BIS 1B (Winter 2008) Study questions: Platyhelminthes (lecture 11) 1. Why are turbellarian flatworms considered to be a paraphyletic group? Turbellarian flatworms represent the least modified of the Platyhelminthes. They are free-living flatworms with a well-developed digestive system and a “typical” cellular (mononucleate) tegument. The parasitic Platyhelminthes (flukes and tapeworms) evidently evolved within the Turbellaria, by further modification. By excluding them from the Turbellaria we make Turbellaria paraphyletic. In other words, some Turbellaria are more closely related to flukes than they are to other turbellarians. 2. Why does the tegument of tapeworms bear many tiny folds? Tapeworms have no mouth or gut. All feeding is done by absorbing nutrients directly across the body wall. The many tiny folds (microvilli) of the tegument have the effect of greatly increasing the surface area available for nutrient absorption. 3. Why don't you expect to see a member of the phylum Platyhelminthes that is one meter long
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