1. An Introduction to Animal Diversity
Chapter 32
An Introduction to Animal Diversity
"It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life." Lewis Wolpert (1986)

2. 32.1 Nutritional Mode, Cell Structure and Specialization
Animals are heterotrophs that ingest their food
Animals are multicellular eukaryotes
Their cells lack cell walls
Their bodies are held together by structural proteins such as collagen
Nervous tissue and muscle tissue are unique to animals
1.3 million living species of animals have been identified

3. Reproduction and Development
Most animals reproduce sexually, with the diploid stage usually dominating the life cycle
After a sperm fertilizes an egg, the zygote undergoes rapid cell division called cleavage

4. Reproduction and Development
Cleavage leads to formation of a blastula
The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues
Blastocoel
Endoderm
Cleavage
Cleavage
Blastula
Figure 32.2 Early embryonic development in animals
Ectoderm
Archenteron
Zygote
Eight-cell stage
Gastrulation
Gastrula
Blastocoel
Blastopore
Cross section
of blastula

5. Larval Stages
Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis (think insects!)

6. Homeotic (Hox) genes
All animals, and only animals, have Hox Genes that regulate the development of body form
Although the Hox family of genes has been highly conserved, it can produce a wide diversity of animal morphology

7. From: http://learn. genetics. utah
From: (Left) Normal fruitfly; (Right) Fruitfly with mutation in antennapedia gene Bottom: (Left) Normal fruitfly; (Right) Fruitfly with a homeotic mutation that gives it two thoraxes. Bottom images courtesy of the Archives, California Institute of Technology.

8. 32.3: Animals can be characterized by “body plans” - symmetry
Zoologists sometimes categorize animals according to a body plan, a set of morphological and developmental traits
Animals can be categorized according to the symmetry of their bodies, or lack of it
Some animals have radial symmetry

9. (b) Bilateral symmetry
Fig. 32-7
(a) Radial symmetry
Figure 32.7 Body symmetry
(b) Bilateral symmetry

10. Two-sided symmetry is called bilateral symmetry
Bilaterally symmetrical animals have:
A dorsal (top) side and a ventral (bottom) side
A right and left side
Anterior (head) and posterior (tail) ends
Cephalization, the development of a head

11. 32.3: Characterization by Tissues
Ectoderm is the germ layer covering the embryo’s surface
Endoderm is the innermost germ layer and lines the developing digestive tube, called the archenteron
Diploblastic animals have ectoderm and endoderm
Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians

12. Body Cavities Most triploblastic animals possess a body cavity
A true body cavity is called a coelom and is derived from mesoderm
Coelomates are animals that possess a true coelom

13. A pseudocoelom is a body cavity derived from the mesoderm and endoderm
Triploblastic animals that possess a pseudocoelom are called pseudocoelomates

14. Protostome and Deuterostome Development
Based on early development, many animals can be categorized as having protostome development or deuterostome development

15. Cleavage
In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate

16. Cleavage
With indeterminate cleavage, each cell in the early stages of cleavage retains the capacity to develop into a complete embryo
Indeterminate cleavage makes possible identical twins, and embryonic stem cells

17. Protostome development Deuterostome development (examples: echinoderm,
Fig. 32-9
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderm,
chordates)
(a) Cleavage
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
Key
(b) Coelom formation
Coelom
Ectoderm
Mesoderm
Archenteron
Endoderm
Coelom
Mesoderm
Blastopore
Blastopore
Mesoderm
Solid masses of mesoderm
split and form coelom.
Folds of archenteron
form coelom.
Figure 32.9 A comparison of protostome and deuterostome development
(c) Fate of the blastopore
Anus
Mouth
Digestive tube
Mouth
Anus
Mouth develops from blastopore.
Anus develops from blastopore.

18. Coelom Formation
In protostome development, the splitting of solid masses of mesoderm forms the coelom
In deuterostome development, the mesoderm buds from the wall of the archenteron to form the coelom

19. Fate of the Blastopore
The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula

20. Fate of the Blastopore
In protostome development, the blastopore becomes the mouth
In deuterostome development, the blastopore becomes the anus
"It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life." Lewis Wolpert (1986)

21. Figure 32.9 A comparison of protostome and deuterostome development

22. Figure 32.9 A comparison of protostome and deuterostome development

23. Phyla
Roundworms
Annelids
Mollusks
Chordates
Flatworms
Arthropods
Sponges
Echinoderms
Cnidarians