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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
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


Embryological development

Protostome – blastopore becomes mouth

Deuterostome – blastopore becomes anus

Embryological development

gastrulation in sea urchin


Echinoderm pluteus larvae
Echinoderm “pluteus” larvae

brittle star

sea cucumber

sea lily

sea urchin

sea star


Echinoderm diversity
Echinoderm diversity

(also sea cucumbers)


Echinoderm characteristics
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
Lower Chordates

  • Phylum Chordata includes us

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

    • Urochordates

    • Cephalochordates


Chordate characteristics
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



Urochordates
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
Cephalochordates

  • “head chordates”

    • notochord extends into head

  • lancelets

  • adults have chordate characters

  • filter feeders


Burgess shale fauna
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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