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Explore the diverse characteristics of flatworms and roundworms, from their anatomy to their life cycles as parasites. Learn about the different types, behaviors, and impacts of these fascinating organisms in the animal kingdom.
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Flatworms and Roundworms Section 28.3
Flatworms • The largest group of acoelomate worms • Contain a mesoderm • Has tissues organized into organs • Bilaterally symmetrical • Flat, ribbon-like body • Have a highly branched gastrovascular cavity • Dissolved substances move through the body by diffusion • Most do not have a respiratory or circulatory system
Flatworms, continued… • Turbellaria • Free-living • Mostly marine • Planarians – freshwater turbellarians • Cestoda • Parasitic tapeworms • Anterior end contains suckers and hooks • Body increases in length by producing segments called proglottids that break off during reproduction • Trematoda • Flukes • Endoparasites (inside) or ectoparasites (outside) • May have complex life cycles with more than 1 host
Roundworms • Also called nematodes • Pseudocoelomates – fluid movement acts as a simple circulatory system • Have a one-way digestive tract
Parasitic roundworms • Three sources of human infection: • Ascaris – eggs in human waste end up in soil, enter through ingestion, end up in respiratory system • Trichinella – passed to humans through undercooked pork, causes a disease called trichinosis • Necator (hookworms) – larvae can penetrate the soles of bare feet and enter the bloodstream
