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Overview of Animal Diversity

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Title: Overview of Animal Diversity


1
Overview of Animal Diversity
  • Chapter 32

2
General Features of Animals
  • Animals are the consumers of the Earth
  • They are a very diverse group
  • However, they share major characteristics
  • Are heterotrophs
  • Are multicellular
  • Have cells without cell walls
  • Most are able to move

3
General Features of Animals
  • Are very diverse in form and habitat
  • Most reproduce sexually
  • Have a characteristic pattern of embryonic
    development
  • Cells of all animals (except sponges) are
    organized into tissues

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6
Evolution of the Animal Body Plan
  • Five key transitions can be noted in animal
    evolution
  • 1. Tissues
  • 2. Symmetry
  • 3. Body cavity
  • 4. Development
  • 5. Segmentation

7
Evolution of the Animal Body Plan
  • Evolution of tissues
  • Parazoa (Sponges - the simplest animals) lack
    defined tissues and organs
  • Have the ability to disaggregate and aggregate
    their cells
  • Eumetazoa (all other animals) have distinct and
    well-defined tissues
  • Have irreversible differentiation for most cell
    types

8
Evolution of the Animal Body Plan
  • 2. Evolution of symmetry
  • Sponges also lack any definite symmetry
  • Eumetazoa have a symmetry defined along an
    imaginary axis drawn through the animals body
  • There are two main types of symmetry

9
Evolution of the Animal Body Plan
  • Radial symmetry
  • Body parts arranged around central axis
  • Can be bisected into two equal halves in any 2-D
    plane
  • Bilateral symmetry
  • Body has right and left halves that are mirror
    images
  • Only the sagittal plane bisects the animal into
    two equal halves

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11
Evolution of the Animal Body Plan
  • Bilaterally symmetrical animals have two main
    advantages over radially symmetrical ones
  • 1. Cephalization
  • -Evolution of a definite brain area
  • 2. Greater mobility

12
Evolution of the Animal Body Plan
  • 3. Evolution of a body cavity
  • Eumetazoa produce three germ layers
  • Outer ectoderm (body coverings and nervous
    system)
  • Middle mesoderm (skeleton and muscles)
  • Inner endoderm (digestive organs and intestines)
  • Body cavity Space surrounded by mesoderm tissue
    that is formed during development

13
Evolution of the Animal Body Plan
  • 3. Evolution of a body cavity
  • Three basic kinds of body plans
  • Acoelomates No body cavity
  • Pseudocoelomates Body cavity between mesoderm
    and endoderm
  • Called the pseudocoel
  • Coelomates Body cavity entirely within the
    mesoderm
  • Called the coelom

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Evolution of the Animal Body Plan
  • The body cavity made possible the development of
    advanced organs systems
  • Coelomates developed a circulatory system to flow
    nutrients and remove wastes
  • Open circulatory system blood passes from
    vessels into sinuses, mixes with body fluids and
    reenters the vessels
  • Closed circulatory system blood moves
    continuously through vessels that are separated
    from body fluids

16
Evolution of the Animal Body Plan
  • 4. Evolution of different patterns of development
  • The basic Bilaterian pattern of development
  • Mitotic cell divisions of the egg form a hollow
    ball of cells, called the blastula
  • Blastula indents to form a two-layer-thick ball
    with
  • Blastopore Opening to outside
  • Archenteron Primitive body cavity

17
Evolution of the Animal Body Plan
  • Bilaterians can be divided into two groups
  • Protostomes develop the mouth first from or near
    the blastopore
  • Anus (if present) develops either from
    blastopore or another region of embryo
  • Deuterostomes develop the anus first from the
    blastopore
  • Mouth develops later from another region of the
    embryo

18
Evolution of the Animal Body Plan
  • Deuterostomes differ from protostomes in three
    other fundamental embryological features
  • 1. Cleaveage pattern of embryonic cells
  • Protostomes Spiral cleavage
  • Deuterostomes Radial cleavage
  • 2. Developmental fate of cells
  • Protostomes Determinate development
  • Deuterostomes Indeterminate development

19
Evolution of the Animal Body Plan
  • -3. Origination of coelom
  • Protostomes Forms simply and directly from the
    mesoderm
  • Deuterostomes Forms indirectly from the
    archenteron
  • Deuterostomes evolved from protostomes more than
    500 MYA

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21
Evolution of the Animal Body Plan
  • 5. Evolution of segmentation
  • Segmentation provides two advantages
  • 1. Allows redundant organ systems in adults such
    as occurs in the annelids
  • 2. Allows for more efficient and flexible
    movement because each segment can move
    independently
  • Segmentation appeared several times in the
    evolution of animals

22
Traditional Classification of Animals
  • Multicellular animals, or metazoans, are
    traditionally divided into 36 or so distinct
    phyla based on shared anatomy and embryology
  • Metazoans are divided into two main branches
  • Parazoa Lack symmetry and tissues
  • Eumetazoa Have symmetry and tissues
  • Diploblastic Have two germ layers
  • Triploblastic Have three germ layers

23
A New Look At Metazoans
  • The traditional animal phylogeny is being
    reevaluated using molecular data
  • Myzostomids are marine animals that are parasites
    of echinoderms
  • Have no body cavity and only incomplete
    segmentation
  • And so have been allied with annelids

24
A New Look At Metazoans
  • Recent analysis of the translation machinery
    revealed that myzostomids have no close link to
    the annelids at all

-Instead, they are more closely allied with the
flatworms (planaria and tapeworms)
25
A New Look At Metazoans
  • Therefore, 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

26
A New Look At Metazoans
  • Most new phylogenies agree on two revolutionary
    features
  • 1. Separation of annelids and arthropods into
    different clades
  • 2. Division of the protostome group into
    Ecdysozoa and Spiralia
  • The latter is then broken down into
    Lophotrochozoa and Platyzoa

27
A New Look At Metazoans
28
Evolutionary Developmental Biology
  • Most taxonomists agree that the animal kingdom is
    monophyletic
  • Three prominent hypotheses have been proposed for
    the origin of metazoans from single-celled
    protists

29
Evolutionary Developmental Biology
  • 1. The multinucleate hypothesis
  • 2. The colonial flagellate hypothesis
  • 3. The polyphyletic origin hypothesis
  • Molecular systematics using rRNA sequences
    settles this argument in favor of the colonial
    flagellate hypothesis

30
Evolutionary Developmental Biology
  • Molecular analysis may also explain the Cambrian
    explosion
  • The enormous expansion of animal diversity in the
    Cambrian period (543 to 525 MYA)
  • The homeobox (Hox) developmental gene complex
    evolved
  • Provided a tool that can produce rapid changes
    in body plan

31
Evolutionary Developmental Biology
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