BIO 203 Lecture Notes - Lecture 35: Cuvierian Tubules, Amphisbaenidae, Commensalism
6 Dec 2016
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Examine this new (2013) phylogeny of cnidaria (slide #6 & #7) Protostomes (includes lophotrochozoa and ecdysozoa) undergo spiral cleavage. The zygote (a single cell where egg & sperm come together and plasyogamy and karyogamy occur to form zygote) is a fertilized egg that divides into smaller cells named blastomeres. Spiral cleavage: cell cleaves obliquely to the axis and typically produces a quartet of cells. Each blastomere of the early embryo, if separated, forms a defective partial embryo. Deuterostomes such as echinoderms and chordates (you) undergo radial cleavage. In radial cleavage, planes are symmetrical to the polar axis and produce layers. Each blastomere of the early embryo, if separated, can regulate its development into a complete embryo. (think identical twins) Embryo continues to divide, forming the blastula and gastrula. Blastopore in protostomes becomes the mouth, in deuterostomes becomes the anus. The body of a deuterostome looks like an upside-down protostome. A primary reason for this difference is the expression of bmp4.
