1. Evolution of Animal Body Plans
Anatomical features in animals’ body plans mark the branching points on the evolutionary tree.
Relationships on this tree are inferred by studying similarities in embryological development and shared anatomical features.
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Animal Body Plans

2. Development of Tissues
The first major change in body plan was the development of tissues.
Sponges are the only animal without true tissues.
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Animal Body Plans

3. Symmetry Symmetry is the next branching point after tissues.
Symmetry is the balance or similarity of body structures of an organism.
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Animal Body Plans

4. Symmetry Asymmetry Radial symmetry Bilateral symmetry
Irregular shape, no symmetry or balance in body structures.
Radial symmetry
An animal with radial symmetry can be divided along any plane, through a central axis, into roughly equal halves.
Bilateral symmetry
Bilateral symmetry means an animal can be divided into mirror image halves along only one plane.
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Animal Body Plans

5. Symmetry Bilateral symmetry
Animals with bilateral symmetry also have anterior (head) and posterior (tail) ends.
This body plan is called cephalization, and involves a tendency to concentrate nervous tissue and sensory organs at the anterior end of the animal.
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Animal Body Plans

6. Body Cavities
Animals with bilateral symmetry have a gut, which is either a sac inside the body or a tube that runs through the body, where food is digested.
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Animal Body Plans

7. Body Cavities Coelomates
A coelom is a mesoderm-lined, fluid-filled cavity between the gut and the outside body wall.
Specialized organ and body systems develop from the mesoderm that encloses and lines the coelom.
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Animal Body Plans

8. Body Cavities Pseudocoelomates
A pseudocoelom is a fluid-filled body cavity that develops between the mesoderm and the endoderm.
Only partially lined with mesoderm.
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Animal Body Plans

9. Body Cavities Acoelomates Acoelomates do not have a coelom.
Have solid bodies without a fluid-filled body cavity between the gut and the body wall
Nutrients and wastes diffuse between cells; no circulatory system
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Animal Body Plans

10. Development in Coelomate Animals
Protostomes
Organisms that are protostomes develop mouths from the first opening in the gastrula.
As the embryo develops, the mesoderm splits down the middle to form the coelom.
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Animal Body Plans

11. Development in Coelomate Animals
Deuterostomes
In organisms that are deuterostomes, the anus develops from the first opening in the gastrula.
Coelom develops from two pouches in the mesoderm.
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Animal Body Plans

12. Segmentation
Segmented animals can be “put together” from a succession of similar parts.
Can survive damage to one segment
Movement is more effective
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Animal Body Plans