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 and other animals we may encounter
Figure 32.1

3. Several characteristics of animals
Concept 32.1: Animal are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers
Several characteristics of animals
Sufficiently define the group

4. Animals are heterotrophs
Nutritional Mode
Animals are heterotrophs
That ingest their food

5. Cell Structure and Specialization
Animals are multicellular eukaryotes
Their cells lack cell walls

6. Their bodies are held together
By structural proteins such as collagen
Nervous tissue and muscle tissue
Are unique to animals

7. Reproduction and Development
Most animals reproduce sexually
With the diploid stage usually dominating the life cycle

8. After a sperm fertilizes an egg
The zygote undergoes cleavage, leading to the formation of a blastula
The blastula undergoes gastrulation
Resulting in the formation of embryonic tissue layers and a gastrula

9. Cross section of blastula
Early embryonic development in animals
The zygote of an animal undergoes a succession of mitotic cell divisions called cleavage. 1
Only one cleavage
stage–the eight-cell
embryo–is shown here. 2
In most animals, cleavage results in the
formation of a multicellular stage called a blastula.
The blastula of many animals is a hollow ball of cells. 3
Zygote
Cleavage
Eight-cell stage
Blastula
Cross section of blastula
Blastocoel
Gastrula
Gastrulation
Endoderm
Ectoderm
Blastopore
The endoderm of
the archenteron de-
velops into the tissue
lining the animal’s
digestive tract. 6
The blind pouch
formed by gastru-
lation, called
the archenteron,
opens to the outside
via the blastopore. 5
Most animals also undergo gastrulation, a rearrangement of the embryo in which one end of the embryo folds inward, expands, and eventually fills the blastocoel, producing layers of embryonic tissues: the ectoderm (outer layer) and the endoderm (inner layer). 4
Figure 32.2

10. 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

11. The animal kingdom includes not only great diversity of living species
Concept 32.2: The history of animals may span more than a billion years
The animal kingdom includes not only great diversity of living species
But the even greater diversity of extinct ones as well

12. The common ancestor of living animals
May have lived 1.2 billion–800 million years ago
May have resembled modern choanoflagellates, protists that are the closest living relatives of animals
Single cell
Stalk
Figure 32.3

13. Was probably itself a colonial, flagellated protist
Colonial protist,
an aggregate of
identical cells
Hollow sphere of unspecialized cells (shown in cross section)
Beginning of cell specialization
Infolding
Gastrula-like “protoanimal”
Somatic cells
Digestive
cavity
Reproductive cells
Figure 32.4

14. Neoproterozoic Era (1 Billion–524 Million Years Ago)
Early members of the animal fossil record
Include the Ediacaran fauna
(a)
(b)
Figure 32.5a, b

15. Paleozoic Era (542–251 Million Years Ago)
The Cambrian explosion
Marks the earliest fossil appearance of many major groups of living animals
Is described by several current hypotheses
Figure 32.6

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

17. Cenozoic Era (65.5 Million Years Ago to the Present)
The beginning of this era
Followed mass extinctions of both terrestrial and marine animals
Modern mammal orders and insects
Diversified during the Cenozoic

18. Concept 32.3: Animals can be characterized by “body plans”
One way in which zoologists categorize the diversity of animals
Is according to general features of morphology and development
A group of animal species
That share the same level of organizational complexity is known as a grade

19. The set of morphological and developmental traits that define a grade
Are generally integrated into a functional whole referred to as a body plan

20. Animals can be categorized
Symmetry
Animals can be categorized
According to the symmetry of their bodies, or lack of it

21. Some animals have radial symmetry
Like in a flower pot
Radial symmetry. The parts of a radial animal, such as a sea anemone (phylum Cnidaria), radiate from the center. Any imaginary slice through the central axis divides the animal into mirror images.
(a)
Figure 32.7a

22. Some animals exhibit bilateral symmetry
Or two-sided symmetry
Bilateral symmetry. A bilateral animal, such as a lobster (phylum Arthropoda), has a left side and a right side. Only one imaginary cut divides the animal into mirror-image halves.
(b)
Figure 32.7b

23. 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

24. Tissues Animal body plans Tissues
Also vary according to the organization of the animal’s tissues
Tissues
Are collections of specialized cells isolated from other tissues by membranous layers

25. Triploblastic animals
Animal embryos
Form germ layers, embryonic tissues, including ectoderm, endoderm, and mesoderm
Diploblastic animals
Have two germ layers
Triploblastic animals
Have three germ layers

26. In triploblastic animals
Body Cavities
In triploblastic animals
A body cavity may be present or absent

27. A true body cavity Is called a coelom and is derived from mesoderm
Figure 32.8a
Coelom
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Coelomate. Coelomates such as annelids have a true coelom, a body cavity completely lined by tissue derived from mesoderm.
(a)

28. A pseudocoelom
Is a body cavity derived from the blastocoel, rather than from mesoderm
Pseudocoelom
Muscle layer
(from
mesoderm)
Body covering
(from ectoderm)
Digestive tract
Pseudocoelomate. Pseudocoelomates such as nematodes have a body cavity only partially lined by tissue derived from mesoderm.
(b)
Figure 32.8b

29. Organisms without body cavities
Are considered acoelomates
Body covering
(from ectoderm)
Tissue-
filled region
(from
mesoderm)
Digestive tract
(from endoderm)
Acoelomate. Acoelomates such as flatworms lack a body cavity between the digestive tract and outer body wall.
(c)
Figure 32.8c

30. Protostome and Deuterostome Development
Based on certain features seen in early development
Many animals can be categorized as having one of two developmental modes: protostome development or deuterostome development

31. In protostome development
Cleavage
In protostome development
Cleavage is spiral and determinate
In deuterostome development
Cleavage is radial and indeterminate
Protostome development
(examples: molluscs, annelids,
arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(a) Cleavage. In general, protostome development begins with spiral, determinate cleavage. Deuterostome development is characterized by radial, indeterminate cleavage.
Figure 32.9a

32. Coelom Formation In protostome development In deuterostome development
The splitting of the initially solid masses of mesoderm to form the coelomic cavity is called schizocoelous development
In deuterostome development
Formation of the body cavity is described as enterocoelous development
Figure 32.9b
Archenteron
Blastopore
Mesoderm
Coelom
Schizocoelous: solid
masses of mesoderm
split and form coelom
Enterocoelous:
folds of archenteron
form coelom
(b) Coelom formation. Coelom formation begins in the gastrula stage. In protostome development, the coelom forms from splits in the mesoderm (schizocoelous development). In deuterostome development, the coelom forms from mesodermal outpocketings of the archenteron (enterocoelous development).

33. In protostome development
Fate of the Blastopore
In protostome development
The blastopore becomes the mouth
In deuterostome development
The blastopore becomes the anus
Figure 32.9c
Anus
Mouth
Mouth develops
from blastopore
Anus develops
Digestive tube

34. Zoologists currently recognize about 35 animal phyla
Concept 32.4: Leading hypotheses agree on major features of the animal phylogenetic tree
Zoologists currently recognize about 35 animal phyla
The current debate in animal systematics
Has led to the development of two phylogenetic hypotheses, but others exist as well

35. One hypothesis of animal phylogeny based mainly on morphological and developmental comparisons
Porifera
Cnidaria
Ctenophora
Phoronida
Ectoprocta
Brachiopoda
Echinodermata
Chordata
Platyhelminthes
Mollusca
Annelida
Arthropoda
Rotifera
Nemertea
Nematoda
“Radiata”
Deuterostomia
Protostomia
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
Figure 32.10

36. One hypothesis of animal phylogeny based mainly on molecular data
Calcarea
Silicarea
Ctenophora
Cnidaria
Echinodermata
Chordata
Brachiopoda
Phoronida
Ectoprocta
Platyhelminthes
Nemertea
Mollusca
Annelida
Rotifera
Nematoda
Arthropoda
“Radiata”
“Porifera”
Deuterostomia
Lophotrochozoa
Ecdysozoa
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
Figure 32.11

37. Points of Agreement
All animals share a common ancestor
Sponges are basal animals
Eumetazoa is a clade of animals with true tissues

38. Most animal phyla belong to the clade Bilateria
Vertebrates and some other phyla belong to the clade Deuterostomia

39. Disagreement over the Bilaterians
The morphology-based tree
Divides the bilaterians into two clades: deuterostomes and protostomes
In contrast, several recent molecular studies
Generally assign two sister taxa to the protostomes rather than one: the ecdysozoans and the lophotrochozoans

40. Ecdysozoans share a common characteristic
They shed their exoskeletons through a process called ecdysis
Figure 32.12

41. An ectoproct, a lophophorate Structure of trochophore larva
Lophotrochozoans share a common characteristic
Called the lophophore, a feeding structure
Other phyla
Go through a distinct larval stage called a trochophore larva
Figure 32.13a, b
Apical tuft
of cilia
Mouth
Anus
(a)
An ectoproct, a lophophorate
(b)
Structure of trochophore larva

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