A detailed morphological description of a species, in the literature referred to as Didymozoon tenuicolle (Rudolphi, 1819) is given, the species being transferred to a newly-erected genus Neolamprididymozoon. Differences in the parasite size relative to their location in hosts were found. Additionally, the Lampris guttatus muscles were found to contain Metadidymocystis cymbiformis Yamaguti, 1970, previously recorded only in the Pacific; the dimensions and drawings of the trematodes are given.;