From
The X-files:
Flukeman (a.k.a Flukey) was born "in a
primordial soup of
radioactive sewage." Flukeman was found in the
Newark sewage system after being dumped from the
bilge of a
Russian salvage ship.
In
The Host,
Mulder and
Scully try to figure out what exactly is this man/
worm (played by Darin Morgan) and stop it from killing workers and reproducing.
At the end, the Flukeman is
severed in half, which Mulder and Scully believe to be the end of Flukey, but we see the top half of its body floating in the
sewers clearly
alive.
See The X-files: Season 2