Morphology, seasonality and molecular characterization of Ceratomyxa draconis n. sp. parasite of Trachinus draco (L.) from the Bay of Bizerte, Tunisia

Morphological and molecular characterization of Chloromyxum dasyatidis n. sp. (Myxosporea: Chloromyxidae) in the common stingray Dasyatis pastinaca (Linnaeus) from Tunisian waters (Central Mediterranean Sea)

A new species of Chloromyxum Mingazzini, 1890, C. dasyatidis n. sp., is described from the gallbladder of the elasmobranch fish Dasyatis pastinaca (Linnaeus) from the Mediterranean coast off Tunisia. Mature myxospores were subspherical measuring 13.0 ± 0.3 (12.5-13.9) µm in length, 11.3 ± 0.5 (10.2-12.2) µm in width, and 11.8 ± 0.5 (11.4-12.7) µm in thickness. Four pyriform polar capsules 4.4 ± 0.3 (4.0-4.9) µm long and 3.5 ± 0.3 (3.0-3.8) µm wide. Valves were ornamented by 5 to 7 elevated surface ridges and displayed short caudal filaments. Chloromyxum dasyatidis n. sp. had an overall prevalence of infection of 38.5%, with significant seasonal variation, being more prevalent during summer (60.0%) and autumn (70.8%). Phylogenetically, this species grouped within the Chloromyxum sensu stricto lineage, forming a small clade together with the genetically more similar species C. acuminatum and C. myolibati, both from stingray hosts.

Morphological and molecular characterization of a new freshwater Ceratomyxa species (Cnidaria: Myxozoa) from the yellow catfish, Trachysurus fulvidraco in China

Ceratomyxa Thélohan, 1892 is one of the largest genera of the sub-phylum Myxozoa, and has a worldwide geographical distribution. Ceratomyxa species mainly infect the gallbladder of marine fish and rarely infect histozoically or coelozoically freshwater fish. In the present study, yellow catfish, Trachysurus fulvidraco (Siluriformes, Actinopteri) collected from the low reach of Yellow River was first found to be infected with an unknown Ceratomyxa species in their gallbladder which was identified to be new to science and nominated as Ceratomyxa huangheensis n. sp. by an integrative taxonomic approach for myxosporeans. Spores are typical of the genus Ceratomyxa, and matures spores are arcuate, with posterior angle of 139.2 ± 11.6 (137.0-156.0)° and rounded ends, and measures 4.7 ± 0.6 (3.3-5.5) μm in length, and 10.7 ± 1.3 (8.5-13.3) μm in thickness. Two spore valves are slightly unequal and present elongated ovoid in the lateral view. Two equal spherical polar capsules, measuring 2.2 ± 0.4 (1.4-2.8) μm × 2.0 ± 0.4 (1.0-2.5) μm in size locates adjacent to the straight suture line. The obtained partial small subunit ribosomal DNA (SSU rDNA) sequence was unique among all myxozoans in GenBank, and the highest similarity is 85.3% with Ceratomyxa sparusaurati, a marine fish-infecting congener. Phylogenetic analysis further indicated that this novel species did not cluster with other freshwater fish-infecting congeners from South America to form an independent clade, but was phylogenetically positioned within the marine fish-infecting clade. The possible presence of different radiation trajectories between Ceratomyxa huangheensis n. sp. and Amazonian freshwater Ceratomyxa lineage was discussed. This is the first report of Ceratomyxa species in the Yellow River basin and the second freshwater Ceraotomyxa species in China, even in Asia.

Myxidium tunisiensis n. sp. (Myxosporea: Myxidiidae) infecting the rough skate Raja radula Delaroche, 1908 (Rajiformes: Rajidae) from North East Tunisia

A new marine myxosporean, Myxidium tunisiensis n. sp. (Myxosporea: Myxidiidae), is described infecting the gallbladder of the rough skate Raja radula Delaroche, 1908 (Chondrichthyes: Rajidae) harvested from the Bay of Bizerte, Tunisia. Observed stages of the parasite were floating free in the bile. Plasmodia, disporic or polysporic, contain disporic pansporoblasts measuring 23.0-27.2 μm in maximum diameter and 21.0-25.5 μm in minimum diameter. Mature myxospores, which are elongated, typically fusiform measured 18.6 ± 1.7 (17.2-22.0) μm in length, 8.6 ± 1.2 (7.2-11.2) μm in width and 8.2 ± 0.9 (6.4-10.1) in thickness. Myxospore valves are symmetrical with 9-10 longitudinal striations. Two polar capsules, pyriform, were equal in size, measuring 5.8 ± 0.4 (5.2-6.7) μm in length and 3.1 ± 0.2 (3.0-3.2) μm in width, with 5-6 polar filament turns. The infection was prevalent throughout the year with the highest prevalence in autumn (81.8%) and the lowest in winter (32.3%). The seasonal prevalence of M. tunisiensis n. sp. in the Bay of Bizerte appeared to fluctuate according to seawater temperature. The morphological and morphometrical differences with all Myxidium spp. described so far, complemented by molecular data, prove clearly that the present species is a new member of the genus Myxidium. The SSU rDNA phylogenetic analyses revealed that Myxidium tunisiensis n. sp. clustered within the oligochaete-gallbladder clade in a basal position to the marine subclade of Myxidium baueri and Myxidium coryphaenoideum. While the new species branching pattern is stable in the ML and the BI analyses, it changed in the MP analysis. This is the first molecular study of a Myxidium species infecting an elasmobranch host inhabiting the Mediterranean Sea.

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.