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CHAPTER 9

Architectural Pattern of an Animal

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Animal Body Plans

n  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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n  Radial symmetry n Body 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

Animal Body Plans

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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

Animal Body Plans

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n  Regions of bilaterally symmetrical animals n  Anterior

n Head end n  Posterior

n Tail end n  Dorsal

n Back side n  Ventral

n Front or belly side n  Medial

n Midline of body n  Lateral

n Sides

Animal Body Plans

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n  Distal n Parts farther from the middle of body

n  Proximal n Parts are nearer the middle of body

n  Frontal plane (coronal plane) n Divides bilateral body into dorsal and ventral

halves n  Sagittal plane

n Divides body into right and left halves n  Transverse plane (cross section)

n Divides body into anterior and posterior portions

Animal Body Plans

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Body Cavities and Germ Layers

n  Body cavity n  Sponges

n Acoelomate: no body cavity n In 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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n  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

Body Cavities and Germ Layers

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n  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)

Body Cavities and Germ Layers

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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

Body Cavities and Germ Layers

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n  Few diploblasts and triploblasts form blind gut n  Same opening for entrance of food and

exit of wastes n  Most form a complete gut

n  Allows for one-way flow of food from mouth to anus

n  Tube-within-a-tube design

A Complete Gut Design and Segmentation

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A Complete Gut Design and Segmentation

n  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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