1. Introduction to Animal Diversity
Packet #37
Chapter #32

2. Animal Diversity
Biologists have identified 1.3 million living species if animals.
Estimates put the range much higher
10 – 200 million

3. Characteristics Most Common to Animals
Eukaryotic
Multicellular
Heterotrophic
Animals use enzymes to digest their food after they have ingested it.

4. Characteristics Common to Most Animals Reproduction
Most animals reproduce sexually and have a diploid stage that is dominant in the life cycle.
Sperm and egg unite to form a zygote
Zygote undergoes cleavage
Multiple cell divisions result in the development of a hollow ball of cells
Blastula
Blastula undergoes gastrulation.
Embryonic tissues are formed
Developmental stage is called the gastrula.

5. Characteristics Common to Most Animals Reproduction
Some animals develop directly into adults
After transient stages of maturation
However, life cycle of many animals include larval stages.
Larva
Sexually immature form of an adult
Morphologically distinct
Usually eats different food
Inhabits different areas than the adult
Must undergo metamorphosis to become an adult

6. Characteristics Common to Most Animals Reproduction
Animals share a unique homeobox
Family of genes
Hox genes
The number of hox genes is correlated with the complexity of the animal’s anatomy.

7. The “Evolution” of Animals

8. Figure 32.4

9. Introduction I
Animal diversification, according to the theory of evolution, began more than one billion years ago.
Most systematists believe that the Kingdom Animalia is monophyletic.
Theory is that a colonial flagellated protist, related to today’s chanoflagellates, was the start of the Animal Kingdom.

10. Introduction II
Ediacaran fauna is considered to be the first generally accepted fossil of animals.
According to the theory of evolution they are 542 to 525 million years old
Cambrian Explosion
Ecological causes
Predator/prey relationships
Geological causes
Rise in atmospheric oxygen
Genetic causes
Evolution of the Hox gene complex
At the end of the period, developmental patterns, that constrained evolution, caused no additional phyla to evolve after that period.

11. Grades vs. Clades Grade Clade
A group of animal species that share the same level of organized complexity.
Does not have a monophyletic ancestor
Body Plan
Set morphological and developmental traits that define a grade.
Basic structure of the body used to infer evolutionary relationships.
Clade
Group of species that includes ancestral species and all of its descendents
Have a monophyletic ancestor

12. Body Plans
Symmetry

13. Symmetry Radial Symmetry
Describes how the parts of an animal radiate from the center.
Any imaginary slice through the central axis divides the animal into mirror images.
Sea anemones have a top (oral, mouth) side and a bottom (aboral) side.

14. Symmetry II Bilateral Symmetry Describes a two sided body plan.
Animal has a left side and right side
Imaginary slice can only be placed in one location in order to divide the animal mirror images.
Lobster has a dorsal (top) side, a ventral (bottom) side, a left and right side, an anterior (head) with a mouth and a posterior (tail) end.

15. Symmetry III
Animals can be categorized according to the symmetry of their bodies or lack of it.
Sponges lack symmetry
It was hypothesized that cnidarians and ctenophores were closely related because they share radial symmetry.
Symmetry Reflects Lifestyle
Radial animals are sessile or planktonic
Bilaterial animals more actively from one place to another
The nervous system enables these organisms to move.

16. Relationships Via Tissue

17. Tissue I
Embryonic Tissue, called germ layers, are produced via gastrulation
Germ Layers
Ectoderm
Outer layer
Gives rise to the body covering and the nervous system
Endoderm
Inner layer
Gives rise to the lining of the gut (archenteron) and other digestive organs
Mesoderm
Middle layer
Gives rise to most other body structures.
Including muscle

18. Diploblastic vs. Triploblastic
Animals with only two layers
Ectoderm and Endoderm
Jellies
Corals
Comb jellies
Triploblastic
Animals with all three layers
Include all bilaterally symmetric animals.

19. Body cavities

20. Body Cavity I
Triploblastic animals have traditionally been classified as
Acoelomates
No body cavity
Lack a coelom.
Pseudocoelomate
Body cavity not completely lined with mesoderm
Body cavity formed from the blastocoel.
Coelomate
True coelom
Body cavity completely lined with mesoderm.

21. Functions of Body Cavities
Provides protection to internal organs
Allow organs to grow and move independently of the outer body wall.

22. Formation of the Coelom
During gastrulation, developing digestive tube forms the archenteron.
Protostomes
Development of the coelom forms from splits in the mesoderm
Schizocoelous Development
Deuterostomes
Development of the coelom forms from outpocketing of the mesodermal tissue of the archenteron.
Enterocoelous Development

23. Evolutionary Branches of Coelomates

24. Introduction I Protostomia Deuterostomia Mollusks Annelids Arthropods
Enchinoderms
Chordates

25. Protosomes Blastopore develops into the mouth
Undergo spiral and determinate cleavage
Spiral cleavage
Describes how the planes of cell division are diagonal to the vertical axis of the embryo.
Smaller cells lie in the grooves between larger, underlying cells
Determinate cleavage
Indicates that the developmental fate of each embryonic cell is determined at fertilization.
If cell is isolated it will form an inviable embryo.

26. Deuterostomes Blastopore typically becomes the anus.
Undergo radial and indeterminate cleavage.
Radial cleavage
Cleavage planes are either parallel or perpendicular to the vertical axis of the egg
Indeterminate cleavage
Each cell produced by early cleavage divisions has the capacity to develop into a complete embryo.