First off, although it looks like it should be pronounced "Geo (like Flanders' car)-Duck", it's actually pronounced "Gooey (like marshmallow)-Duck". The latter is obviously much cuter.

And it's not even a duck! It's actually a big ol' clam who likes to hide out underground. What we're seeing here is just his siphons. But if you touch him (like Chris did), he'll quickly retreat his siphons below the ground.