Ugliest Creature on Earth - Cymothoa exigua

Back to lifeforms, there's creature that ugly and yet small. Size doesn't matter.

Don't underestimate this tiny creature.

"The Tongue-Eating Bug, Cymothoa exigua, slowly eats away it's victims tongue until only a stub remains, and then latches itself into the mouth to become a "replacement" tongue." - via YesButNoButYes.