1. Overview of metazoan Diversity

2. LEARNING OUTCOMES
Identify three features that characterize all animals and four that characterize only some types of animals.
Understand how the metazoans are organized and how this organization is different from that of plants, fungi, protists, and prokaryotes.
Know the five key innovations in body plans.
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.

3. Differentiate between protostomes and deuterostomes.
Understand the advantages of segmentation; give at least one example of segmentation in each of the coelomate phyla.
Compare the tradition methods using morphology in classification of metazoans to the new molecular systematics using DNA and RNA analysis to classify related metazoan groups. What is the problems of classification regarding homology and analogy?

4. General Features of metazoans
Are “metazoans” monophyletic?
Animals are so diverse that few criteria fit them all. But some, such as metazoans being eaters, or consumers, apply to all.
ALL:
Are heterotrophs
Are multicellular (It was such a great move, it evolved at least 16 different times. Animals, land plants, fungi and algae all joined in)
Have cells without cell walls

5. General Features of Animals
MOST:
Most are able to move
Are very diverse in form and habitat
Most reproduce sexually
Have a characteristic pattern of embryonic development
Cells of all metazoans (except sponges) are organized into tissues

6. Traditional Classification of Metazoans
Five key innovations can be noted in animal evolution:
1. The evolution of symmetry
2. The evolution of tissues, allowing specialized structures
and functions
3. The evolution of a body cavity
4. The evolution of various patterns of embryonic
development
5. The evolution of segmentation, or repeated body units

7. Problem: these comparisons can be analogous or homologous.
Traditional methods of classification:
Morphology
Embryology
Symmetry
Germ layers
Problem: these comparisons can be analogous or homologous.
What’s the difference?
What is the difference in classification and phylogenetics?

8. Classification of Animals 5 Key Transitions
Tissues
Body Symmetry
Body Cavity
Development
Segmentation
Figure 31.3
Chapter 31

9. Phylogeny Parazoa = Lack symmetry and tissues
Metazoans are divided into two main branches:
Parazoa = Lack symmetry and tissues
These “simplest” metazoans lack defined tissues and organs
Have the ability to disaggregate and aggregate their cells
Eumetazoa = Have symmetry and tissues
Diploblastic = Have two germ layers
Triploblastic = Have three germ layers

10. Evolution of the Animal Body Plan
1. Evolution of tissues—Parazoa/Eumetazoa split
Have irreversible differentiation for most cell types
The evolution of tissues allowed for specialized structures and functions
Eumetazoa (all other metazoans) have distinct and well-defined tissues

11. Evolution of the Animal Body Plan
2. Evolution of symmetry
Radiata/Bilateria split.
Sponges lack any definite symmetry
Eumetazoa have a symmetry defined along an imaginary axis drawn through the metazoan’s body
There are two main types of symmetry

12. Evolution of the Animal Body Plan
-Radial symmetry (The Radiata)
-Body parts arranged around central axis
-Can be bisected into two equal halves in any 2-D plane
-Bilateral symmetry (The Bilateria)
-Body has right and left halves that are mirror images
-Only the sagittal plane bisects the animal into two equal halves

13. Top
Back
Front
Bottom

14. Evolution of the Animal Body Plan
Bilaterally symmetrical metazoans have two main advantages over radially symmetrical ones
1. Cephalization
-Evolution of a definite brain area
2. Greater mobility

15. Evolution of the Animal Body Plan
3. Evolution of a body cavity
Eumetazoa produce two or three germ layers
Body cavity = Space surrounded by mesoderm tissue that is formed during development

16. 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

17. 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 intestines
Mesoderm – skeleton and muscles

19. 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?

21. 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
Blastula indents to form a two-layer-thick ball with:
-Blastopore = Opening to outside
-Archenteron = Primitive body cavity

22. 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 blastopore or another region of embryo
-Deuterostomes develop the anus first from the blastopore
-Mouth develops later from another region of the embryo

23. Embryonic development in protostomes and deuterostomes
Coelom
Archenteron
Mesoderm splits
Mouth forms
from blastopore
Mouth
Coelom
Anus
Mesoderm
Blastopore
Blastula
Coelom
Archenteron
Archenteron outpockets
to form coelom
Mouth
Coelom
Anus
Anus forms
from blastopore
Blastopore
Blastula
Deuterostomes

24. Evolution of the Animal Body Plan
Deuterostomes differ from protostomes in three other fundamental embryological features:
-1. Cleaveage pattern of embryonic cells
-Protostomes = Spiral cleavage
-Deuterostomes = Radial cleavage
-2. Developmental fate of cells
-Protostomes = Determinate development
-Deuterostomes = Indeterminate development

25. Evolution of the Animal Body Plan
-3. Origination of coelom
Protostomes = Forms simply and directly from the mesoderm
Deuterostomes = Forms indirectly from the archenteron
Deuterostomes evolved from protostomes more than 500 MYA

27. (5) - Segmentation Segmentation- Body is assembled from succession
of similar segments
Each segment may develop into complete set of adult organs
Damage to one segment is less fatal
Locomotion is easier when segments can move independently
Earthworms, Arthropods, and Chordates
Originated multiple times in metazoans.

28. A New Look At Metazoans
The traditional metazoan phylogeny is being reevaluated using molecular data. (Remember the homology/analogy problem.)
Therefore, key morphological characters used in traditional classification are not necessarily conservative
Molecular systematics uses unique sequences within certain genes to identify clusters of related groups

29. A New Look At Metazoans
Molecular data has helped to clarify the relationship of different groups with the animals (metazoans) for example annelids and arthropods

30. A New Look At Metazoans

31. Evolutionary Developmental Biology
Most taxonomists agree that the metazoan kingdom is monophyletic
Three prominent hypotheses have been proposed for the origin of metazoans from single-celled protists

32. Evolutionary Developmental Biology
1. The multinucleate hypothesis
2. The colonial flagellate hypothesis
3. The polyphyletic origin hypothesis
Molecular systematics using rRNA sequences settles this argument in favor of the colonial flagellate hypothesis