Molecular Evidence for Two Cryptic Species of Homalometron (Digenea: Apocreadiidae) in Freshwater Fishes of the Southeastern United States

The identities of 2 freshwater adult digenean species from the southeastern United States belonging in the Apocreadiidae, and consistent with the genus Homalometron Stafford, 1904, are investigated. One species is from the intestine of Aplodinotus grunniens from the Pearl River bordering Louisiana and Mississippi, U.S.A., and the other is from the intestine of Lepomis microlophus in the Pascagoula River, Mississippi, U.S.A. Both species closely resemble Homalometron armatum (McCallum, 1895) Manter, 1947, and differentiation among the 3 forms by conventional morphological features is found to be ambiguous and unreliable. Ribosomal DNA, consisting of the partial 18S nuclear rDNA gene, internal transcribed spacer regions (=ITS1 + 5.8S + ITS2), and partial 28S gene, is compared among the 3 foam, revealing considerable genetic differences. The 2 adult forms are consequently considered cryptic species in Homalometron. Additionally, metacercariae from snails collected from the same or similar habitats that support the 2 cryptic species are identified by matching their rDNA sequences with those from adults. The metacercariae from both forms are found to be present in south central Louisiana, U.S.A., and the metacercariae of the adult form from the Pearl River are found to occur in the Pascagoula River.