Slipper animalcule is the common name for:

Paramecium.Animalcule is a old term for a microorganism; it just means small animal. Other better-known animalcules include: Amoeba, called Proteus animalcule; Noctiluca scintillans, commonly called the Sea Sparkles; Rotifers, called wheel animalcules, etc. A paramecium is shaped somewhat like a slipper (a soft shoe), so it is called the slipper animalcule.