Integrated evidence reveals a new species of Cosmocerca (Ascaridomorpha: Cosmocercoidea) from the Asiatic toad Bufo gargarizans Cantor (Amphibia: Anura)

Species of Cosmocerca Diesing, 1861 (Ascaridomorpha: Cosmocercoidea), are common nematode parasites of amphibians. In the present study, a new species of Cosmocerca , namely C. simile n. sp., was described using light and scanning electron microscopy, and sequencing different nuclear and mitochondrial genetic markers (i.e. small ribosomal DNA (18S), large ribosomal DNA (28S), internal transcribed spacer (ITS) and cytochrome c oxidase subunit 1 ( cox 1)). Cosmocerca simile n. sp. differs from its congeners based on body size, morphology and number of plectanes, relative length of spicules and gubernaculum and spicules to total body length and morphology and length of tail. Molecular analysis showed no nucleotide polymorphisms among different individuals of the new species regarding nuclear DNA. Very low intraspecific nucleotide variation (0.52–0.78%) was detected in cox 1 mtDNA. In contrast, the level of interspecific nucleotide variation between C. simile n. sp. and its congeners were distinctly higher (2.74–18.1% in the partial ITS region and 10.2–13.5% in the partial cox 1 region, respectively) than that of intraspecific variation. Phylogenetic analyses using maximum likelihood (ML) inference based on the partial ITS and cox 1 sequence data both supported the new species to be a member of the genus Cosmocerca , and formed a sister relationship to C. japonica. The newly obtained genetic data are important for further studies of DNA-based taxonomy, population genetics and phylogenetics of the Cosmocercoidea.