Integrative taxonomy reveals two new species of Nicoll, 1907 (Digenea: Microphallidae Ward, 1901), parasitizing birds in the Gulf of Mexico.

Members of the genus Nicoll, 1907 include endoparasites of aquatic birds and mammals, distributed worldwide. Adult specimens were collected from the intestines of three bird species (the great black hawks, Gmelin; laughing gull, Linnaeus; and the willet, Gmelin) in three localities along the Gulf of Mexico. were sequenced for the large subunit (LSU) from nuclear rDNA, and the new sequences were aligned with other microphalloid sequences available in GenBank. The maximum likelihood and Bayesian inference analyses revealed three independent lineages, one corresponding to a previously described species, Hernández-Orts, Pinacho-Pinacho, García-Varela & Kostadinova, 2016, and two representing two undescribed species. These two new species are described in the current study. n. sp. can be morphologically differentiated from its four congeneric species occurring in coastal areas of Mexico by having smaller oral (20-29 × 20-38 μm) and ventral (20-39 × 19-33 μm) suckers. In addition, n. sp. possess annular vitellarium instead of a horseshoe-shaped vitellarium. n. sp. can be distinguished from its congeneric species reported from Mexico by possessing a larger oesophagus (44-117μm) and by having a vitellarium distributed in both the hindbody and forebody. is the third species recorded in this study parasitizing the great black hawk (); this represents a new host and locality record, expanding its distribution range from the Mexican Pacific Ocean to the Gulf of Mexico.