Biodiversity Lecture 6

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BiodiversityLecture 6

• Animals
• Multicellular Heterotrophic Eukaryotes

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What Characterizes an Animal?

• They are multicellular heterotrophic eukaryotes
• They must take organic molecules into their body
  through ingestion (eating)
• Lack cell walls
• They have cell membranes, as do all living
  organisms, but have no other structure external
  to the cell membrane.
• Have muscle and nervous tissue
• Diploid stage of life cycle is dominant

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Origin of Animals

• First Appearance of an animal
• About 700 million years ago
• It is believed that an ancestral protist acquired
  multicellularity. This would have been considered
  the first animal
• Animals have been evolving ever since this time
• Four major branch points have occurred during the
  evolution of animals.

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Animal Evolution Branch Point 1

• Branch Point 1
• Eumetazoans separate from Parazoans
• Parazoans Animals without true tissues
• Para Beside
• Zoa Animals
• Dont look like animals, hence their name,
  beside the animals . They are given their own
  special subkingdom Parazoa
• One Phylum Porifera (pore bearers), the Sponges
• Eumetazoans Animals with true tissues
• Eu Good
• Meta After
• Eumetazoan Good after animals
• A Subkingdom within the animal kingdom- the
  good animals- that came after the first
  animals (proto- zoans)
• Includes all animals except sponges

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Animal Evolution Branch Point 2

• Branch Point 2
• Bilaterally symmetrical animals (Bilateria)
  separate from radially symmetrical animals
  (Radiata)
• Radiata Radially symmetrical
• Animals that can be divided multiple times
  through a central axis creating multiple mirror
  images.
• Have a top and bottom but no left nor right, no
  head nor tail.
• Example Phylum CnidariaJelly fish sea
  anemones
• Bilateria Bilaterally symmetrical
• Animals that can only be cut in one plane to
  create a mirror image.
• Have top (dorsal), bottom (ventral), head
  (anterior), tail (posterior), right side, left
  side.
• Cephalization Concentration of nervous tissue in
  the head region begins to happen- origin of the
  brain

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Animal Evolution Branch Point 2

• Second major distinction between Radiata and
  Bilateria are the number of tissue layers (AKA
  Germ Layers)
• Radiata
• Diploblastic
• Diplo Two
• Blast Bud, sprout, germ
• have two tissue layers (germ layers)
• Ectoderm Outer skin
• Endoderm Inner skin
• Bilateria
• Triploblastic have three tissue layers (germ
  layers)
• Ectoderm Outer skin
• Mesoderm Middle skin
• Endoderm Inner skin

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Animal Evolution Importance of the Coelom

• How are all the bilaterally symmetrical animals
  distinguished from one another?
• By the presence or absence of a particular body
  cavity called the coelom (pronounced sea-loam)
• It is a body cavity found within the mesoderm
• It splits the mesoderm
• Bilateria are in one of three categories
  depending on types of body cavities
• Acoelomates
• Psuedocoelomates
• Coelomates

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Animal Evolution Branch Point 3

• Acoelomates
• No coelom
• Have solid bodies with no body cavities
• Note The digestive tract is not a body cavity
• Example Flatworms
• Pseudocoelomates
• False coelom
• Have a body cavity between the mesoderm and
  endoderm.
• Example Nematode (roundworms)
• Coelomates
• True Coelom
• Have a body cavity within the mesoderm
• Example All other animals- annelids (segmented
  worms), etc.

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Animal Evolution Branch Point 4

• Final major branch point in animal evolution
• Coelomates are divided into two categories
• Protostomes
• Deuterostomes
• The division into these two categories is based
  on three events that occur during the early
  embryological development of these animals. It is
  important to note that you would never be able to
  place these animals into these two categories
  based on the way they look as adults. The
  embryologist is the scientist who is primarily
  responsible for categorizing these animals. Here
  are the three things they look for. . .
• The cleavage pattern of the zygote
• Cleavage Cell division without growth during
  early embryonic development that converts the
  zygote (fertilized egg) into a ball of cells.
• How the coelom forms
• The fate of the blastopore
• Blastopore An opening into the archenteron that
  appears during early embryonic development. It
  will eventually become either the mouth or the
  anus of the animal.

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Animal Evolution Branch Point 4- Cleavage

• Cleavage
• Spiral and Determinate
• Seen in Protostomes
• New cells sit in grooves of cells beneath them
  (see picture)
• Each cell has a predetermined fate hence the
  term determinate
• Each cell will become a specific type of tissue.
• Radial and Indeterminate
• Seen in Deuterostomes
• New cells sit on top of cells beneath them (see
  picture)
• Each cell could potentially become a complete
  embryo, its fate is not yet determined, hence
  the term indeterminate

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Animal Evolution Branch Point 4- Coelom
Formation

• Coelom Formation
• Schizocoelous
• Seen in Protostomes
• Schizo to split (like schizophrenia- split
  personality)
• Coelous Refers to the coelom
• Coelom forms by the splitting of the mesoderm
• Enterocoelous
• Seen in Deuterostomes
• Entero Intestine
• Coelom forms by the budding of the archenteron
  (primitive intestine)
• Arch Old
• Archenteron Old intestine

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Animal Evolution Branch Point 4-Blastopore Fate

• Fate of the Blastopore
• When the archenteron forms an opening called the
  blastopore is created. In protostomes (as seen in
  the left diagram above), the mouth develops from
  this blastopore and the anus develops secondarily
  somewhere else. This is why protostomes were
  named as such
• Proto First
• Stome Mouth
• In deuterostomes the mouth is formed from the
  secondary opening and the blastopore forms the
  anus, hence the name, deuterostomes
• Deutero second

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