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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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Kingdom Animalia
• What are the characteristics of 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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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
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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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LE 32-7a
• Some animals have radial symmetry, the form
found in a flower pot
Radial symmetry
LE 32-7b
The two-sided symmetry seen in a shovel is an
example of bilateral symmetry
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
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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
Coelom
Digestive tract
(from endoderm)
Coelomate
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Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
• A pseudocoelom is a body cavity derived from
the blastocoel, rather than from mesoderm
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
Pseudocoelomate
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Muscle layer
(from
mesoderm)
• Acoelomates are organisms without body cavities
Body covering
(from ectoderm)
Wall of digestive cavity
(from endoderm)
Acoelomate
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Tissuefilled region
(from
mesoderm)
Fate of the Blastopore
• In protostome development, the blastopore
becomes the mouth
• In deuterostome development, the blastopore
becomes the anus
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
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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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings