Another chloromyxid lineage: molecular phylogeny and redescription of Chloromyxum careni from the Asian horned frog Megophrys nasuta

Infection with Chloromyxum careni Mutschmann, 1999 was found in the Asian horned frog Megophrys nasuta from Malaysia and Indonesia. Kidney was the only organ infected. Coelozoic plasmodia up to 300 μm were localized in Bowman's space, embracing the glomerulus from all sides, or rarely in lumina of renal tubules. Plasmodia are polysporic, containing disporic pansporoblasts. Myxospores observed by light microscopy are colorless, variable in shape and size, measuring 6.0-8.5 × 5.0-6.5 μm, composed of two symmetrical valves joined by a meridian suture, containing four pyriform polar capsules 3.0-4.0 × 2.5-3.0 μm and a single sporoplasm. Each valve possesses 14-24 (median 21) fine longitudinal ridges clearly visible only in scanning electron microscopy. Rarely, atypical spores with a markedly pointed posterior pole and only 6-10 surface ridges are present in plasmodia together with typical spores. Both small subunit (SSU) and large subunit (LSU) rRNA gene sequences possess extremely long GU-rich inserts. In all SSU and LSU rDNA-based phylogenetic analyses, C. careni clustered as a distinct basal branch to the Myxobolus+Myxidium lieberkuehni clade, out of the marine Chloromyxum clade containing Chloromyxum leydigi, the type species of the genus. These morphological and phylogenetic data suggest erection of a new genus for the C. careni lineage, but we conservatively treat it as a Chloromyxum sensu lato until more information is available.