This monster "lives in piles of dung and rubbish" and "has a sensory organ stalk and two tentacle arms which protrude from its hideous body". It also has a mouth that is "sucker-like and filled with many teeth" although that's not really depicted in the illustration. Which is probably a good thing for legal reasons, since earlier in 1977 a little movie called "Star Wars" came out and featured a tentacled, garbage dwelling monster with a periscope like "sensory organ stalk" which, like the Oh Yuck, was "thrust above the offal the creature lairs under".
AD&D has horrible grappling rules though, so while Luke Skywalker had to wrestle in the muck with a tentacle wrapped around his neck, your D&D character only has to deal with the tentacles making regular hitting attacks.
The Internet tells me the Star Wars monster was called a "Dianoga" but they never called it that in the movie. I bet they had their own non-official names for it, like an "Oh Gross!" or something.
