Myxospore Morphology Research Articles

Characterization of Myxidium spinibarba sp. nov. (Cnidaria, Myxosporea, Myxidiidae) from Spinibarbus sinensis (Bleeker, 1871) in Chongqing China.

In the present study, we described a new species of Myxidium Bütschli, 1882, obtained from the gallbladder of Spinibarbus sinensis (Bleeker, 1871) from the Jialing River in Chongqing, China. Myxidium spinibarba sp. nov. was identified based on morphological and SSU rDNA sequence data. The mature myxospores were fusiform in valvular view and ovoid in sutural view, with somewhat protrusive poles and mean dimensions (all in μm) of 11.8 ± 0.5 (10.6-12.4) in length and 6.1 ± 0.5 (5.5-7.2) in width. The polar capsules were pyriform and equal in size with mean dimensions of 3.6 ± 0.4 (3.0-4.4) in length and 3.0 ± 0.2 (2.7-3.2) in width. The new species was distinct from related species of Myxidium in its morphology and molecular characteristics. Phylogenetic analysis indicated the clustering of species based on the presence or absence of valvular striations. Moreover, myxospore morphology, rather than the host environment, played an important role in the partial phylogenetic clustering.

First molecular data on the validity of Myxobolus ichkeulensis (Cnidaria: Myxosporea) from Mugil cephalus (Mugilidae) in Turkish waters

To date, there is no report on molecular characterisation of Myxobolus ichkeulensis in Mugil cephalus (Mugilidae) in Turkish marine waters. The aim of the current research was to provide the first molecular data on M. ichkeulensis from M. cephalus in Turkish Black Sea coasts. A total of 40 M. cephalus specimens were examined for the presence of M. ichkeulensis in the Turkish Black Sea coasts during January 2017 and April 2017. In the present study, M. ichkeulensis was identified based upon the myxospore morphology, host and tissue specificity, and SSU rRNA sequence. Phylogenetic analysis using neighbor-joining also revealed that our isolate (#GZP-2018-Samsun1) was clustered with other Myxobolus species that infect M. cephalus. The current study includes the morphological and histopathological descriptions and first molecular data on M. ichkeulensis in M. cephalus in Turkish marine waters. M. ichkeulensis was also reported from the M. cephalus in the coast of the Black Sea in Turkey for the first time. Moreover, our current genetic data was recorded as the new valid SSU rRNA sequence (MH374629) for M. ichkeulensis in the GenBank database.

Henneguya (Cnidaria: Myxosporea: Myxobolidae) infections of cultured barramundi, Lates calcarifer (Perciformes: Latidae) in an estuarine wetlands system of Malaysia: description of Henneguya setiuensis n. sp., Henneguya voronini n. sp. and Henneguya calcarifer n. sp.

Examination of 35 barramundi (Lates calcarifer) from aquaculture cages in Setiu Wetland, Malaysia, revealed a single fish infected with three Henneguya spp. (Cnidaria: Myxosporea). Characterization of the infections using tissue tropism, myxospore morphology and morphometry and 18S rDNA sequencing supported description of three new species: Henneguya setiuensis n. sp., Henneguya voronini n. sp. and H. calcarifer n. sp. Myxospores of all three species had typical Henneguya morphology, with two polar capsules in the plane of the suture, an oval spore body, smooth valve cell surfaces, and two caudal appendages. Spores were morphometrically similar, and many dimensions overlapped, but H. voronini n. sp. had shorter caudal appendages compared with H. calcarifer n. sp. and H. setiuensis n. sp. Gross tissue tropism distinguished the muscle parasite H. calcarifer n. sp. from gill parasites H. setiuensis n. sp. and H. voronini n. sp.; and these latter two species were further separable by fine-scale location of developing plasmodia, which were intra-lamellar for H. setiuensis n. sp. and basal to the filaments for H. voronini n. sp. small subunit ribosomal DNA sequences distinguished all three species: the two gill species H. setiuensis n. sp. and H voronini n. sp. were only 88% similar (over 1708 bp), whereas the muscle species H. calcarifer n. sp. was most similar to H. voronini n. sp. (98% over 1696 bp). None of the three novel species was more than 90% similar to any known myxosporean sequence in GenBank. Low infection prevalence of these myxosporeans and lack of obvious tissue pathology from developing plasmodia suggested none of these parasites are currently a problem for barramundi culture in Setiu Wetland; however additional surveys of fish, particularly at different times of the year, would be informative for better risk assessment.

Host-parasite relationship of Ortholinea lauquen sp. nov. (Cnidaria: Myxozoa) and the fish Galaxias maculatus in northwestern Patagonia, Argentina.

Galaxias maculatus (Jenyns, 1842) is a widespread freshwater fish and an important component of the economically important whitebait fisheries across the Southern Hemisphere. We report a new myxosporean parasite (Cnidaria: Myxozoa) infecting the kidney of G. maculatus from northwestern Patagonia (Argentina). Ortholinea lauquen sp. nov. was characterized using myxospore morphology, morphometrics and small subunit rDNA (ssrDNA) sequence data. Our ssrDNA phylogenetic analyses showed that O. lauquen sp. nov. is a member of the oligochaete-freshwater urinary tract clade and basal to a clade containing 4 different spore morphotypes (Chloromyxum, Myxidium, Zschokkella, Hoferellus). We explored host-parasite relationships at the macro- and microscale by analyzing the distribution, tissue tropism and pathology of O. lauquen sp. nov. Prevalence was relatively low (7%) by microscopy, but PCR detection revealed hidden levels of infection (49%), with the highest detection in lakes Morenito and Moreno (63-90%, Río Negro Province). The only locality negative by both microscopy and PCR was the Caleufu River (Neuquén Province), suggesting differences in fish life history traits (landlocked vs. potamodromous) or preference of the putative obligate invertebrate host for lentic habitats. O. lauquen sp. nov. sporulates in the renal tubules and occasionally in the glomerular space. The plasmodia frequently occluded the tubule lumina, and cellular necrosis and disintegration of the epithelium were observed. O. lauquen sp. nov. could represent a potential threat to G. maculatus culture under intensive farming conditions.

Morphological and molecular characterization of the muscle-infecting myxosporean Myxobolus xinyangensis sp. nov. from Abbottina rivularis in China

During an environmental assessment on the Huang River in Xinyang City (Henan Province, China), a novel Myxobolus species (Myxozoa: Myxobolidae) was found infecting the trunk muscle of Chinese false gudgeon Abbottina rivularis Basilewsky, 1855 (Gobioninae, Cyprinidae). Plasmodia of the new myxozoan, nominated herein as Myxobolus xinyangensis sp. nov., are round and yellowish, symmetrically and bilaterally located dorsal to the openings of the 2 opercula, and measure about 4.5 mm in diameter. The mature myxospores are orbicular in frontal view and fusiform in sutural view, with slightly tapered anterior end and rounded posterior end, and measure 9.4 ± 0.5 (8.7-10.6) µm long, 8.6 ± 0.6 (7.3-9.5) µm wide and 6.4 ± 0.3 (5.8-7.1) µm thick (mean ± SD, range). The ratio of spore length to spore width is close to 1. Two slightly unequal pyriform polar capsules, with tapering anterior ends and rounded posterior ends, measure 5.6 ± 0.67 (4.3-6.8) µm long and 3.0 ± 0.3 (2.4-3.6) µm wide, present as a figure 8 in the anterior part of spores and tightly converge at the top end of spores. Polar filament coils show 4 to 5 turns and are situated perpendicularly to the longitudinal axis of the polar capsules. No intercapsular appendix or sutural folds at the posterior end of spores were observed. The obtained partial small subunit ribosomal DNA sequence did not match any available data in GenBank and showed the highest sequence identity (93%) with 2 cyprinid trunk muscle-infecting Myxobolus species, M. pseudodispar and M. klamathellus. Phylogenetic analysis clearly showed that M. xinyangensis sp. nov. clustered within a cyprinid trunk muscle-infecting Myxobolus subclade at the basal position, but as an independent branch which was a possible reflection of its distinct myxospore morphology. This is the first record of infection of Myxobolus species in the trunk muscle of Abbotina fish.

Studies of Myxidium giardi C\xe9p\xe8de, 1906 infections in Icelandic eels identifies a genetically diverse clade of myxosporeans that represents the Paramyxidium n. g. (Myxosporea: Myxidiidae)

BackgroundThe 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.ResultsThe 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.ConclusionsThere 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.

Novel Henneguya spp. (Cnidaria: Myxozoa) from cichlid fish in the Amazon basin cluster by geographic origin.

We describe three new Henneguya spp. (Myxobolidae) found parasitizing two species of cichlid fish from the Amazon basin, Brazil: H. tucunarei n. sp. from gill filaments of Cichla monoculus and H. tapajoensis n. sp. from gill filaments of Cichla pinima, both from the Tapajós River, Pará State and H. jariensis n. sp. in the fins of Cichla monoculus from the Jari River, Amapá State. We based descriptions on myxospore morphology and small subunit ribosomal DNA sequences, and used a phylogenetic analysis to compare the new Henneguya species with known relatives. Spores of the three species had similar morphology and morphometrics, but differed molecularly 5-7.5%, and were no more than 94% similar to any other sequence in GenBank. Together with having different hosts, these data supported the diagnosis of the parasites as distinct, novel species. Maximum likelihood and Bayesian analyses showed that H. tucunarei n. sp., H. tapajoensis n. sp., and H. jariensis n. sp. plus Henneguya paraensis (which parasitizes Cichla temensis) formed a well-supported sub-clade of Henneguya parasites of cichlids from the Amazon basin, in a lineage sister to those in characiforms hosts. Our analysis was consistent with previous studies that suggest that aquatic environment and vertebrate host group are the strongest correlates with phylogenetic signals in the Myxobolidae.

The description of two new species of Chloromyxum from skates in the Argentine Sea reveals that a limited geographic host distribution causes phylogenetic lineage separation of myxozoans in Chondrichthyes.

During a survey on the myxosporean fauna of Rajiformes from the Atlantic coast of Argentina, in waters off Buenos Aires Province (34°–42°S; 53°–62°W), the gall bladders of 217 specimens belonging to seven species of skates, representatives of two families, were examined. As a result, three species of Chloromyxum Mingazzini, 1890, namely C. atlantoraji n. sp., C. zearaji n. sp. and C. riorajum Azevedo, Casal, Garcia, Matos, Teles-Grilo and Matos, 2009 were found infecting three endemic host species, the spotback skate Atlantoraja castelnaui (Arhynchobatidae), the yellownose skate Zearaja chilensis (Rajidae) and the Rio skate Rioraja agassizii (Arhynchobatidae), respectively. These species were described based on myxospore morphology and morphometry characterization, as well as by providing their small subunit ribosomal DNA (SSU rDNA) sequences. The SSU rDNA-based phylogenetic analyses showed that these three species constituted a well-established monophyletic subclade within the marine Chloromyxum clade, while branches subtending the other Chloromyxum species were poorly resolved or unresolved, independently of the host taxonomic identities (Carchariniformes, Myliobatiformes, Orectolobiformes, Pristiophoriformes, Rajiformes, Squaliformes and Torpediniformes) and/or host geographic distribution (Atlantic coast of Portugal, Atlantic coast of the USA, Australian waters or Mediterranean Sea). The possible causes of these discrepancies are discussed, providing new insights into the phylogeny of the marine Chloromyxum clade.

A new pathogen, Myxobolus holzerae (Myxosporea: Myxozoa) causing severe gill disease in an Indian major carp Labeo rohita in a cold water wetland, Punjab (India)

The Indian major carp, Labeo rohita Hamilton, 1822 is a tropical freshwater cyprinid fish native to inland waters in Asia. Herein, we describe a novel myxozoan forming plasmodia in the gill lamellae of L. rohita from Ranjit Sagar Wetland in Punjab, India. Myxospores were consistent with the genus Myxobolus, round to elliptical in valvular view, lemon shaped in side view with a characteristic protrusion at the anterior end and a round posterior end; length 7.65 ± 0.07 μm, width 4.62 ± 0.09 μm. There were two polar capsules of equal length, pear shaped, length of polar capsule 2.54 ± 0.05 μm, width 1.60 ± 0.02 μm, with 5–6 turns of the polar filament. The 890 bp 18S rDNA sequence was up to 97% similar to M. catlae from other cyprinid fishes in India. In having, unique myxospore morphology and 18S rDNA sequence, we propose Myxobolus holzerae as new to science.

Morphological and molecular characterization of Myxobolus puntiusii n. sp. (Cnidaria: Myxosporea) infecting Puntius sophore Hamilton, 1822 from Ranjit Sagar Wetland, Punjab (India)

The pool barb, Puntius sophore Hamilton, 1822, is a tropical freshwater cyprinid fish native to inland waters in Asia. Herein, a novel myxozoan from plasmodia on the caudal fin of P. sophore from Ranjit Sagar Wetland in Punjab, India is described. Myxospores were consistent with the genus Myxobolus, ellipsoidal in frontal view, lemon-shaped in lateral view; length 7.76 ± 0.28 µm, width 5.36 ± 0.15 µm. There were two polar capsules of unequal size: a larger polar capsule, length 3.01 ± 0.08 µm, width 1.83 ± 0.11 µm, with 6-7 turns of the polar filament, and a smaller polar capsule, length 1.71 ± 0.15 µm, width 0.94 ± 0.07 µm, with 3-4 turns of the polar filament. The 1183 bp 18S rDNA sequence was up to 95% similar to Myxobolus spp. from other cyprinid fishes in India. Given the novel host, unique myxospore morphology, and 18S rDNA sequence, we propose Myxobolus puntiusii n. sp.

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.

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

BackgroundTraditional 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.MethodsHistozoic 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.ResultsThe 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.ConclusionsTo 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.

Morphological, Histological, and Molecular Description of Unicauda fimbrethilae n. sp. (Cnidaria: Myxosporea: Myxobolidae) from the Intestinal Tract of Channel Catfish Ictalurus punctatus.

The channel catfish Ictalurus punctatus is a known host for 10 species of Henneguya, but few other myxozoan genera are described from this species. Unicauda is a genus of myxozoan parasites within the family Myxobolidae that consists of 10 valid species from freshwater fish. Herein, we describe a novel species of Unicauda from the intestinal tract of farm-raised channel catfish in Mississippi. Myxospores were consistent with the genus Unicauda but exhibited a unique branching at the terminal end of the caudal process that has not previously been reported. Myxospores measured 90.39 ± 14.97 μm (mean ± SD; range = 70.88-126.02 μm) in total length. The spherical spore body measured 7.31 ± 0.26 μm (6.75-7.84 μm) in length and 7.01 ± 0.63 μm (6.1-8.01 μm) in width. The 2 polar capsules measured 3.45 ± 0.33 μm (3.02-4.03 μm) in length and 2.65 ± 0.32 μm (2.18-3.11 μm) in width. The single caudal process measured 82.98 ± 14.97 μm (63.39-118.63 μm) in length from the base of the spore body to the end of the most terminal projection. Terminal projections measured 26.83 ± 8.8 μm (12.34-42.29 μm) in length and 0.95 ± 0.23 μm (0.52-1.6 μm) in width. The 18S rRNA gene sequence obtained did not match any published sequences. Given the uniqueness of the myxospore morphology, histological presentation, and gene sequence data, we describe this as an unreported species, Unicauda fimbrethilae n. sp.

Morphological and molecular characterization of Henneguya bicaudi n. sp. (Myxosporea: Myxobolidae) infecting gills of Cirrhinus mrigala (Ham.) in Harike Wetland, Punjab (India).

In the present study, Henneguya bicaudi n. sp. infecting gills of Cirrhinus mrigala (Ham.) an Indian major carp from Harike Wetland in Punjab, India, has been described on the basis of myxospore morphology and partial amplification of the SSU rRNA gene. The pseudocysts of H. bicaudi n. sp. were located within the gill filament, whitish with round to irregular outer margin and 0.5-0.7 mm in diameter, 3-4 pseudocysts each containing about 50-100 myxospores were detected per gill. Mature myxospores were oblongate, 21.0 × 6.2 μm had a caudal appendage bifurcating into two thin thread-like branches starting posterior to middle of its length. The two equal polar capsules were 3.14 × 2.02 μm. The present species was compared morphologically with 21 species of the genus Henneguya infecting fresh water fishes in India and related geographical area. H. bicaudi n. sp. differed in having a peculiar oblongate shape and size of the myxospore, equal polar capsules, and also by the location of the point of bifurcation of the caudal appendage. 18S rDNA sequences of H. bicaudi n. sp. obtained revealed 96% homogeneity with H. pseudorhinogobi (Kageyama et al., Fish Sci 75:657-663, 2009) infecting gill filaments of Rhinogobius sp. (Rutter, PANS Philad 56-90, 1897) in Japan. The intensity of infection was determined by the gill pseudocyst index (GPI) based on the number of countable pseudocysts by stereo zoom trinocular microscopy per gill (on one side).

18S rRNA gene sequencing identifies a novel species of Henneguya parasitizing the gills of the channel catfish (Ictaluridae).

In the southeastern USA, the channel catfish Ictalurus punctatus is a host to at least eight different species of myxozoan parasites belonging to the genus Henneguya, four of which have been characterized molecularly using sequencing of the small subunit ribosomal RNA (SSU rRNA) gene. However, only two of these have confirmed life cycles that involve the oligochaete Dero digitata as the definitive host. During a health screening of farm-raised channel catfish, several fish presented with deformed primary lamellae. Lamellae harbored large, nodular, white pseudocysts 1.25 mm in diameter, and upon rupturing, these pseudocysts released Henneguya myxospores, with a typical lanceolate-shaped spore body, measuring 17.1 ± 1.0 μm (mean ± SD; range = 15.0-19.3 μm) in length and 4.8 ± 0.4 μm (3.7-5.6 μm) in width. Pyriform-shaped polar capsules were 5.8 ± 0.3 μm in length (5.1-6.4 μm) and 1.7 ± 0.1 μm (1.4-1.9 μm) in width. The two caudal processes were 40.0 ± 5.1 μm in length (29.5-50.0 μm) with a spore length of 57.2 ± 4.7 (46.8-66.8 μm). The contiguous SSU rRNA gene sequence obtained from myxospores of five excised cysts did not match any Henneguya sp. in GenBank. The greatest sequence homology (91% over 1,900 bp) was with Henneguya pellis, associated with blister-like lesions on the skin of blue catfish Ictalurus furcatus. Based on the unique combination of pseudocyst and myxospore morphology, tissue location, host, and SSU rRNA gene sequence data, we report this isolate to be a previously unreported species, Henneguya bulbosus sp. nov.

Supplemental Description ofMyxobolus squamalis(Myxozoa)

Myxobolus squamalis is a myxozoan skin parasite first reported from rainbow trout (Oncorhynchus mykiss). Identification of the parasite based on myxospore morphology is unreliable because M. squamalis is similar to several other myxobolids that share host species and geographic ranges. The only ssrRNA gene sequence available for M. squamalis is from Chinook salmon, Oncorhynchus tschawytscha, but these data are not linked with any information on spore morphology. Here we provide a supplemental description of M. squamalis from its type host, O. mykiss, using myxospore morphology, morphometry, and ssrRNA gene sequence data. Our ssrRNA sequence data were only 78% similar to the GenBank M. squamalis sequence from Chinook salmon, which raises the possibility of misidentification. We suggest that Chinook salmon are not a host of the parasite, as no infections were found in current stocks or in >30 yr of historical data from hatchery fish held in waters that harbored M. squamalis in rainbow trout, and we could find no well-identified report of M. squamalis from Chinook salmon. Our complementary morphological and molecular data sets will facilitate unambiguous future identification of M. squamalis.

New species of Myxosporea from frogs and resurrection of the genus Cystodiscus Lutz, 1889 for species with myxospores in gallbladders of amphibians

Two new myxosporean species in the gallbladders of frogs have recently spread across eastern Australia and cause disease. Cystodiscus axonis sp. n. and Cystodiscus australis sp. n. are species of Myxosporea (Myxozoa) identified from a range of Australian frogs and tadpoles including the introduced Cane toad (Rhinella marina). The new species are defined by their distinct genetic lineage, myxospore morphology and ultrastructure of the pre-sporogonic development. Spores of both species are produced in the gallbladder. Spores of C. axonis sp. n. possess distinct filiform polar appendages (FPA). The pre-sporogonic development of C. axonis sp. n. is within myelinated axons in the central nervous system of hosts, as well as bile ducts of tadpoles. Pre-sporogonic and sporogonic development of C. australis sp. n. is confined to tadpole bile ducts and myxospores of C. australis sp. n. are devoid of FPA. The genus Cystodiscus Lutz, 1889 introduced for Cystodiscus immersus Lutz, 1889 is emended to accompany myxosporean parasites affecting amphibians previously classified in the genus Myxidium sensu lato. A synopsis of described species within Cystodiscus is provided.

Myxosporean hyperparasites of gill monogeneans are basal to the Multivalvulida

BackgroundMyxosporeans are known from aquatic annelids but parasitism of platyhelminths by myxosporeans has not been widely reported. Hyperparasitism of gill monogeneans by Myxidium giardi has been reported from the European eel and Myxidium-like hyperparasites have also been observed during studies of gill monogeneans from Malaysia and Japan.The present study aimed to collect new hyperparasite material from Malaysia for morphological and molecular descriptions. In addition, PCR screening of host fish was undertaken to determine whether they are also hosts for the myxosporean.ResultsHeavy myxosporean infections were observed in monogeneans from two out of 14 fish and were detected from a further five fish using specific PCRs and pooled monogenean DNA. Positive DNA isolates were sequenced and were from a single species of myxosporean. Myxospore morphology was consistent with Myxidium with histozoic development in the parenchymal tissues of the monogenean. Simultaneous infections in the fish could not be confirmed microscopically; however, identical myxosporean DNA could be amplified from kidney, spleen and intestinal tract tissues using the specific PCR. Small subunit (SSU) rDNA for the myxosporean was amplified and was found to be most similar (92%) to that of another hyperparasitic myxosporean from a gill monogenean from Japan and to numerous multivalvulidan myxosporeans from the genus Kudoa (89-91%). Phylogenetic analyses placed the hyperparasite sequence basally to clades containing Kudoa, Unicapsula and Sphaerospora.ConclusionsThe myxosporean infecting the gill monogenean, Diplectanocotyla gracilis, from the Indo-Pacific tarpon, Megalops cyprinoides, is described as a new species, Myxidium incomptavermi, based on a histozoic development in the monogenean host and its phylogenetic placement.We have demonstrated for the first time that a myxosporean hyperparasite of gill monogeneans is detectable in the fish host. However, myxospores could not be isolated from the fish and confirmation was by PCR alone. The relationship between the myxosporean infection in gill monogeneans and the presence of parasitic DNA in fish is not yet fully understood. Nonetheless, myxospores with a Myxidium-like morphology, two of which we have shown to be phylogenetically related, have now been reported to develop in three different gill monogeneans, indicating that myxosporeans are true parasites of monogeneans.

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.

Replacement of ATCC 25944T, the current type strain of Melittangium lichenicola, with ATCC 25946. Request for an Opinion

It is proposed that the type strain of Melittangium lichenicola (Thaxter 1892) McCurdy 1971 is ATCC 25946 (=DSM 14877), which was originally designated as a reference strain by McCurdy, and not ATCC 25944(T), as given in the Approved Lists. Swarm appearance, myxospore morphology and 16S rRNA gene sequence data suggest that ATCC 25946 is a representative of the species Melittangium lichenicola, while strain ATCC 25944 is clearly a member of the Myxococcus-Corallococcus clade. A Request for an Opinion to this effect is made to the Judicial Commission of the International Committee on Systematics of Prokaryotes.