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 gastrulation in sea urchin

Echinoderm “pluteus” larvae sea lily sea starsea urchin brittle starsea cucumber

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