Other facets of invertebrate embryology

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Other facets of invertebrate embryology
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Stages of development

• Egg and sperm
• Fertilized embryo
• Cell division resulting in a multicellular embryo
  (cleavage)
• Radial cleavage
• Spiral cleavage
• Morula--solid ball of cells
• Blastula-hollow ball of cells
• Gastrula

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The outcomes of gastrulation

• Diploblasty
• Formation of the primitive gut
• Name of the entrances and exits
• If the first opening becomes the mouth,
  protostomates
• If the first opening becomes the anus,
  deuterostomates

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Formation of mesoderm in the eucoelomates

• Protostomates
• Solid mass of mesodermal cells in blastocoel
• Schizocoely--split in the mesoderm to form the
  coelom
• Deuterostomates
• Budding off of the archenteron
• enterocoely

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Outcomes in the pattern of development

• Protostomates, have spiral cleavage
• Determinate--cell futures are predictable
• Deuterostomates, have radial cleavage
• Indeterminate--cell futures are not predictable
  at the eight cell stage

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Phylogenetic relationships

• Protostomates
• Annelida
• Mollusca
• Arthropoda
• Deuterostomates
• Echinodermata
• Chordata
• Invertebrate chordates
• Vertebrates

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Origin of the eucoelomates

• Relationship to the platyhelminthes
• Larval relationships
• Protostomates have a larval stage trochophore
• Platyhelminthes larvae Mullers larvae