Accacoeliid trematodes in two sunfish species, Masturus lanceolatus and Mola mola, in Japanese waters

Trematodes of the family Accacoeliidae Odhner, 1911 are well known as parasites of sunfishes. Herein, we report the accacoeliid trematode fauna of two sunfish species, Mola mola (Linnaeus) and Masturus lanceolatus (Liénard), in Japanese waters. Between 2023 and 2025, four individuals of each host species were examined, yielding 497 trematodes. These trematodes specimens were assigned to ten accacoeliid species (497 individuals in total) belonging to five genera through morphological and molecular analyses based on partial sequences of the nuclear 28S ribosomal RNA and mitochondrial cytochrome c oxidase subunit I genes. Four of the ten species were identified as new to science: Accacladocoelium latens n. sp., Accacladocoelium mayosenase n. sp., Accacladocoelium mica n. sp., and Rhynchopharynx yarimanbou n. sp. Detailed morphological descriptions were also provided for six known species: Accacladium serpentulum Odhner, 1928; Accacoelium contortum (Rudolphi, 1819); Accacladocoelium nigroflavum (Rudolphi, 1819); Accacladocoelium petasiporum Odhner, 1928; Odhnerium calyptrocotyle (Monticelli, 1893); and Rhynchopharynx paradoxa Odhner, 1928. Furthermore, Accacladocoelium alveolatum Robinson, 1934 was synonymized with Accacladocoelium nigroflavum based on molecular and morphological evidence.