Lecture 16 1) Major splits along the phylogenic tree: a) Parazoa (No true tissue) vs. Eumetazoa (“True Tissue”) – True tissue is an integrated group of cells with common structure or function. In parazoa, cells can reaggregate and form a new sponge, so no true tissue. Also they are totipotent, so any cell type in the sponge can turn into any other cell type. b) Radial Symmetry, Diploblastic vs. Bilateral Symmetry, Triploblastic – Radial symmetry = circularly symmetric. Bilateral symmetry has an anterior, posterior, left, right, ventral dorsal planes, you can only get symmetry by cutting along one of these planes. Diploblastic blastula only has endoderm ectoderm, triploblastic blastula has ectoderm (skin) mesoderm (muscle) and endoderm (digestive). Radial symmetry benefits immotile (cessile) organisms, bilateral symmetry benefits motile organisms. c) Deuterostome vs. Protostome Development – Deuterostome has the blastopore form the anus first, and the mouth is secondary. Protostome has the blastopore form the mouth
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