Flukeman

The Flukeman, played by Darin Morgan in the episode "The Host": The Flukeman, a being born in a "soup" of radioactive sewage from Chernobyl, is a tapeworm-like humanoid that lived in sewers. It bit humans and injected small flukes, which eventually kill their hosts. Mulder investigated its attacks, finding the creature in a sewage treatment plant. The creature escaped and returned to the sewers, where Mulder seemingly killed it by slicing it in half. The episode's conclusion, however, shows that the Flukeman continues to live. In a later episode, a newspaper shows a drawing of the Flukeman on the cover, the caption stating that it ended up in Martha's Vineyard, Massachusetts.