They are failed experiments of Professor Monkey-For-A-Head, and the Professor unleashes the mutants upon Earthworm Jim in repeated efforts to reclaim the Super Suit which the Professor designed, and which Jim is wearing.
They are massively enlarged, transparent amoebas, with what appears to be eyes, mouths and/or beaks inside. The mutant amoebas only appear in a few sections of Level 5 where Jim is trapped in a metal cage. The Professor unleashes dozens of mutant amoebas down various chutes at the cage, from all different directions, and very rapidly, so Jim has to be on-the-ball with his Plasma Blaster. They can prove to be one of the more troublesome enemies in the level when unleashed on Jim in droves.
- Despite being a dangerous enemy, these experiments can also serve a useful purpose. When Jim is captured by the Robotic Chicken for the first time, Jim can release mutant amoebas from above onto the boss to damage it. This is done by whipping the target with Jim's worm head, which shoots a mutant amoeba down from the ceiling chute, that will explode on contact.