01:119:116 Lecture Notes - Lecture 5: Hydrostatic Skeleton, Triploblasty, Cambrian Explosion
28 Feb 2017
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Lecture 5 - unikont diversity 2: ancestral characteristics of animals. Meiosis - sperm and egg: development. Larva - sexually immature & look different from the adult. Metamorphosis - change in form: evolution. Morphologically, choanoflagellates & choanocytes are almost indistinguishable. Diverged 675 and 875 million years ago. Hox regulates the development of body form/segmentation (jellyfish - two hox genes, bilateria have at least seven) Body plan - morphological and developmental traits. Animals can be categorized according to the symmetry of their bodies, or lack of it. Heads - cephalization, the development of a head. A dorsal (top) & ventral (bottom) side. Anterior (head) & posterior (tail: embryonic tissue development. Germ layers - concentric layers of embryonic tissue. An animal must be triploblastic to have a coelom. Sponges and jellies are not triploblastic so no coelom at all. A true coelom is the ancestral trait in most triploblasts. Variations on the coelom have evolved in some groups.
