Dactylogyrids are a group of monogenean gill parasites which about 95% of species are found on cyprinids. In this study, eighty nine common carp and twenty five grass carp were collected from Mashhad in the northeast of Iran. A total of 31 Dactylogyrus specimens, 20 and 11 specimens from the gills of common carp and grass carp were collected, respectively. Morphological and molecular analyses based on 28S rDNA revealed four lineages of Dactylogyrus were present in Iran; D. anchoratus, D. extensus, D. lamellatus and a new species of Dactylogyrus. Phylogenetic analyses showed that two species, namely D. extensus and D. lamellatus were completely identical to those previously reported. In addition, sequencing results from D. anchoratus showed the closest homology (93.01%) with species registered as D. inexpectatus in BLAST database. The new Dactylogyrus sp. formed a distinct clade of its own in the phylogram. Based on morphological, molecular and phylogenetic evidences, we propose that this isolate is elevated as a single new species within the genus Dactylogyrus. Further phylogenetic analysis, however, including the incorporation of additional molecular targets is required for Dactylogyrus species to infer interspecific relationships between species in this genus.

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