A Novel Amphibian Myxosporean, Cystodiscus chongqingensis n. sp., Infecting the Asiatic Toad (Bufo gargarizans) from China

In a parasitological survey of Asiatic toads (Bufo gargarizans) from Chongqing, China, a novel myxosporean was encountered. The species, Cystodiscus chongqingensis n. sp., was found in the gallbladder of toads. The elliptoid myxospores were morphologically consistent with a Cystodiscus species but were distinct from other congeners by myxospore dimensions and DNA sequence comparisons. Myxospores were 14.2 ± 0.4 μm long (13.6-14.9 μm) and 11.1 ± 0.5 μm wide (10.4-12.0 μm), and the polar capsules were 4.6 ± 0.3) μm long (4.0-5.1 μm) and 3.4 ± 0.3 μm wide (2.6-3.8 μm). Phylogenetically, this new species was sister to all previously described and sequenced Cystodiscus species. Also, the predicted secondary structures of helices 18 and 24 in its small subunit ribosomal RNA were distinct from those of other Cystodiscus species, highlighting its unique phylogenetic position within Cystodiscus. Divergence time estimates suggest that C. chongqingensis n. sp. emerged in the Paleogene Period, significantly earlier than other Cystodiscus species. The discovery of this novel species that represents a unique Cystodiscus lineage warrants further investigations to evaluate whether other Asian Cystodiscus species fall within the same lineage.