A worm of a phylum that includes the planarians together with the parasitic flukes and tapeworms. They are distinguished by having a simple flattened body that lacks blood vessels, and a digestive tract that, if present, has a single opening.
- Phylum Platyhelminthes: several classes.
- Planarians are free-living flatworms, and have a much simpler life history.
- Among the earliest hunters, flatworms were simple but effective killing machines.
- All the ponds hosted parasitic flatworms called trematodes.
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