Instructions for printer-friendly copy.

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    The Wonderful World of Animalia

    Animals possess all the synapomorphies unique to eukaryotes.
    But what makes an animal an animal?

    • Animals are multicellular.

    • Animals have true tissues (simple and complex).

    • Animals are ingestive heterotrophs.

    • Animals have Hox genes that determine body segment identity.

    • Animals have characteristic embryo development.

    • Animals have a nervous system.

    • Animals have a muscular system.

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(click on pic for source)

    Energy Storage

    Animals store energy as

    • glycogen (short term)
    • fat (long term)

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    Which is why they require cookies.

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    Metazoa

    Metazoa - all multicellular animals.

    Eumetazoa - animals with true tissues.

    • The Radiata - radially symmetrical.

    • The Bilateria - bilaterally symmetrical.

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    Animals Undergo Unique Ontogeny

    Ontogeny (= embryogenesis) is embryo development.
    Animal ontogeny is unlike that of plants.

    Ontogenetic similarities among animal taxa are not trivial.
    They comprise synapomorphies that reveal evolutionary relationships.

    • The zygote undergoes a series of cleavages
    • The resulting cells are called blastomeres.
    • Multiple cleavages yield a hollow ball of cells, the blastula.
    • The blastula invaginates to produce a cup-shaped gastrula

    Gastrulation produces two embryonic germ (tissue) layers:

    • ectoderm (lining the outer surface)
    • endoderm (lining the inner surface)

    In more derived taxa, some endoderm will differentiate into

    • mesoderm (lying between ectoderm and endoderm)

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    Gastrulation: Primitive Taxa

    In the earliest animals (Cnidarians, flatworms)
    • the blastopore becomes the mouth
    • there is no anus

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    Gastrulation: Protostomes

    In more derived animals (later Protostomes)
    • the blastopore becomes the mouth
    • a secondary opening at the animal pole becomes the anus

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(click on pic for source)

    Gastrulation: Deuterostomes

    In other derived animals (Deuterostomes)

    • the blastopore becomes the anus
    • a secondary opening at the animal pole will become the mouth

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(click on pic for source)

    Morphogenesis

    The gastrula undergoes morphogenesis ("origin of form")
    to become an embryo (encased) or larva (free-living).

    The larva/embryo undergoes metamorphosis
    in the course of acquiring its adult form.

    This process may take place

    • in an aquatic environment
    • within an egg
    • within the body of the female parent

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    Body Symmetry

    Metazoans can be categorized on the basis of body symmetry:
    • asymmetry (Poriferans)
    • radial symmetry (Cnidaria, Ctenophora, Placozoa)
    • bilateral symmetry (Everyone Else)

    Bilaterally symmetrical animals have sense organs concentrated at the
    anterior end of the body, a phenomenon known as cephalization.

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(click on pic for source)

    Animal Organ Systems

    True animals (Eumetazoa) are characterized by
    • true tissues
    • organs
    • organ systems

    Not all organ systems are present in all animals.

    The evolution of animal complexity included
    the evolution of new organ systems.

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    Animal Organ Systems

    • integumentary system - protection against mechanical injury, infection, desiccation
    • digestive system - food processing
      • mouth
      • pharynx (sometimes with a grinding organ, such as a gizzard or mastax)
      • esophagus
      • stomach/crop
      • intestine
      • anus

    • nervous system - rapid coordination of body activities; response to environmental stimuli
    • muscular system - movement
    • reproductive system - the obvious
    • skeletal system - structural support; muscle attachment
    • respiratory system - gas exchange (O2 in <--> CO2 out)
    • circulatory system - internal distribution of materials
    • excretory system - removal of nitrogenous waste (<-- required link) from body fluid
    • endocrine system - slower coordination of body activities, response to environmental stimuli
    • lymphatic systems - provides plasma and supports immune system
    • immune systems - defense against pathogens and cancer

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    The Origin of Animal Multicellularity

    Sponge-like organisms first appeared about 770 million years ago.

    Their closest relatives are colonial choanoflagellates,
    which strongly resemble sponge choanocytes.

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    Adhesion Proteins

    Multicellularity may have evolved several times, independently.

    In each case, cell adhesion was the new trait
    critical to more complex structure.

    Cadherins (Calcium-dependent adhesion proteins)
    are trans-membrane proteins involved in

    • cell adhesion
    • intercellular signaling

    Catenins are proteins that

    • connect cadherins to the actin filaments of the cytoskeleton
    • strengthen cell-to-cell junctions
    • allow formation of epitheia
    • are involved with diverse cellular functions

    Early aggregate organisms gradually evolved cellular division of labor.

    Once this was achieved, they could be considered colonial.

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    The First Animal

    The earliest animal ancestor resembled a gastrula,
    but was a sexually mature adult.

    The term gastrea distinguishes it from an embryo.

    The gastrea shared these animal characters:

    • multicellularity
    • cilia/flagella
    • radial/bilateral symmetry
    • simple gut (mouth, but no anus)
    • diploblasty (i.e., ectoderm and endoderm)

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    Front, Back, Up, Down

    A concentration of sense organs at one end of a bilaterally symmetrical body
    defines that end of the body as the anterior.

    The end of the body away from the anterior is defined as the posterior.

    Reproductive system and organs dedicated to waste removal
    tend to be concentrated at an animal's posterior end.

    Which seems like a good arrangement.

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    The Cambrian Explosion

    About 540 million years ago, marine animal diversity
    expanded dramatically, an event known as the
    Cambrian Explosion or Cambrian Radiation.

    Over a (geologically) short time span, all extant animal phyla
    --as well as many now extinct--arose from simple ancestral forms.


    (required video)

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(click on pic for source)

    Eumetazoa: The True Animals

    The Cambrian Explosion saw the rise of animals with

    • true body symmetry
      • radial
      • bilateral

    • tissues derived from embryonic germ layers
      • diploblastic (ectoderm and endoderm only)
      • triploblastic (endoderm, ectoderm and mesoderm)

    Embryonic germ layers develop into four types of adult tissues:
    • epithelial tissue
    • connective tissue
    • muscle tissue
    • nervous tissue

    Combinations of different types of these tissues comprise
    organs and organ systems.

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    Epithelium

    An epithelium is a sheet of cells covering
    an internal or external body surface.

    An epithelium may be
    • simple - single layer of cells
    • stratified - multiple layers of cells
    • pseudostratified - single layer of cells
      of different shapes having the appearance
      of stratification

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    Connective Tissue

    Connective tissues serve a variety of binding and structural functions.

    They are composed of:

    • cells (relatively few)
    • fibers (many)
    • matrix/ground substance (fluid or gel in which the above are embedded)

    Vertebrates have two basic types of connective tissue:

    • loose (forms the matrix of organs and soft tissues)
    • dense (tendons, ligaments, bone, cartilage)

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    Muscle Tissue

    Together with the nervous system, muscle tissue facilitates movement.

    Vertebrates have three types of muscle tissue, each specialized for different functions.

    • skeletal striated muscle (voluntary control)
    • cardiac striated muscle (involuntary control)
    • smooth muscle (involuntary control)

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    Nervous Tissue

    Nervous tissue mediates rapid response to internal and external stimuli.
    • neurons conduct electrical impulses (action potentials)
    • glial cells insulate and support neurons

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    Animal Body Plans

    Eumetazoans can be categorized on the basis
    of what lies between the ectoderm and endoderm.

    There are three basic body plans

    • acoelomate
    • pseudocoelomate
    • coelomate

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    Acoelomate

    An acoelomate (ay-SEE-low-mate) animal has no internal body cavity.

    The space between ectoderm and endoderm is filled with either

    • mesogloea - a clear, jelly-like proteinaceous matrix
    • mesenchyme - loose cells embedded in a protein/fluid matrix

    • Platyhelminthes

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    Pseudocoelomate

    A pseudocoelomate (SOO-doh-see-low-mate) animal has an internal body cavity lined with mesoderm only on the parietal surface.

    The body cavity is called the pseudocoelom (pronounced SOO-doh-seal-ohm)or pseudocoel (pronounced SOO-doh-seal)

    It is essentially a persistent blastocoel.

    The pseudocoelom has evolved independently in diverse taxa.

    • Rotifera
    • Nematoda
    • many other (less familiar) phyla

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    Coelomate

    A coelomate (SEE-low-mate) animal has an internal body cavity lined with mesoderm on both visceral and parietal surfaces.

    The body cavity is called the coelom (pronounced SEE-lohm).

    • Annelida
    • Mollusca
    • Arthropoda
    • Echinodermata
    • Chordata

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    Protostomes and Deuterostomes

    Coelomates can be classifed on the basis of ontogenetic character states.
    Because convergence can sometimes obscure common ancestry,
    ontogenetic events must be carefully scrutinized.

    Research has supported the monophyly of Deuterostomia.
    However, Protostomia is likely paraphyletic.

    Relationships among these taxa are controversial,
    and it's possible that Protostomia and Deuterostomia
    won't last.

    So don't get too attached.

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    Ontogenetic Events

    Conventional wisdom (which might not be all that wise for long):

    • Protostomes
      • blastopore becomes the mouth
      • second opening becomes the anus

    • Deuterostomes
      • blastopore becomes the anus
      • second opening becomes the mouth

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(Photo by Andrew Warren, Butterflies of America)

    Determinate vs. Indeterminate Cleavage

  • Protostomes
    • determinate cleavage
      • totipotency/pluripotency lost relatively early in development
      • blastomere developmental fate set early in development
      • (Nondisjunction at first cleavage can yield a gynandromorph!) (<-- required link!)

  • Deuterostomes
    • indeterminate cleavage
      • totipotency/pluripotency retained far into development
      • blastomere developmental fate set late in development

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    Spiral vs. Radial Cleavage

  • Protostomes
    • spiral cleavage (unique to the Spiralian Lophotrochozoans)

  • Deuterostomes
    • radial cleavage
    Spiral Cleavage:

    Radial Cleavage:

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    Coelom Formation

  • Protostomes

  • Deuterostomes

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(click on pic for source)

    Nervous and Circulatory Systems

  • Protostomes
    • circulatory system primitively dorsal
    • nervous system primitively ventral
    • Phyla Mollusca, Annelida, Arthropoda and others

  • Deuterostomes
    • circulatory system primitively ventral
    • nervous system primitively dorsal
    • Phyla Echinodermata, Hemichordata, Chordata and others

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    Metamerism

    More derived animal lineages exhibit
    an important anatomical innovation, metamerism,
    the division of the body into similar, repeating segments. .

    Each body segment is known as a
    metamere or somite.

    Somites are arranged in serial fashion, with
    muscles, organs and other anatomical structures
    duplicated in each segment.

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    Tagmosis

    Tagmatization is the developmental fusion of
    groups of metameres into functionally distinct
    body regions, or tagmata (singular = tagma).

    This process allows specialization of body regions
    for specific functions.

    Example: The Arthropod body exhibits tagmosis:

    • head
    • thorax
    • abdomen

    ...each of which is composed of multiple, fused metameres.

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    Secondary Loss of Metamerism is Derived

    As evolution proceeded, some animals secondarily lost obvious segmentation.



    Need a hint?

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    Cephalization

    Cephalization is the concentration of major sense organs at the anterior end of the body,
    defining a cephalon (Greek for "head").

    • The head enters the environment first, and is able to sense
      environmental cues and react to them.

    • The mouth is located on the head, which makes food gathering more efficient.

    Bilaterally symmetrical animals exhibit polarization of function
    along an anteroposterior (head to tail) axis.

    • sensing at the head end
    • organs operate the body in the middle region
    • reproductive structures near the caudal (tail) region

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    Anatomical Terminology

    You might as well learn it now.
    • dorsal - the "back" surface
    • ventral - the "belly" surface
    • cranial/cephalic - the head end
    • caudal - the tail end

    • lateral - towards the side
    • medial - towards the inside of the body
    • proximal - part of a limb or structure closest to the body
    • distal - part of a limb or structure away from the body
    • rostral - towards the end of the nose/head
    • plantar - bottom of the foot

    • longitudinal/sagittal plane - parallel craniocaudal body axis
    • transverse/cross plane - perpendicular to the body axis
    • median/mid-sagittal plane - center of the craniocaudal body axis

    Be able to identify these regions on your own body, or that of any animal.



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Okay, here's your hint.