Overview of Animal Diversity

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Overview of Animal Diversity

• Chapter 31

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General Features of Animals

• Heterotrophs
• Multicellular
• Able to move from place to place
• Diverse in form and habitat
• Sexual reproduction
• Characteristic embryonic development

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Diverse Kingdom

• Traditional classification of animals
• multicellular animals, metazoans, traditionally
  divided into 35 distinct phyla
• First branch - tissues
• Parazoa lack definite symmetry and do not possess
  tissues or organs.
• Eumetazoa have definite shape and symmetry and
  usually have organs and organ systems.

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Traditional Classification of Animals

• Second branch - symmetry
• Eumetazoan branch has two principles branches.
• Radiata - radial symmetry
• Bilateria - bilateral symmetry
• Further branches were assigned by comparing key
  shared features of the body plan.
• body cavity
• coelom

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Broad Groupings of Kingdom Animalia
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Key Transitions in Body Plan

• Evolution of tissues
• first key transition in animal body plan
• Evolution of bilateral symmetry
• radial symmetry - regular arrangement of parts
  around central axis
• bilateral symmetry - right and left halves form
  mirror images
• dorsal vs. ventral
• anterior vs. posterior

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Radial and Bilateral Symmetry
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Bilateral Symmetry

• Bilaterally symmetrical eumetazoans produce three
  germ layers.
• ectoderm
• endoderm
• mesoderm
• Much of the nervous system is in the form of
  major longitudinal nerve cords.
• ultimately led to evolution of definite head
• cephalization

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Three Body Plans
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Key Transitions in Body Plan

• Evolution of a body cavity
• Presence of a body cavity allows digestive tract
  to be larger and longer.
• storage of undigested food
• more complete digestion
• more space for gonads to expand

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Key Transitions in Body Plan

• Kinds of body cavities
• acoelomates - no body cavity
• pseudocoelomates - possess pseudocoel
• coelomates - possess coelom

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Coelomates

• Coelom poses circulation problem
• solved by circulatory system
• open circulatory system
• Blood passes from vessels into sinuses, mixes
  with body fluid, and reenters vessels in another
  location.
• closed circulatory system
• Blood is physically separated from other body
  fluids and can be separately controlled.

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Key Transitions in Body Plan

• Advantages of a coelom
• Allows contact between mesoderm and endoderm, so
  that primary induction can occur during
  development.

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Key Transitions in Body Plan

• Evolution of deuterostome development
• mitotic egg division leads to blastula
• indents to form blastopore, opening to the
  archenteron
• Bilaterians can be divided into protostomes
  (mouth-first) and deuterstomes (mouth-second).

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Protostome and Deuterostome Differences

• Cleavage
• spiral
• radial
• Fate of embryonic cells
• determinate - predetermined fate
• indeterminate - identical daughter cells
• Fate of blastopore
• mouth or anus develops near blastopore
• Formation of coelom

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Embryonic Development
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Key Transitions in Body Plan

• Evolution of segmentation
• advantages
• Each segment may go on to develop a more or less
  complete set of adult organs.
• Locomotion is far more effective when individual
  segments can move independently due to
  flexibility of movement.

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Animal Classification is Being Reevaluated

• New look at metazoan family tree
• New taxonomical comparisons using molecular data
  have come to new, different conclusions.
• hint that key morphological characters used in
  traditional classification are not necessarily
  conservative
• Molecular systematics uses unique sequences
  within certain genes to identify clusters of
  related groups.

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Roots of the Animal Family Tree

• Origins of metazoans
• Most taxonomists agree the animal kingdom is
  monophyletic.
• Three prominent hypotheses exist for origin from
  single-celled protists.
• multinucleate hypothesis
• colonial flagellate hypothesis
• polyphyletic origin hypothesis
• debate over cause of Cambrian explosion