We reach the final post in this series with the monsters that are, anatomically speaking, the simplest of them all. The idea of monstrous slime is essentially a modern one; some antecedents may exist here and there, but generally, we're thinking of the likes of the 1958 film
The Blob or Clark Ashton Smith's formless spawn of Tsathoggua, which made their debut in 1931.
The 1E Monster Manual includes a number of creatures that could loosely be described as oozes but only four of these have consistently appeared in the core rulebooks (excluding 4E, as I usually do, which retains just two of them in the MM1). Three of these are entirely amorphous, although the one that's perhaps the most notorious does at least have a shape.