What term was used for the first microorganisms seen under a microscope that was found in pond water?

The term used for the first microorganisms seen under a microscope in pond water is "animalcules." This term was coined by Antonie van Leeuwenhoek in the late 17th century, specifically around the 1670s. Van Leeuwenhoek was a Dutch scientist who is credited with the development of the microscope and his observations of these tiny creatures were among the first documented instances of observing microorganisms. He described various microorganisms, including bacteria and protozoa, which he observed in water samples, dental plaque, and other substances, realizing that these previously unseen forms of life existed. This discovery laid the groundwork for microbiology as a scientific field.