Systematic position and relationships of Paracreptotrematina limi, based on partial sequences of 28S rRNA and cytochrome c oxidase subunit 1 genes.

Paracreptotrematina limi Amin and Myer, 1982 (Trematoda), an intestinal fluke specific to the mudminnow, Umbra limi, is conventionally classified within the papillose Allocreadiidae. Its unusual morphology (lack of identifiable vitellaria, large fully embryonated terminal eggs), assumptions of homology of its 2 atypical muscular oral 'papillae' (lobes) with those of the Bunoderinae, and its unknown life cycle make this classification tenuous. Previous phylogenetic analyses of the papillose allocreadiids, based on morphology, placed P. limi as a basal papillose allocreadiid. We tested this hypothesis with a phylogenetic analysis by using partial sequences of the 28S ribosomal RNA gene and the cytochrome c oxidase subunit I gene from several plagiorchiiform taxa, including reportedly related allocreadiids as well as selected species of Plagiorchiidae, Haematoloechidae, and Macroderoididae. Results of phylogenetic analyses of the 28S rRNA gene fragments by using parsimony criteria support the classification of P. limi as an allocreadiid and place it as a sister taxon to a clade with Allocreadium lobatum Wallin, 1909, Bunodera luciopercae (Müller, 1876) and Crepidostomum cooperi Hopkins, 1931, with Polylekithum ictaluri (Pearse, 1924) basal to all of them. Analysis of the cytochrome c oxidase subunit I gene sequence data from fewer taxa supports the placement of P. limi relative to 3 (A. lobatum, C. cooperi, and P. ictaluri) of the 4 allocreadiid taxa. These results also suggest that the previous conception of the papillose allocreadiids as a monophyletic assemblage that includes P. limi may require a reappraisal.