Description of Cosmocerca kasugaiensis n. sp. (Nematoda: Cosmocercidae) and redescription of Gyrinicola japonicus (Nematoda: Gyrinicolidae) from the Indian rice frog Fejervarya kawamurai (Amphibia: Dicroglossidae).

Two nematode species parasitizing different developmental stages of the Indian rice frog Fejervarya kawamurai collected from Kasugai City, Japan, were examined using an integrative taxonomic approach combining morphology, scanning electron microscopy (SEM), and molecular analyses. Tadpoles of F. kawamurai were found to be infected exclusively by the oxyuroid nematode Gyrinicola japonicus, whereas adult frogs harboured a cosmocercoid nematode representing a new species of Cosmocerca, namely C. kasugaiensis n. sp. Detailed morphological observations revealed diagnostic characters of the new species, including the presence of well-developed lateral alae, equal spicules distinctly longer than the gubernaculum, five pairs of precloacal plectanes surrounded by incomplete circles of tubercles, and somatic papillae in both sexes. Molecular analyses based on nuclear 28S rDNA, internal transcribed spacer (ITS), and mitochondrial cox1 sequences showed no intraspecific variation among individuals of C. kasugaiensis n. sp., and consistently supported its distinctiveness from its congeners by Assemble Species by Automatic Partitioning (ASAP) and Bayesian inference analyses. The redescription of G. japonicus incorporates new features, including cephalic structures and egg morphological details revealed by SEM. This study also provides the ITS and cox1 sequences for this species for the first time. Morphological and molecular analyses confirmed the distinct species position within Gyrinicola.