Download An introduction to animal diversity

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Multicellular heterotrophs
Most have muscle and nervous tissue
Most reproduce sexually, with a
flagellated sperm and a large egg uniting
to form a diploid zygote.
The diploid stage dominates the life
cycle.
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The zygote is a fertilized egg.
The zygote of an animal undergoes a series of mitotic
divisions called cleavage.
An eight-cell embryo is formed by three rounds of cell
division.
Cleavage results in a multicellular stage called the
blastula.
The blastula is typically a hollow ball of cells around a
cavity called the blastocoel.
Most animals also undergo gastrulation, in which one
end of the embryo folds inward to form two layers of
embryonic tissue, ectoderm and endoderm; eventually
fills in the blastocoel to form the gastrula.
cleavage
Zygote
cleavage
8 cell stage
GGastrula
Blastula
Gastrulation
Blastocoel
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The pouch formed by gastrulation is the
archenteron
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Cnidarians and Ctenophores are
diploblastic.
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Ectoderm: Forms epidermal layer of the
skin and nervous system
Endoderm: Forms the lining of the gut
the liver and the lungs.
Mesoderm forms muscles, bone, kidney,
gonads, and connective tissue.
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Symmetry is the overall shape of the
body.
If an animal is symmetrical, it can be
divided along at least one plane into
similar halves.
Animals that have no plane of symmetry
are asymmetrical. SPONGES are
asymmetrical.
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Simplest form of symmetry is spherical
symmetry, in which body parts radiate out from
a central point. In infinite number of planes can
pass through the central point and divide the
organism into halves. Unicellular protists.
Radial Symmetry: one main axis and any plane
cutting through that axis divides the animal into
similar parts. Cnidarians and Ctenophores,
adult Echinoderms
Bilateral Symmetry: Animal can be divided into
a mirror “right” and “left” halves. Animals that
move in one direction; Associated with
cephaliztion.
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Concentration of sensory equipment at
one end (the anterior or head end) of the
organism.
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Acoelomate animals, such as flatworms lack
an enclosed, fluid-filled body cavity, the
space is filled with masses of cells called
mesenchyme.
Pseudocoelomate animals have a body
cavity called a pseudcoel, in which many of
the internal organs are suspended. It is
enclosed by muscles only on the outside.
Coelomate animals have a body cavity that
develops within the mesoderm. The coelom
is enclosed on both sides by mesoderm.
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Cushions the suspended organs
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Acts as a hydrostatic skeleton
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Enables internal organs to grow and
move independently
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Many animals have bodies that are
divided into segments.
Segments allow specialization of body
parts.
Allow animals to alter shape of body to
control movements and separate body
cavity into compartments.
Arthropods and Annelids show
segmentation.
Some animals have only internal
segmentation, as in vertebrate embyos.
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Protostomes:
Mouth forms from the
blastopore
Spiral, determinate
cleavage
Determinate means cells
are commited to a
specific fate as early as
two cell stage
Coelom forms from
splits in the mesoderm
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Deuterostomes
Mouth forms from
secondary opening
Radial, indeterminate
cleavage
Indeterminate cleavage
means cells are not
fated until later in
development
Coelom forms from outpockets of the mesoderm
lining the archenteron
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Lacks symmetry and true tissues?
Show radial symmetry and are
diploblastic?
Have three tissue layers, but lack body
cavity?
Show bilateral symmetry and have a
psuedocoelom?
Have a true coelom and are protostomes?
Have a true coelom and are
deuterostomes?