The Flatworms 1

The flatworms 1. Bilateral symmetry 2. Flattened dorsoventrally 3. Tissues, organs and organ systems 4. Acoelomate 5. Mostly monoecious 6. Can be free living and parasitic • Platyhelminthes- 20,000 species • Basic cephalization • Mouth on ventral side • Anterior and posterior ends • Acoelomate - no body cavity • 3 layers of tissue: ectoderm, mesoderm, endoderm • Have muscular system • Free-living worms are carnivores or scavengers • Digestive cavity has one opening • Muscular pharynx extends from the mouth for feeding • Branching gastrovascular cavity • Extracellular digestion • Hammerhead feeding • http://www.youtube.com/watch?v=zE84U4ctSLY • Flatworm steals daphnia • http://www.youtube.com/watch?v=Yk7_O11kS-4 • Feeding and Regurgitation • http://www.youtube.com/watch?v=rUq_H9qHj0A • Parasitic worms feed on blood or tissues • Reduced digestive systems • Small flat bodies rely on diffusion • O2 and CO 2 • All cells are close to the surface • Excretory system •Flame cells and tubules • Whipping cilia creates current •Removes waste • Have nervous system •Cerebral ganglia •Nerve cords and nerve net • Eyespots (ocelli) sense light • Auricles contain sensory cells •Sense chemical, touch and water current • Some secrete a mucus track, then use cilia to move them along • Larger worms move by muscular contraction • Leopard Flatworm • http://www.youtube.com/watch?v=zCH37KI_R_E • Flatworm landing • http://www.youtube.com/watch?v=7UkZHDIujUc • Have reproductive system • Asexual reproduction •Divide by transverse fission •Regeneration • Sexual reproduction •Monoecious - hermaphrodites •Individuals exchange sperm •Fertilization occurs and eggs are laid • Planarians • Free-living: freshwater or marine • 5mm-50 cm • Fluke worms • Parasites- eat host cells • Flat, oval bodies • 1mm - 6 cm • Attach to host using suckers • Individuals live at least 2 different hosts • Most complex life cycles in animal kingdom • Chinese Liver Fluke ( Clonorchis sinesis ) • Sheep Liver Fluke ( Fasciola hepatica ) • Blood Flukes ( Shistosoma spp.) • Lung Flukes • Intestinal Flukes • Tapeworms • Intestinal parasites • Long, flattened bodies • Uses sucker(scolex) to attach to intestinal wall •No mouth •No digestive system • Body units called proglottids. •Each produces eggs and breaks off when mature. Over 50,000 eggs • 3500 species • Most vertebrate species have a corresponding tapeworm species • Beef Tapeworm • Pork Tapeworm • Broad Fish Tapeworm .

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A Non-Bilaterian Perspective on the Development and Evolution of Animal Digestive Systems
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