Echinoderms early chordates
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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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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

Deuterostome – blastopore becomes anus

Embryological development

gastrulation in sea urchin


Echinoderm “pluteus” larvae

brittle star

sea cucumber

sea lily

sea urchin

sea star


Echinoderm diversity

(also sea cucumbers)


Echinoderm characteristics

  • adults have secondary radial symmetry

  • spiny “skin” (calcium plates below skin)

  • water vascular system

    • movement

    • circulation

  • complete gut

  • entirely marine

    • only phylum


Lower Chordates

  • Phylum Chordata includes us

  • Several subphyla are invertebrate (i.e. lack a skeleton)

    • Urochordates

    • Cephalochordates


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


Nervous system development


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


Cephalochordates

  • “head chordates”

    • notochord extends into head

  • lancelets

  • adults have chordate characters

  • filter feeders


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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