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CHAPTER 9
Architectural Pattern
of an Animal
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Animal Body Plans
n 
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Animal Symmetry
n  Symmetry
n  Correspondence of size and shape of parts on opposite
sides of a median plane
n  Spherical symmetry
n  Any plane passing through center divides body into
mirrored halves
n  Best suited for floating and rolling
n  Found chiefly among some unicellular forms
n  Rare in animals
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Animal Body Plans
n  Radial
n  Body
symmetry
divided into similar halves by more than
2 planes passing through longitudinal axis
n  Biradial symmetry
n  Variant form radial symmetry
n  Have part that is single or paired rather
than radial
n  Only 2 planes passing through
longitudinal axis produces mirrored
halves
n  Usually sessile, freely floating, or weakly
swimming animals
n  No anterior or posterior end
n  Can interact with environment in all directions
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Animal Body Plans
n  Bilateral
Symmetry
n  Organism
can be divided along a sagittal plane
into two mirror portions
n 
Right and left halves
n  Much
better fitted for directional (forward)
movement
n  Associated with cephalization
n 
Differentiation of a head region with concentration of
nervous tissue and sense organs
n  Advantageous
to an animal moving through its
environment head first
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Animal Body Plans
n 
Regions of bilaterally symmetrical animals
n 
n 
n 
n 
n 
n 
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Anterior
n  Head end
Posterior
n  Tail end
Dorsal
n  Back side
Ventral
n  Front or belly side
Medial
n  Midline of body
Lateral
n  Sides
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Animal Body Plans
n 
Distal
n  Parts
n 
Proximal
n  Parts
n 
farther from the middle of body
are nearer the middle of body
Frontal plane (coronal plane)
n  Divides
halves
n 
Sagittal plane
n  Divides
n 
bilateral body into dorsal and ventral
body into right and left halves
Transverse plane (cross section)
n  Divides
body into anterior and posterior
portions
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Body Cavities and Germ Layers
n 
Body cavity
n  Sponges
n  Acoelomate:
n  In
no body cavity
sponges
n  After blastula formation, cells
reorganize to form adult body
n  Blastula has no external opening
n  No gut forms
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Body Cavities and Germ Layers
n 
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Other animal phyla
n  Development proceeds from blastula to gastrula
n  Invagination of surface cells form the primitive gut
n  Opening to the primitive gut is the blastocoel
n  Becomes the mouth or the anus
n  Gut is lined by endoderm
n  Outer layer of cells is ectoderm
n  Embryo now has 2 cavities
n  Gut and blastocoel
n  Blastocoel persists in some animals
n  In others, becomes filled with a 3rd germ layer,
mesoderm
n  Cells forming mesoderm
n  Derived from endoderm
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Body Cavities and Germ Layers
n 
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Three body plans are possible
n  Acoelomate plan
n  Mesodermal cells completely fill the blastocoel
n  Gut is only body cavity
n  Pseudocoelomate plan
n  Mesodermal cells line the outer edge of the
blastocoel
n  2 body cavities formed
n  Persistent blastocoel (pseudocoelom) and a gut
cavity
n  Pseudocoelom is a false body cavity (only partially
lined with mesoderm)
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Body Cavities and Germ Layers
n  Schizocoelous
(Eucoelomate) plan
n  Mesodermal cells fill blastocoel
n  Mesoderm splits
n  The space is called a coelom
n  True body cavity (completely lined
by mesoderm)
n  2 body cavities formed
n  Gut and coelom
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A Complete Gut Design and Segmentation
n 
n 
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Few diploblasts and triploblasts form blind
gut
n  Same opening for entrance of food and
exit of wastes
Most form a complete gut
n  Allows for one-way flow of food from
mouth to anus
n  Tube-within-a-tube design
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A Complete Gut Design and Segmentation
n 
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Metamerism (Segmentation)
n  Serial repetition of similar
body segments along
longitudinal axis of body
n  Each segment is a
metamere or somite
n  Permits greater body
mobility and complexity
of structure and
function
n  Annelids, Arthropods,
Chordates
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