What organisms are smallest in number?

Answer 1

The smallest organisms in terms of number are often considered to be certain types of extremophiles, such as specific archaea and bacteria that thrive in extreme environments, like deep-sea vents or highly acidic lakes. Additionally, rare species with limited populations, such as some endangered microorganisms or unique symbiotic bacteria, can also be counted among the smallest in number. However, in a broader sense, the smallest organisms by size are typically viruses, which exist in vast quantities but can be classified as less numerous in specific environments.