Migration and ultrastructure of the acanthocephalan Echinorhynchus gadi Zoega in Müller, 1776 in intermediate host under experimental conditions.

Amphipods Eogammarus tiuschovi were experimentally infected by the acanthocephalan Echinorhynchus gadi (Acanthocephala: Echinorhynchidae). Within the first four days post-infection, acanthors of the acanthocephalan caused the cellular response of the host, which ended with their complete encapsulation on day 4 post-infection. The acanthors obtained through the experiment were examined ultrastructurally. Two syncytia (frontal and epidermal) and a central nuclear mass are found in the acanthor's body. The frontal syncytium has 3-4 nuclei and contains secretory granules with homogeneous, electron-dense contents. Since the secretory granules occupy only the anterior one-third of this syncytium, it is suggested that the contents of these granules are involved in the acanthor's migration through the gut wall of the amphipod. The central nuclear mass consists of an aggregation of fibrillar bodies and a few electron-light nuclei distributed on the periphery. Some of these nuclei, located near the central nuclear mass, are assumed to be a source of the acanthocephalan's internal organs. The epidermal syncytium surrounds the frontal syncytium and the central nuclear mass. It is represented by a superficial cytoplasmic layer, but the bulk of the cytoplasm is concentrated in the posterior one-third of the acanthor's body. Syncytial nuclei are evenly distributed throughout the cytoplasm. The muscular system of the acanthors consists of 10 longitudinal muscle fibers located below the superficial cytoplasmic layer and two muscle retractors crossing the frontal syncytium.

Morphological and molecular characterization of the marine-teleost parasitizing acanthocephalan Echinorhynchus hexagrammi (Syndermata: Palaeacanthocephala) from a new host, Liparis sp. (Actinopterygii: Scorpaeniformes).

Originally described from the masked greenling Hexagrammos octogrammus (Pallas, 1814), the palaeacanthocephalan Echinorhynchus hexagrammi Baeva, 1965 has so far been known from seven species in six families of marine teleosts distributed in the Sea of Okhotsk off Sakhalin and in the Northwestern Pacific off Hokkaido, Japan. In this study, we examined the phylogenetic position of E. hexagrammi based on material obtained from the intestine of an unidentified snailfish, Liparis sp., dredged in Akkeshi Bay, Hokkaido, Japan. We performed an analysis using two gene markers, the mitochondrial cytochrome c oxidase subunit I and the nuclear 28S rRNA, along with other sequences available in public databases. In the resulting tree, E. hexagrammi was more closely related to two species complexes, the E. bothniensis Zdzitowiecki and Valtonen, 1987 complex and the E. gadi Zoega in Müller, 1776 complex, rather than to E. brayi Wayland, Sommerville, and Gibson, 1999, E. cinctulus (Porta, 1905), E. salmonis Müller, 1784, and E. truttae Schrank, 1788. The morphology of the examined material herein identified as E. hexagrammi is briefly described. This study represents the first host record of E. hexagrammi from the snailfish family Liparidae.

Morphological and molecular description of a distinct population of Echinorhynchus gadi Zoega in Müller, 1776 (Paleacanthocephala: Echinorhynchidae) from the pacific halibut Hippoglossus stenolepis Schmidt in Alaska.

PURPOSE: Echinorhynchus gadi is one of the most widely distributed and commonly described acanthocephalans in marine fishes throughout the world. We provide a detailed morphometric and molecular description of a distinct Alaska population collected from the Pacific halibut Hippoglossus stenolepis Schmidt (Pleuronectidae) compared to those from other hosts and regions, illustrating new features never previously reported. METHODS: We described new specimens by microscopical studies, augmented by SEM, Energy Dispersive x-ray and molecular analyses, and histopathology. RESULTS: Specimens from Alaska were distinguished from those collected from the other geographical areas in proboscis size and its armature, especially number of hook rows and hooks per row, and length of hooks. The size of the receptacle, lemnisci, and reproductive structures in some other collections also varied from the Alaska material. X-ray scans of the gallium cut hooks depict prominent layering with high Sulfur content for tip cuts and increased calcium and phosphorus content in the base area of the hook. Sections of E. gadi specimens in the host tissue show prominent hook entanglement with subsequent connective tissue invasion also depicting the internal anatomy of certain worm structures not readily seen by other means. Molecular analyses clearly confirmed the identity of our E. gadi sequences. CONCLUSION: Our Alaska population of the E. gadi complex appears to represent a novel population distinguishable by its distinct morphometrics, geography and host species. We further establish new information on the Energy Dispersive X-ray analysis in our Alaska material for future comparisons with the other siblings and explore genetic relationships among echinorhynchid genera and species.

First steps to understand the systematics of Echinorhynchidae Cobbold, 1876 (Acanthocephala), inferred through nuclear gene sequences.

Acanthocephalans of the order Echinorhynchida are one of the most diverse groups in their phylum, with approximately 470 species classified into 11 families that largely consist of parasites of freshwater, brackish and marine fishes and, sporadically, reptiles and amphibians distributed worldwide. Previous phylogenies inferred with molecular data have supported the paraphyly or polyphyly of some families, suggesting that most of them have been diagnosed based on unique combinations of characters, rather than shared derivative features. We expand the taxonomic sampling of several genera such as Acanthocephalus, Echinorhynchus and Pseudoacanthocephalus of Echinorhynchidae from diverse biogeographical zones in the Americas, Europe and Asia with the aim of testing the monophyly of the family by using two molecular markers. Sequences from small (SSU) and large (LSU) subunits of ribosomal DNA were obtained for six species representing the genera Acanthocephalus and Echinorhynchus from the Neotropical, Nearctic, Palearctic and Oriental regions. These sequences were aligned with other sequences available in the GenBank dataset from Echinorhynchidae. Phylogenetic trees inferred with the combined (SSU + LSU) and the individual data sets consistently placed the genera Acanthocephalus, Pseudoacanthocephalus and Echinorhynchus into three independent lineages. Two families, Paracanthocephalidae Golvan, 1960, and Pseudoacanthocephalidae Petrochenko, 1956, were resurrected to accommodate the genera Acanthocephalus and Pseudoacanthocephalus, respectively. The species of the genus Acanthocephalus from the Nearctic, Palearctic and Oriental biogeographic regions formed a clade that was well supported. However, Acanthocephalus amini from the Neotropical region was nested inside Arhythmacanthidae. Therefore, the genus Calakmulrhynchus was created to accommodate A. amini and resolve the paraphyly of Acanthocephalus. Finally, the diagnoses of the families Echinorhynchidae and Arhythmacanthidae were amended. The molecular phylogenies should be used as a taxonomic framework to find shared derived characters (synapomorphies) and build a more robust classification scheme that reflects the evolutionary history of the acanthocephalans.

Unravelling the hidden biodiversity - the establishment of DNA barcodes of fish-parasitizing Acanthocephala Koehlreuther, 1771 in view of taxonomic misidentifications, intraspecific variability and possible cryptic species.

Acanthocephalans are obligate parasites of vertebrates, mostly of fish. There is limited knowledge about the diversity of fish-parasitizing Acanthocephala in Austria. Seven determined species and an undetermined species are recorded for Austrian waters. Morphological identification of acanthocephalans remains challenging due to their sparse morphological characters and their high intraspecific variations. DNA barcoding is an effective tool for taxonomic assignment at the species level. In this study, we provide new DNA barcoding data for three genera of Acanthocephala (Pomphorhynchus Monticelli, 1905, Echinorhynchus Zoega in Müller, 1776 and Acanthocephalus Koelreuter, 1771) obtained from different fish species in Austria and provide an important contribution to acanthocephalan taxonomy and distribution in Austrian fish. Nevertheless, the taxonomic assignment of one species must remain open. We found indications for cryptic species within Echinorhynchus cinctulus Porta, 1905. Our study underlines the difficulties in processing reliable DNA barcodes and highlights the importance of the establishment of such DNA barcodes to overcome these. To achieve this goal, it is necessary to collect and compare material across Europe allowing a comprehensive revision of the phylum in Europe.

Prevalence and genetic diversity of Echinorhynchus gymnocyprii (Acanthocephala: Echinorhynchidae) in schizothoracine fishes (Cyprinidae: Schizothoracinae) in Qinghai-Tibetan Plateau, China.

BACKGROUND: The schizothoracine fishes, an excellent model for several studies, is a dominant fish group of the Qinghai-Tibet Plateau (QTP). However, species populations have rapidly declined due to various factors, and infection with Echinorhynchus gymnocyprii is cited as a possible factor. In the present study, the molecular characteristics of E. gymnocyprii in four species of schizothoracine fishes from the QTP were explored. METHODS: We investigated the infection status of E. gymnocyprii in 156 schizothoracine fishes from the upper Yangtze River, upper Yellow River, and Qinghai Lake in Qinghai Province, China. The complete internal transcribed spacer (ITS) of the ribosomal RNA (rRNA) gene and part of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene of 35 E. gymnocyprii isolates from these fishes were sequenced and their characteristics analyzed. In addition, we inferred phylogenetic relationships of the E. gymnocyprii populations based on the rRNA-ITS and cox1 sequences. RESULTS: The total prevalence of E. gymnocyprii in schizothoracine fishes was 57.69% (90/156). However, the prevalence among different species as well as that across the geographical locations of the schizothoracine fishes was significantly different. The results of sequence analysis showed that the four E. gymnocyprii populations from different hosts and regions of Qinghai Province were conspecific, exhibiting rich genetic diversity. Phylogenetic analysis based on rRNA-ITS and cox1 sequences supported the coalescence of branches within E. gymnocyprii; the cox1 gene of E. gymnocyprii populations inferred some geographical associations with water systems. In addition, three species of schizothoracine fishes were recorded as new definitive hosts for E. gymnocyprii. CONCLUSIONS: To the best of our knowledge, this is the first molecular description of E. gymnocyprii populations in schizothoracine fishes from the Qinghai-Tibet Plateau that provides basic data for epidemiological surveillance and control of acanthocephaliasis to protect endemic fish stocks.

Acanthocephalan parasites collected from Austrian fishes: molecular barcoding and pathological observations.

Acanthocephalan parasites were collected from the intestinal tracts of 137 predominantly wild fish (1 barbel Barbus barbus, 3 European chub Squalius cephalus, 13 rainbow trout Oncorhynchus mykiss and 120 brown trout Salmo trutta) from 12 localities. The condition factor, intensity of acanthocephalan infection and pathological lesions, if applicable, were documented. Routine bacteriology and virology were performed, and the brown trout were additionally tested for the presence of the myxozoan parasite Tetracapsolioides bryosalmonae by PCR. In total, 113 acanthocephalans were barcoded by sequencing a section of the mitochondrial cytochrome oxidase subunit I (COI) gene. Barcoding of the acanthocephalan tissues resulted in 77 sequences, of which 56 were assigned to Echinorhynchus truttae (3 genotypes), 11 to Pomphorhynchus tereticollis (9 genotypes), 9 to Acanthocephalus sp. (5 genotypes) and 1 to Neoechinorhynchida. Most of these genotypes were detected for the first time. Statistically, the acanthocephalan infection did not have an impact on the condition factor of the brown trout. Infection with P. tereticollis caused more severe pathological changes in the digestive tract than E. truttae. The present study provides new data regarding the distribution of acanthocephalan species in Austria and their impact on individual fish. In addition, new barcoding data from acanthocephalan parasites are presented, and the occurrence of P. tereticollis in European chub in Austria and in brown and rainbow trout in general was confirmed for the first time.

SEM studies on acanthocephalan parasite, Echinorhynchus veli infecting the fish Synaptura orientalis (Bl & Sch, 1801).

Echinorhynchus veli (George and Nadakal, 1978), an acanthocephalid worm infesting the estuarine flat fish, Synaptura orientalis, was collected from the Veli lake, Kerala. The parasite was recovered from the intestine of the host fish. The detailed surface morphology was studied with the help of scanning electron microscope. The study revealed a cylindrical, medially swollen proboscis with a flat apex, backward directed hooks, each with smooth surface, broad base, pointed tip and an epidermal elevation at the point of insertion. A pair of sensory pits was seen at the base of the proboscis. The neck was well developed with densely packed epidermal micropores. Paired sensory pits were seen at the base of the neck and a collar between it and the trunk. The epidermis of the trunk has microtriches and micropores. The female genital pore was circular, and terminal in an elevated orifice. In male, the copulatory bursa was directed ventrally, with well-defined rim and several sensory papillae.

Host condition and accumulation of metals by acanthocephalan parasite Echinorhynchus gadi in cod Gadus morhua from the southern Baltic Sea.

In this study, we analyzed the relationship between concentration of metals in the host-parasite system (cod - acanthocephalan Echinorhynchus gadi) and Fulton's condition factor (FCF) of the host. The relationship between metal (Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Pb, Sr, Zn) concentrations in E. gadi and cod tissues was expressed as a bioconcentration factor (BCF), the ratio of the concentration in the parasite tissue to that in host tissues. Acanthocephalans accumulated mainly toxic metals (Cd, Pb), as well as Sr, Ca, Na. Cadmium showed the highest bioconcentration in parasites (BCF >200) compared to fish muscle. Significant negative correlation was detected between FCF and the concentration of Cd and Hg in cod liver. In contrast, FCF was positively correlated with the concentration of Hg in acanthocephalan tissues.

The Meristogram: a neglected tool for acanthocephalan systematics.

BACKGROUND: The hooks of the acanthocephalan proboscis exhibit serial variation in size and shape. The Meristogram was developed by Huffman and Bullock (1975) to provide a graphical representation of this positional variation in hook morphology. Initial studies demonstrated the ability of the Meristogram to discriminate species within the genera Echinorhynchus and Pomphorhynchus (Huffman and Bullock 1975, Huffman and Nickol 1978, Gleason and Huffman 1981). However, the reliability of the method for taxonomic work was questioned by Shostak et al. (1986) after they found intra-specific variation in two Echinorhynchus species. Uncertainty about the usefulness of the Meristogram and the absence of a readily available software implementation of the algorithm, might explain why this abstract proboscis character has yet to be adopted by acanthocephalan systematists. NEW INFORMATION: The Meristogram algorithm was implemented in the R language and a simple graphical user interface created to facilitate ease of use (the software is freely available from https://github.com/WaylandM/meristogram). The accuracy of the algorithm's formula for calculating hook cross-sectional area was validated by data collected using a digitizing tablet. Meristograms were created from data in public respositories for eight Echinorhynchus taxa: E. bothniensis, E. 'bothniensis', E. gadi spp. A, B and I, E. brayi, E. salmonis and E. truttae. In this preliminary analysis, the meristogram differentiated E. bothniensis, E. brayi, E. gadi sp. B, E. salmonis and E. truttae from each other, and from the remaining taxa in this study, but independent data will be required for validation. Sample sizes for E. 'bothniensis' and E. gadi spp. A and I were too small to identify diagnostic features with any degree of confidence. Meristogram differences among the sibling species of the E. gadi and E. bothniensis groups suggest that the 'intra-specfic' variation in meristogram previously reported for some Echinorhynchus taxa, may have actually represented morphological divergence between unrecognized cryptic species. Hierarchical clustering of taxa based on Meristogram data yielded dendrograms that were largely concordant with phylogenetic relationships inferred from DNA sequence data, indicating the presence of a strong phylogenetic signal.

Sexual segregation of Echinorhynchus borealis von Linstow, 1901 (Acanthocephala) in the gut of burbot (Lota lota Linnaeus).

Helminths often occupy defined niches in the gut of their definitive hosts. In the dioecious acanthocephalans, adult males and females usually have similar gut distributions, but sexual site segregation has been reported in at least some species. We studied the intestinal distribution of the acanthocephalan Echinorhynchus borealis von Linstow, 1901 (syn. of E. cinctulus Porta, 1905) in its definitive host, burbot (Lota lota Linnaeus). Over 80% of female worms were found in the pyloric caeca, whereas the majority of males were in the anterior two-thirds of the intestine. This difference was relatively consistent between individual fish hosts. Worms from different parts of the gut did not differ in length, so site segregation was not obviously related to worm growth or age. We found proportionally more males in the caeca when a larger fraction of the females were found there, suggesting mating opportunities influence gut distribution. However, this result relied on a single parasite infrapopulation and is thus tentative. We discuss how mating strategies and/or sexual differences in life history might explain why males and females occupy different parts of the burbot gut.

The occurrence of Echinorhynchus salmonis Müller, 1784 in benthic amphipods in the Baltic Sea.

The acanthocephalan Echinorhynchus salmonis Müller, 1784 is a common parasite of salmonid fish, but it has rarely been reported from an intermediate host. Samples of benthic amphipods, Monoporeia affinis (Lindström), were taken from multiple, deep sites (usually below 70 m) in the Gulf of Bothnia over the course of more than a decade and examined for acanthocephalans. Overall, only 0.44% of 23 296 amphipods were infected, all with just a single worm. This prevalence is consistent with several previous reports of acanthocephalans in deep-water, benthic amphipods, but it appears low compared to that often reported for acanthocephalan species infecting littoral amphipods. Parasite occurrence did not exhibit a clear regional pattern (i.e. northern vs southern sites) nor did it have any relationship with site depth. At sites sampled over multiple years, parasite abundance was consistently low (mostly < 0.01), though two spikes in abundance (over 0.06) were also observed, indicating that infection can be substantially higher at particular times or in particular places. The median density of E. salmonis in samples containing the parasite was estimated as 8.4 cystacanths per m(2).

Acetylcholinesterase activity in the host-parasite system of the cod Gadus morhua and acanthocephalan Echinorhynchus gadi from the southern Baltic Sea.

Acetylcholinesterase (AChE) activity measurement is widely used as a specific biomarker of neurotoxic effects. The aim of this study was to evaluate AChE activity in a host fish (the cod) and its acanthocephalan parasite Echinorhynchus gadi from the southern Baltic. AChE activity in hosts and parasites was inversely related: the highest cod AChE activity corresponded to the lowest E. gadi enzymatic activity and vice versa ("mirror effect"). This is the first report on the simultaneous application of this biomarker in cod and its acanthocephalan parasites. Results obtained for the host-parasite system are complementary and provide comprehensive information about the response of this biomarker. Analysis of the system allows for detection of a greater number of factors influencing AChE activity in the marine environment than separate analysis of the host and parasites. Thus, AChE activity measurement in a host-parasite system may be considered to be a promising tool for biomonitoring.

Metazoan endoparasites of Pygocentrus nattereri (Characiformes: Serrasalminae) in the Negro River, Pantanal, Brazil / Endoparasitas metazoários de Pygocentrus nattereri (Caraciformes: Serrasalminae) no rio Negro, Pantanal, Brasil

In the period of October 2007 to August 2008, 152 specimens of Pygocentrus nattereri were caught in the Negro River in the Nhecolândia region, central Pantanal wetland, State of Mato Grosso do Sul, Brazil. The specimens were necropsied and a total of 4,212 metazoan endoparasites were recovered, belonging to 10 taxons: Procamallanus (Spirocamallanus) inopinatus, Philometridae gen. sp., Eustrongylides sp., Brevimulticaecum sp., Contracaecum sp. (Nematoda), Echinorhynchus paranensis (Acanthocephala), Leiperia gracile, Sebekia oxycephala, Subtriquetra sp. 1 and Subtriquetra sp. 2 (Pentastomida). This is the first record of two parasite species from P. nattereri: E. paranensis and L. gracile.

No período de outubro de 2007 a agosto de 2008, 152 espécimes de Pygocentrus nattereri foram capturados no rio Negro na região da Nhecolândia, parte central do Pantanal, Mato Grosso do Sul, Brasil. Os espécimes foram necropsiados e um total de 4.212 endoparasitas metazoários foram colhidos, pertencentes a 10 táxons: Procamallanus (Spirocamallanus) inopinatus, Philometridae gen. sp., Eustrongylides sp., Brevimulticaecum sp., Contracaecum sp. (Nematoda), Echinorhynchus paranensis (Acanthocephala), Leiperia gracile, Sebekia oxycephala, Subtriquetra sp. 1 e Subtriquetra sp. 2 (Pentastomida). Este é o primeiro registro de duas espécies de parasitas em P. nattereri: E. paranensis e L. gracile.