Evolutionary origin of Ceratonova shasta and phylogeny of the marine myxosporean lineage

First record and description of actinospore stages (raabeia, triactinomyxon, and aurantiactinomyxon types) of fish parasitic myxozoans from Malaysia

During a 2-month survey in 2023 at Tasik Telabak, Terengganu, Malaysia three distinct actinospore types, namely raabeia, triactinomyxon and aurantiactinomyxon were identified in three invertebrate host species: Aulodrilus acutus, Branchiodrilus sp., and Bothrioneurum sp. utilizing morphometric and molecular analyses. Maximum likelihood of 18S rDNA positioned the raabeia type within the Myxobolus clade from fish of the Order Cypriniformes, suggesting a detected actinospore has a potential life cycle development in Cypriniformes and the genus Myxobolus. Both triactinomyxon and aurantiactinomyxon types were described solely based on morphology and morphometrics due to preservation error preventing the acquisition of 18S rDNA sequences. The triactinomyxon type in this study exhibited distinct morphology in spore shape and dimensions, characterized by a short style and caudal processes. Conversely, the aurantiactinomyxon type described herein possesses prominent elongated pyriform polar capsules not resembling any previously known aurantiactinomyxon types. These distinctive features, along with host species and geographical location justify their classification as novel types. Histological and microscopic analyses revealed the development of pansporocysts in the intestinal epithelium of the oligochaete host. This study marks the first descriptions of actinospore stages of myxozoans in Malaysia and the initial report of actinospores infecting host species of Aulodrilus acutus, Branchiodrilus sp. and Bothrioneurum sp.

Myxobolus acanthogobii Hoshina, 1952 and Myxobolus selari n. sp. (Myxosporea: Myxobolidae) infecting brain of commercial fishes in Terengganu, Malaysia

Myxosporean infection in marine water fishes has drawn less attention than in freshwater fishes, which resulted in a higher taxonomic variety in freshwater in Malaysia. This study aimed to address the gap by conducting a myxosporean survey on two commercially significant marine fish species, Nemipterus furcosus (Valenciennes) (Eupercaria incertae sedis: Nemipteridae) and Selar crumenophthalmus (Bloch) (Carangiformes: Carangidae), collected from the northeastern part of peninsular Malaysia. During the examination of the organs, two distinct Myxobolus Bütschli, 1882 species were discovered in the brain tissue of these fishes, despite the absence of any observable pathological signs. The two Myxobolus species were characterized through morphometry, morphology, and analysis of partial small subunit ribosomal RNA (18S rDNA) gene. As a result, Myxobolus acanthogobii Hoshina, 1952, which infects 2.3% of N. furcosus, is synonymous with a myxobolid species commonly found in Japanese waters, based on its morphological traits, tissue tropism, and molecular diagnostics. Furthermore, a novel species, Myxobolus selari n. sp., was described, infecting the brain of one (11%) individual S. crumenophthalmus. This unique species displayed distinctive features, placing it within a well-supported subclade primarily comprising brain-infecting myxobolids. Maximum likelihood analysis further revealed the close relationships among these brain-infecting myxobolids, underscoring the significance of tissue tropism and host taxonomy for myxobolids. This study represents the initial documentation of Myxobolus species within the southern South China Sea, shedding light on the potential diversity of marine myxosporean in this region. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:7C400E35-7CB8-4DEE-92B7-F75FF3926441.

Morphological and Molecular Characterization of Two New Species of Ceratomyxa Thélohan, 1892 (Cnidaria: Myxosporea) from the Marine Ornamental Fish Zanclus cornutus (Linnaeus, 1758) off Lakshadweep Islands, Arabian Sea

PURPOSE

The present study provides the complete morphological and molecular description of two new species of myxosporeans, Ceratomyxa zancli n. sp. and Ceratomyxa cornuti n. sp. infecting the gallbladder of Zanclus cornutus from the Lakshadweep Islands, Arabian Sea.

METHODS

Zanclus cornutus were screened for the presence of myxosporeans, and the recovered myxospores were morphologically characterized using Nomarski Differential Interference Contrast (DIC) optics. The sequences of SSU rDNA were employed for molecular and phylogenetic studies.

RESULTS

Both the parasites exhibited a prevalence of 21% each. C. zancli n. sp. is characterized by broadly cresentic myxospores with convex anterior and slightly concave to straight posterior margins and rounded ends. Spore valves two, unequal, measured 9.6 ± 0.7 μm × 25.2 ± 1.3 μm. Polar capsules two, unequal, spherical, measured 4 ± 0.6 μm × 3.5 ± 0.6 μm. Polar filament exceptionally long and arranged irregularly. Myxospores of C. cornuti n. sp. are elongated with convex anterior and slightly concave to straight posterior margins. Spore valves two, unequal, measured 7.00 ± 0.4 μm × 26.56 ± 1.8 μm. Polar capsules spherical, unequal, measured 3.52 ± 0.2 × 3.36 ± 0.35. Molecular analysis of C. zancli n. sp. (ON818297) and C. cornuti n. sp. (ON818298) resulted in 1469 and 1491 bp long SSU rDNA sequences, respectively. Molecularly C. zancli n. sp. is close to C. diplodae and C. barnesi with 91.39% similarity, while C. cornuti n. sp. appears closer to C. robertsthomsoni with 97.46% similarity. In phylogenetic analyses, C. zancli n. sp. branched separately within the Ceratomyxa clade while C. cornuti n. sp. clustered with C. robertsthomsoni and C. thalassomae.

CONCLUSION

Based on the differences in morphological, morphometric, molecular, and phylogenetic characteristics, as well as differences in the host and geographic location, the above two species of myxosporeans are considered novel. The study forms the first report of a species of Ceratomyxa from Z. cornutus.

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.

Morphological and genetic analysis of Ceratomyxa saurida Zhao et al. 2015 and Ceratomyxa mai sp. nov. (Myxozoa: Ceratomyxidae) from the East China Sea

We describe Ceratomyxa saurida Zhao et al. 2015 and Ceratomyxa mai sp. nov. (Myxozoa: Ceratomyxidae) from the East China Sea. C. saurida was found in the gallbladders of 3/13 specimens of its type host, Saurida elongata Temminck and Schlegel 1846 (Aulopiformes). Myxospore characters were consistent with the original description to which we have added small subunit (SSU) rRNA gene data. C. mai sp. nov. was found in gallbladders of 3/13 specimens of S. elongata and 5/13 specimens of Neobythites sivicola Jordan and Snyder 1901 (Ophidiiformes). Mature myxospores of C. mai sp. nov. were crescentic in sutural view, with a deeply concave posterior angle 142.2±8.2° (125.8‒158.2°) and an arched anterior side. Shell valves were smooth and equal, 20.9±1.9 (17.3‒24.7) µm thick and 9.2±0.5 (8.1‒9.9) µm long, and joined at a straight, thin sutural plane passing between two nematocysts (polar capsules). The nematocysts were equal-sized, pyriform, 2.6±0.2 (2.4‒2.9) µm long and 2.7±0.2 (2.4‒3.3) µm wide, with their tapered ends pointed toward each other, located in the anterior third of the spore. Sequences of the SSU rRNA gene and internal transcribed spacer 1 showed that the isolates of C. mai sp. nov. obtained from S. elongata and N. sivicola were identical. The SSU rRNA gene sequence of C. mai sp. nov. was distinct from all known myxosporeans and clustered with C. saurida, and then with Ceratomyxa filamentosi Kalatzis, Kokkari and Katharios 2013, both of which also infect Aulopiformes fishes.

Occurrence of two myxosporean parasites in the gall bladder of white seabream Diplodus sargus (L.) (Teleostei, Sparidae), with the morphological and molecular description of Ceratomyxa sargus n. sp

Myxosporeans are widespread cnidarian parasites that usually parasitize fish as part of their complex life cycle, thus constituting a potential threat for the aquaculture industry. White seabream Diplodus sargus (L.) is a commercially valuable sparid fish reared in Southern European aquacultures. Nonetheless, knowledge on myxosporean infections potentially harming the sustainable production of this fish is extremely limited. In this study, a myxosporean survey was conducted on D. sargus specimens reared in two Southern Portuguese fish farms. Two coelozoic myxosporeans were detected infecting the gall bladder, and are herein reported based on microscopic and molecular procedures: Ceratomyxa sargus n. sp. and Zschokkella auratis Rocha et al., 2013, previously described from reared stocks of gilthead seabream Sparus aurata in the same geographic locality. Ceratomyxa sargus n. sp. is the 12^th species of the genus to be reported from Southern European sparids, reinforcing a substantial radiation of Ceratomyxa within this fish family and geographic region. SSU rRNA-based Bayesian inference and maximum likelihood analyses revealed C. sargus n. sp. positioned separately from other sparid-infecting Ceratomyxa spp. reported from Southern European countries, demonstrating that this species does not share a more immediate common ancestor with its closest relatives based on host affinity and geography. The recognition of a novel sparid-infecting lineage within the Ceratomyxa clade strengthens the contention that this genus entered sparid fish multiple times, namely in the Southern European region. The identification of Zschokkella auratis infections in D. sargus demonstrates that host shift has occurred among sparids reared in the Southern Portuguese coast. This agrees with the broad host specificity that is usually attributed to this genus, and that may be suggested to be the outcome of the capacity of the Zschokkella morphotype to undergo host shift/switch based on our findings and the limited molecular data available for this genus. Thus, a better understanding of Zschokkella host-associated diversification and dispersal mechanisms requires the increasing availability of molecular data from infections of the same species occurring in multiple hosts and geographical locations.

Molecular and morphological description of Ceratomyxa scophthalmi sp. nov. (Myxozoa) infecting Scophthalmus maeoticus and first report of Myxidium finnmarchicum in the Black Sea

In the present study, 2 species of myxozoan parasites, the novel Ceratomyxa scophthalmi sp. nov. and Myxidium finnmarchicum, were documented from the gallbladder of Scophthalmus maeoticus inhabiting the Turkish Black Sea coast at Sinop. C. scophthalmi sp. nov. had mostly spherical, clavate, and fine-grained polymorphic plasmodia that ranged in diameter from 16.0 to 29.0 µm. Spores were arcuate with a convex anterior margin and concave posterior. Valves of spores were highly elongated and unequal in thickness with one valve 1.1-1.3 times thicker than the other. Valves narrowed gradually toward slightly truncated ends. The mean (range) dimensions of spores were 9.4 (8.5-10.0) µm in length and 49.6 (44.5-55.0) µm in thickness, with polar capsules that were 3.1 (2.7-3.5) µm in length and 3.2 (2.7-3.5) µm in width. Polar filaments were coiled with 4-5 turns. Large numbers of immature forms of C. scophthalmi sp. nov., which were often 'crumpled', and mature forms were found together in the gallbladder bile. Along with morphological differences, phylogenetic analysis based on 18S rDNA, including pairwise nucleotide similarities with other related Ceratomyxa species, suggests C. scophthalmi as a novel species. Moreover, this report provides the first morphological and molecular descriptions of M. finnmarchicum outside of its original geographical location and type host species.

Kudoa hypoepicardialis and associated cardiac lesions in invasive red lionfish Pterois volitans in Grenada, West Indies

Invasive red lionfish Pterois volitans (Linnaeus, 1758) represent an ongoing ecological threat within temperate and tropical waters. Relatively little is known regarding the overall health of P. volitans and their potential for spreading pathogens in non-native regions. Lionfish collected from inshore reefs of Grenada, West Indies, in 2019 and 2021 were identified as P. volitans based on cytochrome c oxidase subunit 1 barcoding. Gross and microscopic examination of tissues revealed myxozoan plasmodia in the hearts of 24/76 (31.6%) lionfish by histopathology or wet mount cytology. Further histopathologic examination revealed severe granulomatous inflammation and myofiber necrosis associated with developing plasmodia and presporogonic life stages. Fresh myxospores were morphologically and molecularly consistent with Kudoa hypoepicardialis, being quadrate in apical view with 4 valves and 4 equal polar capsules. The spore body was 5.1-7.9 (mean: 6.0) µm long, 8.1-9.8 (8.7) µm wide, and 6.9-8.5 (7.7) µm thick. Polar capsules were 2.3-2.7 (2.5) µm long and 0.9-1.6 (1.3) µm wide. 18S small subunit rDNA sequences were 99.81-99.87% similar to sequence data from the original description of the species. Novel 28S large subunit rDNA and elongation factor 2 data, which did not match any previously reported species, were provided. This is the first account of a myxozoan parasite of P. volitans, a new host record and locality for K. hypoepicardialis, and one of few reports describing pathogen-associated lesions in invasive lionfish.

A novel Ceratomyxa species (Myxozoa: Cnidaria) infecting an Amazonian catfish

Parasites are important organisms for the health of ecosystems. While the Amazon Basin is home to a great diversity of ichthyofauna, our knowledge of myxozoan diversity in the biome remains relatively limited. The present study describes a new myxozoan species, Ceratomyxa mandii n. sp., parasitizing the gallbladder of the Amazonian catfish Pimelodina flavipinnis (Pimelodidae) from the Solimões River, in the region of Manaus, Brazil. Light and electron microscopy,  small subunit ribosomal DNA (SSU rDNA) sequencing and phylogenetic analysis were performed. The new species exhibited worm-like plasmodia with undulatory motility. The SSU rDNA based phylogenetic analysis revealed it to be a sister taxon of C. gracillima, which also parasitizes an Amazonian pimelodid fish, possibly reflecting a host-parasite co-speciation process. This study contributes to our understanding of this little sampled group of organisms.

Morphological Redescription and Phylogenetical Position of Ceratomyxa truncata Thelohan (1895) and Coccomyxa morovi Léger and Hesse, 1907 (Myxozoa: Myxosporea) Infecting the Gall Bladder of Sardina pilchardus (Walbaum) from Tunisian Coast

PURPOSE

Two myxosporean species have been, so far, independently reported from the gallbladder of the European pilchard, Sardina pilchardus (Walbaum) (synonym Clupea pilchardus) in the Northern shore of the Mediterranean Sea; Ceratomyxa truncata Thélohan, and Coccomyxa morovi Léger and Hesse, 1907. The two species were described with incomplete morphological data and based only on line drawings of their mature myxospores.

METHODS

During a parasitological survey in the Southern shores of the Mediterranean coast in the gulf of Gabès off Tunisia, two coelozoic myxosporean species were found in the European pilchard and described using morphological and molecular phylogenetic tools. Morphological characterization was based on the mature myxospore study and some vegetative stages. The SSU rDNA sequences were performed for molecular and phylogenetic study.

RESULTS

The most frequently encountered species belongs to the genus Ceratomyxa Thelohan, 1892. The second species belongs to the genus Coccomyxa. Morphological examinations, allowed us to match these two recorded species with Ceratomyxa truncata and Coccomyxa morovi, respectively, as previously described in the same host species referring to the original manuscripts instead of some morphological differences. Molecular analyses based on the partial SSU rDNA sequences did not much with any of the previously reported myxozoan sequences. Phylogenetic analysis positioned C. truncate in a well-supported clade including Ceratomyxa ssp. from Mediterranean Sea, while C. morovi was positioned on the basis of the subclade grouping all Coccomyxidae species.

CONCLUSION

We provided herein a first morphological redescription of Ceratomyxa truncata and Coccomyxa morovi parasite of Sardina pilchardus from the Southern shores of the Mediterranean Sea and we successfully obtained the SSU rDNA sequences of these two species and positioned them in the phylogenetic tree.

New data on Henneguya postexilis Minchew, 1977, a parasite of channel catfish Ictalurus punctatus, with notes on resolution of molecular markers for myxozoan phylogeny

Previous morphological and histological data are supplemented with molecular and ultrastructural data for a Henneguya sp. isolated from farm-raised channel catfish Ictalurus punctatus in Mississippi, USA. Myxospores were cryptic, encapsulated within a thin layer of epithelium in the gill lamellae with spore measurements consistent with the original description of Henneguya postexilis Minchew, 1977. Myxospores were 42.7-49.1 µm in total length with spore bodies 12.1-17.2 × 3.6-4.8 × 2.9-3 µm. Polar capsules were of unequal length, with the longer capsule being 4.4-6.7 × 1.1-1.6 µm and the shorter capsule being 4.4-6.4 × 1.1-1.6 µm. Polar tubules had 6-8 turns. Caudal processes were 25.7-38.1 µm in length. Spores were encapsulated in a thin layer of epithelium in the gill lamellae. Molecular data from the most commonly used markers for myxozoan identification and phylogeny, partial 18S small subunit ribosomal gene (SSU), partial 28S large subunit ribosomal gene (LSU), and elongation factor 2 (EF2) were generated for H. postexilis. Additionally, novel data for LSU and EF2 were generated for archived myxozoan specimens from farm-raised catfish (H. mississippiensis, H. ictaluri, H. exilis, H. adiposa, H. sutherlandi, H. bulbosus, Unicauda fimbrethilae), as well as archived specimens from wild fish (H. laseeae [from Pylodictis olivaris], Hennegoides flockae [from Aphredoderus sayanus], Myxobolus cloutmani [from Cycleptus elongatus]. These include the first EF2 sequence data for the genera Hennegoides and Unicauda. Phylogenetic analyses using these data placed H. postexilis in well supported clades with other ictalurid-infecting Henneguya species. Phylogenetic signal assessments on these analyses suggest that while SSU provided the greatest phylogenetic signal, LSU yielded comparable signal, supporting previous work implying this region may be underutilised in reconstructing myxobolid phylogenies.

Two novel myxosporean parasite species of Ceratomyxa Thélohan, 1892 from the banded cusk-eel Raneya brasiliensis (Kaup) (Ophidiiformes: Ophidiidae) off Patagonia, Argentina

We described two novel myxozoan parasite species Ceratomyxa argentina n. sp. and Ceratomyxa raneyae n. sp. from the gall bladder of Raneya brasiliensis (Kaup) from the Patagonian coast of Argentina. Both species can be distinguished from other ceratomyxids by myxospore and polar capsule (nematocyst) morphology and morphometry, fish host and geographic locality. Phylogenetic reconstruction using ssrDNA gene sequences showed that the two new species are placed in a long-branching ceratomyxid clade which also include Ceratomyxa appendiculata Thélohan, 1892, Ceratomyxa anko Freeman, Yokoyama and Ogawa, 2008, Ceratomyxa pantherini Gunter, Burger and Adlard, 2010 and Pseudoalataspora kovalevae Kalavati, MacKenzie, Collins, Hemmingsen and Brickle, 2013. This study documents additional biodiversity of marine myxozoans in the South Atlantic, a region still largely unexplored for this group of parasitic cnidarians.

Morphological and molecular characterization of Ceratomyxa xanthopteri n. sp. (Myxosporea: Ceratomyxidae) from the marine ornamental fish Acanthurus xanthopterus Valenciennes 1835 (Acanthuridae) off Vizhinjam coast, Kerala

A new species of Ceratomyxa infecting the gallbladder of the marine ornamental fish Acanthurus xanthopterus collected from the Vizhinjam coast of Kerala is described. The parasite exhibited a prevalence of 100%. Mature spores recovered from the gallbladder were slightly crescentic with rounded lateral extremities and possessed convex anterior and slightly concave to straight posterior margins. Spore valves two, equal, joined by a straight and prominent suture. Myxospores measured 5.5 ± 0.6 μm in length and 15.9 ± 2.3 μm in thickness. Polar capsules two, equal, spherical, positioned anteriorly on either sides of the suture, 2.3 ± 0.2 μm long and 2.2 ± 0.2 μm wide. Polar filament with four to five coils, 21.2 ± 0.6 μm when extruded. Posterior angle 173.6 ± 5.2°. Early sporogonic stages and monosporic, disporic, and multisporic plasmodial stages were spherical to irregular in shape, with or without filopodia. Histopathologic analysis revealed that spores and developing stages were attached to the gallbladder wall as well as found free in the lumen. Morphologic and morphometric comparison of the present parasite with known species of Ceratomyxa indicated significant differences. In molecular and phylogenetic analyses, the present myxosporean revealed high divergence with related forms and occupied an independent position within the Ceratomyxa clade with high nodal support. Considering the morphological, morphometric, molecular, and phylogenetic dissimilarities with the previously described species of Ceratomyxa and the differences in host and geographic locations, the present species of myxosporean is treated as new and is named Ceratomyxa xanthopteri n. sp.

Zschokkella epinepheli n. sp. (Myxosporea: Myxidiidae) infecting the gallbladder of the white grouper Epinephelus aeneus (Serranidae) from Tunisian waters

A new coelozoic myxosporean species, Zschokkella epinepheli n. sp., collected from the gallbladder of the white grouper Epinephelus aeneus (Perciformes: Serranidae) from the bay of Bizerte, Tunisia, is described based on morphological and molecular characteristics. Myxospores and plasmodia were observed floating free in the bile. Mature plasmodia were polysporic and subspherical in shape, measuring 85.0-94.0 μm long and 70.0-82.0 μm wide. Mature myxospores were ovoid in valvular view, measuring 10.0 ± 1.7 (8.0-11.0) μm in length and 7.0 ± 0.3 (6.6-7.5) μm in width. Polar capsules were pyriform and equal in size, measuring 3.0 ± 0.2 (2.8-3.6) μm in length and 2.3 ± 0.3 (1.8-2.7) μm in width. Myxospore valves had 12-14 longitudinal striations. Based on the small subunit rDNA, the new species Z. epinepheli n. sp. differs from all other Zschokkella species for which there is a DNA sequence deposited in GenBank. Phylogenetic analysis revealed that Z. epinepheli n. sp. clustered in the marine subclade of Zschokkella species within the biliary tract IV clade. This is the first report of a Zschokkella species from the gallbladder of an epinephelin fishes.

Growing diversity supports radiation of an Ellipsomyxa lineage into the Amazon freshwater: Description of two novel species parasitizing fish from Tapajós and Amazon rivers

Species of the genus Ellipsomyxa Køie, 2003, parasitize mostly marine and brackish fish around the world. In the present study, we describe two novel species of Ellipsomyxa: Ellipsomyxa plagioscioni n. sp. parasitizing the gall bladder of Plagioscion squamosissimus (Sciaenidae), a freshwater fish but commonly found in brackish water in the Amazonian estuarine environment; and Ellipsomyxa paraensis n. sp. infecting Cichla monoculus (Cichlidae), a strictly freshwater fish. The host specimens were caught from the Amazon and Tapajós rivers, in the municipal region of Santarém, in the State of Pará, Brazil. The study was performed using a combination of morphological, biological, and SSU rDNA-based phylogeny, which suggested that marine transgressions of the Miocene epoch, in the central region of South America, were a pathway for the adaptation and radiation of these cnidarian parasites in the freshwater environment. Both disporic plasmodia and mature myxospores were found floating freely in the bile. Mature myxospores from both species were ellipsoidal in the valvular and sutural views, with thin smooth valves elongated in the direction perpendicular to the plane of the transverse sutural line. Ellipsomyxa plagioscioni n. sp. myxospores measured 11.1 (10.2-12.8) µm in length and 6.6 (5.6-7.6) µm in width. Two pyriform polar capsules discharging on opposite sides, some distance from both the sutural line and the spore ends, measured 3.8 (3.2-4.4) µm in length and 2.8 (2.3-3.3) µm in width, with 5-6 coil polar tubules. Ellipsomyxa paraensis n. sp. myxospores measured 11.5 (10.5-12.4) µm in length and 7.5 (6.6-8.6) µm in width. Two pyriform polar capsules which discharged on opposite sides some distance from both the sutural line and spore ends, measured 3.2 (2.1-3.9) µm in length and 2.6 (2.0-3.3) µm in width, with 2-3 coil polar tubules. Valvular protrusions were observed, associated with the tips of the polar capsules. Molecular analysis based on the SSU rDNA sequences indicated that the two novel Ellipsomyxa species were distinct from all other sequences deposited in the GenBank database. The phylogenetic trees clustered E. plagioscioni n. sp. as a basal species of a lineage of the marine/estuarine Ellipsomyxa, while E. paraensis n. sp. clustered together with other Amazonian species.

A novel histozoic myxosporean, Enteromyxum caesio n. sp., infecting the redbelly yellowtail fusilier, Caesio cuning, with the creation of the Enteromyxidae n. fam., to formally accommodate this commercially important genus

Gastrointestinal myxosporean parasites from the genus Enteromyxum are known to cause severe disease, resulting in high mortalities in numerous species of cultured marine fishes globally. Originally described as Myxidium spp., they were transferred to a new genus, Enteromyxum, to emphasize their novel characteristics. Their retention in the family Myxidiidae at the time was warranted, but more comprehensive phylogenetic analyses have since demonstrated the need for a new family for these parasites. We discovered a novel Enteromyxum in wild fish from Malaysia and herein describe the fourth species in the genus and erect a new family, the Enteromyxidae n. fam., to accommodate them. Enteromyxum caesio n. sp. is described infecting the tissues of the stomach in the redbelly yellowtail fusilier, Caesio cuning, from Malaysia. The new species is distinct from all others in the genus, as the myxospores although morphologically similar, are significantly smaller in size. Furthermore, small subunit ribosomal DNA sequence data reveal that E. caesio is <84% similar to others in the genus, but collectively they form a robust and discrete clade, the Enteromyxidae n. fam., which is placed as a sister taxon to other histozoic marine myxosporeans. In addition, we describe, using transmission electron microscopy, the epicellular stages of Enteromyxum fugu and show a scanning electron micrograph of a mature myxospore of E. caesio detailing the otherwise indistinct sutural line, features of the polar capsules and spore valve ridges. The Enteromyxidae n. fam. is a commercially important group of parasites infecting the gastrointestinal tract of marine fishes and the histozoic species can cause the disease enteromyxosis in intensive finfish aquaculture facilities. Epicellular and sloughed histozoic stages are responsible for fish-to-fish transmission in net pen aquaculture systems but actinospores from an annelid host are thought to be necessary for transmission to fish in the wild.

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

The specimens of Trachinus draco collected from the Bay of Bizerte were found to be infected with a new Ceratomyxa species described as Ceratomyxa draconis n. sp. The sequence of small subunit ribosomal RNA gene obtained in this study differs from other Ceratomyxa sequences available in GenBank. Mature spores of this species were elongated and crescent-shaped in sutural view, measuring 7.4 ± 0.77 (6.4-8.0) μm in thickness and 30.8 ± 1.65 (28.8-32.8) μm in width. The polar capsules were spherical, equal in size, and measuring 3.3 ± 0.2 (3.6-4.0) μm in diameter. The Ceratomyxa draconis n. sp. showed a clearly seasonal variation of prevalence with highest prevalence noted during summer months.

Evolutionary dynamics of Ceratonova species (Cnidaria: Myxozoa) reveal different host adaptation strategies

The myxozoan parasite Ceratonova shasta is an important pathogen that infects multiple species of Pacific salmonids. Ongoing genetic surveillance has revealed stable host-parasite relationships throughout the parasite's endemic range. We applied Bayesian phylogenetics to test specific hypotheses about the evolution of these host-parasite relationships within the well-studied Klamath River watershed in Oregon and California, USA. The results provide statistical support that different genotypes of C. shasta are distinct lineages of one species, which is related to two other Ceratonova species in the same ecosystems; Ceratonova X in speckled dace and C. gasterostea in threespine stickleback. Furthermore, we found strong support for the hypothesis that C. shasta type 0 in native steelhead trout and type I in Chinook salmon each evolved with a specialist host adaptation strategy, while C. shasta type II in coho salmon resulted from a generalist host adaptation strategy. Inferred date and host species of the most recent common ancestor of extant Klamath basin types indicate that it occurred between 14,000 and 21,000 years ago, and most likely infected a native steelhead or rainbow trout host.

A new species Myxodavisia jejuensis n. sp. (Myxosporea: Sinuolineidae) isolated from cultured olive flounder Paralichthys olivaceus in South Korea

A new myxosporean parasite, Myxodavisia jejuensis n. sp. (Myxozoa; Bivalvulida) is described from the urinary bladder of olive flounder Paralichthys olivaceus cultured on Jeju Island, Korea. Two long lateral appendages with whip-like extensions were attached to mature spores of triangular to semi-circular shape. The spores were measured at 13.1 ± 1.1 μm in length, 17.2 ± 1.0 μm in thickness, and 13.1 ± 1.0 μm in width. Two spherical polar capsules, with a diameter of 5.0 ± 0.4 μm, were observed on opposite sides in the middle of the spore. The suture line was straight or slightly sinuous on the middle of spores. The 18S rDNA from M. jejuensis n. sp. was used in BLAST and molecular phylogenetic analysis. The results demonstrated that M. jejuensis n. sp. was closest to Sinuolinea capsularis and that the infection site tropism was correlated with the phylogeny of marine myxosporeans. In addition, we designed specific primers to detect the 18S rDNA gene of M. jejuensis n. sp.; the results showed specific amplification in M. jejuensis n. sp. among the myxosporeans isolated from the urinary bladder of the cultured olive flounder.

Morphological and Molecular Identification of a Novel Species, Ceratomyxa siganicola n. sp. (Myxozoa: Ceratomyxidae) from Siganus fuscescens, in East China Sea

INTRODUCTION

Ceratomyxa Thélohan, 1892 is one of the largest genera under Myxosporea Butschli, 1881, and has a worldwide distribution, but little attention has been paid to myxosporean parasites from the Chinese seawaters, East China Sea.

METHODS

Morphology and molecular biology methods were combined for species identification and phylogenetic analysis.

RESULTS

A new coelozoic myxosporean species, Ceratomyxa siganicola n. sp., was found to infect the gallbladder of Siganus fuscescens (Houttuyn, 1782) (Perciformes, Siganidae) from coastal waters of Xiamen, East China Sea, China. Mature myxospores of the novel species exhibited the morphologically typical features of the genus Ceratomyxa. They were slightly crescent shaped with rounded ends, measuring 5.6 ± 0.5 (4.8-6.5) μm in length and 19.1 ± 1.8 (16.0-22.1) μm in thickness. The posterior angle was slightly convex to straight and measured 177.1 ± 0.5 (175.2-178.4)°. Spore valves were slightly unequal and smoothly ovoid in the lateral view. Two polar capsules were spherical, equal in size and measured 2.7 ± 0.2 (2.1-3.0) μm in diameter. The 18S rDNA sequence of C. siganicola n. sp. was unique among all myxozoans, and the highest similarity was 97.4% with Ceratomyxa barnesi. Phylogenetic analysis showed that C. siganicola n. sp. was clustered within the clade of siganid ceratomyxids. The present results also indicated that the species radiation of Ceratomyxa occurred not only within host affinity but also within locality.

Sinuolinea capsularis (Myxosporea: Sinuolineidae) Isolated from Urinary Bladder of Cultured Olive Flounder Paralichthys olivaceus

Sinuolinea capsularis Davis, 1917 is myxosporean that infect the urinary system of the host fish. Insufficient morphological and molecular data of S. capsularis exits, and it is therefore difficult to make an accurate identification of the parasite. We tried a series of morphological and molecular analysis to identify an myxosporean isolated from urinary bladder of cultured olive flounder, Paralichthys olivaceus, from Jeju island in the Republic of Korea. Some of them were observed under a light microscope and SEM, and remain samples were used molecular and phylogenetic analysis. Mature spores were subspherical, measuring 13.9±0.6 μm in length and 13.8±0.8 μm in width. Two spherical polar capsules on opposite sides in the middle of the spore had a diameter range of 4.3±0.4 μm. Scanning electron microscopy revealed that spores a severely twisted the suture line. By the morphological comparison and analysis, it was identified as S. capsularis. In addition, we obtained the partial 18S rDNA of S. capsularis and first registered it in NCBI. Phylogenetic analysis showed that S. capsularis clustered with Zschokkella subclade infecting the urinary system of marine fish, and it supported the infection site tropism effect on phylogeny of marine myxosporeans as well as the origin of Sinuolinea is not monophyly.

Multiple evolutionary routes of the single polar capsule in Thelohanellus species (Myxozoa; Myxobolidae)

Thelohanellus Kudo, 1933 is a species rich genus of Myxosporea, sharing many morphological similarities with species of Myxobolus but the former possesses a single polar capsule, and the latter has two. Based on molecular phylogenetic analyses, this single distinguishing feature is not monophyletic, and members of Thelohanellus are intermixed with Myxobolus species, calling into question the validity of genus Thelohanellus. The occurrence of two polar capsules in a small proportion of Thelohanellus spores as observed in this study suggests that these species have the capacity to express this Myxobolus-like trait, clouding the distinction of these two genera further. Herein, using the most comprehensive data set to date, we explored the phylogenetic relationships of Thelohanellus to other myxobolids, to investigate the evolutionary history of the genus Thelohanellus and the origins of single polar capsule in this group. The phylogenetic analyses and statistical tests of topology revealed Thelohanellus as a strongly supported polyphyletic lineage, clustering in five distinct branches within Myxobolus clade. Ancestral state reconstruction for polar capsule number showed that Thelohanellus species have evolved from myxosporean species with two polar capsules at least four times, which could be classified in three possible evolutionary pathways. The polyphyly of Thelohanellus and the multiple evolutionary origins of single polar capsule of Thelohanellus demonstrate that the distinction of this genus from Myxobolus is largely for convenience, and does not reflect their evolutionary history.

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Atypical Thelohanellus spores with two polar capsules were firstly observed.

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Most myxobolid genera involved including Thelohanellus were poly- or paraphyletic.

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Thelohanellus species have evolved at least four times which could be classified in three different evolutionary pathways.

Studies of Myxidium giardi Cépède, 1906 infections in Icelandic eels identifies a genetically diverse clade of myxosporeans that represents the Paramyxidium n. g. (Myxosporea: Myxidiidae)

BACKGROUND

The myxosporean Myxidium giardi Cépède, 1906 was described infecting the kidney of the European eel, Anguilla anguilla (L.), having spindle-shaped myxospores and terminal sub-spherical polar capsules. Since then, numerous anguillid eels globally have been documented to have similar Myxidium infections. Many of these have been identified using the morphological features of myxospores or by the location of infection in the host, and some have been subsequently synonymised with M. giardi. Therefore, it is not clear whether M. giardi is a widely distributed parasite, infecting numerous species of eels, in multiple organs, or whether some infections represent other, morphologically similar but different species of myxosporeans. The aim of the present study was to assess the status of M. giardi infections in Icelandic eels, and related fish hosts in Malaysia and to use spore morphology and molecular techniques to evaluate the diversity of myxosporeans present.

RESULTS

The morphologies of the myxospores from Icelandic eels were very similar but the overall dimensions were significantly different from the various tissue locations. Myxospores from the kidney of the Malaysian tarpon, Megalops cyprinoides (Broussonet), were noticeably smaller. However, the SSU rDNA sequences from the different tissues locations in eels, were all very distinct, with percentage similarities ranging from 92.93% to as low as 89.8%, with the sequence from Malaysia being even more dissimilar. Molecular phylogenies consistently placed these sequences together in a clade that we refer to as the Paramyxidium clade that is strongly associated with the Myxidium clade (sensu stricto). We erect the genus Paramyxidium n. g. (Myxidiidae) to accommodate these histozoic taxa, and transfer Myxidium giardi as Paramyxidium giardi Cépède, 1906 n. comb. as the type-species.

CONCLUSIONS

There is not a single species of Myxidium (M. giardi) causing systemic infections in eels in Iceland. There are three species, confirmed with a robust phylogeny, one of which represents Paramyxidium giardi n. comb. Additional species probably exist that infect different tissues in the eel and the site of infection in the host fish is an important diagnostic feature for this group (Paramyxidium n. g. clade). Myxospore morphology is generally conserved in the Paramyxidium clade, although actual spore dimensions can vary between some species. Paramyxidium spp. are currently only known to infect fishes from the Elopomorpha.

Parvicapsula curvatura n. sp. in cultured olive flounder Paralichthys olivaceus and phylogenetic characteristics of the genus Parvicapsula

Parvicapsula curvatura n. sp. (Myxozoa; Bivalvulida) was found in the urinary bladder of olive flounder Paralichthys olivaceus cultured in a fish farm on Jeju Island, ROK. When laterally viewed, the parasite has asymmetrical curved spores that measure 9.6-11.6 µm in length. Furthermore, it has 2 subspherical polar capsules at the apex. Based on the phenotypical traits, it is most similar to P. limandae but differs in the shape of polar capsule, locality, and host specificity (family level). BLAST analysis indicated that P. curvatura was closest to P. unicornis and P. petuniae via 18S and 28S rDNA sequences, respectively. The 18S rDNA from P. curvatura was used in molecular phylogenetic analyses of Parvicapsula spp. to examine the congruence of phylogeny with spore morphology, locality, and host specificity. The results demonstrated that the spore morphotype was correlated with the phylogeny of the genus Parvicapsula, and the parasites have speciated into an oblong and semicircular spore type.

Morphological and molecular analyses of Bipteria lusitanica n. sp. in wild white seabream, Diplodus sargus (Linnaeus, 1758) in Portugal

The present study records the presence of Bipteria lusitanica n. sp. in wild white seabream, Diplodus sargus (Linnaeus, 1758) off the Portuguese coast. Myxosporean parasites were found in the interstitial tissue of kidney and free in urinary bladder of D. sargus with a 33.3% of prevalence of infection. Myxospores were triangular or inversely pyramidal in shape and anteriorly wider in frontal view, measuring 11.2 ± 1.0 μm in length, 12.6 ± 0.9 μm in width, and 11.6 ± 0.4 μm in thickness. The sinuous sutural line was parallel to the axis that connects the center of the two polar capsules. Spore valves were smooth without ridges. Wing-like appendages extended from the posterior part of each valve in sutural view, measuring 3.9 ± 1.1 μm in length. Spherical polar capsules measured 4.4 ± 0.2 μm in diameter and the polar filaments were helical arranged in 5-6 turns. Molecular data showed that this parasite clusters within species of the Sinuolineidae Shulman, 1959 family, and they all infect the urinary bladder. Using molecular and morphological characterization, we were able to identify this parasite as a novel species of the genus Bipteria Kovaleva, Zubtchenko, and Krasin, 1983.

Ceratomyxa gouletti n. sp. (Myxosporea: Ceratomyxidae), a parasite of the red scorpionfish Scorpaena scrofa (L.) from Tunisian waters

Ceratomyxa gouletti n. sp. is a new parasite described from the gallbladder of the red scorpionfish Scorpaena scrofa (Scorpaeniformes: Scorpaenidae) collected from La Goulette in the Northeast of Tunisia. The parasite develops disporic plasmodia, elliptical to ovoid in shape, measuring up to 33.1 ± 3.6 (28.0-38.2) μm in length and 12.5 ± 2.1 (11.3-14.0) μm in width. Mature spores are elongated transversely and crescent-shaped with rounded ends and unequal shell valves, measuring 8.1 ± 1.27 (7.2-9.0) μm in length and 32.0 ± 2.5 (27.0-38.2) μm in thickness. Sutural line is straight and visible between valves. Polar capsules are subspherical with 3.15 ± 0.63 (2.7-3.6) μm long and 1.9 ± 0.14 (1.8-2.0) μm wide. Posterior spore angle is slightly concave 160°-175°. Molecular analysis based on the small subunit 18S rDNA sequence shows that C. gouletti n. sp. is different from all other ceratomyxid species DNA sequences in GenBank. Phylogenetic trees clustered the new species with long-branching Ceratomyxa species, and it was closely related to the species Ceratomyxa longipes from two gadid fish hosts with 89% bootstrap support.

Synopsis of the species of Ceratomyxa Thélohan, 1892 (Cnidaria, Myxosporea, Ceratomyxidae) described between 2007 and 2017

A synopsis of the species of Ceratomyxa Thélohan, 1892 (Cnidaria, Myxosporea, Ceratomyxidae) described between 2007 and 2017 is presented, including 83 nominal species. For each species, the most important morphological and morphometric features are indicated in tabulated format. Included are also the site of infection within the host, and geographical location, plus a full bibliography of the original records of species. Molecular data (GenBank accession numbers) are also provided whenever possible.

Life in a rock pool: Radiation and population genetics of myxozoan parasites in hosts inhabiting restricted spaces

Introduction

Intertidal rock pools where fish and invertebrates are in constant close contact due to limited space and water level fluctuations represent ideal conditions to promote life cycles in parasites using these two alternate hosts and to study speciation processes that could contribute to understanding the roles of parasitic species in such ecosystems.

Material and methods

Gall bladder and liver samples from five clinid fish species (Blenniiformes: Clinidae) were morphologically and molecularly examined to determine the diversity, prevalence, distribution and host specificity of Ceratomyxa parasites (Cnidaria: Myxozoa) in intertidal habitats along the coast of South Africa. Phylogenetic relationships of clinid ceratomyxids based on the SSU rDNA, LSU rDNA and ITS regions were assessed additionally to the investigation of population genetic structure of Ceratomyxa cottoidii and subsequent comparison with the data known from type fish host Clinus cottoides.

Results and discussion

Seven Ceratomyxa species including previously described Ceratomyxa dehoopi and C. cottoidii were recognized in clinids. They represent a diverse group of rapidly evolving, closely related species with a remarkably high prevalence in their hosts, little host specificity and frequent concurrent infections, most probably as a result of parasite radiation after multiple speciation events triggered by limited host dispersal within restricted spaces. C. cottoidii represents the most common clinid parasite with a population structure characterized by young expanding populations in the south west and south east coast and by older populations in equilibrium on the west coast of its distribution. Parasite and fish host population structures show overlapping patterns and are very likely affected by similar oceanographic barriers possibly due to reduced host dispersal enhancing parasite community differentiation. While fish host specificity had little impact on parasite population structure, the habitat preference of the alternate invertebrate host as well as tidal water exchange may be additional crucial variables affecting the dispersal and associated population structure of C. cottoidii.

Ceratomyxa gracillima n. sp. (Cnidaria: Myxosporea) provides evidence of panmixia and ceratomyxid radiation in the Amazon basin

We describe a new freshwater myxosporean species Ceratomyxa gracillima n. sp. from the gall bladder of the Amazonian catfish Brachyplatystoma rousseauxii; the first myxozoan recorded in this host. The new Ceratomyxa was described on the basis of its host, myxospore morphometry, ssrDNA and internal transcribed spacer region (ITS-1) sequences. Infected fish were sampled from geographically distant localities: the Tapajós River, Pará State, the Amazon River, Amapá State and the Solimões River, Amazonas State. Immature and mature plasmodia were slender, tapered at both ends, and exhibited vermiform motility. The ribosomal sequences from parasite isolates from the three localities were identical, and distinct from all other Ceratomyxa sequences. No population-level genetic variation was observed, even in the typically more variable ITS-1 region. This absence of genetic variation in widely separated parasite samples suggests high gene flow as a result of panmixia in the parasite populations. Maximum likelihood and maximum parsimony analyses placed C. gracillima n. sp. sister to Ceratomyxa vermiformis in a subclade together with Ceratomyxa brasiliensis and Ceratomyxa amazonensis, all of which have Amazonian hosts. This subclade, together with other Ceratomyxa from freshwater hosts, formed an apparently early diverging lineage. The Amazonian freshwater Ceratomyxa species may represent a radiation that originated during marine incursions into the Amazon basin that introduced an ancestral lineage in the late Oligocene or early Miocene.

Morphometeric criteria and partial sequence of the 18S rRNA gene of Ceratomyxa sultani n. sp. from the gallbladder of Upeneus margarethae in the Arabian Gulf, with a note on its seasonal prevalence

This paper describes a new coelozoic myxosporean parasite named Ceratomyxa sultani n. sp. isolated from the gallbladder of Upeneus margarethae sourced from the Arabian Gulf off Saudi Arabia. Of 104 U. margarethae specimens examined, 27 (26%) were infected, with the highest prevalence in winter and lowest in autumn. The pseudoplasmodia were disporous and irregularly elliptical in shape, with an average size of 22 × 17 μm. Mature spores were mostly elliptical with symmetrical valves and equal spherical polar capsules. Spores were 9 µm in length and 25 µm in thickness, while polar capsules were 4 µm wide with four filament coils. The paper further provides a morphological comparison with closely related Ceratomyxa spp. together with phylogenetic analysis based on the partial 18S rRNA sequence, which revealed that C. sultani n. sp. clustered within a robust clade of Ceratomyxa species from the Arabian Gulf and Red Sea or nearby geographic regions.

Amazonian waters harbour an ancient freshwater Ceratomyxa lineage (Cnidaria: Myxosporea)

A new species of Ceratomyxa parasitizing the gall bladder of Cichla monoculus, an endemic cichlid fish from the Amazon basin in Brazil, is described using morphological and molecular data. In the bile, both immature and mature myxospores were found floating freely or inside elongated plasmodia: length 304 (196-402) μm and width 35.7 (18.3-55.1) μm. Mature spores were elongated and only slightly crescent-shaped in frontal view with a prominent sutural line between two valve cells, which had rounded ends. Measurements of formalin-fixed myxospores: length 6.3±0.6 (5.1-7.5) μm, thickness 41.2±2.9 (37.1-47.6) μm, posterior angle 147°. Lateral projections slightly asymmetric, with lengths 19.3±1.4μm and 20.5±1.3μm. Two ovoid, equal size polar capsules, length 2.6±0.3 (2-3.3) μm, width 2.5±0.4 (1.8-3.7) μm, located adjacent to the suture and containing polar filaments with 3-4 turns. The small subunit ribosomal DNA sequence of 1605 nt was no more than 97% similar to any other sequence in GenBank, and together with the host, locality and morphometric data, supports diagnosis of the parasite as a new species, Ceratomyxa brasiliensis n. sp. Maximum parsimony and maximum likelihood analyses showed that C. brasiliensis n. sp. clustered within the marine Ceratomyxa clade, but was in a basally divergent lineage with two other freshwater species from the Amazon basin. Our results are consistent with previous studies that show Ceratomyxa species can cluster according to both geography and host ecotype, and that the few known freshwater species diverged from marine cousins relatively early in evolution of the genus, possibly driven by marine incursions into riverine environments.

Motility, morphology and phylogeny of the plasmodial worm, Ceratomyxa vermiformis n. sp. (Cnidaria: Myxozoa: Myxosporea)

The Myxozoa demonstrate extensive morphological simplification and miniaturization relative to their free-living cnidarian ancestors. This is particularly pronounced in the highly derived myxosporeans, which develop as plasmodia and pseudoplasmodia. To date, motility in these stages has been linked with membrane deformation (e.g. as pseudopodia and mobile folds). Here we illustrate a motile, elongate plasmodium that undergoes coordinated undulatory locomotion, revealing remarkable convergence to a functional worm at the cellular level. Ultrastructural and confocal analyses of these plasmodia identify a highly differentiated external layer containing an actin-rich network, long tubular mitochondria, abundant microtubules, a secreted glycocalyx layer, and an internal region where sporogony occurs and which contains homogeneously distributed granular/fibrillar material. We consider how some of these features may support motility. We also describe the species based on spore morphology and SSU rDNA sequence data, undertake molecular phylogenetic analysis to place it within an early-diverging clade of the ceratomyxids, and evaluate the resultant implications for classification (validity of the genus Meglitschia) and for inferring early host environments (freshwater) of ceratomyxids.

Ultrastructure and phylogeny of Ceratomyxa diplodae (Myxosporea: Ceratomyxidae), from gall bladder of European seabass Dicentrarchus labrax

The myxosporean parasite Ceratomyxa diplodae Lubat et al. 1989 sensu Sitjà-Bobadilla & Álvarez-Pellitero, 1993, originally described from the annular seabream Diplodus annularis in the Adriatic Sea, has subsequently been reported from several other sparid hosts, and also a moronid fish, the European seabass Dicentrarchus labrax from the Mediterranean Sea. Here, molecular identity and additional morphological data are given for this parasite infecting the gall bladder of D. labrax in a southern Portuguese fish farm. In the bile, disporic plasmodia were spherical to subspherical with a smooth surface membrane. Most myxospores were crescent-shaped, 5.1 ± 0.5 (4.8-6.7) µm long (mean ± SD) and 21.9 ± 1.0 (20.4-23.9) µm thick; a few were more arcuate, 5.7 ± 0.4 (5.3-6.3) µm long and 17.3 ± 1.0 (16.3-19.1) µm thick. The wall consisted of 2 symmetrical valves united along a slightly curved suture line, with moderately tapering to rounded ends. Two spherical polar capsules, measuring 2.9 ± 0.3 (2.5-3.4) µm in diameter, contained a polar filament forming 8 to 9 coils organized in 2 rows. Host species, tissue tropism, and myxospore morphology supported species identification. Phylogenetic analyses of the small subunit ribosomal RNA sequence positioned the parasite among most sparid-infecting Ceratomyxa spp., suggesting the existence of a common ancestor for these species. The acquisition of molecular data from infections of C. diplodae in its original host and in other sparids is essential in order to ascertain if the morphological and biological variations found among reports of this parasite are intra- or inter-specific.

Morphological description and phylogeny of Ceratomyxa scorpaeni n. sp. (Myxosporea: Ceratomyxidae) infecting the gallbladder of Scorpaena porcus (L.) (Scorpaeniformes: Scorpaenidae) from the bay of Bizerte in Tunisia

A new marine myxosporean species Ceratomyxa scorpaeni n. sp. is described using morphological characteristics and small subunit ribosomal DNA (rDNA) sequence data. The parasite was found infecting the gallbladder of Scorpaena porcus Linnaeus, 1758 collected from the Bay of Bizerte. Mature plasmodia were disporous free floating in the bile. Spores were transversely elongated and crescent-shaped with unequal shell valves and measured 7.6 ± 0.2 (7.2-8.0) μm in length and 32.8 ± 0.3 (21.6-44.0) μm in thickness. Two sub-spherical polar capsules equal in size, situated at the same level and measured 3.0 ± 0.2 (3.0-3.2) μm in length and 2.4 ± 0.3 (2.3-3.3) μm in width. The infection with C. scorpaeni n. sp. was prevalent throughout the year with a maximum prevalence of infection during spring and summer. Molecular analysis of the SSU rRNA gene confirmed the parasite as a new member of the genus Ceratomyxa and showed close relationship with the species of Ceratomyxa infecting the gallbladders of Sparidae from the Mediterranean Sea. This is the first report of Ceratomyxa species from the gallbladder of S. porcus in Tunisian coastal waters.

Molecular evidence of undescribed Ceratonova sp. (Cnidaria: Myxosporea) in the freshwater polychaete, Manayunkia speciosa, from western Lake Erie

We used PCR to screen pooled individuals of Manayunkia speciosa from western Lake Erie, Michigan, USA for myxosporean parasites. Amplicons from positive PCRs were sequenced and showed a Ceratonova species in an estimated 1.1% (95% CI=0.46%, 1.8%) of M. speciosa individuals. We sequenced 18S, ITS1, 5.8S, ITS2 and most of the 28S rDNA regions of this Ceratonova sp., and part of the protein-coding EF2 gene. Phylogenetic analyses of ribosomal and EF2 sequences showed the Lake Erie Ceratonova sp. is most similar to, but genetically distinct from, Ceratonova shasta. Marked interspecific polymorphism in all genes examined, including the ITS barcoding genes, along with geographic location suggests this is an undescribed Ceratonova species. COI sequences showed M. speciosa individuals in Michigan and California are the same species. These findings represent a third parasite in the genus Ceratonova potentially hosted by M. speciosa.

Histozoic myxosporeans infecting the stomach wall of elopiform fishes represent a novel lineage, the Gastromyxidae

BACKGROUND

Traditional studies on myxosporeans have used myxospore morphology as the main criterion for identification and taxonomic classification, and it remains important as the fundamental diagnostic feature used to confirm myxosporean infections in fish and other vertebrate taxa. However, its use as the primary feature in systematics has led to numerous genera becoming polyphyletic in subsequent molecular phylogenetic analyses. It is now known that other features, such as the site and type of infection, can offer a higher degree of congruence with molecular data, albeit with its own inconsistencies, than basic myxospore morphology can reliably provide.

METHODS

Histozoic gastrointestinal myxosporeans from two elopiform fish from Malaysia, the Pacific tarpon Megalops cyprinoides and the ten pounder Elops machnata were identified and described using morphological, histological and molecular methodologies.

RESULTS

The myxospore morphology of both species corresponds to the generally accepted Myxidium morphotype, but both had a single nucleus in the sporoplasm and lacked valvular striations. In phylogenetic analyses they were robustly grouped in a discrete clade basal to myxosporeans, with similar shaped myxospores, described from gill monogeneans, which are located at the base of the multivalvulid clade. New genera Gastromyxum and Monomyxum are erected to accommodate these myxosporean taxa from fish and gill monogeneans respectively. Each are placed in a new family, the Gastromyxidae with Gastromyxum as the type genus and Monomyxidae with Monomyxum as the type genus.

CONCLUSIONS

To improve modern systematics of the myxosporeans it is clear that a combination of biological, ecological, morphological and molecular data should be used in descriptive studies, and the naming and redistribution of taxa and genera is going to be necessary to achieve this. Here we demonstrate why some Myxidium-shaped myxospores should not be included in the family Myxidiidae, and create two new families to accommodate them based on their site of infection, host biology / ecology, DNA sequence data and morphological observations. Subsequent descriptive works need to follow a similar course if we are going to create a prevailing and workable systematic structure for the Myxosporea.

Ceratomyxa tunisiensis n. sp. (Myxosporea: Bivalvulida) from the Gallbladders of Two Carangid Fish Caught Off the Coast of Tunisia

A new coelozoic Myxozoan species, Ceratomyxa tunisiensis n. sp., was found infecting the gallbladders of two carangid fish, Caranx rhonchus and Trachurus trachurus (Perciforme, Carangidae), from the Gulf of Gabès, on the southern coast of Tunisia. The parasite develops in spherical mono-, diplo-, or polysporic tropozoites in the gallbladder of the hosts. Mature spores are typical of the genus Ceratomyxa. They are transversely elongated and narrowly crescent-shaped with a slightly convex anterior and concave posterior, and measure 23 ± 0. 27 (20-25) μm width × 6 ± 0.26 (5-8) μm in length. Spore shell valves are symmetrical with rounded ends. Two spherical polar capsules situated on either side of the sutural line measure 2.2 μm (2.0-3.0) in diam. Periodical sampling of C. rhonchus and T. trachurus from Marsh 2012 to February 2013 showed that infection due to C. tunisiensis occurs in 59% and 69% of the examined fish, respectively. Molecular analysis based on the small subunit (SSU) rRNA sequence shows high genetic divergence with all other ceratomyxid species. A Maximum Likelihood phylogenetic tree shows association with the species C. leatharjecketi Fiala, kova, Kodadkova, Freeman, Bartošova-Sojkova, and Atkinson, 2015 reported from the gallbladder of Aluterusmonoceros (L.) caught in the Andaman Sea, off Malaysia. Nonetheless, the SSU rRNA sequences of C. tunisiensis and C. leatharjecketi have only a 90% similarity.