腹毛动物门是动物界的一个门。是生活在海洋或淡水中的、身体腹面披有纤毛一类小型动物。大约有400种，一般认为是假体腔动物中最原始的一类。

腹毛动物超门分为2个亚门：

The gastrotrichs (phylum Gastrotricha), commonly referred to as hairybacks, are a group of microscopic (0.06-3.0 mm), worm-like, pseudocoelomate animals, and are widely distributed and abundant in freshwater and marine environments. They are mostly benthic and live within the periphyton, the layer of tiny organisms and detritus that is found on the seabed and the beds of other water bodies. The majority live on and between particles of sediment or on other submerged surfaces, but a few species are terrestrial and live on land in the film of water surrounding grains of soil. Gastrotrichs are divided into two orders, the Macrodasyida which are marine (except for two species), and the Chaetonotida, some of which are marine and some freshwater. Nearly eight hundred species of gastrotrich have been described.