I don't have the lyrics handy, but I can remember the first verse and chorus, so that will have to do.
The wholesome kids got puppies
The indoor kids got cats
The gentle folk got rabbits
And the weird kids wanted bats
While macroscopic mammals might be alright for some
The only pet for me is a paramecium
Paramecium! Paramecium! Bigger than a molecule
Paramecium! Paramecium! My favorite animalcule
Tiny and transparent, its virtues were inherent
Paramecium, Paramecium, the only pet for me.