1. The Noncoelomate Animals
Chapter 44
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2. 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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3. 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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5. 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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6. 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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7. 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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8. 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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9. 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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10. 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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12. Eumetazoa: The Radiata
Cnidarians
Nearly all marine.
Carnivorous
Cnidocytes
Nematocysts
Two basic body plans.
Polyps and Medusae
Fertilized eggs give rise to planulae.
Internal extracellular digestion.
Distinct tissues
Epidermis and nervous system develop from ectoderm.
Gastrodermis develops from endoderm.
True body symmetry
Radiata
Cnidaria
Ctenophora
Bilateria
All others
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13. 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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14. 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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15. Eumetazoa: The Bilateral Acoelomates
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16. 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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18. 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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19. Eumetazoa: The Bilateral Acoelomates
Phylum Nemertea: The Ribbon Worms
Simplest animals that possess a complete digestive system.
Mouth and anus.
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20. 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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21. 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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22. 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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23. 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
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24. Raven - Johnson - Biology: 6th Ed
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25. Raven - Johnson - Biology: 6th Ed
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26. Copyright © McGraw-Hill Companies Permission required for reproduction or display
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