New species of Myxosporea from frogs and resurrection of the genus Cystodiscus Lutz, 1889 for species with myxospores in gallbladders of amphibians.

Two new myxosporean species in the gallbladders of frogs have recently spread across eastern Australia and cause disease. Cystodiscus axonis sp. n. and Cystodiscus australis sp. n. are species of Myxosporea (Myxozoa) identified from a range of Australian frogs and tadpoles including the introduced Cane toad (Rhinella marina). The new species are defined by their distinct genetic lineage, myxospore morphology and ultrastructure of the pre-sporogonic development. Spores of both species are produced in the gallbladder. Spores of C. axonis sp. n. possess distinct filiform polar appendages (FPA). The pre-sporogonic development of C. axonis sp. n. is within myelinated axons in the central nervous system of hosts, as well as bile ducts of tadpoles. Pre-sporogonic and sporogonic development of C. australis sp. n. is confined to tadpole bile ducts and myxospores of C. australis sp. n. are devoid of FPA. The genus Cystodiscus Lutz, 1889 introduced for Cystodiscus immersus Lutz, 1889 is emended to accompany myxosporean parasites affecting amphibians previously classified in the genus Myxidium sensu lato. A synopsis of described species within Cystodiscus is provided.