Animal Evolution

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Animal Evolution
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The Basics

• Animals multicellular, heterotrophic
• Life history
• Sexual w/ flagellated sperm/nonmotile egg
• Development cleavage, blastula, gastrula, some
  have larval stage, metamorphosis
• Probably evolved from a flagellated protist

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1st Major Division Parazoa/Eumetazoa

• Parazoa
• No true tissues
• Phylum Porifera (sponges)
• Eumetazoa
• Have true tissues

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2nd Major DivisionRadiata/Bilateria

• Radiata
• Have radial symmetry
• Top and bottom sides
• Oral mouth side
• Aboral other side
• Only ecto/endoderm diploblastic
• 2 phyla Cnidaria (ex jelly fish) Ctenophora
• Bilateria
• Bilateral symmetery
• 3 axes Dorsal/ventral, anterior/posterior,
  right/left.
• 3 germ layers triploblastic-ectoderm, mesoderm,
  endoderm

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Radial symmetry Symmetry around a central point
Asymmetry No planes of symmetry
Bilateral symmetry Symmetry across the sagittal
plane
dorsal
sagittal plane
posterior
anterior
ventral
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Bilateral symmetry

• Associated w/ cephalization
• Concentration of sensory organs _at_ anterior end
• Many animals have CNS in head a nerve cord
  extending posterior
• Adaptation for movement/predation

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Acoelomates, Pseudocoelomates, Coelomates

• Acoelomates 3 layers, but no body cavity
• Ex Platyhelminthes (flatwoms)
• Psedocoelomates cavity, but not completely
  lined by mesoderm
• Ex Phylum Nematoda, Rotifera
• Coelomates True fluid-filled cavity, completely
  lined by mesoderm
• Have mesentaries connect layers, suspend organs

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No coelom (acoelomate)
ectoderm
mesoderm
endoderm (gut)
flatworm
Pseudocoel
ectoderm
mesoderm
pseudocoel (mesoderm on one side only)
endoderm (gut)
roundworm
Coelom
ectoderm
mesoderm
coelom (surrounded by mesoderm)
endoderm (gut)
earthworm
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4th Major Division Protostomes/Deuterostomes

• Protostomes
• Cleavage Spiral, determinate
• Coelom formation schizocoelous
• Blastopore becomes mouth
• Deuterostomes
• Cleavage Radial, indeterminate
• Coelom formation enterocoelus
• Blastopore becomes anus

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LE 32-9b
Protostome development (examples
molluscs, annnelids, arthropods)
Deuterostome development (examples
echinoderms, chordates)
Coelom formation
Coelom
Archenteron
Coelom
Blastopore
Mesoderm
Blastopore
Mesoderm
Enterocoelous folds of archenteron form coelom
Schizocoelous solid masses of mesoderm split and
form coelom
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LE 32-9c
Protostome development (examples
molluscs, annnelids, arthropods)
Deuterostome development (examples
echinoderms, chordates)
Fate of the blastopore
Mouth
Anus
Digestive tube
Anus
Mouth
Anus develops from blastopore
Mouth develops from blastopore
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a Early embryo
b Adult
dorsal heart
ventral nerve cord
mouth
anus
anus
mouth
blastopore
invagination
dorsal nerve cord
ventral heart
mouth
anus
anus
mouth
blastopore
invagination
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