Phylum Platyhelminthes (flatworms)

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Phylum Platyhelminthes (flatworms)

• 18,500 spp.
• most primitive bilateral animals
• acoelomate
• triploblastic
• minimal cephalization
• no circulatory system
• nervous system- ladder-like

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Taxonomy

• Class Turbellaria (planarians)
• Class Trematoda (flukes)
• Class Cestoda (tapeworms)

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Flatworm Physiology

• Respiration and excretion via diffusion through
  the body wall
• hermaphroditic w/ internal fertilization
• asexual reproduction via fragmentation

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Class Turbellaria (planarians)

• fresh water, terrestrial, mostly marine
• ciliated epidermis
• evertable pharynx
• example Planaria

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Class Trematoda (flukes)

• 11,000 spp.
• medically important
• endoparasites of vertebrates
• eggs void in feces
• free swimming larvae
• example Clonorchis Chinese liver fluke

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Class Cestoda (tapeworms)

• 3400 spp.
• endoparasites of vertebrates
• scolex- holdfast
• proglottids
• example Taenia- beef tapeworm

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