Molecular phylogeny and morphology of Prohemistomum (Diplostomoidea: Cyathocotylidae) support the synonymisation of Linstowiella and

Abstract

Cyathocotylid genera Prohemistomum Odhner, 1913, Linstowiella Szidat, 1933, and Paracoenogonimus Katsurada, 1914 have a convoluted history associated with continuing uncertainty regarding their validity and the systematic position of their constituent species. During a survey of helminths of ospreys, Pandion haliaetus (L.), we collected representatives of Prohemistomum and Neogogatea Chandler et Rausch, 1947. Morphological examination and sequencing of partial 28S rDNA and cytochrome c oxidase subunit I ( cox1 ) mtDNA genes were conducted to assess their systematic relationships and provide sequence data for future species-level comparisons. We describe Prohemistomum ravindrai n. sp. from ospreys in Georgia and provide molecular data and a supplementary morphological description for Neogogatea kentuckiensis (Cable, 1935). Phylogenetic analysis of 28S sequences recovered a strongly supported Prohemistomum clade containing species previously assigned to Prohemistomum , Linstowiella , and Paracoenogonimus. Morphological characters traditionally used to distinguish these genera, including the presence or absence of a ventral sucker, degree of opisthosoma development, and relative sizes of the oral sucker, pharynx, and cirrus sac, were found to be inconsistent and systematically uninformative. Based on the combined molecular and morphological evidence, we consider Linstowiella and Paracoenogonimus to be junior synonyms of Prohemistomum and transfer their constituent species accordingly. Revised diagnoses for Prohemistomum and Neogogatea are provided. These findings highlight the importance of integrating morphology with molecular phylogenetic data when evaluating generic boundaries.