Most nematode species are bacterivorous: soil bacteria are their primary food source. Some bacterivorous nematodes use probolae, processes projecting from the lip region, to harvest soil bacteria. Others such as Acrobeles complexus and most members of the order Rhabditida ingest soil fluid with bacteria without specific morphological adaptations. As can be seen below, Cruznema tripartitum has a tube shaped mouth used to take up soil fluid.
Apart from being responsible for turnover of carbon and nitrogen in the soil through grazing on bacteria, there is some preliminary scientific evidence that bacterivorous nematodes stimulate plant root growth through the stimulation of plant hormone production. This occurs due to changes in the rhizosphere microbial community as a result of grazing.
More pictures of Cruznema:
(Click on the pictures for an enlargement, © Wageningen University & Research, Laboratory of Nematology/Pictures: Hanny van Megen)