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Echinoderms and Chordates

3 Pages

Biology (Sci)
Course Code
BIOL 111
Irene Gregory- Eaves

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27/10/10 Echinoderms & Chordates Protostomes vs Deuterostomes: (stome = mouth) Two major evolutionary lineages in Bilateria - splits at Cambrian (~500mya) Differences in embryonic development – though both bilaterally symmetrical (started with flat worms) Protostomes Deuterostomes - First comes mouth - Second comes mouth - Central nervous system ventral - Central nervous system is dorsal - Anus is 1 opening - Anus forms 1st - Circulatory system has a dorsal heart - Circ sys has a ventral heart - Hard skeleton is external - Hard skeleton is internal - Coelom develops from schizocoely - Ceolom develops from enterocoely: (splitting within the mesoderm in (mesoderm forms pockets from gut in protostomes) deuterostomes) Major advancements in evolution: Evolutionary Developments: - multicellularity - nervous system - tissues - anus - gut - circulatory system system - mesoderm - hard skeleton - head - ceolom - segmentation =points of differentiation btw protostomes and deuterostomes Embryonic development: Radial cleavage: ancestral condition for animals Spiral cleavage: seem in some lophotorochazoans (spirilians) Deuterostomes: Eg. Echinoderms, hemichordates, chordates (urochordates, cephalochardates, vertebrates) Echinoderms: spiny skin ~ 7000 extant species - strictly marine - benthic (bottom dwellers) - diverse modes of nutrition ex. Sea stars, sea urchins, sand dollars - Hard endoskeleton: composed of CaCO3 plates - Continuous growth: plates enlarge and new ones are added - Covered by thin layers of skin and muscle - Pentaradian symmetry: 5 part symmetry in adults
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