Beside plant parasites, fungal and bacterial feeders some nematodes in the terrestrial and aquatic environment feed on other nematodes. Members of the family Mononchidae are typical representatives for this carnivorous behavior although juveniles, with a smaller mouth cavity, also feed on bacteria. Mononchus truncates has been described by Bastian in 1865. Since then, many related species have been described resulting in many new genera and ultimately three families. Mononchus truncates is a freshwater nematode which can also be found in wet soils, it has a worldwide distribution. The name Mononchus refers to the single tooth in the mouth cavity. Mononchids are active nematodes which damage the cuticle of other nematodes and subsequently consume the content.