Evolutionary Trends

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Evolutionary Trends

• 1. Trends in Symmetry
• 2. Trends in Digestive Tracts
• 3. Trends in Body Cavities
• 4. Trends in Cephalization
• 5. Trends in Segmentation

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Symmetry

• Asymmetry ( No Symmetry )
• Radial Symmetry
• Bilateral Symmetry

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Asymmetrical Sponge
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Radial Symmetry
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Bilateral Symmetry
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Digestive System

• Incomplete
• Complete

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Incomplete
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Complete Digestive System
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Body Cavity

• Acoelom (No Coelom )
• Pseudocoelom (False Body Cavity)
• Coelom (True Coelom)

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Acoelomate (no body cavity)
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Acoelom
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Pseudocoelom

• false
  body cavity
• this
  body cavity is
• located
  between the
• mesoderm
  and
• endoderm

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Coelom

• true
  body cavity
• This
  body cavity is
• located
  within the
• mesoderm

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Protostomes and Deuterostomes

• Protostomes or First Mouth Animals
• During their embryonic development the mouth
  forms first and the anus second.
• Deuterostomes Second Mouth Animals
• During their embryonic development the anus
  forms first and the mouth second.

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Blastula
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Early Gastrulation
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Late Gastrulation
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Is this larva a protostome or deuterostome?
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Larva
Deuterostome
Protostome
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Sponges (Porifera)
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Cnidaria
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The Two Basic Body Forms
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Life Cycle of Obelia
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Flatworms (Platyhelminthes)

• Fluke

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Tapeworms
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Nematoda

• Roundworms are round in cross section rather than
  flat.
• The most abundant animals on earth.
• Biologist A.M.Cobb once said that if all our
  planets land and seas were swept away, but with
  the nematodes somehow stayed in place, a clear
  outline of the earth and its geological features
  would remain.

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Nematoda
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The Advantages of a Coelom or a Pseudocoelom

• The reproductive and digestive organs can evolve
  more complex shapes and functions.
• The gut tube and other organs are cushioned and
  thus better protected.
• Can act as hydroskeleton providing support and
  rigidity for the soft animal.
• The activities of the suspended gut can take
  place undisturbed by the activity of the animals
  outer body wall.

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Molluscan Body Plan