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

First description of Chloromyxum squali Gleeson and Adlard, 2012 (Myxozoa) in the Mediterranean Sea in a new host Squalus blainville (Chondrichthyes: Squalidae): morphological, ultrastructural and phylogenetic data

Chloromyxum squali Gleeson and Adlard, 2012 originally described from Squalus acanthias Linnaeus, 1758 is reported for the first time from the gallbladder of Squalus blainville (Risso, 1827) caught from the eastern coast of Tunisia. In the present study, this chloromyxid was described based on morphological and ultrastructural features combined with molecular analysis of 18S rDNA. Young plasmodia were found attached to the gallbladder, while mature plasmodia and myxospores were observed floating free in the bile. Mature plasmodia were polysporic, subspherical in shape, measured 97.8 ± 0.5 µm long and 63.4 ± 0.4 µm wide. Mature myxospores were ovoid with a pointed anterior end, measuring 10.2 ± 0.5 µm long and 8.3 ± 0.5 µm wide. Two asymmetrical shell valves adhered together along an S-shaped suture line. Each valve has 5-7 elevated surface ridges parallel to suture line. A bundle of long caudal filaments extended from the basal end of shell valves. Four pyriform polar capsules equal in size, measuring 3.1 ± 0.4 µm long and 2.5 ± 0.3 µm wide, were situated at the same level in the anterior pole of the myxospore, each with a polar filament coiled in 7-8 turns. Pairwise comparisons among the SSU rDNA sequences revealed significant similarity between Chloromyxum squali infecting S. acanthias with the sequence obtained in this study. Phylogenetic analysis revealed that C. squali clustered in the clade of Chloromyxum species infecting the gallbladder of marine Chondrichthyes. Chloromyxum squali showed a seasonal variation of prevalence with significantly higher prevalence noted in summer and in autumn and absence of infection in winter.

Morphological and molecular-genetic characterization of Chloromyxum trilineatum n. sp. (Myxosporea: Bivalvulida) in the gall bladder of pale chub (Zacco platypus) in Japan

The genus Chloromyxum (Myxozoa: Myxosporea: Bivalvulida) is defined as having ridged or smooth bivalvular myxospores containing four polar capsules, with/without caudal filaments. Currently containing more than 140 nominal species, this genus is reasonably speciose with myxospores of unique but heterogeneous morphology. Recent phylogenetic studies have demonstrated its polyphyletic nature. During our myxosporean survey of freshwater fish, a new coelozoic myxosporean species, Chloromyxum trilineatum n. sp., was detected in the gall bladder of the pale chub, Zacco platypus (Cypriniformes: Cyprinidae), which originated from central Japan. Spores were subspherical, measuring 8.5-9.1 (8.8) μm in length, 7.6-8.2 (8.0) μm in width, and 6.8-7.8 (7.4) μm in thickness (n = 20). The valvular surface was smooth and three or four distinct ridges ran parallel to the suture line. Four almost equal polar capsules, 2.9-3.8 (3.3) μm in length and 1.6-2.4 (2.0) μm in width, assembled at the apical part of the spores. The partial nucleotide sequence of the 18S ribosomal RNA gene, 2014 bp in length, was closest to that of morphologically distinct Chloromyxum ellipticum, infecting the gall bladder of grass carp (Ctenopharyngodon idella) in China with 96.99% (1673/1725) identity and three insertion/deletion (indel) sites, followed by Chloromyxum legeri, infecting the gall bladder of common carp (Cyprinus carpio) in the Czech Republic with 89.97% (1803/2004) identity and 14 indel sites. Other myxosporean species, including Chloromyxum spp. from the gall bladder or urinary system of freshwater and marine fish, were phylogenetically distant from the present species.

Morphological and molecular characterization of Chloromyxum argusi n. sp. (Myxosporea) infecting the urinary bladder of Scatophagus argus Linnaeus 1766 (Scatophagidae) from the southwest coast of India

The present paper describes a new species of Chloromyxum infecting the urinary bladder of the estuarine fish, Scatophagus argus, from the southwest coast of India. The parasite exhibited an overall prevalence of 41.93%; the prevalence is influenced by host size and seasons. Mature spores are subspherical, measure 9.40 ± 0.66 by 9.32 ± 0.87 μm, and are characterized by the presence of sutural and extra-sutural ridges, binucleated sporoplasm, and a pair of caudal extensions. Four pyriform, unequal polar capsules with raised polar filament discharge pores and ribbon-like polar filaments are present. Polar filament coils numbered four to five in large polar capsules and three in small polar capsules. Pansporoblast is irregular with granulated cytoplasm and has fine villosites on its surface. Plasmodia are spherical/irregular with monosporic and polysporic forms. In molecular and phylogenetic analysis, the myxosporean stands out with a high bootstrap value and was positioned as a sister branch of Chloromyxum kurisi. In view of the morphologic, morphometric, and molecular differences with the existing species of Chloromyxum, and considering the differences in hosts and geographic locations, the present species is treated as new and the name Chloromyxum argusi n. sp. is proposed.

Morphological and molecular characterization of a new cyprinid gall bladder-infecting Chloromyxum species, Chloromyxum peleci sp. n. (Myxozoa: Chloromyxidae), from Pelecus cultratus (L.) in Russia

Extensive sampling to get rich data is very important to resolve the current taxonomic problem of Chloromyxum genus and elucidate the nature phylogenetic relationships among congeneric species. During the parasitological survey of cyprinid fish in Gulf of Finland off the coast of St. Petersburg, a new Chloromyxum species, named as Chloromyxum peleci sp. n., was found to infect the gall bladder of sichel, Pelecus cultratus (L.). Here, we provided the morphological, ultrastructural, and molecular features to describe it. Infection was represented by mono- or disporic plasmodia and mature free-floating spores in the gall bladder. Mature spores are typical of freshwater Chloromyxum species, spherical or subspherical in lateral view, measuring 8.8 ± 0.5 μm (7.4-9.5) in length, 7.8 ± 0.3 μm (7.0-8.8) in width, and 7.5 ± 0.4 μm (6.8-8.2) in thickness. Spores have a cog-like appearance in apical view for sutural ridge, and eight to ten widely spaced extrasutural ridges per valve protrude from the spore valve margin. The surface ridge patterns of the new species are similar with those of Chloromyxum auratum and Chloromyxum cristatum, with some branching. Four polar capsules of slightly unequal in two pairs were oval in apical view and pyriform in side view, locating at the anterior end of the spores. Polar filaments coil with four to five turns. The obtained almost full length of 18S ribosomal DNA (rDNA) of Ch. peleci sp. n. does not match any sequences available in GenBank but was most closely related to that of Chloromyxum fluviatile (97.9%). Phylogenetic analysis indicated that Ch. peleci sp. n. clustered in a Chloromyxum subclade infecting the gall bladder of freshwater teleost, with robust nodal support. However, Chloromyxum sensu lato infecting gall bladder of freshwater teleost was again proved to be polyphyletic. The possible evolutionary history of Chloromyxum morphotype of Chloromyxum sensu lato was discussed based on the rDNA-referred phylogeny. This is the second Chloromyxum species from sichel.