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Chapter 32
• An Introduction to Animal Diversity
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• Welcome to Your Kingdom
• The animal kingdom extends far beyond
humans and other animals we may encounter
Figure 32.1
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• Animal are multicellular, heterotrophic
eukaryotes with tissues that develop from
embryonic layers
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Nutritional Mode
• Heterotrophs ingest their food
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Cell Structure and Specialization
Multicellular eukaryotes,
Cells lack cell walls
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• Bodies are held together by structural proteins,
e.g. collagen
• Nervous tissue and muscle tissue
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Reproduction
• Most animals reproduce sexually
– Diploid stage dominating the life cycle
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Development
• Sperm fertilizes egg zygote cleavage
blastula gastrulation formation of
embryonic tissue layers gastrula
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• Early embryonic development in animals
1 The zygote of an animal
undergoes a succession of mitotic
cell divisions called cleavage.
2 Only one cleavage
stage–the eight-cell
embryo–is shown here.
3 In most animals, cleavage results in the
formation of a multicellular stage called a blastula.
The blastula, a hollow ball of cells.
Blastocoel
Cleavage
Cleavage
6 The endoderm of
the archenteron develops into the tissue
lining the animal’s
digestive tract.
Zygote
Eight-cell stage
Blastula
Cross section
of blastula
Blastocoel
Endoderm
5 The blind pouch
formed by gastrulation, called
the archenteron,
opens to the outside
via the blastopore.
Ectoderm
Gastrula
Gastrulation
Blastopore
Figure 32.2
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4 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).
• Hox genes regulate development of body form
• Hox family of genes has been highly
conserved, yet produces a wide diversity of
animal morphology
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• The history of animals spans more than a
billion years
• Great diversity of living species and even
greater diversity of extinct ones
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• Common ancestor of living animals
– Lived ~1 billion million years ago
– May have resembled modern choanoflagellates,
protists that are the closest living relatives of
animals
Single cell
Stalk
Figure 32.3
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– Was probably a colonial, flagellated protist
Digestive
cavity
Somatic cells
Reproductive cells
Colonial protist,
an aggregate of
identical cells
Hollow sphere of
unspecialized
cells (shown in
cross section)
Beginning of cell
specialization
Figure 32.4
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Infolding
Gastrula-like
“protoanimal”
Neoproterozoic Era (1 Billion–524 Million Years Ago)
• Early members of the animal fossil record
Figure 32.5a, b
(a)
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(b)
Paleozoic Era (542–251 Million Years Ago)
• The Cambrian explosion
– Earliest fossil appearance of many major
groups of living animals
– Several current hypotheses
Figure 32.6
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Mesozoic Era (251–65.5 Million Years Ago)
•
Dinosaurs were 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)
• Mass extinctions of terrestrial and marine
animals
• Modern mammal orders and insects diversified
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Body Plans
• Radial symmetry
– Like in a flower pot
(a) 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.
Figure 32.7a
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• Bilateral symmetry
– two-sided symmetry
(b) 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.
Figure 32.7b
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• Bilateral animals
– Dorsal (top) side and a ventral (bottom) side
– Right and left side
– Anterior (head) and posterior (tail) ends
– Cephalization, the development of a head
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Tissues
• Collections of specialized cells isolated from
other tissues by membranous layers
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• Animal embryos
– Form germ layers, embryonic tissues,
including ectoderm, endoderm, and mesoderm
• Diploblastic animals
– two germ layers
• Triploblastic animals
– three germ layers
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Body Cavities
• In triploblastic animals
– body cavity may be present or absent
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Coelom
• A true body cavity derived from mesoderm
Coelom
(a)
Coelomate. Coelomates such as
annelids have a true coelom, a body
cavity completely lined by tissue
derived from mesoderm.
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Digestive tract
(from endoderm)
Figure 32.8a
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Body covering
(from ectoderm)
Pseudocoelom
• Body cavity not lined w/ mesoderm
Body covering
(from ectoderm)
(b) Pseudocoelomate. Pseudocoelomates
such as nematodes have a body cavity only
partially lined by tissue derived from
mesoderm.
Pseudocoelom
Digestive tract
(from ectoderm)
Figure 32.8b
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Muscle layer
(from
mesoderm)
Acoelomates
• No body cavities
Body covering
(from ectoderm)
(c) Acoelomate. Acoelomates such as
flatworms lack a body cavity between
the digestive tract and outer body wall.
Digestive tract
(from endoderm)
Figure 32.8c
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Tissuefilled region
(from
mesoderm)
Protostome and Deuterostome Development
• Distinction based on early development
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Cleavage
• Protostomes
– Cleavage is spiral and determinate
• Deuterostomes
– Cleavage is radial and indeterminate
Protostome development
(examples: molluscs, annelids,
arthropods)
Eight-cell stage
Spiral and determinate
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Radial and indeterminate
Figure 32.9a
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(a) Cleavage. In general, protostome
development begins with spiral,
determinate cleavage.
Deuterostome development is
characterized by radial, indeterminate
cleavage.
Coelom Formation
• Protostomes
– Splitting of mesoderm  coelom (schizocoelous
development)
• Deuterostomes
– Enterocoelous development
Coelom
Archenteron
Coelom
Mesoderm
Blastopore
Mesoderm
Blastopore
Enterocoelous:
Schizocoelous: solid
folds of archenteron
masses of mesoderm
form coelom
split and form coelom
Figure 32.9b
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(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).
Fate of the Blastopore
• Protostomes
– Blastopore becomes the mouth
• Deuterostomes
– Blastopore becomes the anus
Mouth
Anus
Digestive tube
Mouth
Figure 32.9c
Mouth develops
from blastopore
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Anus
Anus develops
from blastopore
“Radiata”
Deuterostomia
Metazoa
Figure 32.10
Ancestral colonial
flagellate
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Nematoda
Nemertea
Rotifera
Arthropoda
Annelida
Protostomia
Bilateria
Eumetazoa
Mollusca
Platyhelminthes
Chordata
Echinodermata
Brachiopoda
Ectoprocta
Phoronida
Ctenophora
Cnidaria
Porifera
• Hypothesis of animal phylogeny based on
anatomy
Arthropoda
Nematoda
Rotifera
Annelida
Mollusca
Nemertea
Platyhelminthes
Ectoprocta
Phoronida
Brachiopoda
Chordata
Echinodermata
Cnidaria
Ctenophora
Silicarea
Calcarea
• Hypothesis based on molecular data
“Radiata”
“Porifera”
Deuterostomia
Lophotrochozoa
Bilateria
Eumetazoa
Metazoa
Figure 32.11
Ancestral colonial
flagellate
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Ecdysozoa