BIOL 111 Lecture Notes - External Fertilization, Commensalism, Tube Feet

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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)
- First comes mouth
- Central nervous system ventral
- Anus is 1st opening
- Circulatory system has a dorsal heart
- Hard skeleton is external
- Coelom develops from schizocoely
(splitting within the mesoderm in
Major advancements in evolution:
- multicellularity
- tissues
- gut
- mesoderm
- head
- segmentation
- Second comes mouth
- Central nervous system is dorsal
- Anus forms 1st
- Circ sys has a ventral heart
- Hard skeleton is internal
- Ceolom develops from enterocoely:
(mesoderm forms pockets from gut in
Evolutionary Developments:
- nervous system
- anus
- circulatory system system
- hard skeleton
- ceolom
=points of differentiation btw
protostomes and deuterostomes
Embryonic development:
Radial cleavage: ancestral condition for animals
Spiral cleavage: seem in some lophotorochazoans (spirilians)
Eg. Echinoderms, hemichordates, chordates (urochordates, cephalochardates,
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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