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The Noncoelomate Animals
Chapter 44
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General Features of Animals
•
Classification of Animals
 Two subkingdoms generally
recognized:
- Parazoa - Lack definite
symmetry and posses neither
tissues or organs.
ex: sponges
-
Eumetazoa - Definite shape
and symmetry, and tissues
organized into organs.
 Radiata - Diploblastic
Endoderm and ectoderm

Bilateria - Triplobalstic
endoderm, ectoderm &
mesoderm
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Key Transitions in Body Plan
•
Evolution of Tissues
 First key transition in animal
body plan.
•
Evolution of Bilateral Symmetry
 Radial Symmetry - Regular
arrangement of parts around
central axis.

Bilateral Symmetry - Right and
left halves form mirror images.
- Dorsal vs. Ventral
- Anterior vs. Posterior
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Key Transitions in Body Plan
•
Evolution of a Body Cavity
 Presence of a body cavity allows digestive
tract to be larger and longer.
- Storage of undigested food.
- More complete digestion.
- More space for gonads to expand.
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Key Transitions in Body Plan
Kinds of Body Cavities
- Acoelomates - No body cavity.
-
-
Pseudocoelomates - Possess
pseudocoelom.
Coelomates - Possess
coelom.
 Parietal peritoneum Epithelium lining outer wall
of coelom.
 Visceral peritoneum Epithelium covering
internal organs.
 Advantages of a Coelom
 Allows contact
between mesoderm
and endoderm, so that
primary induction can
occur during
development.
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Key Transitions in Body Plan
•
Evolution of
Protostome and
Deuterostome
 Cells of embryonic
Protostome each
contain different
portion of regulatory
signals.
 Any cell of
Deuterostome can
develop into a
complete organism.
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Key Transitions in Body Plan
Open circulatory system
- Blood passes from vessels into sinuses,
mixes with body fluid, and then reenters
vessels in another location.
 Closed circulatory system
- Blood is physically separated from other
body fluids and can be separately
controlled.

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Key Transitions in Body Plan
•
Evolution of Segmentation
 Each segment may go
on to develop a more or
less complete set of
adult organs.

Locomotion is far more
effective when individual
segments can move
independently due to
flexibility of movement.
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Parazoa
•
Sponges (Porifera)
 Most lack symmetry.
 Adults are sessile.
 Little coordination among cells.
 Three functional layers
- Choanocytes
- Mesohyl
- Outer epithelial layer
 Spicules
•
•
Beating of flagella lining interior
draws water in through
numerous pores.
 Small organisms are filtered
out of the water, which flows
through passageways and
eventually out an osculum.
Reproduction done by
fragmentation as well as
sexually.
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Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Eumetazoa: The Radiata
•
•
Distinct tissues
 Epidermis and nervous
system develop from
ectoderm.
 Gastrodermis develops from
endoderm.
True body symmetry
 Radiata
- Cnidaria
- Ctenophora
 Bilateria
- All others
•
Cnidarians
 Nearly all marine.
 Carnivorous
- Cnidocytes
 Nematocysts
 Two basic body plans.
- Polyps and Medusae
 Fertilized eggs give rise to
planulae.
 Internal extracellular digestion.
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Eumetazoa: The Radiata

•
Classes of Cnidarians
- Hydrozoa - Hydroids
- Scyphozoa - Jellyfish
- Cubozoa - Box Jellyfish
- Anthozoa - Sea
Anemones and Corals
Ctenophorans (Comb Jellies)
 Propel through the water by
means of eight comb-like
plates of fused cilia.
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Eumetazoa: The Bilateral Acoelomates
•
Bilateral Symmetry
 Digestive tract is only internal
cavity.
•
Phylum Platyhelminthes: The
Flatworms
 Among simplest bilaterally
symmetrical animals, but
have a definite head at the
anterior end, and do possess
organs.
•
Flatworms
 Cannot feed, digest, and
eliminate food
simultaneously.
 Absorb food directly through
body walls.
 Have excretory system.
 Most are hermaphroditic.
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Eumetazoa: The Bilateral Acoelomates
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Eumetazoa: The Bilateral Acoelomates


Class Turbellarians:
Turbellarians
- Only one of three classes
are freeliving.
Class Trematoda: The Flukes
- Liver Fluke Clonorchis
sinensis
 Miracidium - Eggs
(passed in feces)
 Rediae - Elongated,
nonciliated larvae.
 Cercariae - Tadpole-like
larval stage
 Metacercariae - Adult
stage
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Eumetazoa: The Bilateral Acoelomates

Class Cestoda: The
Tapeworms
- Hang on to the inner walls
of their hosts by means of
specialized terminal
attachment organs, and
absorb food through their
skins.
 Scolex - Attachment
organ
 Neck - Unsegmented
 Proglottids Repetitive segments.
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Eumetazoa: The Bilateral Acoelomates
•
Phylum Nemertea: The Ribbon Worms
 Simplest animals that possess a complete
digestive system.
- Mouth and anus.
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The Pseudocoelomates
•
Internal Body Cavity
 Pseudocoel serves
as hydrostatic
skeleton.
- Gains rigidity from
being filled with
fluid under
pressure.
 Lack a defined
circulatory system.
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The Pseudocoelomates
•
Phylum Nematoda: The
Roundworms
 Bilaterally symmetrical
unsegmented worms
- Covered by flexible, thick
cuticle.
 Mouth equipped with stylets.
 Food passes through mouth
as result of sucking action of
pharynx.
 Lack flagella or cilia.
 Reproduction is sexual.
 Trichinella regularly
parasitize humans.
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The Pseudocoelomates
•
•
Phylum Rotifera: Rotifers
 Small, bilaterally
symmetrical, basically
aquatic animals with a
crown of thick cilia at
their heads.
 Well developed food
processing apparatus.
 “Wheel Animals”
Phylum Cycliophora
 Relatively New
- Circular mouth
surrounded by fine,
hairlike cilia.
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Reevaluating Animal Body Plan Evolution
•
Biologists have traditionally inferred the
general relationships among animal phyla by
examining what appeared to be fundamental
characters.
 These key morphological characters are
not as conservative as previously believed.
- Molecular Phylogenies
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
Raven - Johnson - Biology: 6th Ed. - All Rights Reserved - McGraw Hill Companies