Gastrotrich

The gastrotrichs, commonly called hairybellies or hairybacks, are a phylum of microscopic, cylindrical animals, ranging from 0.06 to 3.0 millimeters long, widely distributed and abundant in freshwater and marine environments. Most are benthic, living within the periphyton, the layer of tiny organisms and detritus on the beds of water bodies, on or between sediment particles or other submerged surfaces, though a few species are terrestrial and live in the water film surrounding soil grains. Gastrotrichs are divided into two orders, the marine Macrodasyida and the Chaetonotida, some of which are marine and some freshwater; as of 2019 more than 860 species had been described.