Other facets of invertebrate embryology Stages of development

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 • 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