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Notes - 9.14.2010

Notes - 9.14.2010 - -Indirect development is considered...

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Evolution of direct vs. indirect development in Echinoids Lecithotrophic vs plankototrophic larvae Embryo larva adult (indirect) A pair of sea urchins: - heliocidaris tuberculata o egg is about 100 microns in diameter, radial symmetry Four big cells in middle, bunch of little ones below… mesomeres, macromeres, micromeres o develops into a pluteus larva which is ciliated and it swims in the water will spend four to six weeks in the plankton o will eventually land on a surface, then o has bilateral symmetry - heliocidaris erythrogramma o egg about 500 microns in diameter pile of cells, develops into “shmoo”, falls to bottom of ocean pretty fast within a few hours, this is developing into a juvenile sea urchin -
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Unformatted text preview: -Indirect development is considered ancestral. Direct development is far less common appears to have evolved multiple times-ancestral echinoderms are thought to have had larvae, and those were lost many tim independently What has changed in development?-Fate mapping. What cells contribute to what tissues?-Origins of larvae-Possibly the larval forms might have been the original adult form-Life evolved in the water (we think)-Trochophore larva : present in a lot of phyla-Larve are able to skip the adult thing and become reproductively capable o But can they skip the adult stage permanently? o “larvaceans” do so Evolution of primary axis specification-...
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