BIOL110 Lecture 7: Phyla Cnidaria and Ctenophora
23 Nov 2017
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Some key terms: cnidocytes, diploblasts, diescious, zooxanthellae, planual larvae, polyp and medusa, rhopalia, strobilation, hermatypic, coral bleaching, colloblasts. Cnidaria: blastula: ball of cells that develop from a zygote (critical stage of embryonic development) Inside it is a fluid-filled cavity called the bastocoel. In sponges: zygote blastula cells reorganize to lose the blastocoel, no remainin. Develop internal cavities (cells on one side push inward, form a cavity) No true tissues (just random cells together doing their own thing) Firing cnidocytes: prey can be detected by touch, organic molecules in the water (need chemosensory supporting cells, cnidocil: trigger-modified cilium sensitive to touch, two forces contribute: Structural, develop during formation: tension, osmotic pressure. Large conc. gradient in cnidocyte open operculum(cover) water rush in high water volume causes nematocyte to shoot out. Cnidocil is a trigger sensor that detects touch. Medusa forms are dioecious (may be m or. Obelia) has both asexual polyp and sexual medusa stage.
