BIO 2135 Chapter Notes - Chapter 1: Dugesia, Flatworm, Starfish
2 Mar 2017
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Hard to compete against coelomate animals in freshwater --> adapts to live in fluid filled cavities of animals --> parasite! Parasite needs to stay attached to host, yet still reproduce. Improved locomotion from muscles in new layer of mesoderm. Actually, despite having no complete gut are near top of protostome lineage. Studying dugesia, (the adorable one with a triangle head and eyes) Originally thought they were at the bottom but they are really near the top. Platyhelminthes have fluid-in body cavity and no anal opening of alimentary tract. When mesoderm occurred, it already had a cavity. Other animals have also reduced or gotten rid of anal opening eg the sea star in echinoderms. Dorsal (back) and ventral (front, like belly) surface. Two eyespots, auricles on either side of the head. Dual-gland adhesive organs on outer edge of ventral surface of body. Good for where currents would dislodge a gliding flaty wormy. Flapping whole body, not effective, but it"s ok.
