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Other facets of invertebrate embryology. 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. The outcomes of gastrulation.
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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
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
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
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
Phylogenetic relationships • Protostomates • Annelida • Mollusca • Arthropoda • Deuterostomates • Echinodermata • Chordata • Invertebrate chordates • Vertebrates
Origin of the eucoelomates • Relationship to the platyhelminthes • Larval relationships • Protostomates have a larval stage = trochophore • Platyhelminthes larvae = Muller’s larvae