Recent molecular studies suggest that the Platyhelminthes as a whole That is, they contain some but not all descendants of a common ancestor. It now seems likely that the first two of these groups are paraphyletic They also show anatomical and life history modifications for The Cestoda, or tapeworms, are intestinal parasites in vertebrates, and Parasitic in one, two, or more intermediate hosts before reachingĪdulthood, at which time they parasitize a definitive host. Pass through a number of juvenile stages that are Members of one major taxon of flukes, the Digenea - which includes the Have complex life cycles specialized for parasitism in animal tissues. The Trematoda, or flukes, are all parasitic, and In the oceans, in fresh water, and in moist terrestrial habitats,Īnd a few are parasitic. Include the planarian, Dugesia, shown above these are found (Click on either of the pictures above for a larger image).įlatworms were once divided into three groups.
They inhabit freshwater, and are carnivores (even without teeth) or scavengers. Planarians are free-living flatworms, and have a much simpler life history. Life without a coelom : The image at left is a fluke (possibly a speciesįlukes, like other parasitic flatworms, have complex life cycles often No cell can be too far from the outside, making a flattened shape necessary. The lack of a cavity alsoĬonstrains flatworms to be flat they must respire by diffusion, and To transport food to all parts of the body. Lack of any other body cavity, in larger flatworms the gut is often very Pharyngeal opening both takes in food and expels waste. Flatworms have no body cavity other than the gut (and the smallestįree-living forms may even lack that!) and lack an anus the same (composed of three fundamental cell layers) are the Platyhelminthes, theįlatworms. That are bilaterally symmetrical and triploblastic Introduction to the Platyhelminthes Introduction to the Platyhelminthes Life in two dimensions.
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