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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 32
An Overview of Animal Diversity
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
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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Nutritional Mode
• Animals are heterotrophs that ingest their food
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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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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
© 2011 Pearson Education, Inc.
Figure 32.2-1
Zygote
Cleavage
Eight-cell
stage
Figure 32.2-2
Zygote
Cleavage
Blastocoel
Cleavage
Eight-cell
stage
Blastula
Cross section
of blastula
Figure 32.2-3
Zygote
Cleavage
Blastocoel
Cleavage
Eight-cell
stage
Blastula
Cross section
of blastula
Gastrulation
Blastocoel
Endoderm
Ectoderm
Archenteron
Cross section
of gastrula
Blastopore
• 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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• 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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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
© 2011 Pearson Education, Inc.
Figure 32.3
Individual
choanoflagellate
Choanoflagellates
OTHER
EUKARYOTES
Sponges
Animals
Other animals
Collar cell
(choanocyte)
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
© 2011 Pearson Education, Inc.
RESULTS
1 Early stages of
development
100 m
Figure 32.6
2 32-cell stage
Site of
gastrulation
3 Early gastrula
stage
4 Embryos with
blocked -catenin
activity
Site of
gastrulation
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
© 2011 Pearson Education, Inc.
Figure 32.7
(a) Radial symmetry
(b) Bilateral 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
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• 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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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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• 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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• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 32.8
(a) Coelomate
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
Muscle layer
(from
mesoderm)
(c) Acoelomate
Body covering
(from ectoderm) Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
Figure 32.8a
(a) Coelomate
Coelom
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
• A pseudocoelom is a body cavity derived from the
mesoderm and endoderm
• Triploblastic animals that possess a
pseudocoelom are called pseudocoelomates
© 2011 Pearson Education, Inc.
Figure 32.8b
(b) Pseudocoelomate
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
Muscle layer
(from
mesoderm)
• Triploblastic animals that lack a body cavity are
called acoelomates
© 2011 Pearson Education, Inc.
Figure 32.8c
(c) Acoelomate
Body covering
(from ectoderm)
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
• 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 descendants
© 2011 Pearson Education, Inc.
Protostome and Deuterostome Development
• Based on early development, many animals can
be categorized as having protostome
development or deuterostome development
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 32.9
Protostome development
(examples: molluscs,
annelids)
(a) Cleavage
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(b) Coelom formation
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
(c) Fate of the
blastopore
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
Figure 32.9a
(a) Cleavage
Protostome development
(examples: molluscs,
annelids)
Eight-cell stage
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Key
Ectoderm
Mesoderm
Endoderm
Spiral and determinate
Radial and indeterminate
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
© 2011 Pearson Education, Inc.
Figure 32.9b
(b) Coelom
formation
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
Coelom
Archenteron
Coelom
Key
Ectoderm
Mesoderm
Endoderm
Mesoderm
Blastopore
Solid masses of mesoderm
split and form coelom.
Blastopore
Mesoderm
Folds of archenteron
form coelom.
Fate of the Blastopore
• 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
© 2011 Pearson Education, Inc.
Figure 32.9c
(c) Fate of the
blastopore
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
Anus
Mouth
Digestive tube
Key
Ectoderm
Mesoderm
Endoderm
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
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
© 2011 Pearson Education, Inc.
Points of Agreement
1. All animals share a common ancestor
2. Sponges are basal animals
3. Eumetazoa is a clade of animals
(eumetazoans) with true tissues
4. Most animal phyla belong to the clade Bilateria,
and are called bilaterians
5. Chordates and some other phyla belong to the
clade Deuterostomia
© 2011 Pearson Education, Inc.
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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Figure 32.12
• Some lophotrochozoans have a feeding
structure called a lophophore
• Others go through a distinct developmental stage
called the trochophore larva
© 2011 Pearson Education, Inc.
Figure 32.13
Lophophore
Apical tuft
of cilia
Mouth
Anus
(a) Lophophore feeding
structures of an ectoproct
(b) Structure of a trochophore
larva
Future Directions in Animal Systematics
• Phylogenetic studies based on larger databases
will likely provide further insights into animal
evolutionary history
© 2011 Pearson Education, Inc.
Figure 32.UN03
Common ancestor
of all animals
Metazoa
Porifera
(basal animals)
Eumetazoa
Ctenophora
Cnidaria
Acoela (basal
bilaterians)
Deuterostomia
Bilateral
symmetry
Three germ
layers
Lophotrochozoa
Ecdysozoa
Bilateria (most animals)
True
tissues