Transcript 25.1 Animal Origins

25.1 Animal Origins

What is an animal?
• Multicelled,
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•
•
•
heterotroph
Most motile
Reproduce sexually
Unwalled
Most have tissue
and organs
Evolutionary Tree
Tissues

Key innovation in
complexity:
• Ability to interact in
functional units
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Epithelium
• Sheet like array
• Functions: absorption,
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secretion, sensory
1st epidermis
2nd gastrodermis
cont.
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Connective tissue
• All contain
• Most have a matrix in which living cells and
protein fibers (collagen) exist
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Embryo forming – 2 primary tissue layers
• Outer ectoderm
• Inner endoderm
• mesoderm
Body Size

How to deal with increasing constraints of
SA-V ratios of cells?
• Pseudopds and microvilli in single cell species
• Simple animals are sheets/ribbons
• circulatory system in large animals
Where did it all start?
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Colonial Theory
• 1st animals evolved
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from tiny colony of
flagellated, amoeba
like cells
Choanoflagellates
Share common
ancestor with
sponges
25.2 Basic Body Plans
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Body Symmetry
• Polarity – front to
•
back axis, with
anterior and
posterior ends
Radial – organized
around main axis,
water
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Bilateral – right
and left halves
along a main
axis
Cephalization –
distinct head region
Gut and Body Cavity
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Incomplete gut
• Sac-like
• One opening
• 1st to evolve
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Complete gut
• Tubular
• 2 openings
• Mouth (specialized
feeding structures)
to anus
Formation of Complete Gut
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Protostomes
• 1st opening
•
becomes mouth
Flatworms,
mollusks, annelids,
roundworms,
arthropods
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Deuterostomes
• 1st opening
•
becomes anus
Echinoderms,
chordates
epidermis
No coelom
(acoelomate
animals)
gut
cavity
organs packed between
gut and body wall
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None – flatworms, few
invertebrates
• Tissue and organs fill
region between gut and
body wall
Fig. 25-6a, p.406
gut
cavity
epidermis
Pseudocoel
(pseudocoelomate
animals)
unlined body cavity around gut
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Pseudocoel – roundworms
• In some protostomes coelom is reduced/lost
Fig. 25-6b, p.406
gut
cavity
epidermis
Coelom
(coelomate
animals)
peritoneum
body cavity with
lining that
holds internal
organs in place
Fig. 25-6c, p.406
Repeating Units
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Favors regional specialization in structure
and function
Segmentation – annelids, arthropods,
vertebrates
• Divide into a series of functionally connected units
along main body axis
Phylum
Examples
Evolutionary Milestone
Porifera
sponges
multicellularity
Cnidaria
jellyfish, hydra, coral tissues
Platyhelminthes
flatworms
bilateral symmetry
Nematoda
roundworms
pseudocoelom
Mollusca
clams, squids, snails
coelom
Annalida
earthworms, leeches
segmentation
Arthropoda
insects, spiders,
crustaceans
jointed appendages
Echinodermata
starfish
deuterostomes
Chordata
vertebrates
notochord