Description of a New Species of Bacciger (Digenea: Gymnophalloidea) Infecting the American Gizzard Shad, Dorosoma cepedianum (Lesueur, 1818), and Molecular Characterization of Cercaria rangiae Wardle, 1983, with Molecular Phylogeny of Related Digenea

Abstract

ABSTRACT: A new species of Bacciger Nicoll, 1914, is described from the digestive tract of the American gizzard shad, Dorosoma cepedianum (Lesueur), in some inland waterways of Mississippi, and in Mobile Bay, Alabama, U.S.A. This now represents the only nominal species in the genus from the northwest Atlantic Ocean or inland tributaries of eastern North America north of Mexico. Two potentially close relatives that range in the northwest Atlantic Ocean are Baccigeroides ovatus (Price, 1934) Cutmore, Bray and Cribb, 2018, and Pseudobacciger manteri Nahhas and Cable, 1964. The new species differs from Bo. ovatus mainly by having the genital pore opening immediately anteriad from the ventral sucker rather than far anteriad from it at the pharynx level, and from P. manteri mainly by having a distinct cirrus sac rather than having the terminal genitalia free in the parenchyma. The 3 genera are currently classified in the Faustulidae Poche, 1926. Although life cycles are unknown for the American species, evidence from life history of the related species Bacciger bacciger (Rudolphi, 1819) Nicoll, 1914, and Pseudobacciger harengulae (Yamaguti, 1938) Nahhas and Cable, 1964, combined with molecular phylogenetic evidence, indicate that the studied digeneans likely have a nonoculate trichocercous cercaria. We discovered sporocysts containing nonoculate trichocercous cercariae we identified as Cercaria rangiae Wardle, 1983, infecting the viscera of the Gulf wedge clam, Rangia cuneata (G. B. Sowerby I), in the Pascagoula River, Mississippi, U.S.A. We generated the internal transcribed spacer 2 (ITS2) region and a portion of the 28S rDNA gene from the new species and C. rangiae. Dissimilarity at both sequences demonstrated that the stages were not conspecific. Bayesian inference analyses applied separately to the ITS2 region, and the partial 28S rDNA gene, resulted in trees with similar topology, both depicting the new species and C. rangiae as sister taxa. The possible identity of C. rangiae and the phylogenetic relationships among species of Bacciger and related genera are discussed. We consider Bacciger lesteri Bray, 1982, and Bacciger sprenti Bray, 1982, incertae sedis in the Microphalloidea Ward, 1901. All other species of Bacciger, and species belonging in Pseudobacciger Nahhas and Cable, 1964, and Baccigeroides Dutta, 1995, are transferred from the Faustulidae to the Gymnophalloidea Odhner, 1905, where their familial affinities remain incertae sedis.