Myxobolus turpisrotundus (Myxosporea: Bivalvulida) spores with caudal appendages: investigating the validity of the genus Henneguya with morphological and molecular evidence

Henneguya (Cnidaria: Myxobolidae) species infecting Oligosarcus jenynsii (Characiformes: Characidae) in a Neotropical shallow lake from Argentina: morphological and molecular characterisation

Two previously undescribed myxozoan species, Henneguya sardellae sp. n. and H. margaritae sp. n., found infecting connective tissues of the Neotropical characid fish Oligosarcus jenynsii (Günther) from Argentina are morphologically and molecularly characterised. Mature spores of H. sardellae sp. n. are ellipsoid, with two, straight and visibly fused caudal appendages cleaved at its blunt terminal end; measuring 33.5 ± 1.2 (30.9-35.5) μm in total length, spore body 17.5 ± 0.6 (16.3-18.6) µm, 7.8 ± 0.4 (7.0-8.8) µm wide and 6.9 ± 0.2 (6.6-7.2) µm thick, with two elongated, unequally-sized polar capsules situated at anterior end, and 11-13 turns of polar tubules. Mature spores of H. margaritae sp. n. are pyriform, with two caudal appendages visible fused together and much longer than spore body, with unequal endings; measuring 35.9 ± 2.8 (29.2-40.7) µm in total length, spore body 11.5 ± 0.9 (9.2-13.0) µm long, 5.8 ± 0.4 (5.1-6.7) µm wide and 5.5 ± 0.2 (5.1-5.8) µm thick, with two polar capsules similar in size, pyriform polar capsules containing polar tubules with 4-5 coils. Both species showed a membraneous sheath surrounding the spore body and caudal appendages; in H. sardellae sp. n. this feature can deploy laterally. Phylogenetic analyses based on SSU rDNA sequences showed that H. sardellae sp. n. and H. margaritae sp. n. clustered with other myxobolids parasitising Characiformes in Brazil, Cichliformes in Mexico and Cyprinodontiformes in Mexico and the United States. The description of these two new species of Henneguya as the first described species of the genus that parasitise freshwater fish in Argentina highlights the importance of further research on the diversity and distribution of myxozoans in this region.

The description of Myxobolus meijiangensis n. sp. (Myxozoa: Myxobolidae) and its pathogenicity to the gills of goldfish

Myxobolus Bütschli, 1882 is the most speciose myxozoan genus, although some species have only been described according to the morphological characteristics of spores. In the present study, a new Myxobolus species infecting the gill lamellae of goldfish from Chongqing, China, was described using a comprehensive analysis of morphological, molecular, and histological data. Mature spores were flat-pear in valvular view with tapering anterior and rounded posterior ends, measuring 11.0 ± 0.4 (10.4-11.6) μm in length and 10.3 ± 0.3 (9.6-11.0) μm in width. Two equal-sized elongate pyriform polar capsules were 5.6 ± 0.6 (4.5-6.4) μm long and 3.5 ± 0.5 (2.4-4.1) μm wide. Polar tubules were coiled with 8 or 9 turns. The small-subunit ribosomal DNA gene sequence length of the present species was 1951 nt, and the highest similarity was 97.99% with M. pyramidis. Comparative analysis of the morphological and molecular data revealed that the present species was distinct from other known myxosporeans. Plasmodia were located at the interlamellar troughs nearing the top of the primary gills. Infection by the present species destroyed the original structure of gill lamellae and caused an inflammatory response, eventually leading to fish dyspnea. The morphological, molecular, and pathological data from the present study can be used for aquaculture since they provide guidance for easy detection and future control of this myxosporidiosis.

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.

A new Myxobolus (Cnidaria: Myxosporea: Myxobolidae) from the gills of the southern striped shiner, Luxilus chrysocephalus isolepis (Cypriniformes: Leuciscidae), from southwestern Arkansas, USA

The southern striped shiner, Luxilus chrysocephalus isolepis (Hubbs & Brown) is a relatively large minnow belonging to the true minnow family Leuciscidae Bonaparte. Between May 2020 and January 2022, 55 L. c. isolepis were collected from watersheds in Montgomery (n = 6), Polk (n = 17) and Sevier (n = 32) counties, Arkansas, USA, and their gills, gallbladders, urinary bladders, fins, integument, other major organs, and musculature were examined for myxozoans. Gills of 11 (34%) individual southern striped shiners from Sevier County were infected with a new myxozoan, Myxobolus carlhubbsi n. sp. A qualitative and quantitative morphological description was based on formalin-fixed preserved myxospores, and molecular data consisted of a 1,970 base pair sequence of the partial small subunit rRNA gene from ethanol-preserved specimens. Histologically, plasmodia filled and expanded interlamellar troughs. Hyperplastic epithelial and goblet cells filled interlamellar troughs adjacent to plasmodia, but inflammatory response was limited to scattered lymphocytes. Phylogenetic analysis revealed that M. carlhubbsi n. sp. is a member of a clade of species with pyriform myxospores parasitizing North American Pogonichthyinae Girard and North American and Eurasian Leuciscinae Bonaparte. This is the first report of a myxozoan from L. c. isolepis. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:D10D71C2-2C75-4A1C-80ED-B98FF36CB509.

A NEW SPECIES OF MYXOBOLUS (CNIDARIA: MYXOSPOREA: MYXOBOLIDAE) FROM THE GILLS OF CREEK CHUB, SEMOTILUS ATROMACULATUS (CYPRINIFORMES: LEUCISCIDAE: PLAGIOPTERINAE), FROM THE OUACHITA DRAINAGE OF ARKANSAS

During October and November 2021, 33 creek chubs, Semotilus atromaculatus, were collected from 3 sites in Polk County, Arkansas (Ouachita River drainage), and their gills, gallbladder, fins, integument, musculature, and other major organs were examined for myxozoans. The gills of 9 (27%) were infected with a new myxozoan, Myxobolus fountainae n. sp. Qualitative and quantitative morphological data were from fresh and formalin-fixed preserved spores, while molecular data consisted of a 1918 base pair sequence of the partial small subunit ribosomal RNA gene. Phylogenetic analysis grouped M. fountainae n. sp. with the other leuciscid-infecting myxobolids from North America and within a larger clade of European myxozoans. In addition, histological information is provided on the infection. A previous record of Myxobolus muelleriBütschli, 1882, from the gills and ureters of S. atromaculatus is considered invalid and represents an unknown species. Myxobolus fountainae n. sp. is the only named myxozoan known to infect the gill filaments of S. atromaculatus, whereas Myxobolus pendula (Guilford, 1967) infects the gill arches.

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.

A new myxozoan parasite, Myxobolus allami sp. n. (Myxozoa: Myxobolidae) from the intestinal wall of Sparidentex hasta (Valenciennes) in Arabian Gulf

Myxobolus allami sp. n. is described from the intestinal wall of the silvery black porgy, Sparidentex hasta (Valenciennes), off Saudi Arabian coast of Arabian Gulf. Two of 20 examined fish were found to be infected with irregular-shaped plasmodia 3-8 mm long × 2-3 mm wide. Mature myxospores are subspherical to elliptical in the valvular view and oval in the sutural view, and are 11-13 (12) µm long, 7-8 (7.5) µm wide and 10-12 (10.8) µm thick. Spores have relatively thin valves and mostly (~ 72%) end with short caudal appendages of ~3 µm long. The spores also have two polar capsules, which are oval to elliptical and measure 5-7 (5.7) µm in length and 2-3 (2.7) µm in width. Polar filaments are coiled, with three turns. Transmission electron microscopy revealed that caudal appendages originated from the sutural edge at the posterior pole of the myxospore with density similar to that of its valves. The SSU rRNAgene sequence of the present species does not match any available sequences in GenBank. Phylogenetically, this species is sister to Myxobolus khaliji Zhang, Al-Qurausihy et Abdel-Baki, 2014 within a well-supported clade of Myxobolus-Henneguya with species infecting marine fishes. The combination of molecular data and morphological differences between this and other species of Myxobolus Bütschli, 1882 lead us to propose that the present form be established as a new species, M. allami. The present study also provides more evidence for the idea that caudal appendages cannot be reliably used to distinguish the species of the genera Myxobolus and Henneguya Thélohan, 1892.

Morphological and molecular analysis of Henneguya lagunensis n. sp. (Cnidaria, Myxosporea) parasitizing the gills of Eugerres brasilianus from Brazil

Plasmodia containing myxospores belonging to the genus Henneguya Thélohan, 1892 were found in the gills of Eugerres brasilianus (Cuvier, 1830). Despite the economic importance, few parasitological studies have been done with this species. We describe Henneguya lagunensis n. sp. using morphological and molecular data. The mature myxospores were rounded, measuring 29.1 ± 2.2 μm in total length, 8.2 ± 1.0 μm in body length, 7.9 ± 0.2 μm in body width, 20.7 ± 2.4 μm in tail length and 4.8 ± 1.0 μm in thickness. The polar capsules measured 3.3 ± 0.4 in length and 1.7 ± 0.3 μm in width. Polar filaments had 4-5 turns, helical. Phylogenetic analysis showed Henneguya lagunensis n. sp. as a sister species of Henneguya cynoscioni Dyková, Buron, Roumillat and Fiala, 2011, within a clade that contained mostly Henneguya species that parasitize marine fish of the order Perciformes. This is the first report of a species of Henneguya parasitizing Eugerres brasilianus.

Native parasite affecting an introduced host in aquaculture: cardiac henneguyosis in the red seabream Pagrus major Temminck & Schlegel (Perciformes: Sparidae) caused by Henneguya aegea n. sp. (Myxosporea: Myxobolidae)

BACKGROUND

Henneguya Thélohan, 1892 (Myxobolidae) is one of the most species-rich genera of myxosporean parasites infecting fish. Although common in nature, there are few reports of these parasites causing important disease in aquaculture. In this paper, we describe a new species of Henneguya infecting Pagrus major (Temminck & Schlegel), a fish host introduced to the Mediterranean Sea from Japan in the late 1980s.

RESULTS

Large plasmodia of the parasite were found in the bulbus arteriosus and in the ventricle of the infected fish. Spores were found mainly in the kidney and heart and were accompanied by melanized macrophages or vascular intimal proliferation mixed with a mild non-suppurative response, respectively. Comparisons of morphometric data for spore and polar capsule length and width, suggest a unique combination of features in the newly described species. Molecular analysis, based on 18S rDNA sequence of the parasite, followed by phylogenetic analysis, indicated that the parasite described here is a novel species of Henneguya, clustered with the marine congeneric species.

CONCLUSIONS

Henneguya aegea n. sp. infects in aquaculture P. major, a host introduced as eggs to the Mediterranean from Japan. Despite the high host specificity of the myxobolid parasites, H. aegea n. sp. seems to be able to use P. major as a host and propagate successfully, causing morbidity and mortality. This could result in spillback of the new species from high density cultured non-native P. major to native fish hosts.

Pathological and immunological analyses of Thelohanellus kitauei (Myxozoa:Myxosporea) infection in the scattered mirror carp, Cyprinus carpio

Thelohanellus kitauei is a spore-forming myxosporean parasite prevalent in scattered mirror carp (Cyprinus carpio) that generates numerous cysts in the intestine and causes mass mortality in fish. To investigate the infection and mortality induced by T. kitauei in pond-reared farms in Luo-Jiang (104°51’N, 31°31’E), southwest China, morphological and molecular analyses of infected fish were conducted. Natural and specific immune indicators were further evaluated to determine the immunological effects of response to parasitic infection. The infectious parasite was identified as Thelohanellus kitauei based on morphological, 18S rDNA and infectious characteristics. Scattered mirror carp was determined as the specific intermediate host of the parasite. However, T. kitauei still caused considerable damage to the fish, in particular, injury and blockage of the intestines, resulting in malnutrition and even death. The mature spores of T. kitauei colonize the intestinal submucosa of carp and form cysts of various sizes that block the intestinal tract and release spores into the enteric cavity upon rupture, leading to the next phase of T. kitauei growth. Moreover, T. kitauei-infected carp showed weaker innate immunity. IgM is involved in the fight against parasitic infection while cytokines, such as IL-6, IL-1β and TNF-α, had an impact on infection processes. To our knowledge, this is the first report to show that T. kitauei infects and causes death in scattered mirror carp. Our collective findings from systematic pathology, morphology and immunology experiments provide a foundation for further research on infections by this type of parasite and development of effective treatment strategies.

Myxobolus pelecicola Voronin et Dudin 2015 is a junior synonym of Myxobolus ladogensis Rumyantsev et Schulman 1997 (Myxosporea: Myxobolidae) infecting the skeletal muscle of sichel Pelecus cultratus (Actinopterygii: Cyprinidae) in Russia

Myxobolus pelecicola Voronin et Dudin, 2015 was recently described from the skeletal musculature of sichel Pelecus cultratus. However, another species, Myxobolus ladogensis Rumyantsev et Schulman, 1997, was described previously from the same host, displaying identical tissue localization and spore morphology as in M. pelecicola. Unfortunately, M. ladogensis was overlooked when M. pelecicola was described, resulting in the superfluous description of the latter species, which, according to the International Code of Zoological Nomenclature, is a junior synonym of M. ladogensis. The description of M. ladogensis is supplemented with SSU rDNA sequence analysis supporting the conspecificity with M. pelecicola. The closest relatives of Myxobolus ladogensis (syn. M. pelecicola) include several muscle-infecting Myxobolus spp. with sequence similarity below 97%.

Phylogeny of Myxobolidae (Myxozoa) and the evolution of myxospore appendages in the Myxobolus clade

Genera Myxobolus Bütschli, 1882 and Henneguya Thélohan, 1892 (Myxobolidae) are specious myxozoan genera. They comprise nearly half of overall known myxozoan species diversity. A typical spore feature of Henneguya is the presence of two caudal appendages of the spore valves, which distinguishes them from species of the genus Myxobolus. Several Myxobolus spp., however, were reported to show aberrant spores with Henneguya-like caudal appendages. We found such aberrant spores in Myxobolus tsangwuensis and Myxobolus wulii. We studied the ultrastructure of M. wulii and Myxobolus oralis spores with caudal appendages by transmission electron microscopy (TEM). TEM of these aberrant spores revealed that their caudal appendages have the same ultrastructure as the appendages of Henneguya spp. Small caudal appendages of M. wulii spores observed only on TEM suggested that this character may be often overlooked and more Myxobolus species potentially have the ability to express the caudal appendages on the myxospore. In order to trace the evolution of this character, we performed broad phylogenetic analysis of all species of the family Myxobolidae which are available in GenBank including nearly 300 taxa. We found at least eight independent evolutionary origins of spores with two appendages, three origins of a single appendage and 12 apparent secondary losses of the spore projections. Therefore, genus Henneguya with typical two-tailed myxospores is polyphyletic, however a majority of its species has a common ancestor and groups in the second largest subclade of the Myxobolus clade. We also mapped the biological characteristics (host, site of infection and environment) of Myxobolidae species on the phylogenetic tree. We revealed an evident host-associated evolutionary pattern in all parts of the Myxobolus clade with a distinct and species-rich subclade containing almost exclusively species infecting species of the Order Cypriniformes.

Supplemental diagnosis and phylogeny of Myxobolus absonus (Cnidaria, Myxozoa) from the eye of the freshwater fish Pimelodus maculatus (Siluriformes, Pimelodidae)

Myxobolus absonusCellere et al., 2002 was originally described as having free cysts in the opercular cavity of the freshwater fish Pimelodus maculatus in Brazil. The present study provides a supplemental description of this parasite from the eye of its type host, with basis on morphological, ultrastructural, and molecular data of the SSU rRNA gene. The parasite formed spherical whitish cysts, which wall presented numerous microvilli that attached to the collagen layers of the corneal stroma. Myxospores were oval in valvular and sutural view, measuring 13.2 ± 0.4 μm in length, 8.5 ± 0.4 μm in width, and 6.6 ± 0.3 μm in thickness. Two asymmetric pyriform polar capsules were located at the anterior pole: the larger 6.2 ± 0.4 μm long and 3.6 ± 0.3 μm wide, containing a polar filament coiled in 6 turns; and the smaller 3.5 ± 0.3 μm long and 1.9 ± 0.1 μm wide, containing a polar filament coiled in 4 turns. At the posterior pole, the sporoplasm displayed two nuclei and numerous spherical sporoplasmosomes. Phylogenetic analysis using maximum likelihood, Bayesian inference and maximum parsimony revealed M. absonus clustering within a well-supported clade with poorly-resolved internal nodes, amongst the SSU rRNA sequences of other myxobolids that infect siluriform and characiform fish hosts, as well as the perciform-infecting species Myxobolus acanthogobii, Triangula percae and Cardimyxobolus japonensis. This clade appeared separated from the other clades comprising most of the species that infect siluriform and characiform hosts, showing that more than one myxobolid lineage evolved while parasitizing these taxonomic groups of fish.

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

Mullets inhabit a wide range of habitats from tropical to temperate regions and play a critical role in their ecosystems. This commercially important fish group constitutes a significant source of food in several geographic regions, and the production of some species for consumption is an increasing trend. About 64 myxosporean species have been reported in mullets, some of which are cryptic, as is the case ofMyxobolus exiguus, andM. muelleri. This paper provides, for the first time, a detailed and critical revision of the data available for myxobolids reported in mullets, determining the species that havebona fidemugiliform fish hosts, in accordance with the original species descriptions, the available molecular data and the currently accepted taxonomic and phylogenetic criteria. Phylogenetic analyses using Bayesian inference and maximum-likelihood methodologies suggest that the evolutionary history of myxobolids withbona fidemugiliform fish hosts reflects that of its vertebrate hosts, while reinforcing known evolutionary factors and old systematic issues of the clade of myxobolids. A comprehensive morphological, ultrastructural and molecular redescription is also provided for the cryptic speciesM. exiguus, from infections in the visceral peritoneum of the thinlip-grey mulletChelon ramadain the River Minho, Portugal.

First molecular evidence of Thelohanellus wallagoi Sarkar, 1985 (Myxozoa) from economically important food fish, freshwater shark Wallago attu (Siluridae) in India

The freshwater shark Wallago attu (Bl. and Schn.) is a frequent silurid in the River Ganga and one of the most commercially exploit fish in India. In a survey on its infection with myxosporeans, spore type belongs to Thelohanellus species was found in the gills, kidney and intestine respectively. Through morphological and molecular investigations, we identified the spore as Thelohanellus wallagoi Sarkar, 1985. They were pyriform in valvular view and slim in sutural view, and had one pyriform polar capsule with four to five turns. The spores measured 8.0 × 4.0 × 2.3 μm. T. wallagoi developed in small cysts in the gill lamellae, whereas cyst and scattered spores of T. wallagoi were also found in the kidney and intestine respectively. The 18S rDNA sequence of T. wallagoi isolates recovered from gills, kidney and intestine were found similar to each other and differed from any other Thelohanellus species available in GenBank and validated its status after 32 years of original description. Phylogenetic analysis signified that T. wallagoi was placed sister to Myxobolus species in the clade that indicated the polyphyletic nature of the genus Thelohanellus.

Morphological, histological, and molecular description of Myxobolus ompok n. sp. (Myxosporea: Myxobolidae), a kidney myxozoan from Pabdah catfish Ompok pabda (Hamilton, 1822) (Siluriformes: Siluridae) in India

In a parasitological survey of freshwater fishes near Meerut, Uttar Pradesh, India, myxozoan infections in Pabdah catfish Ompok pabda Ham. (Siluriformes: Siluridae) were found. Round plasmodia and scattered spores of Myxobolus ompok n. sp. were found in the kidney of the host. Plasmodia measuring 150-200 μm were located in the renal interstitium. Spores of Myxobolus ompok n. sp. were elongated pyriform, 13.6-14.4 (14.8 ± 0.42) μm long, 5.6-6.4 (6.5 ± 0.33) μm wide, and 5.2-6.4 (5.9 ± 0.43) μm thick with two equal polar capsules measuring 8.0-8.5 (8.2 ± 0.2) μm in length and 1.5-2.4 (1.8 ± 0.33) in width having six filamental turns. Both the morphology and DNA analysis of the 18S rRNA gene revealed that Myxobolus ompok n. sp. is distinct from previously described species of Myxobolus and shares no significant similarity with any other Myxobolus deposited in the GenBank database. Phylogenetic analysis inferred that this species showed the closest similarity to Myxobolus miyarii (KT001495). This is the first record of any Myxobolus sp. from O. pabda in India.

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

Background

Myxozoa is a well-known economically and ecologically important group of metazoan parasites, phylogenetically related to Cnidaria. High diversity of myxosporeans has been recorded in Russia and China; however, most of the species were solely morphologically characterised. Here, we identified a new gibel carp-infecting Myxobolus species and morphologically and molecularly compared the Russian and Chinese isolates of this new myxosporean.

Results

Myxobolus pronini n. sp. was found free in the abdominal cavity of Carassius auratus gibelio (Bloch, 1782) in Lake Baikal watershed, Russia, and embedded in the visceral serous membranes of the same fish species in Lake Taibai, Hubei province, China. The morphometric data of the plasmodia and mature spores exhibited some differences between the Russian and Chinese isolates, but SSU rDNA sequences indicated that these two geographical isolates are conspecific. The mature spores from the two locations are obovate in frontal view, with wider anterior than posterior end and lemon-shaped in sutural view. Spores of the Russian isolate were 14.3–16.2 (mean 15.1 ± 0.2) μm long, 9.6–10.8 (10.1 ± 0.1) μm wide and 6.4–7.4 (6.7 ± 0.15) μm thick; those of the Chinese isolate were 13.8–15.6 (14.7 ± 0.24) μm long, 9.6–13.3 (9.6 ± 0.65) μm wide and 6.2–7.2 (6.6 ± 0.16) μm thick. The newly-generated rDNA sequences (including SSU rDNA, ITS and LSU rDNA) from the two isolates represented some variations within the intraspecific range. Homology search by BLAST showed that the newly obtained rDNA sequences do not match any sequences available on GenBank. Phylogenetic analysis based on the aligned partial SSU rDNA sequences indicated that this novel species clustered with several gibel carp-infecting Myxobolus spp. with round anterior end of spores. Additionally, phylogenetic analysis based on all obtained ITS sequences showed that distinct genetic geographical differentiation occurred for this new parasite.

Conclusions

Myxobolus pronini n. sp. is described by integrating morphological, ecological and molecular evidence. Two geographical isolates of this species showed some morphological and genetic differences but within the intraspecific range of variation.

Morphology, histology and phylogeny of Henneguya sinova sp. nov. (Myxobolidae: Myxozoa) infecting gills of Parablennius tentacularis in the Black Sea, Turkey

Myxosporeans of the genus Henneguya have a global distribution and infect organs and tissues of both marine and freshwater fishes. Here we describe the morphological, histological and molecular characteristics of Henneguya sinova sp. nov. parasitizing the gill arches of tentacled blenny Parablennius tentacularis (Perciformes: Blenniidae) collected from the coast of Sinop on the Black Sea in Turkey. Several oval whitish plasmodia of different sizes in the gill arches of fish were found. The mature spores were rounded oval in frontal view, with a mean (range) total length 57.5 (51.5-68.0) µm; the spore body was 11.7 (11.3-12.0) µm in length by 7.6 (7.3-8.3) µm in width and 6.7 (6.6-6.8) µm in thickness. The caudal appendages, measuring 46.0 (40.0-55.0) µm in length, were very thin at the tapered end. The prevalence of infection by H. sinova sp. nov. was 35.5%. Phylogenetic analysis of nuclear small subunit ribosomal DNA (SSU rDNA) clearly suggested H. sinova as a new species which is clustered within the marine Henneguya lineage. Pairwise nucleotide similarities and DNA distance values of SSU rDNA between H. sinova sp. nov. and other related Henneguya species also supported this suggestion.

Phylogenetic study of the genus Kudoa (Myxozoa: Multivalvulida) with a description of Kudoa rayformis sp. nov. from the trunk muscle of Pacific sierra Scomberomorus sierra

Kudoa rayformis n. sp. (Myxozoa; Multivalvulida) was observed in the trunk muscle of Pacific sierra Scomberomorus sierra caught off the coast of Tonosi, Panama. The species formed pseudocysts in myofibers and infection was subclinical. The myxospores possessed four polar capsules and spore valves, one of which had a distinct filamentous extension. This unique morphological characteristic of the myxospore validated this as a new species of Kudoa. Genetically, K. rayformis n. sp. is closest to K. inornata, with 98% and 91% similarity in 18S and 28S rDNA, respectively, but its spore shape was clearly distinct. The 18S rDNA and concatenated sequences from K. rayformis were used in molecular phylogenetic analyses of kudoids to examine the congruence of phylogeny with infection site tropism, spore morphology and cyst/pseudocyst formation. The results demonstrated that the phenotypic traits were correlated with the phylogeny of Kudoidae, and that the biological features of K. rayformis originated from the ancient Kudoidae as exhibited by the non-specific infection site tropism and the ability to infect muscle and form pseudocysts.

Supplemental description and molecular characterization of Myxobolus miyarii Kudo, 1919 (Myxosporea: Myxobolidae) infecting intestine of Amur catfish (Silurus asotus)

Myxobolus miyairii Kudo, 1919 was first reported from the intestines of the Amur catfish (Silurus asotus) in Japan and then in China and Russia, but with incomplete description. During the investigation of fish myxosporean diversity in Poyang Lake, the biggest lake along the Yangtze River, China, two Amur catfish highly infected with M. miyairii in the intestine wall were sampled. So, the complete description of this species with morphological and molecular data was presented here. A large number of whitish, round or ellipsoidal pseudocysts 0.32-0.78 mm in diameter could be found in the external intestinal wall after dissecting the infected fish. Mature spores of M. miyairii were elongated and ellipsoidal in the frontal view and narrow fusiform in the lateral view, with a slightly pointed anterior end and a bluntly rounded posterior end and measured 13.3 ± 0.49 (12.5-14.7) μm × 6.6 ± 0.27 (6.2-7.4) μm × 5.0 ± 0.26 (4.4-5.7) μm in size. Spore surface was smooth and two spore valves symmetrical, with a thin and straight sutural ridge. Interestingly, two types of caudal appendage (single or bifurcated) were occasionally present on the posterior end of some spores which has not previously been reported. The two equal pyriform polar capsules measured 6.5 ± 0.30 (6.2-7.5) μm long and 1.9 ± 0.14 (1.5-2.3) μm wide and situated at the anterior end of the spore. Polar filaments coiled with eight to nine turns, perpendicularly to the longitudinal axis of the polar capsules. Histopathological analysis showed that the plasmodium developed in the circular muscle layer of intestinal wall of Amur catfish, but no obvious inflammatory responses were observed. Phylogenetic analysis based on the partial 18S small subunit ribosomal DNA sequences indicates that M. miyairii cluster within a clade of Siluriforme-infecting Henneguya species with the support of a high bootstrap value, but also evolutionarily independent from the Henneguya clade infecting the epithelium of fish of the Ictaluridae family. Additionally, Myxobolus species reported with caudal processes dispersed within the Henneguya-Myxobolus clade.

Henneguya doneci (Myxosporea: Bivalvulida) in the gill filaments of Prussian carp Carassius gibelio (Bloch) from the upper Yellow River running through Inner Mongolia, China

We examined 11 Prussian carp, Carassius gibelio (Bloch), from the upper Yellow River running through Inner Mongolia (Wuhai City) to record myxosporean species. Between 6 and 15 elongated cysts of Henneguya doneci were located at the basal part of the gill filaments of 3 carp (27.3%); no more myxosporean plasmodia were found in other organs. Although the morphology and morphometric values of the spores (average measurements of 14 spores in µm: 11.4 long by 9.2 wide with 7.5 in thickness; 2 polar capsules, equal, 5.5 long by 3.2 wide; and a bifurcated caudal process, 51.6 long) with an evident intercapsular appendix were basically coincident with the species, the dimensions of the spore bodies were marginally larger, and the length of the caudal processes was distinctly longer than previously reported values for H. doneci (44.2-59.2 µm vs. 26.8-42.6 µm, respectively). Genetic analysis of the 18S ribosomal RNA gene (rDNA) found few nucleotide substitutions when compared with 3 deposited sequences of H. doneci collected around the Yangtze River (Sichuan and Hubei Provinces), China, indicating that the uniqueness of some of the morphological features exhibited by the present Wuhai isolate should be ascribed to intraspecific variation.

Myxobolus neurophilus Guilford 1963 (Myxosporea: Myxobolidae): a common parasite infecting yellow perch Perca flavescens (Mitchell, 1814) in Saskatchewan, Canada

The goal of this study was to identify a myxosporidian parasite infecting the central nervous system of yellow perch Perca flavescens (Mitchell, 1814) observed while investigating a fish kill in Saskatchewan, Canada. Fish were collected from seven different lakes, from two distinct watersheds. Sixty-four per cent (54/86) of yellow perch contained myxozoan pseudocysts located throughout the spinal cord and brain. Myxospores measured 16.5 μm (range 16.2-16.8) long and 8.2 μm (range 7.9-8.4) wide and contained two pyriform, mildly dissymmetrical, polar capsules measuring 7.7 μm (range 7.3-8.1) long and 2.7 μm (range 2.4-3.0) wide. The polar capsules each contained a single polar filament, with 7-9 turns per polar filament coil. Sequencing of the 18S SSU rDNA gene demonstrated >99% similarity to Myxobolus neurophilus. In 60% of infected fish, there was a mild to moderate, non-suppurative myelitis or encephalitis, or both, associated with myxospores. Axonal degeneration was present in rare cases. These findings extend the geographical distribution of M. neurophilus and suggest it may be widespread in yellow perch populations in Saskatchewan.

Ultrastructure and phylogeny of the parasite Henneguya carolina sp. nov. (Myxozoa), from the marine fish Trachinotus carolinus in Brazil

Microscopic and molecular procedures are used to describe a new myxosporean species, Henneguya carolina sp. nov., found infecting the intestine of the marine teleost fish Trachinotus carolinus on the southern Atlantic coast of Brazil. Spherical to ellipsoid cysts, measuring up to ~750 µm, display synchronous development. Mature myxospores are ellipsoidal with a bifurcated caudal process. Myxospore body length, width, and thickness are 12.7 ± 0.8 (12.0-13.4) µm, 8.8 ± 0.6 (7.5-9.6) µm, and 5.8 ± 0.4 (5.0-6.4) µm, respectively; 2 equal caudal processes are 16.8 ± 1.1 (15.9-18.0) µm long, and the total myxospore length is 29.4 ± 0.8 (28.4-30.4) µm. Two pyriform polar capsules measure 5.0 ± 0.5 (4.6-5.6) × 2.4 ± 0.4 (1.9-2.9) µm, and each contains a polar filament forming 3 to 4 coils. Sporoplasm is binucleated and presents a spherical vacuole surrounded by numerous globular sporoplasmosomes. Molecular analysis of the small subunit rRNA gene by maximum parsimony, neighbor joining, and maximum likelihood reveals the parasite clustering together with other myxobolids that are histozoic in marine fish of the order Perciformes, thereby strengthening the contention that the host phylogenetic relationships and aquatic environment are the strongest evolutionary signal for myxosporeans of the family Myxobolidae.

Thelohanellus testudineus n. sp. (Myxosporea: Bivalvulida) infecting the skin of allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China

A Thelohanellus species was encountered during a survey on Thelohanellus diversity of Carassius auratus gibelio (Bloch) in China. The infection is characterized by the presence of large cysts of 1.4-3.2 cm in diameter in the skin of host. Mature spores were ampullaceous in frontal view and testudinate in lateral view, measuring 19.7 ± 0.7 (18.6-20.8) μm long, 7.6 ± 0.4 (6.6-8.4) μm wide and 7.3 ± 0.5 (6.6-8.8) μm thick. The single polar capsule was elongated pyriform, with 11.1 ± 0.5 (10.0-11.9) μm long and 5.3 ± 0.3 (4.3-5.8) μm wide. Polar filaments coiled with 7-8 turns. Scanning electron microscopy revealed a smooth spore surface with flat side and convex side. The sutural line was straight or 'S' like, running near the middle of the valves. Histologically, the large cysts consisting of numerous small plasmodia developed in the dermis of the skin. The BLAST search indicated that the newly obtained ssrRNA gene sequences did not match any available sequences in GenBank and phylogenetic analysis placed it in the Thelohanellus clade. Based on morphology and molecular differences with reported Thelohanellus spp., this parasite was described as a new species of genus Thelohanellus.

Synopsis of the species of Myxobolus Bütschli, 1882 (Myxozoa: Myxosporea, Myxobolidae) described between 2005 and 2013

A synopsis of the species of Myxobolus Bütschli, 1882 (Myxozoa, Myxosporea, Myxobolidae) described between 2005 and 2013 is presented, including 112 nominal species. For each species the most important morphological and morphometric features are indicated in tabulated format. Included are also accession numbers for molecular data (when available), site of the infection within the host, features of the vegetative stage, organ infected, etc., plus a full bibliography of the original records for these species.

The phylogenetic study on Thelohanellus species (Myxosporea) in relation to host specificity and infection site tropism

Thelohanellus kitauei (Myxobolidae) infects cyprinid fish. The evolution of species derived from common ancestors results in the sharing of biological features. To reveal the origin of T. kitauei biological features, the correlation between phylogeny and biological features of Myxobolidae was investigated by Bayesian inference tree and Bayesian tip association significance testing. The results demonstrated that host specificity and infection site tropism were correlated with the phylogeny of Myxobolidae, and that the biological features of T. kitauei originated from the ancient Myxobolidae as exhibited by the non-specific infection site tropism and the ability to infect cyprinids.

Updated morphology, histopathology and molecular phylogeny of Myxobolus hearti, cardiac myxosporea in gibel carp, Carassius gibelio (Bloch)

The original description of Myxobolus hearti is supplemented with new data on spore morphology, histopathology and molecular phylogeny. Myxobolus hearti are found in the heart ventricle of the gibel carp, Carassius gibelio (Bloch), where they form whitish oval or irregularly shaped plasmodia. Mature spores are oval or shortly ellipsoidal in frontal view, lemon-shaped in sutural view and eye-shaped in apical view. The spores are 14.12 ± 0.35 (13.6-15) μm long (mean ± SD), 11.85 ± 0.34 ± 0.36 (11-12) μm wide and 7.32 ± 0.36 (7-8) μm thick. The two polar capsules are equal in size, 6.11 ± 0.29 (6-7) μm long and 3.89 ± 0.31(3-4) μm wide, and are long pyriform in shape. Polar filaments have six or seven coils situated perpendicular to the longitudinal axis of the polar capsules. Histopathology indicates that the plasmodia are encased by the host connective tissue, and no inflammatory responses are found in the heart ventricles. Phylogenetic analysis based on the 18S small-subunit ribosomal DNA sequences indicates that M. hearti is, genetically, most similar to Henneguya doneci, a gill-infecting species.

Molecular phylogeny of the Myxobolus and Henneguya genera with several new South American species

The present study consists of a detailed phylogenetic analysis of myxosporeans of the Myxobolus and Henneguya genera, including sequences from 12 Myxobolus/Henneguya species, parasites of South American pimelodids, bryconids and characids. Maximum likelihood and maximum parsimony analyses, based on 18 S rDNA gene sequences, showed that the strongest evolutionary signal is the phylogenetic affinity of the fish hosts, with clustering mainly occurring according to the order and/or family of the host. Of the 12 South American species studied here, six are newly described infecting fish from the Brazilian Pantanal wetland. Henneguya maculosus n. sp. and Myxobolus flavus n. sp. were found infecting both Pseudoplatystoma corruscans and Pseudoplatystoma reticulatum; Myxobolus aureus n. sp. and Myxobolus pantanalis n. sp. were observed parasitizing Salminus brasiliensis and Myxobolus umidus n. sp. and Myxobolus piraputangae n. sp. were detected infecting Brycon hilarii.

Supplementary studies and molecular data on Henneguya cerebralis Pronin, 1972 (Myxozoa: Myxosporea), a parasite from Kosogol grayling Thymallus arcticus nigrescens in Mongolia

Henneguya cerebralis Pronin, 1972 (Myxozoa) was described from Kosogol graylings Thymallus arcticus nigrescens Dorogostaisky, 1923 in Lake Khovsgol (Mongolia) in 1972. H. cerebralis was redescribed using critical morphological features and 18S ribosomal DNA (rDNA) gene sequence. Parasite infects cranial cartilage of fish host. Plasmodia are white rounded or ovoid, by 0.1 to 2mm in size, containing large quantities of spores. Spore body is ovoid or rounded, 11.18 ± 0.13 μm (range 9,71-12,56) in length and 9.06 ± 0.16 μm (range 7.22-10,06) in width with equal polar capsules (4.7×2.6 μm). The two caudal appendages have different lengths (one of them was shorter in 20%). Phylogenetic position inferred by 18S rDNA shows that H. cerebralis is closely related with H. zschokkei, H. nuesslini, H. salminicola and H. cartilaginis which are histozoic parasites of salmonid fish.

Three novel myxobolid species of genera Henneguya and Myxobolus (Myxosporea: Bivalvulida) from marine fish in Japan

Myxosporean genera Henneguya and Myxobolus (Bivalvulida: Myxobolidae) are closely related in morphology and molecular phylogeny, speciose with approximately 1,000 nominal species. The majority of them are recorded from freshwater fish worldwide, and few are known from marine fish. In this study, three myxobolid spp. are described from marine fish around Japan. Two novel Henneguya spp., Henneguya ogawai sp. n. and Henneguya yokoyamai sp. n., are described from two black sea breams (Acanthopagrus schlegelii) fished in the Inland Sea (Setonaikai), Japan. Plasmodia of the former species were localized in the esophageal or intestinal wall, and those of the latter species were in the wall of the gall bladder and peritoneum. Spore development in plasmodia of these two species was synchronous. The spore body of H. ogawai sp. n. was 11.0 (8.9-12.2) μm in length, 6.9 (6.3-7.5) μm in width, 5.9 (5.2-6.6) μm in thickness, with a bifurcated caudal process of equal length, 10.0 (8.4-12.7) μm long; total spore length, 21.1 (19.2-23.4) μm. It contained two polar capsule, 4.3 (3.8-5.2) × 1.9 (1.4-2.3) μm. The spore body of H. yokoyamai sp. n. was 11.0 (10.1-13.7) μm in length, 7.1 (6.6-7.5) μm in width, and 5.6 (4.5-6.4) μm in thickness, with a bifurcated caudal process of equal length, 14.1 (10.8-17.0) μm long; total spore length, 25.0 (21.9-29.2) μm. It contained two polar capsules, 3.7 (3.1-4.2) × 2.0 (1.8-2.4) μm. A novel Myxobolus sp., Myxobolus machidai sp. n., is described from a spotted knifejaw (Oplegnathus punctatus) fished in the Sea of Japan, off Shimonoseki, Yamaguchi Prefecture, Japan. Plasmodia were embedded in the esophageal wall. Its round spore was small in size, 9.0 (8.1-9.4) μm in length, 7.8 (7.5-8.3) μm in width, and 5.5 (5.1-6.0) μm in thickness. It contained two polar capsules, 3.5 (3.2-3.8) × 2.3 (2.2-2.5) μm. Spore development in a plasmodium was asynchronous. Nucleotide sequencing of the small subunit ribosomal RNA gene (SSU rDNA) of these two novel Henneguya spp. revealed a close phylogenetic relationship with the marine clade of Henneguya spp.; however, they were distinct in morphology and SSU rDNA sequence from any known species. M. machidai sp. n. was grouped with freshwater Henneguya spp. in a phylogenetic tree based on the SSU rDNA, distant from a known marine clade of Myxobolus spp. reported mainly from the Mediterranean Sea. This is the first record of Henneguya-Myxobolus spp. from natural marine water in Japan.

Identification and characterization of one novel type of Triactinospomyxon with short spore axis

This study identifies and characterizes one novel type of triactinospomyxon in oligochaete specimen of Branchiura sowerbyi Beddard collected from a fish pond used for rearing gibel carp located in Caidian Experimental Station of the Institute of Hydrobiology. It is nominated as Triactinospomyxon caidianensis type. The spore is of characteristic triactinomyxon "anchor" shape and possesses a spore body with sporoplasm containing 32 germ cells, 3 polar capsules, and 3 caudal processes. Compared with other triactinomyxon spores described previously, T. caidianensis type has a short spore axis with 76.5 μm in length and a very short style with 38.9 μm in length. Molecular analyses on 18S rDNA sequences indicate that the novel T. caidianensis type is most closely related to Triactinomyxon sp SA-2005, Antonactinomyxon sp KAB-2001, and Synactinomyxon sp KAB-2001 with 80.33% to 81.92% identities. On the basis of spore morphology and genetic data, the T. caidianensis type presented in this paper differs from those already known and described in the literatures.

Description of two new gill myxozoans from smallmouth (Micropterus dolomieu) and largemouth (Micropterus salmoides) bass

Two previously undescribed species of myxozoan parasites were observed in the gills of bass inhabiting the Potomac and James River basins. They are described using morphological characteristics and small-subunit (SSU) rDNA gene sequences. Both were taxonomically identified as new species of Myxobolus; Myxobolus branchiarum n. sp. was found exclusively in smallmouth bass, and Myxobolus micropterii n. sp. was found in largemouth and smallmouth bass. Small, spherical, white plasmodia of M. branchiarum from smallmouth bass were observed grossly in the gills; these plasmodia had an average length of 320.3 µm and width of 246.1 µm. The development of the plasmodia is intralamellar in the secondary lamellae of the gills. Mature spores were pyriform in shape with a length of 12.8 ± 1.4 (8.1-15.1) µm and width of 6.9 ± 1.1 (4.0-9.0) µm. Analysis of SSU rDNA identified M. branchiarum in a sister-group to 3 species of Henneguya , although morphologically caudal appendages were absent. Myxobolus micropterii observed in the gills of largemouth and smallmouth bass had larger, ovoid, cream-colored plasmodia with an average length of 568.1 µm and width of 148.1 µm. The cysts developed at the distal end of the gill filament within the primary lamellae. The mature spores were ovoid in shape with a length of 10.8 ± 0.7 (9.2-12.2) µm and width of 10.6 ± 0.6 (9.0-11.8) µm. SSU rDNA analysis placed M. micropterii in a sister group with Henneguya lobosa and Myxobolus oliveirai . The highest prevalence of M. branchiarum was observed in the gills of bass collected from the Cowpasture River (50.9%). Prevalence was 44.6% in bass from the Potomac River and only 4.3% in bass collected from the Shenandoah River. A seasonal study of M. branchiarum , which included both infected and uninfected smallmouth bass, determined that a significantly higher intensity was observed in the spring than in the summer (P < 0.001) or fall (P  =  0.004). In an analysis excluding uninfected bass, a higher intensity was observed in the spring than in the summer (P  =  0.001) or fall (P  =  0.008). Prevalence and seasonal differences were not determined for M. micropterii .

Redescription and molecular analysis of Myxobolus shantungensis Hu, 1965 (Myxozoa: Myxosporea) infecting common carp Cyprinus carpio haematopterus

Myxobolus shantungensis Hu, 1965 infects gill arches of common carp Cyprinus carpio haematopterus (Temminck and Schlegel), causing serious pathological effects on host fish. An inadequate original description and absence of molecular data make accurate early diagnosis challenging. To augment the original description, M. shantungensis is redescribed here using morphological and molecular biological methods. Mature spores of M. shantungensis were ellipsoidal or apple shaped in frontal view and lemon shaped in lateral view, averaging 8.2  ±  0.3 μm (8.0-9.0 μm) ×  10.1 ±  0.5 μm (9.2-11.1 μm)  ×  6.9  ±  0.3 μm (6.0-7.4 μm). Some spores had three to four "V"-shaped valve edge markings on the posterior of the spore. The two equal polar capsules were oval, measuring 4.3  ±  0.3 μm (3.8-5.0 μm)  ×  3.2  ±  0.2 μm (2.8-3.5 μm), situated at the anterior extremity of the spore. Polar filaments coiled with six to seven turns. Scanning electron microscopy revealed that the surface of mature spores of M. shantungensis was generally pitted with a number of irregular ridges in shape. M. shantungensis is also characterized on the molecular level using the sequence of the small subunit ribosomal RNA gene. A BLAST search revealed that this sequence did not match any available sequences in GenBank.

Supplemental diagnosis of a myxozoan parasite from common carp Cyprinus carpio: synonymy of Thelohanellus xinyangensis with Thelohanellus kitauei

Thelohanellus kitauei Egusa et Nakajima, 1981, was described from common carp Cyprinus carpio L. in Japan. In China, a myxosporean infecting the intestinal tissue of the same host species was described as Thelohanellus xinyangensis Xie, Gong, Xiao, Guo, Li et Guo, 2000, despite many similarities to T. kitauei. To examine the potential conspecificity of these species, a morphological and molecular investigation of T. xinyangensis was conducted. Comparing myxospore morphology, the mean spore length and width of each species is not identical between species, but ranges of dimensions overlap. These data are more suggestive of intraspecific variation than distinct species. Comparison of relative ratios of spore length to polar capsule length and spore width to polar capsule width of T. xinyangensis and T. kitauei reveal no differences and scanning electron microscopy reveals a smooth spore surface of T. xinyangensis, which is consistent with that of T. kitauei. Most convincingly, DNA sequences of the small subunit ribosomal RNA (ssrRNA) gene of the two species were identical. From the morphological and molecular biological data, we propose T. xinyangensis from the intestine of common carp is not a distinct species and is synonymous with T. kitauei.