This group includes the parasitic flukes and tapeworms, but further focus falls upon the free-living flatworms. “Dorso-ventrally challenged,” or flattened top to bottom, these primitive, unsegmented flatworms slip along the substrate upon countless tiny cilia (hairs). The photograph shows the white flatworm (PL7). In each species, a simple or branched digestive tract is serviced by only one opening—the mouth doubling as the anus.
At least 126 species of free-living flatworms dwell in the marine waters of the Pacific Northwest, and doubtless many more remain to be discovered and recorded.

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