1. Overview of Animal Diversity

2. General Features of Animals
Animals are a diverse group of consumers that share major characteristics
All are heterotrophs
All are multicellular
Cells do not have cell walls
Most are able to move
All are very diverse in form and habitat
Most reproduce sexually
Have a characteristic patterns of embryonic development
Cells of all animals (except sponges) are organized into tissues

3. Evolution of the Animal Body Plan
Five key transitions in animal evolution
Tissues
Symmetry
Body cavity
Development
Segmentation

4. Evolution of the Animal Body Plan
1. Evolution of tissues
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

5. Evolution of the Animal Body Plan
2. Evolution of symmetry
Parazoa (sponges) lack any definite symmetry
Eumetazoa have a symmetry defined along imaginary axes drawn through the animal’s body
There are two main types of symmetry
Radial symmetry
Bilateral symmetry

6. Evolution of the Animal Body Plan
Radial symmetry
Body parts arranged around central axis
Can be bisected into two equal halves in any 2D plane perpendicular to that axis

7. Evolution of the Animal Body Plan
Bilateral symmetry
Body has right and left halves that are mirror images
Body has distinct anterior/posterior and dorsal/ventral divisions

8. Evolution of the Animal Body Plan
Bilaterally symmetrical animals have two main advantages over radially symmetrical animals
Cephalization
Evolution of a definite brain area
Greater mobility

9. 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)

10. Evolution of the Animal Body Plan
3. Evolution of a body cavity
Three basic kinds of body plans
Acoelomates have no body cavity

11. Evolution of the Animal Body Plan
Pseudocoelomates have a body cavity between mesoderm and endoderm
Called the pseudocoel

12. Evolution of the Animal Body Plan
Coelomates have a body cavity entirely within the mesoderm
Called the coelom

13. Evolution of the Animal Body Plan
The body cavity made possible the development of advanced organs systems
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

14. 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 2-layer-thick ball called a gastrula with:
Blastopore - Opening to outside
Archenteron - Primitive body cavity

15. 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

16. Evolution of the Animal Body Plan
Deuterostomes differ from protostomes in three other embryological features:
Cleaveage pattern of embryonic cells
Protostomes - Spiral cleavage
Deuterostomes - Radial cleavage
Developmental fate of cells
Protostomes - Determinate development
Deuterostomes - Indeterminate development
Origination of coelom
Protostomes - Forms simply and directly from the mesoderm
Deuterostomes - Forms indirectly from the archenteron

17. Evolution of the Animal Body Plan

18. Evolution of the Animal Body Plan
5. Evolution of segmentation
Segmentation provides two advantages
1. Allows redundant organ systems in adults such as occurs in the annelids
2. Allows for more efficient and flexible movement because each segment can move independently
Segmentation appeared several times in the evolution of animals

19. Traditional Classification of Animals
Multicellular animals, or metazoans, are traditionally divided into 36 or so distinct phyla based on shared anatomy and embryology
Metazoans are divided into two main branches:
Parazoa - Lack symmetry and tissues
Eumetazoa - Have symmetry and tissues
Diploblastic - Have two germ layers
Triploblastic - Have three germ layers

20. Going From A single cell to Multicellular Organism

21. This is an example of Phylogenic Tree
As an A & P class will work from left to right throughout the 1st marking period
Do you see any patterns?

22. Cleavage Blastula Gastrulation Gastrula Cell Cycle: G1, S, G2, and Mitosis

23. Fertilization (1n) egg + (1n) sperm=(2n) zygote
The initial event in development in sexual reproduction is fertilization, the union of male and female gametes to form a zygote.
Recombinant of parental and maternal genes
Parthenogenesis-development without fertilization (Example some fish and salamanders)

24. Cleavage and Early Development
During cleavage the embryo divides repeatedly to convert the large cytoplasmic mass into a large cluster of small maneuverable cells called Blastomeres.

25. Cleavage and Early Development
No growth during this period, only subdivisions of mass, which continues until somatic cell size is attained. Think of it a origami!!!!
So, what are somatic cells?
At the end of cleavage 100s to 1000s of cells

26. Cleavage and Early Development
Look at the Diagram to see an example of a VEGETAL POLE AND ANIMAL POLE
What is the role of the yolk?
Do the cells at the poles divide at the same rate?

27. What can we learn from Development?
Developmental Biology is a growing field!!
How can a zygote, a single layer cell, produce a multitude of body parts in an organism and how gene expressions proceeds.
Search for commonalities among organisms.

28. II. An overview of Development Following Cleavage A. Blastulation
Cleavage subdivides the mass of zygote until a cluster of cells called a blastula is formed (looks like a hollow mass of cells).
In most animals, the cells are arranged around a central fluid-filled cavity called a blastocoel.
Formation of a blastula stage, with its one layer of germ cells, occurs in all multicellular animlas.

29. B. Gastrulation and Formation of Two Germ Layers
a. Gastrulation converts the spherical blastula into a more complex configuration and forms a second germ layer.
One side of the blastula bends inward in a process called invagination, forming a new internal cavity. Picture pushing in a beach ball-the inward region forms a pouch.
The internal pouch is the gut cavity called an archenteron or gastrocoel.
The opening to the gut, where the inward bending began, is the blastopore.

30. Gastrulation and Formation of Two Germ Layers
C. The gastrula stage has two layers:
a. An outer layer of cells surrounding the blastocoel, called ectoderm
b. An inner layer of cells is called endoderm
The gut opens only at the blastopore it is called a blind or incomplete gut. Animals with a blind gut must consume food completely digested, or the remains of the food egested through the mouth. Ex sea anemones and flatworms.
Most animals have a complete gut with a second opening, the anus.

31. c. Formation of the Mesoderm, a Third layer
i. Multicellular animals (not sponges) proceed blastula to gastrula
Two germ layers called DIPLOBLASTIC
Three germ layers called TRIPLOBLASTIC
The third layer is called mesoderm

33. C. Formation of the Coelom
Coelomates are animals with a true coelom, a fluid filled body cavity completely lined by tissues derived from mesoderm.
The inner and outer layers of tissue that surround the cavity connect dorsally and ventrally to form mesenteries that suspend the internal organs.

34. Animals can be divided into three body type:
Acoelomate
Pseudocoelomate
Coelomate

35. D. Protostome vs Deuterostome in Coelomates
Mollusks, annelids, arthropods and some other phyla are collectively called protostomes. 
Echinoderms and chordates are called deuterostomes.
4 Fundamental differences between the two groups:
***** See Class Handout or next slide

37. A New Look At Metazoans
The traditional animal phylogeny is being reevaluated using molecular data
Myzostomids are marine animals that are parasites of echinoderms
Have no body cavity and only incomplete segmentation and so have been allied with annelids

38. A New Look At Metazoans
Recent analysis of the translation machinery revealed that myzostomids have no close link to the annelids at all
Instead, they are more closely allied with the flatworms (planaria and tapeworms)

39. A New Look At Metazoans
It seems that key morphological characters used in traditional classification are not necessarily correct
Molecular systematics uses unique sequences within certain genes to identify clusters of related groups

40. A New Look At Metazoans
Most new phylogenies agree on two revolutionary features:
Separation of annelids and arthropods into different clades
Division of the protostome group into Ecdysozoa and Spiralia
The latter is then broken down into Lophotrochozoa and Platyzoa

41. Examples can be found in Table 32.2 of Raven et al.
A New Look At Metazoans
Examples can be found in Table 32.2 of Raven et al.

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

43. 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