The oceanic pleuston community as a potentially crucial life-cycle pathway for pelagic fish-infecting parasitic worms

•Free-floating pleuston harbours large numbers of hemiuroid metacercariae.•Four of seven hemiuroid taxa sampled were molecularly identified to species.•Open ocean hemiuroid life-cycles are highly plastic with low host specificity.•We found low species richness suggesting alternative pelagic or benthic transmission pathways.•Transmission may depend on trophic interactions both at the surface and at depth.