What type of fauna falls within the category of microfauna?

Microfauna refers to tiny organisms that are generally smaller than 100 micrometers (0.1 mm) in size. They typically include microscopic life forms such as protozoa, small nematodes, and other microorganisms that play a crucial role in nutrient cycling and soil health. Such small organisms are vital for soil structure, organic matter decomposition, and nutrient availability, influencing the broader ecosystem.

The other options present categories of fauna that do not align with the definition of microfauna. For instance, fauna larger than 2 mm or those exceeding 20 mm would fall into larger classifications such as mesofauna or macrofauna, which significantly differ in size and ecological roles compared to microfauna. Additionally, medium-sized fauna between 2 mm and 20 mm also comprise organisms that are not considered microfauna, as they are typically classified in the mesofauna range. Understanding these size classifications helps clarify the roles different organisms play in nutrient cycling and ecosystem functioning.