Overview of Animal Diversity

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LEARNING OUTCOMES• Understand how the animals are organized

and how this organization is different from that of plants, fungi, protists, and prokaryotes.

• Compare and contrast Parazoa and Eumetazoa in terms of evolution, complexity, symmetry, and organization of embryonic cell layers.

• Compare and contrast asymmetry, radial symmetry, and bilateral symmetry.

• Differentiate among acoelomate, pseudocoelomate, and coelomate organisms; indicate how they are evolutionarily related and give examples of each.

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• Differentiate between protostomes and deuterostomes.

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General Features of Animals

Animals are the consumers of the EarthThey are a very diverse group

-However, they share major characteristics

-Are heterotrophs-Are multicellular-Have cells without cell walls-Most are able to move

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General Features of Animals

-Are very diverse in form and habitat

-Most reproduce sexually-Have a characteristic pattern of

embryonic development-Cells of all animals (except

sponges) are organized into tissues

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Evolution of the Animal Body Plan

1. Tissues2. Symmetry3. Body cavity4. Development

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Evolution of the Animal Body Plan

1. Evolution of tissuesMetazoans are divided into two main

branches:-Parazoa (Sponges - the simplest animals) lack defined tissues and organs

-Have the ability to disaggregate and aggregate their cells-Eumetazoa (all other animals) have distinct and well-defined tissues

-Have irreversible differentiation for most cell types

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Evolution of the Animal Body Plan

2. Evolution of symmetry-Sponges also lack any definite symmetry

-Eumetazoa have a symmetry defined along an imaginary axis drawn through the animal’s body

-There are two main types of symmetry

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Evolution of the Animal Body Plan

-Radial symmetry

-Body parts arranged around central axis

-Can be bisected into two equal halves in any 2-D plane-Bilateral symmetry

-Body has right and left halves that are mirror images-Only the sagittal plane bisects the

animal into two equal halves

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Top

Bottom

Back

Front

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Evolution of the Animal Body Plan

Bilaterally symmetrical animals have two main advantages over radially symmetrical ones

1. Cephalization-Evolution of a definite brain area

2. Greater mobility

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Evolution of the Animal Body Plan

3. Evolution of a body cavity-Eumetazoa produce three germ layers

-Outer ectoderm (body coverings and nervous system)-Middle mesoderm (skeleton and muscles)-Inner endoderm (digestive organs and intestines)

Body cavity = Space surrounded by mesoderm tissue that is formed during development

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Diploblastic vs. Triploblastic – Cell Layers

Diploblastic – two cell layers– Ectoderm – outer layer– Endoderm – inner layer– The Radiata

Triploblastic – three cell layers– Ectoderm, endoderm– Mesoderm – layer between ectoderm and endoderm– The Bilateria

Ectoderm – outer covering of the body; nervous system

Endoderm – digestive organs and intestinesMesoderm – skeleton and muscles

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Evolution of the Animal Body Plan

3. Evolution of a body cavity-Three basic kinds of body plans-Acoelomates = No body cavity-Pseudocoelomates = Body cavity between mesoderm and endoderm

-Called the pseudocoel -Coelomates = Body cavity entirely within the mesoderm

-Called the coelom

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Evolution of the Animal Body Plan

-The body cavity made possible the development of advanced organs systems

• Pseudocoelomates use pseudocoel for circ.• Coelomates developed a circulatory

system to flow nutrients and remove wastes-Open circulatory system: blood

passes from vessels into sinuses, mixes with body fluids and reenters the vessels -Closed circulatory system: blood

moves continuously through vessels that are separated from body fluids

• Why do you think closed is more advanced?

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Evolution of the Animal Body Plan

4. Evolution of different patterns of development-The basic Bilaterian pattern of development:

-Mitotic cell divisions of the egg form a hollow ball of cells, called the blastula

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Evolution of the Animal Body Plan

Bilaterians can be divided into two groups: -Protostomes develop the mouth first from or near the blastopore

-Anus (if present) develops either from another region of embryo-Deuterostomes develop the anus first from the blastopore

-Mouth develops later from another region of the embryo

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Embryonic development in protostomes and deuterostomes

Mouth formsfrom blastopore

Mouth

CoelomAnusMesoderm

BlastoporeBlastula

CoelomArchenteron

Mesoderm splits

BlastoporeBlastula

Mouth Coelom

AnusAnus formsfrom blastopore

CoelomArchenteron

Archenteron outpocketsto form coelom

Protostomes

Deuterostomes