Myxobolus musseliusae (Myxozoa: Myxobolidae) from the gills of common carp Cyprinus carpio and revision of Myxobolus dispar recorded in China.

During a survey of myxozoan parasites of common carp Cyprinus carpio in Honghu Lake, Hubei Province, China, a parasite was collected that was identified as Myxobolus dispar based on an earlier description from China. However, the small subunit ribosomal DNA of this species shared only 90 % similarity with M. dispar, instead matching M. musseliusae with 100 % identity. To resolve this apparent taxonomic conflict, the validity of M. dispar reported from China was investigated. The species encountered here and in the earlier report from China both bear spores that are notably smaller than those of M. dispar in Europe. In the present study, a mucous envelope was adhered to the posterior of many fresh spores and was observed to expand and surround the spore. This structure has never been reported from fresh spores of M. dispar. Histology showed extravascular plasmodia in the gill filaments in close contact with the cartilaginous ray of the filament, which contrasts with the plasmodia of M. dispar which develop in the arteries of the gill filaments. Phylogenetically, the current species is distinct from M. dispar, instead forming a sister group with M. musseliusae. The data presented here allow us to conclude that the species isolated is M. musseliusae and that prior reports of M. dispar in China are unsubstantiated.