Chapter 32
An Introduction to Animal
Diversity
Modes of Nutrition
• Animals differ in their mode of
nutrition than plants and fungi.
– Animals and fungi are heterotrophic.
– Plants are autotrophic.
– Fungi release exoenzymes.
• Animals ingest their food.
– They release enzymes to break down
their food.
Animal Cells
•
•
•
•
Animal cells lack cell walls.
Fungi have them-Plants have them-The structural integrity of animal
bodies is due to proteins--collagen.
– Tight junctions, gap junctions, and
desmosomes.
• Muscle cells and nerve cells are also
found in animals.
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Animal Reproduction
• Animals reproduce mostly via sexual
reproduction.
– Life cycle dominated by the diploid
stage.
• Usually a small, haploid, flagellated
sperm fertilizes a non-motile egg
forming a diploid zygote.
Cell Division
• Cell Division is known as cleavage
Changes in the Zygote
• After fertilization, the zygote
undergoes cleavage.
• Successive mitotic divisions with no
cell growth.
• This division leads to the formation
of the blastula.
The Blastula
• Is a hollow ball of animal cells.
• The blastula then becomes the
gastrula.
The Gastrula
• The gastrula is the stage that gives
rise to embryonic tissues.
• The embryonic tissues eventually
develop into adult body parts.
Stages of Development
• Some animals go through transient
stages of development.
– Many of them go through at least 1
larval stage.
• A larva is a sexually immature form
of an animal that is morphologically
distinct from the adult.
– Frogs and flies are examples.
Stages of Development
• Recall the importance of the homeobox
genes.
– Hox genes control the segmentation pattern in
animals.
• They are the result of many successive
gene duplications throughout evolution.
• They play important roles in the
development and differentiation of
animals.
• They produce many of the observed
morphological features.
Body Plans
• Body plans are morphological traits
or organizational plans that are
shared by a group of animal species.
Symmetry
• Some animals have symmetry,
others don’t.
• Radial symmetry--top and bottom,
but no front and back.
• Bilateral symmetry--top and bottom,
front and back.
Tissues
• The body plans of animals also
varies according to tissue
organization.
• Tissues are collections of specialized
cells separated from other tissues by
membranous layers.
• Tissues form after gastrulation has
taken place.
Tissues
• Development gives rise to germ
layers which form the various tissues
and organs of the body.
– Ectoderm--outer portion of body--skin.
– Endoderm--innermost layer. Lines the
developing digestive tube. The lining of
the digestive tract and organs derived
from it.
Germ Layers
• Ectoderm and endoderm are the previously
mentioned germ layers.
• Animals with just these two are called
diploblasts.
– Sponges and Coelenterates
• Animals that have a third germ layer, the
mesoderm, are called triploblasts.
– Mesoderm forms the muscles and most other
organs between the digestive tube and the
outside of the animal.
Body Cavities
• Some triploblasts have a body cavity
filled with fluid.
– Called a coelom; derived from
mesoderm.
• It separates the digestive tract from
the outer body wall.
– Animals with a coelom are called
coelomates.
Body Cavities
• Some triploblasts form a body cavity
from the blastocoel rather than the
mesoderm.
– This cavity is functional and is called a
pseudocoelom.
– These animals are called
pseudocoelomates.
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Body Cavities
• Some triploblasts lack a coelom
altogether.
– There is no body cavity between the
digestive tract and the outer body wall.
– These are called acoelomates.
Protostomes and
Deuterostomes
• Many animals can be classified as
either protostomes or
deuterostomes.
• Three features distinguish their
development:
– 1. Cleavage
– 2. Coelom Formation
– 3. Fate of the Blastopore
Cleavage
• Many protostomes have spiral cleavage.
• Cleavage diagonal to the vertical axis of the
embryo.
• The 8-cell stage has smaller cells which lie in the
grooves between the larger underlying cells.
Cleavage
• This so-called determinant cleavage
of some animals determines the
developmental fate of each
embryonic cell very early.
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Cleavage
• Radial cleavage is common in
deuterostomes.
• You either see cleavage planes
parallel or perpendicular to the
vertical axis of the embryo.
• Here, the tiers of the cells are
aligned.
Cleavage
• Most deuterostomes have
indeterminant cleavage.
• This means that each cell in the embryo
can fully develop into a complete
embryo.
– This makes identical twins possible.
– This is why 4-cell stage sea stars can be divided
to give 4 larvae.
– This is why embryonic stem cells have the
capacity to perform so many functions.
Deuterostomes
• Have radial cleavage
• Their archenteron gives rise to the coelom
• The mouth arises from the end of the
embryo opposite the blastopore.
• (The blastopore becomes the anus)
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The Archenteron
• This is the endoderm-lined cavity
that forms during animal
development (gastrulation) and
gives rise to the digestive tract.
Coelom Formation
• In protostome development, as the
archenteron forms during
gastrulation, the mesoderm splits
forming a coelomic cavity.
Coelom Formation
• During deuterostome development,
the mesoderm buds off of the wall of
the archenteron.
• This cavity becomes the coelom.
Fate of the Blastopore
• This is the fundamental characteristic that
distinguishes protostome and
deuterostome development.
• The blastopore is the indentation that leads
to the formation of the archenteron.
Protostomes
• After the
archenteron
develops, a second
opening forms at
the opposite end of
the gastrula.
• Now there are two
openings.
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Protostomes
• In protostomes,
the mouth
develops from the
first opening--the
blastopore.
• The anus develops
from the second
opening.
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Deuterostomes
• In deuterostomes,
the mouth
develops from the
second opening.
• The blastopore
(first opening)
becomes the anus.
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