Where were animalcules found?

Animalcules, a term coined by Antonie van Leeuwenhoek in the late 17th century, were discovered in various environments, including pond water, rainwater, and even in the dental plaque of humans. Leeuwenhoek observed these microscopic organisms using his handcrafted microscopes, which revealed a diverse world of single-celled life, leading to the foundational studies of microbiology. The term "animalcule" generally referred to any microscopic, animal-like organism, highlighting the diversity of life that could be found in small water samples.