microfauna

Microscopic or very small organisms, such as protozoans, that live in soil or benthic sediments.

A fauna in which all the animals are of minute or diminutive size; a congeries of microscopic animals, or sometimes a depauperated fauna.

The smallest of the faunal size divisions, including mainly microorganisms but also sometimes applied to the tiniest species of animal groups such as ticks, insects, etc.