Beside plant parasites, fungal and bacterial feeders some nematodes in the terrestrial and aquatic environment feed on other nematodes. Members of the order Mononchida Jairajpuri, 1969 are typical representatives for this carnivorous behavior although juveniles, with a smaller mouth cavity, also feed on bacteria. The genus Mononchus was described by Bastian in 1865. Since then, many related species have been described resulting in many new genera and ultimately eight families within the order Mononchida. Mononchids are active nematodes which damage the cuticle of other nematodes and subsequently consume the content. The name Mononchus refers to the single tooth in the mouth cavity. They prefer freshwater habitats and moist soils. The type species Mononchus truncates Bastian, 1865 has a worldwide distribution. Mononchus tunbridgensis was also described by Bastian in 1865. It has a smaller and narrower buccal cavity, compared to M. truncatus, and has been found in Europe, Russia, South-Africa, India, Japan, Austalia, North-America, Suriname and Costa Rica.