Revision On Genus Myxobolus (Myxozoa: Myxosporea) And Taxonomy Of Some Myxobolus Species In China

Myxozoans are an economically important group of metazoan endoparasites infecting various fish throughtout the world. The diseases caused by them have resulted in mass mortality or loss of economic value of the cultured and wild fish. Myxobolus Butschli,1882is the genera with the greatest number of described species, with over850species identified throughout the world and320species reported in China. In the present paper, we investigated the taxonomy of Myxobolus, made a systematic revisions on Myxobolus species in China, and identified12Myxobolus species by morphological, histological, and molecular methods. The main results are as follows.Taxonamy of Myxobolus and Henneguya:(1) In the present study, the spores of Myxobolus turpisrotundus, M. tsangwuensis, M. musseliusae and M. oralis were observed intermixed with atypical spores bearing caudal appendages. Ultrastructural observation showed that the caudal appendages on both Myxobolus and Henneguya spores came from the elongation of the posterior of the valves.(2) Phylogenetic analysis based on all the available ribosomal DNA sequence data of Myxobolus and Henneguya species still did not support a separation of these two genera.(3) Tracing the history of caudal appendages evolution showed that the morphology of the ancestral species of Myxobolus and Henneguya did not possess the caudal appendages and that caudal appendages have arisen on multiple occasions independently during the evolution. It is worth noting that some Henneguya-type species could lose their caudal appendages to form Myxobolus-type species. The above results indicated that caudal appendages were not a valid character to separate Myxobolus-type and Henneguya-type species into two separate genera. Genus Henneguya is not valid and its species should be assigned to genus Myxobolus.Systematic revisions on the Myxobolus species in China:(1) Revisons on the list of Myxobolus species in China:30Henneguya and8Myxosoma species described in China were assigned to Myxobolus;9homonyms,1synonym,1invalid species, and41invalid Chinese records were identified and removed from the Chinese Myxobolus list.(2) Identification of the type host and the site of infection:the type host and the site of infection of the Myxobolus species in China were identified according to the original descriptions. In conclusion, the list of Myxobolus species in China includes326normal species infecting115different freshwater fish,1marine fish. Among them,52and25species were identified from gold fish and common carp, respectively. Identification and redescription of12Myxobolus species collected in China:(1) The species infecting the skin, gills and fins of gibel carp Carassius auratus gibelio was identified as M. turpisrotundus.(2) The species infecting the gills of common carp Cyprinus carpio was identified as M. musseliusae.(3) The species infecting the pharynx of gibel carp was identified as M. honghuensis sp. n.(4) The species infecting the palate in the mouth of gibel carp was identified as M. oralis sp. n.(5) M. shantungesis, M. koi, M. cyprinicola, M. wulii, M. ampullicapsulatus, M. nielii, M. doneci, and M. sinipercus were redescribed by their morphological, ultrastructural, histological and molecular characteristics.