Molecular phylogenetic analysis of the genus Gyrodactylus (Platyhelminthes: Monogenea) inferred from rDNA ITS region: subgenera versus species groups

Identification of a new species of Gyrodactylus von Nordmann, 1832 (Monogenoidea Gyrodactylidae) isolated from Diptychus maculatus in Yarkand River, Xinjiang, China

To investigate Gyrodactylus infection of fish in the river system of Xinjiang (China), Gyrodactylus individuals were isolated from specimens of Diptychus maculatus. Morphological characterization and phylogenetic analysis based on ITS1-5.8S-ITS2 rDNA locus revealed that the gyrodactylids belong to new species. Gyrodactylus diptychi n. sp. differs significantly in the morphology of the haptoral structures from 12 known species of Gyrodactylus found in fishes of the subfamily Schizothoracinae. In particular, G. diptychi n. sp. has a relatively short dorsal bar with thick and large ends, flat and straight hamuli roots, and small ventral bar processes. Furthermore, G. diptychi n. sp. is the only representative of Gyrodactylus found on D. maculatus. Using the BLASTn search of ITS1-5.8S-ITS2 rDNA sequences in GenBank and the Bayesian Information and Maximum Likelihood methods, we constructed phylogenetic trees for G. diptychi n. sp. As a result, our studies clearly identified that G. diptychi n. sp. was the first Gyrodactylus monogenean isolated from D. maculatus and a new species belonged to the subgenus Limnonephrotus.

Supplemental description of Gyrodactylus pseudorasborae (Gyrodactylidae) parasitic on topmouth gudgeon Pseudorasbora parva (Cyprinidae) in South China

Based on morphology and ITS sequence data, we identify and supplementally describe Gyrodactylus pseudorasborae Ondračková, Seifertová & Tkachenko, 2023 on the fins of topmouth gudgeon (Pseudoraspora parva) from freshwaters of southern China. The highest similarity (99.57% and 99.47%) to G. pseudorasborae suggested they were the same species. Prevalence and mean intensity were 45% and 2.3, respectively. The gyrodactylid species morphologically resembled G. pseudorasborae recorded from the same host species P. parva in Czech Republic, Ukraine, and Central China. But there were slight morphological differences in the shape and size of the marginal hook. Comparisons of marginal hook sickles of various Gyrodactylus species suggested that G. pseudorasborae and G. parvae were members of the G. wageneri-group. A molecular phylogeny of G. pseudorasborae with related species is presented and discussed within the context of the mechanism of local evolution of these sister species.

New species of Gyrodactylus von Nordmann, 1832 (Monogenoidea: Gyrodactylidae) from Gymnodiptychus dybowskii (Kessler, 1874) (Schizothoracinae) in the Kunes River (Yili River basin), China

Yili River system hosts a diverse fauna of fishes and parasites. Gymnodiptychus dybowskii is a rare and endangered aboriginal cold-water fish inhabit in the Yili river system. Our research identified a new species Gyrodactylus gymnodiptychi n. sp. isolated from G. dybowskii in the Kunes River (Yili River, China). Morphological comparison revealed identifiable differences between the new species and other parasites, including Gyrodactylus aksuensis, and Gyrodactylus tokobaevi, which are two known parasites living in G. dybowskii inhabit in the Aksu River west of Frunze (Kyrgyzstan), as well as Gyrodactylus montanus living in Shizothorax intermedius inhabited in the Tadzhikistan or Uzbekistan. Especially, the dorsal bar of G. gymnodiptychi n. sp. was raised at both ends with a hollow, and its hamulus roots were curved inward. The BLASTN search of GenBank did not detect any other ITS1-5.8S-ITS2 rDNA sequences same as G. gymnodiptychi's. Using the Bayesian Information and Maximum Likelihood methods to analyze the ITS1-5.8S-ITS2 rDNA gene sequences, we constructed phylogenetic trees for G. gymnodiptychi n. sp. Accordingly, our morphological and molecular research indicated that G. gymnodiptychi n. sp. was not only a new species of parasites but also the first Gyrodactylus member identified in the Yili River in China.

Oncoceratium amphidactylum n. gen. n. sp. (Monogenoidea: Gyrodactylidae) from Hoplosternum littorale (Hancock) (Siluriformes, Callichthyidae) from southeastern Brazil

Oncoceratium n. gen. is proposed to accommodate Oncoceratium amphidactylum n. gen. n. sp. (Monogenoidea, Gyrodactylidae). Although the proposed genus is monotypic, the differences presented in the diagnosis clearly establish it as distinct from species from other genera, such as Gyrodactylus von Nordmann, 1832 and especially those that occur exclusively in the Neotropical region. The new genus is diagnosed by the presence of a bulbous male copulatory organ, with one row of spinelets of similar sizes and shapes, while the only spine usually found in the gyrodactylids is absent or not differentiated; a haptor with anchors presenting points folded outwards, and superficial and deep roots continuous and indistinguishable; the absence of a deep bar; and hooks in two bilateral clusters of eight hooks. Oncoceratium amphidactylum n. gen. n. sp. is described from the tamboatá fish, Hoplosternum littorale (Hancock) (Callichthyidae), and is characterized by the presence of a pair of horn-shaped anchors with the point turned outwards, a superficial bar shield and absent deep bar, hooks disposed in bilateral lobes, and a MCO with no spine or with a row with large spinelets visible in place of the spine. In addition to the morphological features, distance analysis and Bayesian inference, based on 5.8s and partial ITS2, support placing the new species in a new genus, and not including it in a cluster of species of Gyrodactylus and near to Gyrodactyloides bychowskii Albova, 1948, Ieredactylus rivuli Schelkle et al., 2011 and Laminiscus gussevi (Bychowsky & Polyansky, 1953) Pálsson & Beverely-Burton, 1983.

Revealing the hidden diversity of Gyrodactylus communities (Monogenea, Gyrodactylidae) from Nearctic Catostomidae and Leuciscidae fish hosts (Teleostei, Cypriniformes), with descriptions of ten new species

Despite the high diversity of freshwater fishes in the Nearctic region, little is known about the composition of their parasite communities. We addressed the diversity of viviparous monogeneans of Gyrodactylus parasitizing highly diversified cypriniform fish inhabiting Nearctic watersheds. Nowadays, a thorough assessment of Gyrodactylus spp. diversity requires both morphological traits and genetic data. A combination of taxonomically important haptoral features and sequences of the ITS regions and 18S rDNA revealed 25 Gyrodactylus spp. parasitizing two catostomid and 15 leuciscid species sampled in six distinct localities in the United States and Canada. These include ten Gyrodactylus species recognized as new to science and described herein (G. ellae n. sp., G. hamdii n. sp., G. hanseni n. sp., G. huyseae n. sp., G. kuchtai n. sp., G. lummei n. sp., G. mendeli n. sp., G. prikrylovae n. sp., G. scholzi n. sp., and G. steineri n. sp.), seven already known species, and finally eight undescribed species. Overall, Nearctic Gyrodactylus spp. exhibited haptoral morphotypes known from fish hosts worldwide and those apparently restricted to Nearctic Gyrodactylus lineages like the typical ventral bar with a median knob and a plate-like membrane, or the additional filament attached to the handles of marginal hooks. The integrative approach further evidenced possible ongoing gene flow, host-switching in generalist Gyrodactylus spp., and regional translocation of monogenean fauna through fish introductions. The study highlights the hitherto underexplored morphological and genetic diversity of viviparous monogeneans throughout the Nearctic region.

The parasites of a successful invader: monogeneans of the Asian topmouth gudgeon Pseudorasbora parva, with description of a new species of Gyrodactylus

Monogenean parasites are often co-introduced with their fish hosts into novel areas. This study confirmed co-introduction of two dactylogyrids, Dactylogyrus squameus Gusev, 1955 and Bivaginogyrus obscurus (Gusev, 1955), and a newly described gyrodactylid species, Gyrodactylus pseudorasborae n. sp. into Europe along with their fish host, the invasive topmouth gudgeon Pseudorasbora parva (Temminck & Schlegel) from East Asia. All three species were observed in the lower Dnieper and middle Danube basin regions and had slightly larger haptoral hard parts than the same parasites in their native range. While dactylogyrids occurred sporadically, we recorded regular infection by G. pseudorasborae n. sp. at relatively high prevalence and abundance. This latter species was observed in both the native and non-native range of topmouth gudgeon, and resembles Gyrodactylus parvae You et al., 2008 recently described from P. parva in China. Both species were distinguished based on genetic analysis of their ITS rDNA sequence (6.6% difference), and morphometric differences in the marginal hooks and male copulatory organ. Phylogenetic analysis of dactylogyrid monogeneans showed that B. obscurus clustered with Dactylogyrus species parasitising Gobionidae and Xenocyprididae, including D. squameus, supporting recent suggestions of a paraphyletic origin of the Dactylogyrus genus. In addition to co-introduced parasites, topmouth gudgeon was infected with a local generalist, G. prostae Ergens, 1964, increasing the number of monogeneans acquired in Europe to three species. Nevertheless, monogenean infections were generally lower in non-native host populations, potentially giving an advantage to invading topmouth gudgeon.

Review of the metazoan parasites of the economically and ecologically important African sharptooth catfish Clarias gariepinus in Africa: Current status and novel records

One of the most widely distributed African freshwater fish is the African sharptooth catfish Clarias gariepinus (Burchell) that is naturally distributed in 8 of the 10 ichthyofaunal regions of this continent. Clarias gariepinus is a highly valued and cheap staple to local communities and an ideal aquaculture species. Consequently, interest in the parasitic communities of C. gariepinus has increased as parasites may accidentally be ingested by humans when eating uncooked fish or can be introduced into culture systems through fish stocks supplied from local rivers which affect yield, growth, and marketability. This review provides an overview of the ∼107 metazoan parasite species known to parasitise C. gariepinus in Africa and their general life cycles, morphology, paratenic and post-cyclic infections, and the biogeography and validity of records are discussed. A brief overview is included on the application of some of these parasites in environmental studies and their link to human health.

First isolation and scanning electron microscopy of haptoral sclerites of Macrogyrodactylus (Monogenea)

Macrogyrodactylus congolensis (Prudhoe, 1957) is one of six species of Macrogyrodactylus, all of which are endemic to Africa. This monogenean is a host-specific ectoparasite of the African sharptooth catfish, Clarias gariepinus (Burchell, 1822). It attaches to the host with a posterior haptor armed with sclerites. The specific morphology of sclerites is taxonomically significant and usually studied using light microscopy. The aim of the present study was to confirm the identification of macrogyrodactylid parasites using classic morphology (light microscopy of glycerine ammonium picrate mounted specimens) and molecular techniques (18S rDNA, ITS rDNA and cytochrome oxidase subunit 1 (COI) mtDNA). Additionally, the sclerites were accurately described with a technique not previously used for the genus, whereby haptoral sclerites were isolated by removing the encapsulating soft tissue with a digestion buffer and studied with scanning electron microscopy (SEM). Morphology and morphometry of studied specimens corresponded to available data for M. congolensis, confirming the identity of the parasite. All previous descriptions were summarized in a table and discrepancies discussed. Molecular analysis also confirmed the specimens to be M. congolensis, but ITS rDNA and COI mtDNA was more reliable than 18S rDNA in this regard. The isolation of haptoral sclerites and their study using SEM was successful, resolving the morphology of all sclerites. This study provided the first reconstruction of the haptor of a Macrogyrodactylus species following SEM analysis, as well as the first mtDNA for M. congolensis. Further study of isolated haptoral sclerites of other macrogyrodactylids is required to determine the full benefits of studying their isolated sclerites.

Description of Gyrodactylus banmae n. sp. (Monogenea, Gyrodactylidae) parasitic on zebrafish, Danio rerio

A new species of Gyrodactylus was described on the body surface of zebrafish (Danio rerio) in China. Basing on morphological characteristics and ITS sequence, we identified the parasite as a new member of the Gyrodactylus-wageneri group. Morphologically, Gyrodactylus sp. nov. is greatly similar to "G. zebrae", another species parasitic on zebrafish: both have moderately stout hamulus, marginal hook sickle with a prominent heel and toe, as well as a curved blade. However, distinct haptoral shape differences were detected between these two species. The dorsal bar is straight in Gyrodactylus sp. nov. but strongly curved in "G. zebrae", and the sickle shaft in Gyrodactylus sp. nov. is approximately perpendicular to the base, but in "G. zebrae" it is slanted downwards. The ITS1-5.8S-ITS2 sequence also indicate that Gyrodactylus sp. nov. exhibits the highest similarity to "G. zebrae": 95.7% sequence identity suggests interspecific differentiation. Phylogenetic analysis of the ITS1-ITS2 sequence showed that Gyrodactylus sp. nov. formed a sister clade with "G. zebrae", and exhibited a relatively close phylogenetic relationship with G. kobayashii, G. gurleyi, and G. longoacuminatus, all of which parasitise on goldfish, Carassius auratus. To test the susceptibility of zebrafish and goldfish to the Gyrodactylus sp. nov., ten gyrodactylids were inoculated to the caudal fin of zebrafish and goldfish. The gyrodactylids exhibited the ability to attach themselves to the goldfish, and some gyrodactylids reproduced a few days after the inoculation. On day 9, however, the mean abundance sharply decreased to zero on goldfish and increased to more than 30 on zebrafish. The result suggested that golfish is an unsuitable host for Gyrodactylus sp. nov. Therefore, on the basis of morphology, molecular sequence similarity, and host susceptibility, we conclude that the gyrodactylid found on the zebrafish is a new species, which we named Gyrodactylus banmae.

Novel distribution records and molecular data for species of Macrogyrodactylus Malmberg, 1957 (Monogenea: Gyrodactylidae) from Clarias gariepinus (Burchell) (Siluriformes: Clariidae) in southern Africa

The viviparous gyrodactylid genus Macrogyrodactylus Malmberg, 1957 is endemic to Africa, composed of nine species from hosts of four freshwater fish families, including catfishes (Siluriformes: Clariidae). Three species, Macrogyrodactylus clarii Gussev, 1961; M. congolensis (Prudhoe, 1957) and M. karibae Douëllou et Chishawa, 1995, are primarily known to parasitise the African sharptooth catfish Clarias gariepinus (Burchell) in various African countries. From November 2017 to September 2019, a total of 184 individuals of C. gariepinus were collected from selected localities in southern Africa and their skin, fins and gills were surveyed for monogeneans. Three species of Macrogyrodactylus (M. clarii, M. congolensis and M. karibae) were found parasitising C. gariepinus from five localities in South Africa and Zambia. Overall prevalence was 50% to 100% with intensities of up to 109 parasites per host individual. New locality records in southern Africa, morphological observations and additional molecular data on the complete Internal Transcriber Spacer (ITS-1-5.8S-ITS-2) regions of the rDNA gene for the three gyrodactylid species are presented in this study.

Description of Tresuncinidactylus wilmienae gen. et sp. n. (Monogenea: Gyrodactylidae), from the gills of the bulldog, Marcusenius macrolepidotus (Peters) from Lake Kariba, Zimbabwe

The African continent has a rich diversity of fish and amphibians in its inland water systems that serve as hosts for monogeneans of seven genera of the Gyrodactylidae van Beneden et Hesse, 1832. In August 2011, eight gyrodactylid parasites were collected from the gills of two specimens of bulldog, Marcusenius macrolepidotus (Peters), from Lake Kariba, Zimbabwe. Morphometric evaluation and sequencing of 18S rDNA confirmed that the specimens represented a species of a new viviparous genus, Tresuncinidactylus wilmienae gen. et sp. n. The attachment apparatus consists of a single pair of large slender hamuli with prominently flattened roots that are connected by a simple, narrow dorsal bar. The ventral bar is small and possesses a thin lingulate membrane but no evident anterolateral processes. There are 16 marginal hooks of one morphological type, but of three different sizes, with large falculate sickles that are proportionaly equal in length to the length of their handles. The two largest pairs of marginal hooks are positioned closest to the opisthaptoral peduncle, the neighbouring two pairs of medium-sized marginal hook sickles are situated along the lateral margins of the opisthaptor. Four pairs of smallest marginal hooks are positioned along the posterior margin of the opisthaptor. The male copulatory organ consists of a muscular pouch armed with approximately 30 gracile spines. Phylogenetic analyses of partial sequences of the 18S rDNA using Maximum Likelihood and Bayesian Inference placed the new genus within the lineage of solely African genera and suggests Afrogyrodactylus Paperna, 1968, Citharodactylus Přikrylová, Shinn et Paladini, 2017 and Mormyrogyrodactylus Luus-Powell, Mashego et Khalil, 2003 as genera most closely related to the new genus.

A new monogenean species, Gyrodactylus ajime n. sp. (Gyrodactylidae), parasitic on Niwaella delicata (Niwa), an endemic loach of Japan

A new gyrodactylid species, Gyrodactylus ajime n. sp., is described from the skin and fins of an endemic and commercially important loach Niwaella delicata (Niwa) (Cypriniformes: Cobitoidea: Cobitidae), from the upper reach of the River Yura in Ashiu, Kyoto Prefecture, Japan with scanning electron microscopy observations and molecular data. This species can be distinguished from congenerics by characteristics of the sickle of the marginal hook: the sickle proper is composed of two straight sections and a curved section; its short point extends beyond the limit of the toe and is directed downwards; and the upper corner of heel angular is slightly raised. There are 31 species and subspecies of native loaches (Cobitoidea) known from Japan, of which 25 are red-listed nationally, and two are commercially important. I reviewed all reports of monogeneans from Japanese loaches, and found that only five fish species have been recorded as hosts of these parasites. This suggests that the parasite fauna of these fishes is poorly described. It is urgent to thoroughly describe the monogenean parasites of loaches in Japan as some of the parasite species may be threatened with co-extinction because their hosts are threatened, and to understand any negative impacts on commercially important fish species.

Gyrodactylus molweni sp. n. (Monogenea: Gyrodactylidae) from Chelon richardsonii (Smith, 1846) (Mugilidae) from Table Bay, South Africa

Gyrodactylus molweni sp. n. is described from the body surface and fins of the South African mullet, Chelon richardsonii (Smith, 1846) collected from Table Bay Harbour, Cape Town and is compared to five other Gyrodactylus species described from grey mullets globally namely G. zhukovi Ling, 1963 and G. mugili Zhukov, 1970 from Planiliza haematocheila (Temminck and Schlegel, 1845); G. mugelus Rawson, 1973 from Mugil cephalus L.; G. curemae Conroy and Conroy, 1985 from Mugil curema Valenciennes, 1836 and G. xiamenensis Zang,Yang and Liu, 2001 from Planiliza macrolepis (Smith, 1846). Morphologically, G. molweni sp. n. has prominent ventral bar processes that near cover the hamulus roots, marginal sickles with large rhomboid heels, slender shafts and fine points that extend beyond the sickle toes. Gyrodactylus molweni sp. n. can, however, be readily differentiated: G. mugili and G. xiamenensis have ventral bars with small ventral processes; G. zhukovi has marginal hooks sickles with slender shafts and proportionately short points and open-faced blades; G. mugelus possesses marginal hook sickles with deep, rounded heels, forward slanting shafts and an angular, square line to the inner face of the blades. Although the length of the marginal hooks of G. curemae are similar to G. molweni sp. n., their hamuli are double the size. A GenBank BlastN search with the 931 bp sequence covering ITS1, 5.8S and ITS2 gave no close hits; the nearest species for which sequences are available is G. nipponensis Ogawa and Egusa, 1978 (identity 96.56%, 899/931 bp). The proposal of G. molweni sp. n. as a new species, therefore, is well supported by both the molecular and morphological analyses presented herein. This Gyrodactylus species is the first to be described from C. richardsonii and only the second Gyrodactylus species to be described from the marine environment off the African continent.

Morphological and molecular characterisation of a new species of Gyrodactylus von Nordmann, 1832 (Monogenoidea: Gyrodactylidae) of cichlid fishes (Perciformes) from Mexico

Gyrodactylus mojarrae n. sp. is described from the gills of the Neotropical cichlids Thorichthys maculipinnis, Rocio octofasciata, Vieja zonata and V. fenestrata from several localities across southern Mexico. The new species is erected on the basis of the morphology of the haptoral elements (anchors, bars and hooks), and its phylogenetic position within the Gyrodactylidae is evaluated based on the analysis of partial sequences of the ITS1, 5.8 rRNA gene and ITS2. Gyrodactylus mojarrae n. sp. differs from other congeneric species by having hooks with a straight shaft and recurved point, pointed toe and convex heel, presence of reduced superficial anchor roots, by the number and disposition of spinelets of the male copulatory organ, and the absence of shield and lateral processes of the superficial bar. Molecular circumscription of isolates of G. mojarrae n. sp. from different host and hydrological basins showed that these isolates are conspecific and represent a distinct lineage from other congeners, including newly sequenced isolates of Gyodactylus sp. A and Gyrodactylus sp. B from Astyanax mexicanus (Characidae) and Gobiomorus dormitor (Eleotridae), respectively. Genetic affinities of Gyodactylus sp. A and B indicate that they might represent undescribed species infecting freshwater fish from the Americas.

An amended description of two Gyrodactylus species (Platyhelminthes: Monogenea) parasitizing Antarctic Notothenioid fish

Species identification based on the morphometry of opisthaptoral hard parts, in combination with internal transcribed spacer ribosomal DNA (ITS rDNA) region sequences, confirmed the presence of four viviparous Gyrodactylus von Nordman, 1832 (Plathyhelminthes, Monogenea) species on Nototheniid fish from the Prince Gustav Channel (Weddell Sea, Antarctica). Gyrodactylus antarcticus Gusev, 1967 was found mostly on Trematomus newnesi Boulenger (93 specimens) but also on T. bernacchii Boulenger (one specimen), the latter representing a new host record for this species. Gyrodactylus byrdi Hargis & Dillon, 1968 and G. coriicepsi Rokicka, Lumme & Ziętara, 2009 were recorded on their type hosts, T. newnesi and Notothenia coriiceps Richardson, respectively. Gyrodactylus wilkesi Hargis & Dillon, 1968 was found mostly on the fins of T. bernacchii (29 specimens), but also on T. hansoni Boulenger (one specimen) and T. newnesi (three specimens). The finding of G. wilkesi on T. newnesi represents a new host record. The low number of Gyrodactylus specimens may indicate an accidental infection. The occurence of all four Gyrodactylus species in the Prince Gustav Channel represents a new locality record. According to phylogentic methods, the newly redescribed monogeneans belong to the Antarctic lineage, forming a sister group to North American and European marine Gyrodactylus species, and consist of two species groups, one comprising G. coriicepsi and G. nudifronsi Rokicka, Lumme & Ziętara, 2009, and the other G. anarcticus and G. wilkesi.

Ancient and modern genome shuffling: Reticulate mito-nuclear phylogeny of four related allopatric species of Gyrodactylus von Nordmann, 1832 (Monogenea: Gyrodactylidae), ectoparasites on the Eurasian minnow Phoxinus phoxinus (L.) (Cyprinidae)

Phylogenetic analyses including four allopatric species of Gyrodactylus von Nordmann, 1832 on the Eurasian minnow Phoxinus phoxinus (L.) (Cyprinidae) revealed incongruence between the nuclear ITS1-5.8S-ITS2 and mitochondrial cox1 phylogenies due to ancient hybridisation. Gyrodactylus pannonicus Molnár, 1968 was sampled close to its type-locality, the upper reaches of River Tisza, tributary of Danube in the Black Sea Basin. Faunistic search detected three new related species with maximum composite likelihood distances in cox1 between 16.8-23.2% (tentatively 1.3 to 1.8 My of divergence). Gyrodactylus albolacustris n. sp. recorded in the White Sea Basin, eastern Baltic Basin and Mongolia was close to G. pannonicus in the nuclear ITS (divergence of 0.9%), but diverged in cox1 by 19.8%. The Mongolian isolate of G. albolacustris n. sp. diverged from the European isolates in cox1 by 8.9%, suggesting 0.7 My of isolation. The two other new species differed from G. pannonicus by >4% in ITS and some large indels in ITS1, and by >20% in cox1. Gyrodactylus danastriae n. sp. was found in River Strwiąż, a tributary of the River Dniester (Black Sea Basin) and was characterised by smaller size of anchors and by 29-41 bp dimorphic insertion in ITS1. Gyrodactylus botnicus n. sp. is considered endemic in the Baltic Basin, but was also found in the White Sea Basin as a postglacial immigrant, where it had hybridised with G. albolacustris n. sp. in spite of the high divergence in ITS (3.9%) and cox1 (22%). The discordant nuclear and mitochondrial phylogenies revealed an ancient mitochondrial introgression: G. albolacustris n. sp. was derived from a hybridisation combining proto-pannonicus ITS with proto-danastriae mitochondria, perhaps 1.3 My ago. The postglacial hybridisation of G. albolacustris n. sp. (as the donor of mtDNA^alb and ITS^alb) and G. botnicus n. sp. (donor of the ITS^bot) offered a model of shuffling of the genomic components: the process of the homogenisation and stabilisation of nuclear ITS (concerted evolution) and the lineage sorting has hardly begun.

Supplementary studies on Anacanthorus penilabiatus and Mymarothecium viatorum (Monogenea: Dactylogyridae) from Piaractus mesopotamicus (Characiformes: Serrasalmidae) in Brazil

The dactylogyrid monogeneans Anacanthorus penilabiatus (Boeger, Husak and Martins, 1995) and Mymarothecium viatorum(Boeger, Piasecki and Sobecka, 2002), commonly found in large quantities in farmed Piaractus mesopotamicus (Holmberg, 1887) in Brazil, were collected from three fish farms located in the State of São Paulo, Brazil. Morphological and molecular identification, scanning electron microscopy, histopathological and descriptive parameters data were performed. A total of 278 specimens of P. mesopotamicus were gathered from February 2008 and July 2010. Prevalence (P) and mean intensity of infection (MII) data was taken at each location. The data showed prevalence and mean intensity of infection annually, with numbers such as P = 91.2% and MII = 50 worms/fish (Pirassununga), P = 60% and MII = 39.2 worms/fish (Mogi Mirim), and P = 100% and MII = 204.8 worms/fish (Itapira). Histopathological results showed hyperplasia of the secondary lamellae, and hypersecretion of mucus was also observed. A phylogenetic topology was inferred using complete SSU (18S) ribosomal rDNA, positioning Anacanthorus penilabiatus and Mymarothecium viatorum among other monopisthocotyleans available in GenBank.

An infection of Gyrodactylus kobayashii Hukuda, 1940 (Monogenea) associated with the mortality of goldfish (Carassius auratus) from central China

Goldfish, Carassius auratus, widely distributed across Eurasia, is one of the earliest fish domesticated for ornamental purposes. A series of diseases break out due to high-density culture of goldfish, causing significant economic losses. Here, we report for the first time an infection of Gyrodactylus kobayashii associated with the high mortality of goldfish from a fish farm in Anziying township of Henan province, China, following their transfer to several aquariums. In the first 2 weeks after goldfish (n = 4200, weight 10.24 ± 1.45 g) transfer to aquariums, a total of 3335 goldfish were lost, representing 79.4 % of the initial stocked biomass. The examination showed that no other pathogens were found in this batch of fishes, except for G. kobayashii. The high burdens of G. kobayashii/fish (264.7, range 100-450) were the primary reason for the high mortality, although this was not the sole cause. In addition, the isolate of G. kobayashii from goldfish (C. auratus) in Henan province of central China was described. The morphological characterization was performed using morphometric measurements and drawings of opisthaptoral hard parts of the parasites. The molecular description was performed based on phylogenetic analysis of a reference DNA sequence spanning 5.8S and ITS-2. Importantly, the present study provides for the first time a full 25 point-to-point morphometric measurements and high-resolution images of attachment organ of G. kobayashii.

The mitochondrial genome of Paragyrodactylus variegatus (Platyhelminthes: Monogenea): differences in major non-coding region and gene order compared to Gyrodactylus

BACKGROUND

Paragyrodactylus Gvosdev and Martechov, 1953, a viviparous genus of ectoparasite within the Gyrodactylidae, contains three nominal species all of which infect Asian river loaches. The group is suspected to be a basal lineage within Gyrodactylus Nordmann, 1832 sensu lato although this remains unclear. Further molecular study, beyond characterization of the standard Internal Transcribed Spacer region, is needed to clarify the evolutionary relationships within the family and the placement of this genus.

METHODS

The mitochondrial genome of Paragyrodactylus variegatus You, King, Ye and Cone, 2014 was amplified in six parts from a single worm, sequenced using primer walking, annotated and analyzed using bioinformatic tools.

RESULTS

The mitochondrial genome of P. variegatus is 14,517 bp, containing 12 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes and a major non-coding region (NCR). The overall A + T content of the mitochondrial genome is 76.3%, which is higher than all reported mitochondrial genomes of monogeneans. All of the 22 tRNAs have the typical cloverleaf secondary structure, except tRNACys, tRNASer1 and tRNASer2 that lack the dihydrouridine (DHU) arm. There are six domains (domain III is absent) and three domains in the inferred secondary structures of the large ribosomal subunit (rrnL) and small ribosomal subunit (rrnS), respectively. The NCR includes six 40 bp tandem repeat units and has the double identical poly-T stretches, stem-loop structure and some surrounding structure elements. The gene order (tRNAGln, tRNAMet and NCR) differs in arrangement compared to the mitochondrial genomes reported from Gyrodactylus spp.

CONCLUSION

The Duplication and Random Loss Model and Recombination Model together are the most plausible explanations for the variation in gene order. Both morphological characters and characteristics of the mitochondrial genome support Paragyrodactylus as a distinct genus from Gyrodactylus. Considering their specific distribution and known hosts, we believe that Paragyrodactylus is a relict freshwater lineage of viviparous monogenean isolated in the high plateaus of central Asia on closely related river loaches.

Phylogeny of the Atlantic and Pacific species of Ligophorus (Monogenea: Dactylogyridae): morphology vs. molecules

Within ectoparasitic fish monogeneans, the genus Ligophorus contains a high number of species from which several were recently described. The precise determination of their taxonomic status requires robust diagnostic morphologic features that rely predominantly on a restricted set of sclerotized structures. In the present study, these morphological characters were used for the reconstruction of a phylogenetic tree, which was compared with a tree built from molecular data (28S and ITS1 DNA sequences). Thirty-eight morphological characters were used in 29 species of Ligophorus from the Atlantic and Pacific regions and 5 species within close genera of Dactylogyridae. The morphological and molecular phylogenetic trees are congruent and suggest that the genus Ligophorus is monophyletic, and that species parasitizing Liza spp. and Chelon labrosus occupy basal positions. The present study suggests that host switching is a common event in this host-parasite association, because about half of the species infecting the same host species are not close relatives. Following host switching, dispersal with vicariance is probably an important force shaping the present distribution and diversity of Ligophorus. The pattern of occurrence of Ligophorus spp. on Mugil cephalus supports that reproductive isolation and therefore parallel speciation are taking place among these parasitic organisms.

Tiny worms from a mighty continent: high diversity and new phylogenetic lineages of African monogeneans

The family Gyrodactylidae contains one of the most significant radiations of platyhelminth fish parasites. The so-called hyperviviparity is very rare in the animal kingdom, and the rapid generation time can lead to an explosive population growth, which can cause massive losses in farmed fish. Here we present the first molecular phylogeny including all-but-one African genera, inferred from ITS and 18S rDNA sequences. The validity of nominal genera is discussed in relation to the systematic value of morphological characters traditionally used for generic identification. New complete 18S rDNA sequences of 18 gyrodactylid species of eight genera together with ITS rDNA gene sequences of eight species representing seven genera were generated and complemented with GenBank sequences. The maximum likelihood and Bayesian analyses pointed to a paraphyletic nature of African Gyrodactylus species. They formed well-supported clades possibly indicating speciation within host taxa: (1) parasites of cichlids (Cichlidae); (2) parasites of catfishes (Siluriformes), consisting of a lineage infecting mochokids and one infecting clariids. Macrogyrodactylus spp. firmly clustered into a monophyletic group. We found that Swingleus and Fundulotrema are very closely related and clearly cluster within Gyrodactylus. This supports earlier claims as to the paraphyly of the nominal genus Gyrodactylus as it is currently defined, and necessitates a revision of Swingleus and Fundulotrema. Molecular dating estimates confirmed a relatively young, certainly post-Gondwanan, origin of gyrodactylid lineages. Building on the previously suggested South-American origin of viviparous gyrodactylids, the dataset suggests subsequent intercontinental dispersal to Africa and from there repeated colonisation of the Holarctic. Even though the African continent has been heavily under sampled, the present diversity is far greater than in the intensively studied European fauna, probably because of the high endemicity of sub-Saharan Africa.

A monogenean fish parasite, Gyrodactylus chileani n. sp., belonging to a novel marine species lineage found in the South-Eastern Pacific and the Mediterranean and North Seas

Gyrodactyluschileani n. sp. is the first Gyrodactylus species reported from Chile. It is an ectoparasite living on fins and skin of a small fish, the Chilean tidal pond dweller Helcogrammoides chilensis (Cancino) (Perciformes: Tripterygiidae). A phylogenetic analysis based on 5.8S+ITS2 of rDNA placed the new species close to marine Gyrodactylus species found in Europe: G. orecchiae Paladini, Cable, Fioravanti, Faria, Cave & Shinn, 2009 on gilthead seabream Sparus aurata L. from the Adriatic and Tyrrhenian Sea fish farms (Perciformes: Sparidae), and an undescribed species on the black goby Gobius niger L. from the North Sea (Perciformes: Gobiidae). A morphological description of the latter species is unavailable. These geographically distant parasite samples on different host families form a new well supported Gyrodactylus orecchiae lineage. Using molecular phylogenetics, it is shown that the marine species groups of Gyrodactylus may have a worldwide distribution.

Molecular phylogeny of species of Ligophorus (Monogenea: Dactylogyridae) and their affinities within the Dactylogyridae

The taxonomic framework of Ligophorus, monogenean specialists of the gills of grey mullets (Mugilidae), is evaluated and its interspecific relationships are assessed for the first time using molecular data. The position of Ligophorus within the paraphyletic Ancyrocephalinae is re-assessed based on newly sequenced species. Furthermore, the relationship between morphometric and genetic interspecific similarities is evaluated. Partial 28S and complete ITS1 rDNA sequences from representatives of 14 of the 16 nominal species of Ligophorus from the Mediterranean, Black and Azov Seas were analysed together with published sequences of members of the Dactylogyridae. The phylogenetic analyses of the Dactylogyridae (i) confirmed the position of Ligophorus within the marine Ancyrocephalinae; (ii) revealed a sister relationship between Ergenstrema and Ligophorus, whose species are all exclusive parasites of grey mullets; and (iii) substantiated the affinities of Ergenstrema with the marine Ancyrocephalinae. The phylogenetic analysis restricted to Ligophorus confirmed the distinct status of the included species. The ITS1 region provided the highest divergence between species and phylograms with the strongest branch support. Both the 28S and ITS1 phylograms revealed two main clades. One included species from hosts with Mediterranean and NE Atlantic distribution and another was formed by species parasitising several Liza spp., including Lz. haematocheilus from the Northwestern Pacific, and Mugil cephalus, which suggests an origin outside the Mediterranean for the latter clade. The phylogenetic evidence presented herein indicated that a combination of host-switching and lineage duplication events accounted for the diversification of this genus in the Mediterranean basin. The agreement between molecular and morphological interspecific similarities observed in Ligophorus supports the validity of morphometric characters used for species identification.

Molecular phylogeny of Gyrodactylus (Monogenea) parasitizing fishes in fresh water, estuarine, and marine habitats in Canada

Gyrodactylus Nordmann, 1832 is a genus of monogenean flatworms that is well-studied in Europe and best known for the destructive pathogen of Atlantic salmon, Gyrodactylus salaris Malmberg, 1957. However, there is a paucity of information on species of Gyrodactylus occurring elsewhere despite that the genus is thought to be extremely speciose. Here we present the first major molecular phylogeny of Gyrodactylus using samples from host fishes in North America. Our aims were to characterize species and molecular diversity of North American Gyrodactylus to allow a determination of their evolutionary relationship with congenerics sampled from Europe. Specimens belonging to 25 species of Gyrodactylus and closely related species from Canada and the northern United States of America were identified using morphology and sequenced at 18S rDNA and ITS2 rDNA (totaling ca. 1430 bp). Significant molecular groups in North American Gyrodactylus were found to correspond to a major division in the genus based on the structure of the male copulatory organ. Results corroborate earlier findings suggesting that the genus Fundulotrema Kritsky and Thatcher, 1977, traditionally thought to be distinct from Gyrodactylus owing to the presence of a peduncular bar, falls within Gyrodactylus. The usefulness and application of the broadly conserved 18S primers as a standard tool for Gyrodactylus taxonomy is discussed and advocated.

First description of monogenean parasites in Lake Tanganyika: the cichlid Simochromis diagramma (Teleostei, Cichlidae) harbours a high diversity of Gyrodactylus species (Platyhelminthes, Monogenea)

Lake Tanganyika harbours the most diverse endemic cichlid fish assemblage of Africa, but its monogenean fish parasites have not been investigated. Here we report, for the first time, on the Gyrodactylus parasites in this hotspot of fish biodiversity. Haptor morphometrics and nuclear ribosomal DNA sequences revealed 3 new species on Zambian Simochromis diagramma: Gyrodactylus sturmbaueri n. sp., G. thysi n. sp. and G. zimbae n. sp. Their distinct morphology and strong genetic differentiation suggest that they belong to distant lineages within the genus Gyrodactylus, and phylogenetic reconstructions suggest affinities with other genera of gyrodactylids. Additional U-shaped haptoral plates in G. thysi n. sp. and a second large spine-like structure in the male copulatory organ of G. zimbae seem to represent new features for the genus. Such large diversity on a single host species can probably be explained by host-switching events during the course of evolution, in agreement with the generally accepted concept that ecological transfer is an important aspect of gyrodactylid speciation. Additional parasitological surveys on other host species, covering a broader phylogenetic and geographical range, should clarify the evolutionary history of Gyrodactylidae on cichlids in the African Great Lake and other parts of Africa.

The description of Gyrodactylus corleonis sp. n. and G. neretum sp. n. (Platyhelminthes: Monogenea) with comments on other gyrodactylids parasitising pipefish (Pisces: Syngnathidae)

The current work describes two new species of Gyrodactylus von Nordmann, 1832 collected from pipefish Syngnathus scovelli (Evermann et Kendall) and Syngnathus typhle L. during two separate gyrodactylosis episodes on fish held in a public aquarium located in northern Italy. The gyrodactylids collected from the skin, fins and gills of pipefish were subjected to a morphological analysis of the attachment hooks and the morphometric data were compared to the four species of Gyrodactylus previously described from syngnathid hosts, namely G. eyipayipi Vaughan, Christison, Hansen et Shinn, 2010, G. pisculentui Williams, Kritsky, Dunnigan, Lash et Klein, 2008, G. shorti Holliman, 1963 and G. syngnathi Appleby, 1996. Principal components analysis (PCA) of the morphological data indicated six clusters; two discrete groups among the specimens taken from the pipefisli held in the Italian aquarium and four further groups representing G. eyipayipi, G. pisculentus, G. shorti and G. syngnathi. Molecular sequences of the ribosomal internal transcribed spacers (ITS1 and ITS2) and the 5.8S gene for the new species considered here were then compared with those available for other species in GenBank. The comparison did not reveal any identical match, supporting the morphological analysis that Gyrodactylus corleonis sp. n. from S. typhle and Gyrodactylus neretum sp. n. from S. scovelli represent distinct species. Both G. corleonis and G. neretum possess robust hamuli, marginal hook blades that curve smoothly from their sickle base to a point beyond the toe and, ventral bars with a broad median portion and a reduced membrane. Gyrodactylus corleonis, however, can be distinguished on the basis of its heart-shaped ventral bar; G. neretum has a 1:2 hamulus point:shaft ratio and a rectangular-shaped ventral bar. A redescription of the haptoral hard parts of the four species previously recorded on pipefish is also presented.

Parasite hybridization in African Macrogyrodactylus spp. (Monogenea, Platyhelminthes) signals historical host distribution

Macrogyrodactylus spp. from the gills of Clarias gariepinus in Zimbabwe and Kenya, and C. anguillaris in Senegal were identified using haptoral sclerite morphology and by sequencing the nuclear ribosomal DNA internal transcribed spacers (ITS) 1 and 2, partial 18S and the complete 5·8S rRNA gene. A molecular phylogeny was constructed using all sequenced Macrogyrodactylus species to date. Based on morphology, Macrogyrodactylus congolensis, M. heterobranchii, M. clarii, and M. karibae were identified, with one specimen from Zimbabwe displaying morphological features that were intermediate between M. heterobranchii and M. clarii. In the intermediate form, the partial 18S and ITS1 sequence was identical to that of M. clarii while the remaining ITS1 and complete ITS2 region was almost identical to M. heterobranchii as was the partial cox1 fragment, thus strongly suggesting a hybrid origin. At present, the catfish host of M. heterobranchii and M. clarii do not co-occur in southern Zimbabwe; this hybridization event is therefore proof of historical sympatry of both fish species.

Morphometric comparison of three members of the Gyrodactylus nemachili-like species group (Monogenea: Gyrodactylidae) on Barbatula barbatula L. in the Czech Republic, with a reinstatement of G. papernai Ergens & Bychowsky, 1967

The Gyrodactylus nemachili-like species complex, parasitising stone loach Barbatula barbatula L. in the Czech Republic, was investigated based on the detailed morphometric analysis of its haptoral hard parts. The existence of two species, G. jiroveci Ergens & Bychowsky, 1967 and G. pseudonemachili Ergens & Bychowsky, 1967 was confirmed. A standard discriminant analysis of the morphometric data showed a clear separation between specimens of G. jiroveci and another species or variant. Based on the morphology of the haptoral hard parts, this third species was more similar to G. jiroveci than to G. pseudonemachili. The differences between G. jiroveci and the third species were mainly in the morphology of the marginal hook sickle, but included the total length of the marginal hook, the length of the hamulus point, the length of the marginal hook sickle, the width of the ventral bar, and the width of the dorsal bar. Based on comparison with the original material, the third species was identified as G. papernai Ergens & Bychowsky, 1967, which has recently been considered a synonym of G. jiroveci. These analyses provided sufficient evidence for the restoration of G. papernai as a valid taxon. Partial sequences of the internal transcribed spacer rRNA genes (ITS rDNA) verified the validity of all three Gyrodactylus species studied.

The biology of gyrodactylid monogeneans: the "Russian-doll killers"

This article reviews the history of gyrodactylid research focussing on the unique anatomy, behaviour, ecology and evolution of the viviparous forms while identifying gaps in our knowledge and directions for future research. We provide the first summary of research on the oviparous gyrodactylids from South American catfish, and highlight the plesiomorphic characters shared by gyrodactylids and other primitive monogeneans. Of these, the most important are the crawling, unciliated larva and the spike sensilla of the cephalic lobes. These characters allow gyrodactylids to transfer between hosts at any stage of the life cycle, without a specific transmission stage. We emphasise the importance of progenesis in shaping the evolution of the viviparous genera and discuss the relative extent of progenesis in the different genera. The validity of the familial classification is discussed and we conclude that the most significant division within the family is between the oviparous and the viviparous genera. The older divisions into Isancistrinae and Polyclithrinae should be allowed to lapse. We discuss approaches to the taxonomy of gyrodactylids, and we emphasise the importance of adequate morphological and molecular data in new descriptions. Host specificity patterns in gyrodactylids are discussed extensively and we note the importance of host shifts, revealed by molecular data, in the evolution of gyrodactylids. To date, the most closely related gyrodactylids have not been found on closely related hosts, demonstrating the importance of host shifts in their evolution. The most closely related species pair is that of G. salaris and G. thymalli, and we provide an account of the patterns of evolution taking place in different mitochondrial clades of this species complex. The host specificity of these clades is reviewed, demonstrating that, although each clade has its preferred host, there is a range of specificity to different salmonids, providing opportunities for complex patterns of survival and interbreeding in Scandinavia. At the same time, we identify trends in systematics and phylogeny relevant to the G. salaris epidemics on Atlantic salmon in Norway, which can be applied more generally to parasite epidemiology and evolution. Although much of gyrodactylid research in the last 30 years has been directed towards salmonid parasites, there is great potential in using other experimental systems, such as the gyrodactylids of poeciliids and sticklebacks. We also highlight the role of glacial lakes and modified river systems during the ice ages in gyrodactylid speciation, and suggest that salmon infecting clades of G. salaris first arose from G. thymalli in such lakes, but failed to spread fully across Scandinavia before further dispersal was ended by rising sea levels. This dispersal has been continued by human activity, leading to the appearance of G. salaris as a pathogen in Norway. We review the history and current status of the epidemic, and current strategies for elimination of the parasite from Norway. Finally, we consider opportunities for further spread of the parasite within and beyond Europe.

The mitochondrial genome of Gyrodactylus salaris (Platyhelminthes: Monogenea), a pathogen of Atlantic salmon (Salmo salar)

In the present study, we describe the complete mitochondrial (mt) genome of the Atlantic salmon parasite Gyrodactylus salaris, the first for any monogenean species. The circular genome is 14 790 bp in size. All of the 35 genes recognized from other flatworm mitochondrial genomes were identified, and they are transcribed from the same strand. The protein-coding and ribosomal RNA (rRNA) genes share the same gene arrangement as those published previously for neodermatan mt genomes (representing cestodes and digeneans only), and the genome has an overall A+T content of 65%. Three transfer RNA (tRNA) genes overlap with other genes, whereas the secondary structure of 3 tRNA genes lack the DHU arm and 1 tRNA gene lacks the TΨC arm. Eighteen regions of non-coding DNA ranging from 4 to 112 bp in length, totalling 278 bp, were identified as well as 2 large non-coding regions (799 bp and 768 bp) that were almost identical to each other. The completion of the mt genome offers the opportunity of defining new molecular markers for studying evolutionary relationships within and among gyrodactylid species.

FIRST REPORT OF GYRODACTYLUS SPP. (PLATYHELMINTHES: MONOGENEA) IN THE WESTERN MEDITERRANEAN SEA: MOLECULAR AND MORPHOLOGICAL DESCRIPTIONS

The Gyrodactylus spp. fauna on species of gobies, Pomatoschistus, Gobiusculus, and Knipowitschia (Gobiidae: Teleostei), from the western Mediterranean and Adriatic seas is strikingly similar to that found in the Baltic Sea and eastern Atlantic Ocean, both in morphology and in internal transcribed spacer (ITS) rRNA. The fauna consisted of Gyrodactylus branchialis, G. ostendicus, G. gondae, G. rugiensis, G. rugiensoides, and G. arcuatus. No new species have been found. A morphometric comparison between G. branchialis from the Mediterranean and Adriatic seas and its type locality in Ostend (Belgium) showed significant differences in ventral bar and marginal hook features. The morphometric variation was lower in G. rugiensis, whereas no significant differences were found in G. ostendicus. Gyrodactylus branchialis and G. ostendicus collected on P. microps were slightly different in the ITS rDNA (-0.6%) compared with specimens on the closely related P. marmoratus, probably reflecting ongoing speciation. A hybrid zone was identified in the Vaccarès lagoon complex (France) where both host species are sympatric. There was no clear geographic or host-related pattern in the variation found in the ITS2 rDNA in G. arcuatus sampled from P. microps, G. flavescens, Pungitius pungitius, K. panizzae, and its original host Gasterosteus aculeatus (2 polymorphic sites). Of all studied species, only G. arcuatus, G. rugiensis, and G. rugiensoides showed minor intraspecific variation in the ITS rDNA. Hence, the physical separation by a shoreline of more than 10,000 km is hardly reflected in the parasite ITS rDNA.

Gyrodactylus neili n. sp. (Monogenea: Gyrodactylidae), a parasite of chain pickerel Esox niger Lesueur (Esocidae) from freshwaters of New Brunswick, Canada

Gyrodactylus neili n. sp. (Monogenea: Gyrodactylidae) is described from the fins and body surface of Esox niger Lesueur (chain pickerel) (Esocidae) from the St. Croix River drainage, New Brunswick, Canada. G. neili n. sp. resembles most closely G. fryi Cone & Dechtiar, 1984, a parasite of E. masquinongy in North America, in having relatively large thin hamuli, well-developed marginal hook sickles with a relatively long, wide blade and short handle, a ventral bar with small antero-lateral processes and tongue-shaped membrane, and a cirrus with many small spines in two rows. The new species is easily separated from G. fryi by the length of the hamuli (70-76 microm versus 92 microm, respectively), by the distal width of the sickle (7-9 versus 14-16 microm, respectively) and by subtle differences in the shape of the toe and heel of the marginal hook sickle. Sequence data (922 bp) of rDNA (internal transcribed spacers 1 and 2 and 5.8S) of G. neili n. sp. returned no identical matches in GenBank. The 5.8 sequence alone, however, was identical to morphologically similar gyrodactylids of the subgenus Gyrodactylus from cyprinid fishes in Eurasia. The discovery of G. neili n. sp. and features of its genetic makeup support the idea that this lineage parasitised ancestral cyprinids and that it radiated, possibly through predator/prey interactions, to an ancestor of contemporary Esox. It is concluded that DNA comparison of monogeneans on Holarctic freshwater hosts, such as E. lucius, may shed light on the nature of speciation of these parasites.

Seasonal occurrence and metrical variability of Gyrodactylus rhodei Žitňan 1964 (Monogenea, Gyrodactylidae)

The seasonal dynamics of Gyrodactylus rhodei, a monogenean ectoparasite of bitterling (Rhodeus sericeus), was studied from June 2000 to May 2001 in the Kyjovka River, Czech Republic. A negative relationship between prevalence and intensity of infection of G. rhodei and water temperature was found. Metrical variability of the hard parts of the parasite haptor was studied throughout the sampling season. A negative relationship between water temperature and the size of the hard parts of the G. rhodei haptor was evident in the measurements of the total length of the marginal hooks, the sickle length of marginal hooks, anchors, anchor point and root, the width of the ventral bar and the membrane processes. Sequences of the partial ITS (rDNA) of specimens collected during the cold and warm seasons were analysed. Sequences of all studied parasite specimens were identical and there was no evidence of intraspecific variability in the sequenced region.

Advances and Trends in the Molecular Systematics of the Parasitic Platyhelminthes

The application of molecular systematics to the parasitic Platyhelminthes (Cestoda, Digenea and Monogenea) over the last decade has advanced our understanding of their interrelationships and evolution substantially. Here we review the current state of play and the early works that led to the molecular-based hypotheses that now predominate in the field; advances in their systematics, taxonomy, classification and phylogeny, as well as trends in species circumscription, molecular targets and analytical methods are discussed for each of the three major parasitic groups. A by-product of this effort has been an ever increasing number of parasitic flatworms characterized genetically, and the useful application of these data to the diagnosis of animal and human pathogens, and to the elucidation of life histories are presented. The final section considers future directions in the field, including taxon sampling, molecular targets of choice, and the current and future utility of mitochondrial and nuclear genomics in systematic study.

Chaetotaxy applied to Norwegian Gyrodactylus salaris Malmberg, 1957 (Monogenea) clades and related species from salmonids

Gyrodactylus salaris Malmberg, 1957 is a major pathogen of wild Salmo salar L. parr populations in Norway, and its delimitation from non-pathogenic species is important. The present study was undertaken to test the power of chaetotaxy to differentiate between three populations belonging to both the same and different clades (as stated by mtDNA) of G. salaris, in addition to three different species of gyrodactylids (G. salaris, G. thymalli and G. caledoniensis). The gyrodactylids were processed for chaetotaxy in situ and a maximum of 50 specimens per collection site were used to construct a generalised map over the sensilla. The sensilla were found in all populations to be symmetrically distributed around the median longitudinal axis, according to a formula of 7 dorsal (34 sensilla) and 8 ventral (44 sensilla) clusters on each side of the median line. The three Norwegian populations of G. salaris were found identical, as were the population of G. thymalli. The specimens of G. caledoniensis from Scotland, however, were found to differ from the Norwegian species G. salaris and G. thymalli by the position of one sensillum in two of the clusters. A comparison of the sensillum pattern of laboratory maintained G. salaris (River Lierelva) with results obtained ten years earlier, questions the temporal stability of the chaetotaxy pattern. The present results indicate that chaetotaxy can be used to discriminate between certain Gyrodactylus spp. but not generally.