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

2. Overview: Welcome to Your Kingdom
The animal kingdom:
Extends far beyond humans & other animals we may encounter
Living animals that have been identified:
1.3 million living species
Video: Coral Reef

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

4. Animal are: Animals are eukaryotes that are: Multicellular
Heterotrophic
With tissues that developed from embryonic layers
Several characteristics, taken together, sufficiently define the group

5. Nutritional Mode, Cell Structure and Specialization
Animals are heterotrophs that ingest their food
They 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

6. Reproduction and Development
Most animals reproduce sexually
The diploid stage usually dominates 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
Video: Sea Urchin Embryonic Development

7. 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

8. Many animals have at least one larval stage
A larva is:
Sexually immature, and
Morphologically distinct from the adult
It eventually undergoes metamorphosis

9. All animals, and only animals, have:
A family of genes called Hox genes
They regulate the development of body form
This Hox family of genes is highly conserved
Yet, it can produce a wide diversity of animal morphology

10. The history of animals spans more than half a billion years
The animal kingdom includes:
A great diversity of living species
An even greater diversity of extinct species
The common ancestor of living animals:
May have lived between 675 and million years ago
May have resembled:
Modern choanoflagellates (protists that are the closest living relatives of animals)

11. Fig. 32-3
Fossil Evidence of Animal Evolution from a Common Ancestor Over Four Geologic Era
Single cell
Stalk
Figure 32.3 Three lines of evidence that choanoflagellates are closely related to animals

12. Neoproterozoic Era (1 Billion–524 Million Years Ago)
Early members of the animal fossil record include:
The Ediacaran biota, which dates from 565 to 550 million years ago

13. (a) Mawsonites spriggi (b) Spriggina floundersi
Fig. 32-4
1.5 cm
0.4 cm
Figure 32.4 Ediacaran fossils
(a) Mawsonites spriggi
(b) Spriggina floundersi

14. 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
Several hypotheses explain the increase in diversity of animal phyla during the Cambrian explosion period:
New predator-prey relationships
A rise in atmospheric oxygen
The evolution of the Hox gene complex

15. Fig. 32-5
Figure 32.5 A Cambrian seascape

16. Mesozoic Era (251–65.5 Million Years Ago)
Coral reefs emerged, becoming important marine ecological niches for other organisms
Dinosaurs were the dominant terrestrial vertebrates during this era
The first mammals emerged

17. Cenozoic Era (65.5 Million Years Ago to the Present)
The Cenozoic era begins :
After mass extinctions of both terrestrial & marine animals
These extinctions included:
The large, non-flying dinosaurs
The marine reptiles
Modern mammal orders and insects diversified during the Cenozoic

18. Animals can be characterized by “body plans”
Zoologists sometimes categorize animals according to:
A body plan
A body plan is a set of:
Morphological & developmental traits
A grade:
Is a group of animal species whose members share key biological features
It is not necessarily a clade, or monophyletic group

19. Symmetry
Animals can be categorized according to the symmetry of their bodies, or lack of it
Some animals have radial symmetry
Others have two-sided symmetry 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

20. Symmetry
(a) Radial symmetry
(b) Bilateral symmetry

21. 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 animal embryonic development:
Three germ layers give rise to the tissues & organs

22. Embryonic Layers Ectoderm: Endoderm: Diploblastic: Triploblastic:
Is the germ layer covering the embryo’s surface
Endoderm:
Is the innermost germ layer
It lines the developing digestive tube
The digestive tube is called the archenteron
Diploblastic:
Animals having ectoderm and endoderm
Triploblastic:
Animals with additional intervening mesoderm
Most possess a body cavity

23. Body Cavities A true body cavity is: Called a coelom
Derived from mesoderm
Coelomates:
Are animals that possess a true coelom

24. (a) Coelomate Coelom Body covering (from ectoderm) Tissue layer
Fig. 32-8a
(a) Coelomate
Coelom
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Figure 32.8a Body cavities of triploblastic animals

25. A pseudocoelom:
Is a body cavity derived from the mesoderm and endoderm
Pseudocoelomates:
Triploblastic animals that possess a pseudocoelom

26. (b) Pseudocoelomate Body covering (from ectoderm) Pseudocoelom
Fig. 32-8b
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
Figure 32.8b Body cavities of triploblastic animals

27. Triploblastic animals that lack a body cavity are called acoelomates
(c) Acoelomate
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)

28. Protostome and Deuterostome Development
Based on early development, many animals can be categorized as having one of two developmental modes:
Protostome development, or
Deuterostome development

29. Cleavage In protostome development:
Cleavage plane is spiral (diagonal to vertical axis) and determinate
In deuterostome development:
Cleavage plane is radial (parallel or perpen- dicular to vericla axis) and indeterminate
With indeterminate cleavage:
Each cell in the early stages of cleavage retains the capacity to develop into a complete embryo. Ex. 4-cell stage of sea urchin
Human zygote? Production of identical twins

30. (a) Cleavage Protostome development (examples: molluscs, annelids)
Fig. 32-9a
(a) Cleavage
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Eight-cell stage
Figure 32.9a A comparison of protostome and deuterostome development
Spiral and determinate
Radial and indeterminate

31. 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

32. (b) Coelom formation Protostome development (examples: molluscs,
Fig. 32-9b
(b) Coelom formation
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
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.

33. Fate of the Blastopore The blastopore: In protostome development:
Indentation forms during gastrulation
Leads to the formation of archenteron
Connects archenteron to the exterior of the gastrula
In protostome development:
The blastopore becomes the mouth
In deuterostome development:
The blastopore becomes the anus

34. (c) Fate of the blastopore
Fig. 32-9c
(c) Fate of the blastopore
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
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.

35. 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.

36. New views of animal phylogeny is emerging from molecular data
Zoologists recognize: about:
About three dozen animal phyla
Current debate in animal systematics has led to the development of:
Two phylogenetic hypotheses
But others exist as well

37. One hypothesis of animal phylogeny is based mainly on comparisons between:
Morphological features, &
Developmental features

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

39. Another hypothesis of animal phylogeny is based mainly on:
Molecular data

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

41. 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

42. Disagreement over Bilaterian Relationships
The morphology-based tree divides bilaterians into two clades:
Deuterostomes
Protostomes
In contrast, recent molecular studies indicate three bilaterian clades:
Deuterostomia
Ecdysozoa, and
Lophotrochozoa
Ecdysozoans:
Shed their exoskeletons through a process called ecdysis

43. Fig
Figure Ecdysis

44. Some lophotrochozoans have a feeding structure called a lophophore
Other phyla go through a distinct developmental stage called the trochophore larva

45. (b) Structure of a trochophore larva
Fig
Lophophore
Apical tuft
of cilia
Mouth
Figure Morphological characteristics found among lophotrochozoans
100 µm
Anus
(a) An ectoproct
(b) Structure of a trochophore
larva

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