Animalcule is an older term for a microscopic animal or protozoan. Some better-known animalcules include:

• Rotifers, called wheel animalcules
• Paramecium, called slipper animalcules
• Stentor, called trumpet animalcules
• Vorticella, and other peritrichs, called bell animalcules
• Actinophrys, and other heliozoa, called sun animalcules
• Amoeba, called proteus animalcules

The term was used by the 17th-century discoverer of microorganisms, Anton van Leeuwenhoek.

Zoology | Animalculum