Introduction To Animal Evolution

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Introduction To Animal Evolution

• Chapter 32

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• Animals 1st appeared in Precambrian in waters,
  spread to land.
• 5 criteria that define animal
• 1Animals multicellular, must get food through
  ingesting other organisms or organic material.

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http//www.biology.wustl.edu/plant/simplealgalsyst
ems1.jpg
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• 2Animals do not have cell walls.
• 3Animals have nervous tissue to conduct impulses
  and muscle tissue for movement.
• 4Most animals reproduce sexually with diploid
  stage being dominate.
• 5Animals have special regulatory genes (Hox
  genes) help zygote form into animal.

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Branching of evolutionary tree

• 1st branch point splits Parazoa (lack true
  tissues) from Eumetazoa (true tissues).
• Parazoa include sponges.
• Eumetazoans divided into 2 major branches, partly
  based on body symmetry.

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http//www.sciencedaily.com/images/2007/07/0707051
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• Radial symmetry - phylum Cnidaria and phylum
  Ctenophora.
• Bilateral symmetry (left and right side) - rest
  of phyla.

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• Bilateral symmetry - cephalization, -
  concentration of sensory equipment towards head.
• Difference between 2 groups - presence of germ
  layers - layers of embryonic tissue that form
  various tissues and organs.

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http//www.guam.net/pub/sshs/depart/science/mancus
o/apbiolecture/27_Animalia/Annelida/Image11.gif
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• Bilaterally symmetric animals - 3 germ endoderm
  (innermost), mesoderm (middle) ectoderm
  (outermost).
• Bilateral animals split according to presence of
  body cavity (fluid-filled space separating
  digestive tract from outer body wall) and what
  cavity looks like.

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http//universe-review.ca/I10-13-layers.jpg
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• Acoelomates (phylum Platyhelminthes) have solid
  body, lack body cavity.
• Some organisms - body cavity - not completely
  lined by mesoderm.
• Pseudocoelomates include rotifers (phylum
  Rotifera), roundworms (phylum Nematoda).

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• Coelomates organisms with true coelom,
  (fluid-filled body cavity completely lined by
  mesoderm).
• Body cavity has many purposes including
  cushioning organs, allowing them more room to
  grow.

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• Coelomate phyla divided based on differences in
  development.
• Many protostomes (mollusks, annelids, arthropods)
  undergo spiral cleavage.
• In many protosomes, blastopore develops into
  mouth 2nd opening at opposite end of gastrula
  develops into anus.

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http//chsweb.lr.k12.nj.us/mstanley/outlines/anima
ls/antax/image51.gif
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• Zygotes of many deuterostomes undergo radial
  cleavage.
• Deuterostomes - blastopore usually develops into
  anus, mouth derived from 2nd opening.

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