chordate characters • filter feeders

  11. Burgess Shale fauna • Pikaia gracilens • earliest known primitive chordate • about 40 mm in length and swam above the sea-floor • only 60 specimens have been found to date. 1 cm Pikaia animation

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