Micrometazoa is a general term used for small multicellular animals that can't be observed with the naked eye. The term encompasses several groups of animals including protozoans, rotifers, nematodes, and tardigrades. There are several synonyms for micrometazoa, some of which include microanimals, meiofauna, and micronekton. These terms are used to describe the same organisms, and there's no difference in their meaning. Microanimals are organisms that range in size from 0.01mm to 2.0mm and encompass several phyla. Meiofauna, on the other hand, refers to the organisms that occupy the spaces between grains of sediment in aquatic environments. Micronekton describes the smallest creatures that live in open water, including planktonic species, small fish, and other small marine invertebrates.