Other facets of invertebrate embryology

1. Other facets of invertebrate embryology

2. 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

3. 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

4. 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

5. 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

6. Phylogenetic relationships • Protostomates • Annelida • Mollusca • Arthropoda • Deuterostomates • Echinodermata • Chordata • Invertebrate chordates • Vertebrates

7. Origin of the eucoelomates • Relationship to the platyhelminthes • Larval relationships • Protostomates have a larval stage = trochophore • Platyhelminthes larvae = Muller’s larvae