1. An Overview of Animal Diversity
Chapter 32
An Overview of Animal Diversity

2. Overview: Welcome to Your Kingdom
The animal kingdom extends far beyond humans and other animals we may encounter
Scientists have identified 1.3 million living species of animals
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3. Figure 32.1
Figure 32.1 Which of these organisms are animals? 3

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
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5. Nutritional Mode Animals are heterotrophs that ingest their food
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6. Cell Structure and Specialization
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, defining characteristics of animals
Tissues are groups of cells that have a common structure, function, or both
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7. 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 multicellular, hollow blastula
The blastula undergoes gastrulation, forming a gastrula with different layers of embryonic tissues
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8. Cross section of blastula Cross section of gastrula
Figure
Zygote
Cleavage
Blastocoel
Cleavage
Eight-cell stage
Cross section of blastula
Gastrulation
Blastula
Figure 32.2 Early embryonic development in animals.
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross section of gastrula
Blastopore 8

9. Many animals have at least one larval stage
A larva is sexually immature and morphologically distinct from the adult; it eventually undergoes metamorphosis
A juvenile resembles an adult, but is not yet sexually mature
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10. Most 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
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11. Concept 32.2: The history of animals spans more than half a billion years
The animal kingdom includes a great diversity of living species and an even greater diversity of extinct ones
The common ancestor of living animals may have lived between 675 and 800 million years ago
This ancestor may have resembled modern choanoflagellates, protists that are the closest living relatives of animals
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12. Individual choanoflagellate
Figure 32.3
Individual choanoflagellate
Choanoflagellates
OTHER EUKARYOTES
Sponges
Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals.
Animals
Collar cell (choanocyte)
Other animals 12

13. Neoproterozoic Era (1 Billion–542 Million Years Ago)
Early members of the animal fossil record include the Ediacaran biota, which dates from 565 to 550 million years ago
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14. (a) Mawsonites spriggi (b) Spriggina floundersi
Figure 32.4
1.5 cm
0.4 cm
Figure 32.4 Ediacaran fossils.
(a) Mawsonites spriggi
(b) Spriggina floundersi 14

15. Paleozoic Era (542–251 Million Years Ago)
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 and decline of Ediacaran biota
New predator-prey relationships
A rise in atmospheric oxygen
The evolution of the Hox gene complex
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16. Figure 32.5
Figure 32.5 A Cambrian seascape. 16

17. Animals began to make an impact on land by 460 million years ago
Animal diversity continued to increase through the Paleozoic, but was punctuated by mass extinctions
Animals began to make an impact on land by 460 million years ago
Vertebrates made the transition to land around 360 million years ago
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18. Mesozoic Era (251–65.5 Million Years Ago)
Coral reefs emerged, becoming important marine ecological niches for other organisms
The ancestors of plesiosaurs were reptiles that returned to the water
During the Mesozoic era, dinosaurs were the dominant terrestrial vertebrates
The first mammals emerged
Flowering plants and insects diversified
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19. Cenozoic Era (65.5 Million Years Ago to the Present)
The beginning of the Cenozoic era followed mass extinctions of both terrestrial and marine animals
These extinctions included the large, nonflying dinosaurs and the marine reptiles
Mammals increased in size and exploited vacated ecological niches
The global climate cooled
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20. 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
Some developmental characteristics are conservative
For example, the molecular control of gastrulation is conserved among diverse animal groups
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21. Early stages of development
Figure 32.6
RESULTS 1
Early stages of development
100 m 2
32-cell stage
Site of gastrulation 3
Early gastrula stage
Site of gastrulation
Figure 32.6 Inquiry: Did -catenin play an ancient role in the molecular control of gastrulation? 4
Embryos with blocked -catenin activity 21

22. Symmetry
Animals can be categorized according to the symmetry of their bodies, or lack of it
Some animals have radial symmetry, with no front and back, or left and right
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23. (b) Bilateral symmetry
Figure 32.7
(a) Radial symmetry
Figure 32.7 Body symmetry.
(b) Bilateral symmetry 23

24. 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
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25. Radial animals are often sessile or planktonic (drifting or weakly swimming)
Bilateral animals often move actively and have a central nervous system
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26. 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
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27. 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
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28. Sponges and a few other groups lack true tissues
Diploblastic animals have ectoderm and endoderm
These include cnidarians and comb jellies
Triploblastic animals also have an intervening mesoderm layer; these include all bilaterians
These include flatworms, arthropods, vertebrates, and others
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29. 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
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30. Body covering (from ectoderm)
Figure 32.8a
(a) Coelomate
Coelom
Body covering (from ectoderm)
Tissue layer lining coelom and suspending internal organs (from mesoderm)
Digestive tract (from endoderm)
Figure 32.8 Body cavities of triploblastic animals. 30

31. A pseudocoelom is a body cavity derived from the mesoderm and endoderm
Triploblastic animals that possess a pseudocoelom are called pseudocoelomates
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32. Body covering (from ectoderm)
Figure 32.8b
(b) Pseudocoelomate
Body covering (from ectoderm)
Pseudocoelom
Muscle layer (from mesoderm)
Digestive tract (from endoderm)
Figure 32.8 Body cavities of triploblastic animals. 32

33. Triploblastic animals that lack a body cavity are called acoelomates
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34. Body covering (from ectoderm) Tissue- filled region (from mesoderm)
Figure 32.8c
(c) Acoelomate
Body covering (from ectoderm)
Tissue- filled region (from mesoderm)
Wall of digestive cavity (from endoderm)
Figure 32.8 Body cavities of triploblastic animals. 34

35. Coelomates and pseudocoelomates belong to the same grade
A grade is a group whose members share key biological features
A grade is not necessarily a clade, an ancestor and all of its descendents
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36. 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
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37. Protostome development (examples: molluscs, annelids)
Figure 32.9
Protostome development (examples: molluscs, annelids)
Deuterostome development (examples: echinoderms, chordates)
(a) Cleavage
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(b) Coelom formation
Coelom
Archenteron
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
Key
Ectoderm
Mouth
Anus
Mesoderm
Mouth develops from blastopore.
Anus develops from blastopore.
Endoderm 37

38. Concept 32.4: New views of animal phylogeny are emerging from molecular data
Zoologists recognize about three dozen animal phyla
Phylogenies now combine morphological, molecular, and fossil data
Current debate in animal systematics has led to the development of multiple hypotheses about the relationships among animal groups
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39. One hypothesis of animal phylogeny is based mainly on morphological and developmental comparisons
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40. One hypothesis of animal phylogeny is based mainly on molecular data
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41. ANCESTRAL COLONIAL FLAGELLATE Ctenophora Metazoa
Figure 32.11
Porifera
ANCESTRAL COLONIAL FLAGELLATE
Ctenophora
Metazoa
Cnidaria
Eumetazoa
Acoela
Echinodermata
Chordata
Deuterostomia
Bilateria
Platyhelminthes
Rotifera
Ectoprocta
Lophotrochozoa
Figure A view of animal phylogeny based mainly on molecular data.
Brachiopoda
Mollusca
Annelida
Nematoda
Ecdysozoa
Arthropoda 41

42. 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
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43. Progress in Resolving Bilaterian Relationships
The morphology-based tree divides bilaterians into two clades: deuterostomes and protostomes
In contrast, recent molecular studies indicate three bilaterian clades: Deuterostomia, Ecdysozoa, and Lophotrochozoa
Ecdysozoans shed their exoskeletons through a process called ecdysis
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44. Some lophotrochozoans have a feeding structure called a lophophore
Others go through a distinct developmental stage called the trochophore larva
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45. Lophophore feeding structures of an ectoproct (b)
Figure 32.13
Apical tuft of cilia
Lophophore
Mouth
Figure Morphological characteristics of lophotrochozoans.
Anus
(a)
Lophophore feeding structures of an ectoproct
(b)
Structure of a trochophore larva 45

46. Future Directions in Animal Systematics
Phylogenetic studies based on larger databases will likely provide further insights into animal evolutionary history
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