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Characteristics
Multicellular heterotroph
Cells lack cell walls
„ Most have nerves, muscles, capacity to
move att some point
i t in
i the
th lif
life cycle
l
„ Ability to reproduce sexually
„ Specialized sensory structures and
nervous system
„
„
Section 4
S i Professor Donald McFarlane
Lecture 11 Animals:
Origins and Bauplans
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Traditional classifications
Most biologists agree kingdom is
monophyletic
„ About 35 recognized animal phyla
„ Most likely ancestor a colonial flagellated
protist similar to choanoflagellates
„
Choanoflagellate
g
cell
Sponge
p g cell
(choanocyte)
… Some
are colonial
… Some cells my have taken on specialized
functions
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(a) Colonial choanoflagellate
(b) Sponge
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Traditional classification based on
body plans
„
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1.
2.
3.
4.
2.
4 main morphological and developmental
features used
Presence or absence of different tissue
types
Type of body symmetry
Presence or absence of a true body
cavity
Patterns of embryonic development
1.
Tissues
…
…
Metazoa - all animals
Divided into
„
Parazoa (no specialized tissues or organs)
…
„
Porifera – sponges
Eumetazoa (more than one type of tissue and
organs)
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Symmetry
…
…
Eumetazoa are radially symmetrical
((Radiata)) or bilaterallyy symmetrical
y
(Bilateria)
Bilateral animals have cephalization and
dorsal and ventral ends
„
…
3 germ layers
Radial animals have oral and aboral sides
„
2 germ layers
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„
Number of cell layers
… Bilateria
are triplobalstic – 3 layers
… Radiata are diploblastic – 2 layers
… Cell layers develop during gastrulation
… Inner layer – endoderm
… Outer layer – ectoderm
… Mesoderm - 3rd layer in bilateral animals
„
Zygote
Forms muscles and most other organs
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Zygote
Zygote
Cleavage
Cleavage
Cleavage
Blastula
(hollow ball)
8-cell stage
8-cell stage
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Endoderm
Zygote
Cleavage
Cleavage
Zygote
Blastula
(hollow ball)
Cleavage
Cleavage
3.
Blastula
(hollow ball)
Mesoderm
8-cell stage
8-cell stage
Archenteron
Gastrulation
Ectoderm
Gastrula
Blastopore
Gastrulation
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Body cavity
…
…
…
…
True coelom – body cavity is completely
lined with mesoderm (coelomates)
(
)
Pseudocoelom – coelom is not completely
lined by tissue derived from mesoderm
(pseudocoelomates)
Acoelomates – lack a body cavity entirely
Fluid-filled body cavity can protect internal
organs or be used as hydrostatic skeleton
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4.
Embryonic development
…
Protostome
„
„
„
…
Spiral cleavage
Cleavage determinate
Blastopore becomes mouth
Deuterostome
„
„
„
Radial cleavage
Cleavage is indeterminate- pluripotent stem cells
Blastopore becomes anus
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Other methods of classification
Possession of exoskeleton
„ Development of notochord
„ Presence or absence of segmentation
„
… Traced
to changes in homeotic or Hox genes
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Changes in Hox Gene Expression Control
Body Segment Specialization
„
„
„
„
„
„
Hox genes involved in pattern formation in early
embryos.
Relatively simple changes in the expression
patterns of these g
p
genes can account for the large
g
variation in arthropod appendage types
Hox genes designated 1-13
Shifts in patterns of gene expression in the embryo
along the anteroposterior axis govern transition
from one type of vertebra to another and short or
long necks
Mice, chicken, goose, and snake
Illustrates descent with modification
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G A G G T T C GA A G A C G A T C A G A T A C C G T C G T A G T T C C G A C C A T A A A C G A T G
Sponge
G A G G T T C GA A G A C G A T C A G A T A C C G T C G T A GT T C C A A C C A T A A A C G A T G
Flatworm
G A G G T T C GA A G A C G A T C A G A T A C C G T C G T A GT T C T G A C C A T A A A C G A T G
Seagull
G GG G A T C A A A G A C G A T C A G A T A C CG T C GT A GT C T T A A C T A T A A A C T A T A
Paramecium
KEY
Fig 32.8
Identical in
all four species
Identical in two
or three species
Dissimilar in
one animal
species
Dissimilar in
the protist
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Similarities between traditional and
molecular phylogeny
1.
2.
3.
4.
The clade called Metazoa is monophyletic, meaning all
animals came from a single common ancestor.
At the earliest stages of evolution, molecular phylogeny
supports the traditional view of the split between
Parazoa and Eumetazoa
Eumetazoa.
There is also agreement about an early split between
Radiata and Bilateria, with most animal phyla belonging
to the Bilateria.
Molecular phylogeny also agrees that the echinoderms
and chordates belong to a clade called the
Deuterostomia.
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2 additional key differences between
traditional and molecular phylogeny
1.
2.
Relationships among Bilateria
Presence or absence of a body cavity
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