Redescription of Chloromyxum ellipticum Li & Nie, 1973 (Myxosporea: Chloromyxidae) infecting the gall bladder of grass carp Ctenopharyngodon idellus Valenciennes, 1844, supplemented by morphological and molecular characteristics

The traditional taxonomy of the genus Chloromyxum Mingazzini, 1890 has been intensively challenged to be paraphyletic by recent ribosomal DNA (rDNA)-based phylogenetic analysis. Undersampling to get rich sequence data to infer more scientific phylogenetic relationships makes scientists conservatively assign all non-marine elasmobranch-infecting species as Chloromyxum sensu lato. Although complex ridge pattern on the spore surface observed by scanning electron microscopy was thought to be critical for the identification of Chloromyxum species, insufficient data also prevent this ultrastructural data to be a valid taxonomic feature for this genus. It is especial for Chloromyxum species to be reported in China. Molecular and ultrastructural characteristics are yet available for all 22 Chloromyxum species recorded in China. During the investigation of the diversity of coelozoic fish myxosporeans, Chloromyxum ellipticum Li & Nie, 1973 was found to highly infect the gall bladder of Ctenopharyngodon idellus Valenciennes, 1844 in Poyang Lake watershed of Jiangxi province, Eastern China. Here, we redescribed it by the currently recommended holistic approach of combining morphological, ultrastructural, and molecular characteristics. Mature spores were found floating free in the gall bladder, but no plasmodium observed. Spores are typical freshwater teleost-infecting Chloromyxum species, spherical or subspherical in lateral view, measuring 7.7 +/- 0.08 mu m (6.9-9.1) in length, 6.3 +/- 0.09 mu m (5.6-7.6) in width, and 5.8 +/- 0.20 mu m (5.2-6.3) in thickness. Four pyriform polar capsules, located at the anterior end of the spores, were equal in size, 3.3 +/- 0.06 mu m (2.2-4.1) long and 2.1 +/- 0.03 mu m (1.7-2.5) wide. Polar filaments coiled with four to five turns. Two equal spore valves are symmetrical, with 10-16 surface extrasutural ridges per valve, aligned along the longitudinal axis. The obtained partial 18S rDNA of C. ellipticum did not match any sequences available in GenBank. Phylogenetic analysis showed that C. ellipticum clustered firstly with Chloromyxum legeri with robust nodal support and grouped then with urinary system of freshwater teleost-infecting Chloromyxum clade, rather than other gall bladder of freshwater teleost-infecting clade

Morphological and molecular characterisation of Myxobolus pronini n. sp (Myxozoa: Myxobolidae) from the abdominal cavity and visceral serous membranes of the gibel carp Carassius auratus gibelio (Bloch) in Russia and China

Background: Myxozoa is a well-known economically and ecologically important group of metazoan parasites, phylogenetically related to Cnidaria. High diversity of myxosporeans has been recorded in Russia and China; however, most of the species were solely morphologically characterised. Here, we identified a new gibel carp-infecting Myxobolus species and morphologically and molecularly compared the Russian and Chinese isolates of this new myxosporean. Results: Myxobolus pronini n. sp. was found free in the abdominal cavity of Carassius auratus gibelio (Bloch, 1782) in Lake Baikal watershed, Russia, and embedded in the visceral serous membranes of the same fish species in Lake Taibai, Hubei province, China. The morphometric data of the plasmodia and mature spores exhibited some differences between the Russian and Chinese isolates, but SSU rDNA sequences indicated that these two geographical isolates are conspecific. The mature spores from the two locations are obovate in frontal view, with wider anterior than posterior end and lemon-shaped in sutural view. Spores of the Russian isolate were 14.3-16.2 (mean 15.1 +/- 0.2) mu m long, 9. 6-10.8 (10.1 +/- 0.1) mu m wide and 6.4-7.4 (6.7 +/- 0.15) mu m thick; those of the Chinese isolate were 13.8-15.6 (14.7 +/- 0.24) mu m long, 9.6-13.3 (9.6 +/- 0.65) mu m wide and 6.2-7.2 (6.6 +/- 0.16) mu m thick. The newly-generated rDNA sequences (including SSU rDNA, ITS and LSU rDNA) from the two isolates represented some variations within the intraspecific range. Homology search by BLAST showed that the newly obtained rDNA sequences do not match any sequences available on GenBank. Phylogenetic analysis based on the aligned partial SSU rDNA sequences indicated that this novel species clustered with several gibel carp-infecting Myxobolus spp. with round anterior end of spores. Additionally, phylogenetic analysis based on all obtained ITS sequences showed that distinct genetic geographical differentiation occurred for this new parasite. Conclusions: Myxobolus pronini n. sp. is described by integrating morphological, ecological and molecular evidence. Two geographical isolates of this species showed some morphological and genetic differences but within the intraspecific range of variation.</p