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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 • 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
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