1. An Introduction to Animal Diversity
Chapter 32
An Introduction to Animal Diversity

2. Overview: Welcome to Your Kingdom
Largest Kingdom, multicellular, heterotrophic, gametes produced in gonads (ovaries & testes)
Life evolved in the sea. The few animal groups that successfully colonized fresh water and land and evolved many adaptations of structure, function, and reproduction to these different environments.
Most animals are made u of three layers: an outer protective and sensory tube, an inner digestive tube, and between them the organs of motion, reproduction, excretion, and transport.
Active carnivores made many of the major evolutionary advances among animals, but most groups then radiated to produce members with other lifestyles such as herbivory, sessile filter feeding, or parasitism.
(Sun coral catching and eating live brine)

3. Fig. 32-1
Figure 32.1 Which of these organisms are animals?

4. Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
There are exceptions to nearly every criterion for distinguishing animals from other life-forms
Several characteristics, taken together, sufficiently define the group
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

5. 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
Cleavage leads to formation of a blastula
The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues
(early embryonic development)
(sea urchin gastrulation)

6. Cleavage Zygote Eight-cell stage Fig. 32-2-1
Figure 32.2 Early embryonic development in animals

7. Cross section of blastula
Fig
Cleavage
Cleavage
Blastula
Zygote
Eight-cell stage
Blastocoel
Figure 32.2 Early embryonic development in animals
Cross section
of blastula

8. Cross section of blastula
Fig
Blastocoel
Endoderm
Cleavage
Cleavage
Blastula
Ectoderm
Archenteron
Zygote
Eight-cell stage
Gastrulation
Gastrula
Blastocoel
Blastopore
Figure 32.2 Early embryonic development in animals
Cross section
of blastula

9. Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis
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

10. Concept 32.2: The history of animals spans more than half a billion years
The Cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals
There are several hypotheses regarding the cause of the Cambrian explosion
New predator-prey relationships – predators acquired novel adaptations, such as forms of locomotion that helped them catch prey, while prey species acquired new defenses, such as protective shells
A rise in atmospheric oxygen – greater oxygen availability would have provided opportunities for animals with higher metabolic rates and larger body sizes to thrive
The evolution of the Hox gene complex – provided the developmental flexibility that resulted in variations in morphology

11. Concept 32.3: Animals can be characterized by “body plans”
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
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

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

13. Tissues
Animal body plans also vary according to the organization of the animal’s tissues
Tissues are collections of specialized cells isolated from other tissues by membranous layers
During development, three germ layers give rise to the tissues and organs of the animal embryo
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

14. Body Cavities Most triploblastic animals possess a body cavity
Fig. 32-8
Body Cavities
Coelom
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
(a) Coelomate
Most triploblastic animals possess a body cavity
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
(b) Pseudocoelomate
Figure 32.8 Body cavities of triploblastic animals
Body covering
(from ectoderm)
Tissue-
filled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c) Acoelomate

15. Coelom Body covering (from ectoderm) Tissue layer lining coelom
Fig. 32-8a
A true body cavity is called a coelom and is derived from mesoderm
Coelomates are animals that possess a true coelom
Coelom
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Figure 32.8a Body cavities of triploblastic animals
(a) Coelomate

16. Body covering (from ectoderm) Pseudocoelom Muscle layer (from
A pseudocoelom is a body cavity derived from the mesoderm and endoderm
Triploblastic animals that possess a pseudocoelom are called pseudocoelomates
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
Figure 32.8b Body cavities of triploblastic animals
(b) Pseudocoelomate

17. Wall of digestive cavity (from endoderm)
Triploblastic animals that lack a body cavity are called acoelomates
Body covering
(from ectoderm)
Tissue-
filled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
Figure 32.8c Body cavities of triploblastic animals
(c) Acoelomate

18. Protostome and Deuterostome Development
Based on early development, many animals can be categorized as having protostome development or deuterostome development
In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate
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

19. 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.

20. Cleavage In protostome development, cleavage is spiral and determinate
In deuterostome development, cleavage is radial and indeterminate
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
Eight-cell stage
Eight-cell stage
Deuterostome development
(examples: echinoderms,
chordates)
Protostome development
(examples: molluscs,
annelids)
(a) Cleavage
Figure 32.9a A comparison of protostome and deuterostome development
Spiral and determinate
Radial and indeterminate

21. Coelom Formation
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
(b) Coelom formation
Coelom
Key
Ectoderm
Archenteron
Mesoderm
Endoderm
Coelom
Mesoderm
Figure 32.9b A comparison of protostome and deuterostome development
Blastopore
Blastopore
Mesoderm
Solid masses of mesoderm
split and form coelom.
Folds of archenteron
form coelom.
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

22. The blastopore forms during gastrulation and connects the archenteron to the exterior of the gastrula
In protostome development, the blastopore becomes the mouth
In deuterostome development, the blastopore becomes the anus
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
(c) Fate of the blastopore
Anus
Mouth
Key
Ectoderm
Digestive tube
Mesoderm
Endoderm
Figure 32.9c A comparison of protostome and deuterostome development
Mouth
Anus
Mouth develops from blastopore.
Anus develops from blastopore.
Fate of the Blastopore

23. Concept 32.4: New views of animal phylogeny are emerging from molecular data
Zoologists recognize about three dozen animal phyla
Current debate in animal systematics has led to the development of two phylogenetic hypotheses, but others exist as well
One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons (This is the one we will follow in chapters 33 & 34)
One hypothesis of animal phylogeny is based mainly on molecular data

24. mainly on morphological and developmental comparison
Fig
“Porifera”
Cnidaria
ANCESTRAL
COLONIAL
FLAGELLATE
Metazoa
Ctenophora
Eumetazoa
Ectoprocta
Brachiopoda
Deuterostomia
Echinodermata
Phylogeny based
mainly on morphological
and developmental comparison
Chordata
Bilateria
Platyhelminthes
Figure A view of animal phylogeny based mainly on morphological and developmental comparisons
Rotifera
Protostomia
Mollusca
Annelida
Arthropoda
Nematoda

25. mainly on molecular data
Fig
Silicea
“Porifera”
Calcarea
ANCESTRAL
COLONIAL
FLAGELLATE
Metazoa
Ctenophora
Cnidaria
Eumetazoa
Acoela
Echinodermata
Deuterostomia
Chordata
Phylogeny based
mainly on molecular data
Bilateria
Platyhelminthes
Rotifera
Ectoprocta
Figure A view of animal phylogeny based mainly on molecular data
Lophotrochozoa
Brachiopoda
Mollusca
Annelida
Nematoda
Ecdysozoa
Arthropoda

26. Points of Agreement All animals share a common ancestor
Sponges are basal animals
Eumetazoa is a clade of animals (eumetazoans) with true tissues
Most animal phyla belong to the clade Bilateria, and are called bilaterians
Chordates and some other phyla belong to the clade Deuterostomia

27. Common ancestor of all animals Sponges (basal animals) Ctenophora
Fig. 32-UN1
Common ancestor
of all animals
Sponges
(basal animals)
Metazoa
Ctenophora
Eumetazoa
Cnidaria
True
tissues
Acoela (basal
bilaterians)
Deuterostomia
Bilateria (most animals)
Bilateral
summetry
Lophotrochozoa
Three germ
layers
Ecdysozoa

28. Fig. 32-T1

29. Fig. 32-UN2

30. You should now be able to:
List the characteristics that combine to define animals
Distinguish between the following pairs or sets of terms: radial and bilateral symmetry; diploblastic and triploblastic; spiral and radial cleavage; determinate and indeterminate cleavage; acoelomate, pseudocoelomate, and coelomate
Compare the developmental differences between protostomes and deuterostomes