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Overview of Animal Diversity


Overview of Animal Diversity Animals can be divided into three body type: Acoelomate Pseudocoelomate Coelomate D. Protostome vs Deuterostome in Coelomates Mollusks ... – PowerPoint PPT presentation

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Title: Overview of Animal Diversity

Overview of Animal Diversity
General Features of Animals
  • Animals are a diverse group of consumers that
    share major characteristics
  • All are heterotrophs
  • All are multicellular
  • Cells do not have cell walls
  • Most are able to move
  • All are very diverse in form and habitat
  • Most reproduce sexually
  • Have a characteristic patterns of embryonic
  • Cells of all animals (except sponges) are
    organized into tissues

Evolution of the Animal Body Plan
  • Five key transitions in animal evolution
  • Tissues
  • Symmetry
  • Body cavity
  • Development
  • Segmentation

Evolution of the Animal Body Plan
  • 1. 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

Evolution of the Animal Body Plan
  • 2. Evolution of symmetry
  • Parazoa (sponges) lack any definite symmetry
  • Eumetazoa have a symmetry defined along imaginary
    axes drawn through the animals body
  • There are two main types of symmetry
  • Radial symmetry
  • Bilateral symmetry

Evolution of the Animal Body Plan
  • Radial symmetry
  • Body parts arranged around central axis
  • Can be bisected into two equal halves in any 2D
    plane perpendicular to that axis

Evolution of the Animal Body Plan
  • Bilateral symmetry
  • Body has right and left halves that are mirror
  • Body has distinct anterior/posterior and
    dorsal/ventral divisions

Evolution of the Animal Body Plan
  • Bilaterally symmetrical animals have two main
    advantages over radially symmetrical animals
  • Cephalization
  • Evolution of a definite brain area
  • Greater mobility

Evolution of the Animal Body Plan
  • 3. Evolution of a body cavity
  • Eumetazoa produce three germ layers
  • Outer ectoderm (body coverings and nervous
  • Middle mesoderm (skeleton and muscles)
  • Inner endoderm (digestive organs and intestines)

Evolution of the Animal Body Plan
  • 3. Evolution of a body cavity
  • Three basic kinds of body plans
  • Acoelomates have no body cavity

Evolution of the Animal Body Plan
  • Pseudocoelomates have a body cavity between
    mesoderm and endoderm
  • Called the pseudocoel

Evolution of the Animal Body Plan
  • Coelomates have a body cavity entirely within the
  • Called the coelom

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

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 2-layer-thick ball
    called a gastrula with
  • Blastopore - Opening to outside
  • Archenteron - Primitive body cavity

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
  • Mouth develops later from another region of the

Evolution of the Animal Body Plan
  • Deuterostomes differ from protostomes in three
    other embryological features
  • Cleaveage pattern of embryonic cells
  • Protostomes - Spiral cleavage
  • Deuterostomes - Radial cleavage
  • Developmental fate of cells
  • Protostomes - Determinate development
  • Deuterostomes - Indeterminate development
  • Origination of coelom
  • Protostomes - Forms simply and directly from the
  • Deuterostomes - Forms indirectly from the

Evolution of the Animal Body Plan
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
  • Segmentation appeared several times in the
    evolution of animals

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

Going From A single cell to Multicellular Organism
  • This is an example of Phylogenic Tree
  • As an A P class will work from left to right
    throughout the 1st marking period
  • Do you see any patterns?

Cleavage Blastula Gastrulation
GastrulaCell Cycle G1, S, G2, and Mitosis
Fertilization (1n) egg (1n) sperm(2n) zygote
  • The initial event in development in sexual
    reproduction is fertilization, the union of male
    and female gametes to form a zygote.
  • Recombinant of parental and maternal genes
  • Parthenogenesis-development without fertilization
    (Example some fish and salamanders)

Cleavage and Early Development
  • During cleavage the embryo divides repeatedly to
    convert the large cytoplasmic mass into a large
    cluster of small maneuverable cells called

Cleavage and Early Development
  • No growth during this period, only subdivisions
    of mass, which continues until somatic cell size
    is attained. Think of it a origami!!!!
  • So, what are somatic cells?
  • At the end of cleavage 100s to 1000s of cells

Cleavage and Early Development
  • Look at the Diagram to see an example of a
  • What is the role of the yolk?
  • Do the cells at the poles divide at the same rate?

What can we learn from Development?
  • Developmental Biology is a growing field!!
  • How can a zygote, a single layer cell, produce a
    multitude of body parts in an organism and how
    gene expressions proceeds.
  • Search for commonalities among organisms.

II. An overview of Development Following
CleavageA. Blastulation
  • Cleavage subdivides the mass of zygote until a
    cluster of cells called a blastula is formed
    (looks like a hollow mass of cells).
  • In most animals, the cells are arranged around a
    central fluid-filled cavity called a blastocoel.
  • Formation of a blastula stage, with its one layer
    of germ cells, occurs in all multicellular

B. Gastrulation and Formation of Two Germ Layers
  • a. Gastrulation converts the spherical blastula
    into a more complex configuration and forms a
    second germ layer.
  • One side of the blastula bends inward in a
    process called invagination, forming a new
    internal cavity. Picture pushing in a beach
    ball-the inward region forms a pouch.
  • The internal pouch is the gut cavity called an
    archenteron or gastrocoel.
  • The opening to the gut, where the inward bending
    began, is the blastopore.

Gastrulation and Formation of Two Germ Layers
  • C. The gastrula stage has two layers
  • a. An outer layer of cells surrounding the
    blastocoel, called ectoderm
  • b. An inner layer of cells is called endoderm
  • The gut opens only at the blastopore it is called
    a blind or incomplete gut. Animals with a blind
    gut must consume food completely digested, or the
    remains of the food egested through the mouth. Ex
    sea anemones and flatworms.
  • Most animals have a complete gut with a second
    opening, the anus.

c. Formation of the Mesoderm, a Third layer
  • i. Multicellular animals (not sponges) proceed
    blastula to gastrula
  • Two germ layers called DIPLOBLASTIC
  • Three germ layers called TRIPLOBLASTIC
  • The third layer is called mesoderm

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C. Formation of the Coelom
  • Coelomates are animals with a true coelom, a
    fluid filled body cavity completely lined by
    tissues derived from mesoderm.
  • The inner and outer layers of tissue that
    surround the cavity connect dorsally and
    ventrally to form mesenteries that suspend the
    internal organs.

  • Animals can be divided into three body type
  • Acoelomate
  • Pseudocoelomate
  • Coelomate

D. Protostome vs Deuterostome in Coelomates
  • Mollusks, annelids, arthropods and some other
    phyla are collectively called protostomes. 
  • Echinoderms and chordates are called
  • 4 Fundamental differences between the two groups
  • See Class Handout or next slide

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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

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)

A New Look At Metazoans
  • It seems that key morphological characters used
    in traditional classification are not necessarily
  • Molecular systematics uses unique sequences
    within certain genes to identify clusters of
    related groups

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

A New Look At Metazoans
Examples can be found in Table 32.2 of Raven et
Evolutionary Developmental Biology
  • Most taxonomists agree that the animal kingdom is
  • Three prominent hypotheses have been proposed for
    the origin of metazoans from single-celled

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
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