Phylogeny and comprehensive revision of mugiliform-infecting myxobolids (Myxozoa, Myxobolidae), with the morphological and molecular redescription of the cryptic species Myxobolus exiguus

Synopsis of the species of Henneguya Thélohan, 1892 (Cnidaria: Myxosporea: Myxobolidae) described since 2012

The genus Henneguya Thélohan, 1892 (Cnidaria: Myxosporea: Myxobolidae) encompasses a large number of species that mostly infect freshwater fish belonging to 71 families of Actinopterygii. A synopsis of Henneguya species described between 2012 and 2022 is herein presented. It includes 57 species described during the last decade, and one species missing from the previous synopses, adding to a total of 254 species that have been formally described within this genus. Biological characters and myxospore morphometry are presented for each species record.

Diversity of myxozoans parasitizing the catfish Rhamdia quelen (Siluriformes: Heptapteridae), in southeastern Brazil, based on morphological and molecular evidence

Rhamdia quelen is a commercially important fish in South America. During the survey of myxozoan infections in fishes from Pardo River, Paranapanema River basin, São Paulo State, Brazil, we describe three new species of Henneguya found parasitizing gills of R. quelen: Henneguya bagre n. sp., Henneguya breviscauda n. sp and Henneguya novaerae n. sp. The descriptions were based on myxospores morphology and small subunit ribosomal DNA partial sequences. Phylogenetic analysis showed a clade formed by species that parasitize Siluriformes, with Henneguya jundiai as a sister species of Henneguya bagre n. sp., Henneguya breviscauda n. sp and Henneguya novaerae n. sp. Our study indicates that the parasites infecting R. quelen belong to a lineage of myxozoans infecting Heptapteridae fishes. Using molecular and morphological characterization, the species were identified as new species for the genus Henneguya. Based on our analysis we recommend monitoring the presence of these parasites in farmed fishes, to analyze possible pathologies caused by them.

Myxozoan infection in thinlip mullet Chelon ramada (Mugiliformes: Mugilidae) in the Sea of Galilee

Mullets (Mugilidae) are economically important fish in Israel. Two species of mugilids (i.e., the thinlip mullet Chelon ramada and the flathead grey mullet Mugil cephalus) have been stocked in the Sea of Galilee (Lake Kinneret) in order to increase fishermen's income and lake water quality. These catadromous species do not reproduce in the lake, consequently, fingerlings have been introduced every year since 1958. Following a survey of myxozoan infections in the Sea of Galilee, we described Myxobolus pupkoi n. sp. infecting the gill arches, and reported Myxobolus exiguus from visceral peritoneum and gall bladder of C. ramada. The prevalence of infection of both Myxobolus pupkoi n. sp. and M. exiguus were 11.5% (2/23). Our study indicates that the parasites infecting C. ramada belong to a lineage of myxozoans infecting mugilids. This result suggests that the infection took place in the Mediterranean Sea, where the fingerlings were caught, before their introduction into the Sea of Galilee. Since 2018 only farm-raised fingerlings have been introduced. We thus recommend to closely monitor the presence of these parasites in the future to determine if the presence of parasites disappear with the introduction of farm-raised fingerlings.

Taxonomy and Systematics of Two New Species of Myxobolus (Cnidaria: Myxobolidae) Parasitizing the Gills of Mugil curema (Mugilidae) from the Brazilian Coast

PURPOSE

We describe two new species of Myxobolus (Myxobolidae) found parasitizing Mugil curema from two locations in Brazil: Myxobolus curemae n. sp. from gill arch and rays and Myxobolus maceioensis n. sp. from gill lamellae.

METHODS

We based the descriptions on myxospore morphology, histology, and small-subunit ribosomal DNA sequences.

RESULTS

Myxospores of the two new species had similar morphology and morphometry but differed in spore body width and length, and ssrDNA sequences differed by 10.5%. These data supported the diagnosis of the parasites as distinct and novel species. The phylogenetic analysis showed a subclade formed by species that parasitize Mugiliformes, with M. maceioensis n. sp. as a sister species of Myxobolus episquamalis and Myxobolus bizerti, while there is a group of six species that are sister related to M. curemae n. sp. Our analysis was consistent with previous studies suggesting that orders of the hosts are strongly correlated with phylogenetic signals in the Myxobolidae.

CONCLUSIONS

Myxobolus curemae n. sp. and M. maceioensis n. sp. are new species identified parasitizing M. curema.

Morphological and molecular description of a new species of Myxobolus (Myxosporea: Myxobolidae) infecting Planiliza macrolepis (Smith, 1846) from India

The present paper describes a novel species of Myxobolus parasitizing the gill filaments of the largescale mullet, Planiliza macrolepis from Cochin backwaters, Kerala, India. The parasite develops in the gill filaments; plasmodia elongated, milky white, measured 1.37-2.18 (1.78 ± 0.35) mm × 0.07-0.12 (0.10 ± 0.02) mm in size. Mature myxospores ovoid in valvular view, biconvex in sutural view with smooth shell valves and measured 6.24-7.02 (6.63 ± 0.23) × 5.01-6.18 (5.68 ± 0.25) μm in size. Polar capsules equal, oval with pointed anterior ends, 3.07-3.58 (3.33 ± 0.12) × 1.68-2.42 (2.09 ± 0.18) μm in size. Polar filaments with 4 coils, measured 29.61 ± 4.75 μm in length when extruded. Sporoplasm binucleate with a rudimentary nucleus and a vacuole. A comparison with related Myxobolus species revealed significant morphological and morphometric differences. In BLASTN and genetic distance analysis, the present parasite showed high divergence with other myxosporean sequences, indicating its molecular uniqueness. In Maximum Likelihood and Bayesian Inference analysis, the present species stands out with M. ramadus as sister branch within the Myxobolus clade. In infected gill filaments, the plasmodia caused swelling/deformation, compression of lamellae and reduction in respiratory surface area. Three of 222 P. macrolepis screened were infected, indicating a prevalence of 1.3%. Considering the morphological, morphometric, molecular and phylogenetic differences with the previously described species of myxosporeans, along with the dissimilarities in host and geographical locations, the present parasite is treated as a new species and the name Myxobolus cochinensis n. sp. is proposed.

Description of myxosporeans (Cnidaria: Myxozoa) infecting the popular food fish Notopterus notopterus (Pisces: Notopteridae) in Malaysia and India

This study was a co-operative investigation of myxosporean infections of Notopterus notopterus, the bronze featherback, which is a popular food fish in the South Asian region. We examined fish from Lake Kenyir, Malaysia and the River Ganga, Hastinapur, Uttar Pradesh, India, and observed infections with two myxosporeans: Myxidium cf. notopterum (Myxidiidae) and Henneguya ganapatiae (Myxobolidae), respectively. These species were identified by myxospore morphology, morphometry and host tissue affinity, and the original descriptions supplemented with small-subunit ribosomal DNA sequences and phylogenetic analysis. Free myxospores of M. cf. notopterum were found in the gallbladder, and measured 14.7 ± 0.6 μm long and 6.3 ± 0.6 μm wide; host, tissue and myxospore dimensions overlapped with the type, but differed in morphological details (spore shape, valve cell ridges) and locality (Malaysia versus India). Plasmodia and spores of H. ganapatiae were observed in gills, and myxospores had a spore body 9.7 ± 0.4 μm long, 4.5 ± 0.5 μm wide; sample locality, host, tissue, spore morphology and morphometry matched the original description. Small-subunit ribosomal DNA sequences were deposited in GenBank (M. cf. notopterum MT365527, H. ganapatiae MT365528) and both differed by >7% from congeneric species. Although the pathogenicity and clinical manifestation of myxozoan in humans are poorly understood, consumption of raw fish meat with myxozoan infection was reported to be associated with diarrhea. Identification of current parasite fauna from N. notopterus is an essential first step in assessing pathogen risks to stocks of this important food fish.

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Two myxozoan species were identified in the important food fish Notopterus notopterus.

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Myxospores of Myxidium cf. notopterum and Henneguya ganapatiae were investigated.

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Although rare myxozoan species can be zoonotic M. cf. notopterum and H. ganapatiae are not known to infect humans.

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Country-specific myxozoan parasites were found in N. notopterus from India and Malaysia.

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DNA sequence data helped to clarify the taxa and improve identification.

Myxozoan hidden diversity: the case of Myxobolus pseudodispar Gorbunova, 1936

Myxobolus pseudodispar Gorbunova, 1936 (Myxozoa) was originally described as a parasite of common roach, Rutilus rutilus (Linnaeus), with developing stages in muscles and spores disseminated in macrophage centres of different organs and tissues. Later, this parasite was described from several other cyprinids, but with relatively large intraspecific differences based on SSU rDNA gene sequences. Within our long-term study on myxozoan biodiversity, we performed a broad microscopic and molecular screening of various freshwater fish species (over 450 specimens, 36 species) from different localities. We investigated the cryptic species status of M. pseudodispar. Our analysis revealed four new unique SSU rDNA sequences of M. pseudodispar as well as an infection in new fish host species. Myxobolus pseudodispar sequence analysis showed clear phylogenetic grouping according to fish host criterion forming 13 well-recognised clades. Using 1% SSU rDNA-based genetic distance criterion, at least ten new species of Myxobolus Bütschli, 1882 may be recognised in the group of M. pseudodispar sequences. Our analysis showed the paraphyletic character of M. pseudodispar sequences and the statistical tests rejected hypothetical tree topology with the monophyletic status of the M. pseudodispar group. Myxobolus pseudodispar represents a species complex and it is a typical example of myxozoan hidden diversity phenomenon confirming myxozoans as an evolutionary very successful group of parasites with a great ability to adapt to a new hosts with subsequent speciation events.

Involvement of sphaeractinomyxon in the life cycle of mugiliform-infecting Myxobolus (Cnidaria, Myxosporea) reveals high functionality of actinospore morphotype in promoting transmission

Four new actinospore types belonging to the sphaeractinomyxon collective group (Cnidaria, Myxosporea) are described from the coelomic cavity of a marine Baltidrilus sp. (Oligochaeta, Naididae) inhabiting a northern Portuguese estuary. Host identification supports the usage of marine oligochaetes, namely of the family Naididae Ehrenberg, 1828, as definitive hosts for myxosporeans inhabiting estuarine/marine environments. The absence of mixed infections in the host specimens analysed is suggested to reflect the influence of host-, parasite- and environmental-related factors regulating myxosporean-annelid interactions. Molecular analyses matched the SSU rDNA sequences of three of the four new types with those of mugiliform-infecting Myxobolus spp., namely Myxobolus mugiliensis and a Myxobolus sp. from flathead grey mullet Mugil cephalus, and Myxobolus labrosus from thicklip grey mullet Chelon labrosus. These results directly link, for the first time, the sphaeractinomyxon collective group to a myxospore counterpart, further confirming their previously hypothesized specific involvement in the life cycle of myxobolids that infect mullets. Acknowledging this life cycle relationship, the functionality of the sphaeractinomyxon morphotype is suggested to have been decisive for the evolutionary hyperdiversification of the genus Myxobolus in mullets. Unlike other actinospore morphotypes, sphaeractinomyxon lack valvular processes, which implies a limited capability for buoyancy. Considering the benthic-feeding nature of mullets, this feature is most likely crucial in promoting successful transmission to the vertebrate host.

Characterisation of sphaeractinomyxon types (Cnidaria: Myxozoa) from marine and freshwater oligochaetes in a Portuguese estuary, with the demise of the endocapsa collective group

Six types of sphaeractinomyxon are reported from the coelomic cavity of oligochaetes collected from the Minho River estuary in northern Portugal. Four new types are morphologically and molecularly described from freshwater species belonging to the genera Psammoryctides Hrabě and Potamothrix Vejdovský et Mrázek in the upper estuary, thus significantly increasing the number of known freshwater sphaeractinomyxon. In the lower estuary, sphaeractinomyxon types 8 and 10 of Rangel et al. (2016) are recorded infecting the marine oligochaete Tubificoides pseudogaster (Dahl). A single specimen of T. pseudogaster further displayed infection by one of the four new types found in the upper estuary, suggesting the involvement of sphaeractinomyxon in the life cycles of myxosporean species that infect migratory fish hosts. The acquisition of these second hosts is proposed to have allowed the myxosporean counterparts of sphaeractinomyxon to cross environmental barriers and conquer new habitats. Phylogenetic analyses of the SSU rRNA gene reveal the four new types clustering within the monophyletic clade of mugiliform-infecting myxobolids, strengthening the previously proposed involvement of the sphaeractinomyxon collective group in the life cycles of this specific group of myxosporeans. Endocapsa types also cluster within the latter clade, having actinospores that differ from those of sphaeractinomyxon only in the presence of valvular swellings that do not change when in contact with water. In this study, however, one type was found displaying actinospores with and without valvular swellings in the same oligochaete specimen. This overlap in actinospore morphology is given as grounds for the demise of the endocapsa collective group.

Molecular Characterization of Two Myxosporean Species, Henneguya namae Haldar et al. 1983 and Myxobolus sophorae Jayasri, 1982 (Myxosporea: Myxobolidae)

In Indian freshwater fish myxosporean infections are among the most cosmopolitan parasites, they are relatively well studied morphologically but their phylogenetic relationships were unclear and the genetic data is limited only to a few species. The study aims to present molecular data for two myxosporean species, Henneguya namae Haldar et al. 1983 and Myxobolus sophorae Jayasri, 1982 collected from Indian freshwater fish, the elongate glass-perchlet Chanda nama (=Ambassis nama) and pool barb Puntius sophore, respectively. In the present study molecular data are provided for H. namae and M. sophorae using nested PCR. The obtained partial 18S rDNA gene sequences were analyzed using maximum likelihood (ML) and Bayesian inference (BI) methods. The 18S rDNA gene sequences of H. namae showed similarity with the sequences of H. chaudhuryi, Henneguya sp. RA-2015, H. voronini and H. setiuensis about 72.1 to 78% and M. sophorae with Myxobolus ticto was about 90% respectively. The aim of this paper was to identify H. namae and M. sophorae morphologically and using molecular methods.

Myxozoan biodiversity in mullets (Teleostei, Mugilidae) unravels hyperdiversification of Myxobolus (Cnidaria, Myxosporea)

Mullets are ecologic and commercially important fish species. Their ubiquitous nature allows them to play critical roles in freshwater and marine ecosystems but makes them more vulnerable to diseases and parasitic infection. In this study, a myxozoan survey was performed on three species of mullet captured from a northern Portuguese river. The results disclose a high biodiversity, specifically due to the hyperdiversification of Myxobolus. Thirteen new species of this genus are described based on microscopic and molecular procedures: 7 from the thinlip grey mullet Chelon ramada, 2 from the thicklip grey mullet Chelon labrosus, and 4 from the flathead grey mullet Mugil cephalus. Myxobolus exiguus and Ellipsomyxa mugilis are further registered from their type host C. ramada, as well as six more myxospore morphotypes that possibly represent distinct Myxobolus species. Overall, the results obtained clearly show that the number of host-, site- and tissue-specific Myxobolus spp. is much higher than what would be expected in accordance to available literature. This higher biodiversity is therefore discussed as either being the result of the usage of poor discriminative criteria in previous studies, or as being a direct consequence of the biological and ecological traits of the parasite and of its vertebrate and invertebrate host communities. Bayesian inference, maximum likelihood and maximum parsimony analyses position the new species within a clade comprising all other Myxobolus spp. that infect mugiliform hosts, thus suggesting that this parasitic group has a monophyletic origin. Clustering of species in relation to the host genus is also revealed and strengthens the contention that the evolutionary history of mugiliform-infecting Myxobolus reflects that of its vertebrate hosts. In this view, the hyperdiversification of Myxobolus in mullet hosts is hypothesized to correlate with the processes of speciation that led to the ecological plasticity of mullets.

New actinosporean description prompts union of the raabeia and echinactinomyxon collective groups (Cnidaria, Myxozoa)

We describe, morphologically and molecularly, a new actinosporean from the intestinal epithelium of the freshwater oligochaete Ilyodrilus templetoni in the upper estuary of the River Minho, Northern Portugal. Mature actinospores resembled both echinactinomyxon and raabeia types, emphasizing the previously known lack of a clear boundary between these 2 collective groups. Historically, raabeia and echinactinomyxon types have been differentiated solely based on the shape of the valvular processes being curved or straight, respectively. Our observations, however, show that this morphological character is too variable for distinguishing between these 2 collective groups, since the actinospores of the raabeia described here displayed valvular processes that could either be straight, downward or upward curved. Several similar cases can be found in the available literature. Considering this overlap in actinospore morphology, we propose that echinactinomyxon be deemed invalid and its types be included in raabeia, as the latter constitutes the older of the 2 groups. Known echinactinomyxon types, however, should not be renamed as raabeia, as this would create unnecessary confusion. Accordingly, a more comprehensive definition of the raabeia collective group is provided. Phylogenetic analyses revealed polyphyletic clustering of raabeia/echinactinomyxon types among members of the myxosporean suborders Variisporina and Platysporina, reiterating the lack of agreement between actinosporean morphotypes and myxosporean genera. The new type described here specifically clusters within the Paramyxidium clade, alongside other SSU rDNA sequences of raabeia, echinactinomyxon, aurantiactinomyxon and synactinomyxon. Considering that most Paramyxidium spp. parasitize Anguilla anguilla (Linnaeus, 1758), future myxozoan surveys in the River Minho should include this species.

Morphological and molecular characterization of myxobolids (Cnidaria, Myxozoa) infecting cypriniforms (Actinopterygii, Teleostei) endemic to the Iberian Peninsula

The Iberian Peninsula provides a unique freshwater ecosystem for native and endemic cypriniforms to thrive. Despite cypriniforms being hosts to multiple myxobolids worldwide, little research has been performed in this geographic location. In this study, the examination of three Iberian endemic cypriniforms showed that myxosporean richness in the Iberian Peninsula is underestimated, with three new and one known myxobolid species being reported based on morphological and molecular data (SSU). Myxobolus arcasii n. sp. is described from the kidney and gonads of the "bermejuela" Achondrostoma arcasii, M. duriensis n. sp. from the gills of the Northern straight-mouth nase Pseudochondrostoma duriense, and Thelohanellus paludicus n. sp. from the intestine of the Southern Iberian spined-loach Cobitis paludica. Myxobolus pseudodispar Gorbunova, 1936 is further reported from several organs of P. duriense, and from the spleen of A. arcasii. The occurrence of M. pseudodispar in endemic Iberian species reveals that host-shift followed its co-introduction with central European leuciscids into this geographic location. Several other myxobolids originally described from barbels in central Europe have also been reported from the Iberian endemic cypriniform Luciobarbus bocagei. Nonetheless, except for M. musculi, the identification of these myxobolids in L. bocagei is here shown to be dubious and require molecular confirmation. Phylogenetic analyses reveal M. arcasii n. sp. and M. duriensis n. sp. clustering within different lineages of leuciscid-infecting species, showing that myxobolids entered Leuciscidae as hosts multiple times during their evolution. Constituting the first myxobolid reported from the subfamily Cobitinae, Thelohanellus paludicus n. sp. stands alone in the tree topology.