Desert Muck Leech

The Desert Muck Leech was a race of simplistic leech creatures living in a puddle on Mars, a puddle which was later paved over for a car park for the new Mars Vegas.

Whether or not the Desert Muck Leeches were actually the Dark Ones or just one of them had taken form in one of them is disputed, but the only who survived the paving of the puddle was a Dark One, whom would later kill Frida Waterfall and Hutch Waterfall, but itself being killed by the Encyclopod.

Trivia

 * The Latin name given for the creature is "Cyprinodon martius", which comes from also Death Valley pupfish or in Latin, "Cyprinodon salinus". The "martius" in the Desert Muck Leech is purely a reference to the fact that it is on Mars.
 * Ken Keeler, writer (specifically of the plot it was involved in), had a personal likeness for this pupfish, which could survive very harsh environments.