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Chapter 32
An Introduction to Animal
Diversity
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Welcome to Your Kingdom
• The animal kingdom extends far beyond humans
and other animals we may encounter
Video: Coral Reef
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
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• Their bodies are held together by structural
proteins such as collagen
• Nervous tissue and muscle tissue are unique to
animals
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Reproduction and Development
• Most animals reproduce sexually, with the diploid
stage usually dominating the life cycle
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• After a sperm fertilizes an egg, the zygote
undergoes cleavage, leading to formation of a
blastula
• The blastula undergoes gastrulation, forming
embryonic tissue layers and a gastrula
Video: Sea Urchin Embryonic Development
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LE 32-2_3
Blastocoel
Cleavage
Cleavage
Eight-cell stage
Zygote
Blastocoel
Endoderm
Ectoderm
Gastrula
Blastopore
Gastrulation
Blastula
Cross section
of blastula
• Many animals have at least one larval stage
• A larva is sexually immature and morphologically
distinct from the adult; it eventually undergoes
metamorphosis
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• 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
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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 also the even greater
diversity of extinct ones
• The common ancestor of living animals may have
lived 1.2 billion–800 million years ago
• This ancestor may have resembled modern
choanoflagellates, protists that are the closest
living relatives of animals
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LE 32-3
Single cell
Stalk
LE 32-4
Somatic cells
Digestive
cavity
Reproductive cells
Colonial protist,
and aggregate of
identical cells
Hollow sphere
of unspecialized
cells (shown in
cross section)
Beginning of cell
specialization
Infolding
Gastrula-like
“protoanimal”
Neoproterozoic Era (1 Billion–524 Million Years Ago)
• Early members of the animal fossil record include
the Ediacaran fauna
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Paleozoic Era (542–251 Million Years Ago)
• The Cambrian explosion marks the earliest fossil
appearance of many major groups of living
animals
• There are several hypotheses regarding the cause
of the Cambrian explosion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
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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
• Modern mammal orders and insects diversified
during the Cenozoic
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Concept 32.3: Animals can be characterized by
“body plans”
• Zoologists sometimes categorize animals
according to morphology and development
• A grade is a group of animal species with the
same level of organizational complexity
• A body plan is the set of traits defining a grade
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Symmetry
• Animals can be categorized according to the
symmetry of their bodies, or lack of it
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• Some animals have radial symmetry, the form
found in a flower pot
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LE 32-7a
Radial symmetry
• The two-sided symmetry seen in a shovel is an
example of bilateral symmetry
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LE 32-7b
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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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
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• Animal embryos have concentric layers called
germ layers that form tissues and organs
• Ectoderm is the germ layer covering the embryo’s
surface
• Endoderm is the innermost germ layer
• Diploblastic animals have ectoderm and
endoderm
• Triploblastic animals also have an intervening
mesoderm layer
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Body Cavities
• In triploblastic animals, a body cavity may be
present or absent
• A true body cavity is called a coelom and is
derived from mesoderm
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LE 32-8a
Coelom
Body covering
(from ectoderm)
Digestive tract
(from endoderm)
Coelomate
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
• A pseudocoelom is a body cavity derived from the
blastocoel, rather than from mesoderm
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LE 32-8b
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
Pseudocoelomate
Muscle layer
(from
mesoderm)
• Acoelomates are organisms without body cavities
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LE 32-8c
Body covering
(from ectoderm)
Wall of digestive cavity
(from endoderm)
Acoelomate
Tissuefilled region
(from
mesoderm)
Protostome and Deuterostome Development
• Based on early development, many animals can
be categorized as having protostome or
deuterostome development
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Cleavage
• In protostome development, cleavage is spiral and
determinate
• In deuterostome development, cleavage is radial
and indeterminate
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LE 32-9a
Protostome development
(examples: molluscs,
annnelids, arthropods)
Eight-cell stage
Spiral and determinate
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Radial and indeterminate
Cleavage
Coelom Formation
• In protostome development, the splitting of 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
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LE 32-9b
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Coelom formation
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Schizocoelous: solid
masses of mesoderm
split and form coelom
Blastopore
Mesoderm
Enterocoelous:
folds of archenteron
form coelom
Fate of the Blastopore
• In protostome development, the blastopore
becomes the mouth
• In deuterostome development, the blastopore
becomes the anus
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LE 32-9c
Protostome development
(examples: molluscs,
annnelids, arthropods)
Deuterostome development
(examples: echinoderms,
chordates)
Mouth
Anus
Digestive tube
Mouth
Mouth develops
from blastopore
Anus
Anus develops
from blastopore
Fate of the blastopore
Concept 32.4: Leading hypotheses agree on major
features of the animal phylogenetic tree
• Zoologists recognize about 35 animal phyla
• Current debate in animal systematics has led to
the development of two phylogenetic hypotheses,
but others exist as well
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• One hypothesis of animal phylogeny based mainly
on morphological and developmental comparisons
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LE 32-10
“Radiata”
Deuterostomia
Protostomia
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
• One hypothesis of animal phylogeny is based
mainly on molecular data
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LE 32-11
“Radiata”
Deuterostomia
Lophotrochozoa
Bilateria
Eumetazoa
Metazoa
Ancestral colonial
flagellate
Ecdysozoa
Points of Agreement
• All animals share a common ancestor
• Sponges are basal animals
• Eumetazoa is a clade of animals with true tissues
• Most animal phyla belong to the clade Bilateria
• Vertebrates and some other phyla belong to the
clade Deuterostomia
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Disagreement over the Bilaterians
• The morphology-based tree divides bilaterians into
two clades: deuterostomes and protostomes
• In contrast, recent molecular studies assign two
sister taxa to protostomes: the ecdysozoans and
the lophotrochozoans
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• Ecdysozoans shed their exoskeletons through a
process called ecdysis
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Lophotrochozoans have a feeding structure called
a lophophore
• Other phyla go through a distinct larval stage
called a trochophore larva
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LE 32-13
Apical tuft
of cilia
Mouth
Anus
An ectoproct, a lophophorate
Structure of trochophore larva
Future Directions in Animal Systematics
• Phylogenetic studies based on larger databases
will likely provide further insights into animal
evolutionary history
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings