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Chapter 3
ANIMAL ARCHITECTURE
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New Designs for Living
• Zoologists recognize 34 major phyla of living
multicellular animals
– Survivors of around 100 phyla that appeared 600
million years ago during Cambrian explosion
• Most important evolutionary event in geological history
of life
• Virtually all major body plans evolved
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Hierarchical Organization of Animal Complexity
• Grades of Organization
– Unicellular protozoans
• Simplest eukaryotic organisms
– Protoplasmic level of Organization
• Perform all basic functions with confines of
single cell
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Hierarchical Organization of Animal Complexity
– Metazoa
• Multicellular animals
– Cells are specialized parts of whole organism
– Cannot live alone
• Cellular Level of Organization
– Simplest metazoans
– Cells demonstrate division of labor but are not
strongly associated to perform a specific collective
function
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Hierarchical Organization of Animal Complexity
• Tissue Level of Organization
– Cells grouped together
– Perform common function as a unit (tissue)
• Tissue-Organ Level of Organization
– Tissues assembled into larger functional units called
organs
– Chief functional cells of organ
» Parenchyma
– Supportive tissues
» Stroma
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Hierarchical Organization of Animal Complexity
– Organ-System Level of Organization
• Organs work together to perform a common
function
• Highest level of organization
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Animal Body Plans
• Animal Symmetry
– Symmetry
• Correspondence of size and shape of parts on
opposite sides of a median plane
– Asymmetrical –no plane through which they can
be divided into identical halves
– Spherical symmetry
• Any plane passing through center divides body into
mirrored halves
• Best suited for floating and rolling
• Rare in metazoans
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Figure 3_01
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Animal Body Plans
– Radial symmetry
• Body divided into similar halves by more than 2 planes
passing through longitudinal axis
– Biradial symmetry
» Variant form radial symmetry
» Have part that is single or paired rather than radial
» Only 1 or 2 planes passing through longitudinal
axis produces mirrored halves
• Usually sessile, freely floating, or weakly swimming
animals
• No anterior or posterior end
– Can interact with environment in all directions
2 phyla primarily radial are Cnidaria and Ctenophora
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Animal Body Plans
– Bilateral Symmetry
• Organism can be divided along a sagittal plane into two
mirror portions
– Right and left halves
• Much better fitted for directional (forward) movement
• Bilateral animals are collectively called Bilateria
• Associated with cephalization
– Differentiation of a head region with concentration of nervous
tissue and sense organs
• Advantageous to an animal moving through its
environment head first
• Always accompanied by differentiation along an
anteroposterior axis (polarity)
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Animal Body Plans
• Regions of bilaterally symmetrical animals
– Anterior
• Head end
– Posterior
• Tail end
– Dorsal
• Back or upper side
– Ventral
• Front or belly side
– Medial
• Midline of body
– Lateral
• Sides
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Figure 3_02
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Development of Animal Body Plans
• Sequence of inherited developmental begins after
fertilization of an egg to form a zygote.
• Sponges and cnidarians lacks a distinct cleavage pattern
• Bilateral animals typically exhibit either radial or spiral
cleavage
• Radial cleavage - the cleavage planes are symmetrical to
the polar axis and produce tiers or layers of cells on top
of each other in an early embryo
• Spiral cleavage -cleaves oblique to axis and typically
produces a quartet of cells that come to lie not on top of
each other but in furrows between the cells
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Figure 3_03
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Figure 3_04
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Development of Animal Body Plans
• Cleavage proceeds until the zygote is divided into
many small cells typically surrounding a fluid-filled
cavity
• Embryo is a blastula, fluid- filled space is blastocoel
• In animals other than most sponges , the blastula
becomes a 2-layered stage called a gastrula with
endoderm and ectoderm
• The outer ectoderm surrounds the blastocoel and
the endoderm surround and defines an inner body
cavity called the gastrocoel
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Body Cavities
The most obvious internal space or body cavity is
a gut developing from an embryonic gastrocoel.
This gut has at least one opening- the
blastophore.
In many other animals, the gut is surrounded by
a fluid-filled cavity
In some animals mesoderm lines the outer edge
of the blastocoel, lying next to ectoderm. When
this occurs the blastocoel is renamed the
pseudocoelom
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Body Cavities
Acoelomate- mesoderm completely fill the
blastocoel
– Gut is only body cavity
• Most bilateral symmetrical animals, the blastocoel
fills with mesoderm and then a new cavity forms
inside the mesoderm. This new cavity is a coelom.
• Schizocoely
– Mesodermal cells migrate to blastocoel
Enterocoely
• Coelom comes from pouches of the archenteron or
primitive gut that push outward into the blastocoel
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Figure 3_06
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Metameric or Segmented Body Plans
• Metamerism (Segmentation)
– Serial repetition of similar body segments along
longitudinal axis of body
• Each segment is a metamere or somite
• Annelids, Arthropods, Chordates
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How Many Body Plans Are There?
• Deuterostomes-the blastopore becomes the anus
• The name means second mouth which refers to the
formation of the mouth from the second opening in
the embryo
• 3 phyla: Echinodermata, Hemichordata and Chordata
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How Many Body Plans Are There?
• Protostomes proceeds through a blastula and gastrula stage
• The name means mouth first and refers to the formation of
the mouth from the embryonic blastophore. The anus forms
secondarily in protostomes
• Coelomate –animals that forms its coelom by schizocoely in
protostomes
• 2 groupsEcdysozoa- include all animals that molt
Lophotrochozoa-some animals have a “crest or tuft” of
tentacles called a lophophore, others have a band of cilia on a
larval stage called a trochophore
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Components of Metazoan Bodies
• Extracellular Components
• Noncellular components of metazoan animals
– Body fluids
– Extracellular structural elements
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Components of Metazoan Bodies
• Cellular Components: Tissues
– Histology is the study of types of tissues
– Four major types of tissues form during embryonic
development
• Epithelial Tissue
• Connective Tissue
• Muscular Tissue
• Nervous Tissue
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Figure 3_10
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Components of Metazoan Bodies
– Epithelial Tissue
• Sheet of cells that covers an internal or external
surface
• Function
–Protection
–Absorption
–Secretion
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Components of Metazoan Bodies
• Simple epithelia
–Found in all metazoan animals
• Stratified epithelia
–Restricted to vertebrates
• Separated from underlying tissues by a
basement membrane
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Components of Metazoan Bodies
• Connective Tissue
– Widespread in body
– Contains relatively few cells, many fibers, and a
ground substance or matrix
– 2 types of connective tissue proper In vertebrates
– Loose connective tissue
– composed of fibers and both fixed and wandering
cells suspended in a syrupy ground substance
– Dense connective tissues
– Characterized by densely packed fibers, much of the fibrous
tissue is composed of collagen which is the most abundant
protein in the animal kingdom and is found wherever both
flexibility and resistance to stretching are required
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Components of Metazoan Bodies
• Muscular Tissue
– Most common tissue in most animals
– Originates from mesoderm
– Muscle cell called a muscle fiber
– Specialized for contraction
– 3 types
• Skeletal- Striated
• Cardiac- Striated
• Smooth- No striations
Unspecialized cytoplasm of muscle is called sarcoplasm
and contractile elements within the fiber are myofibrils
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Components of Metazoan Bodies
• Nervous Tissue
• Specialized to receive stimuli and conduct
impulses from one region to another
• 2 basic cell types
– Neurons
• Structural and functional unit of nervous system
– Neuroglia
• Insulate and support neurons.
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Extracellular Components of the Metazoan Body
• Metaozoan animals contain 2 important noncellular
components: body fluids and extracellular structural
elements
• Body fluids
• Intracellular space -occupy space within the body’s
cells
• Extracellular space -occupy space outside the cell
• Animals with closed vascular systems fluids are
subdivided into blood plasma, lymph, and interstitial
fluid
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Complexity and Body Size
• More complex grades of metazoan organization
– Permit and promote evolution of large body size
• As an animal becomes larger
– Surface area increases as the square of body length
– Volume increases as the cube of body length
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Complexity and Body Size
• A large animal has less surface area compared to its
volume than does a smaller animal
– May be inadequate for respiration and nutrition by cells
located deep within the body
• Fold or invaginate the body surface to increase
surface area, as in flatworms
• Most large animals developed internal transports
systems to shuttle nutrients, gases and waste
products, as they became larger
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Complexity and Body Size
• Benefits of Being Large
– Buffers against environmental fluctuations
– Provides protection against predation and
promotes offensive tactics
– Cost of maintaining body temperature is less per
gram of body weight than in small animals
– Energy costs of moving a gram of body weight
over a given distance less for larger animals
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