A new free-living marine nematode species, Oncholaimus moanae sp. nov., is described from intertidal fine sand in southern
New Zealand. Oncholaimus moanae sp. nov. can be distinguished from other species of the genus by the presence of a precloacal
papilla bearing four pairs of short, stout spines, a post-cloacal papilla, long (.70 mm) spicules, and a demanian system
with two openings situated laterally at level of uvette. The d13C signature of O. moanae sp. nov. suggests that benthic microalgae
are the main carbon source for this species, but an elevated d15N signature suggests predatory feeding habits. The fatty
acid composition of O. moanae sp. nov. is rich in highly unsaturated fatty acids, which are likely to originate from heterotrophic
protists (e.g. ciliates). The data obtained in this study suggest, for the first time, that marine nematodes can be a high
quality food source (i.e. rich in highly unsaturated fatty acids) to predators. Large nematodes living near or at the sediment
surface, in particular, may represent an important trophic link between heterotrophic protists and higher trophic levels in
marine sediments.