New Salinity Tolerant Species of Gyrodactylus (Platyhelminthes, Monogenea) on Intertidal and Supratidal Fish Species from the Chilean Coast

Supplemental description of Gyrodactylus olsoni (Monogenea van Beneden, 1858) from Gillichthys mirabilis (Gobiidae) including molecular phylogeny and ecology

Additional morphology, new sequence (482 bp SSU rRNA gene, 902 bp ITS Region), and ecological data for Gyrodactylus olsoni Mizelle and Kritsky, 1967 parasitizing longjaw mudsucker, Gillichthys mirabilis Cooper (Gobiiformes: Gobiidae) from coastal waters of California, are provided. The parasite was found on 96% of 617 mudsuckers collected from Tijuana Estuary to Arcata Bay, California. It was present on gills, fins, and body surfaces. Samples from gills and fins shared identical sequence data indicating a lack of site specificity for the parasite. The new material matched the description of G. olsoni in features of the haptoral hard parts and MCO, but trichrome-stained specimens and scanning electron microscopy showed a pair of shallow tissue pads immediately anterior to the folded anchor roots. The pads, which appear partially hardened on the curved inner surface typically with two thin marginal ribs each, likely serve as a cushioning brace for any forward action of the folded anchor roots. Similar pads have only occasionally been reported in Gyrodactylus, with one species being G. proterorhini Ergens, 1967 from gobies in European freshwaters. Based on available sequences, the SSU rRNA gene was most similar to G. curemae Conroy and Conroy, 1985 from a mullet in coastal Venezuela, while the ITS was most similar to G. proterorhini. The relationship of G. olsoni to other species in the genus is discussed with support of a molecular phylogeny that finds G. olsoni to be a member of a widespread, mostly marine lineage that has radiated along with gobiid and blenniid fishes during their global radiation. Gyrodactylus olsoni has not yet been found on other species of gobies.

Molecular and morphological characterisation of Gyrodactylus alviga (Monogenea: Gyrodactylidae) from the Black Sea, and its synonymisation with G. pterygialis from the North European seas

Sequences of the ITS1-5.8S-ITS2 rDNA of Gyrodactylus alviga Dmitrieva & Gerasev, 2000 from Merlangius merlangus L. (Gadiformes: Gadidae) in the Black Sea were obtained for the first time. Gyrodactylus alviga is 0.2% distinct from G. pterygialis Bychowsky & Polyansky, 1953 parasitising the gadid fish Pollachius virens L. in the Norwegian Sea and Gyrodactylus sp. from Microgadus tomcod Walbaum of the same fish family in the Northwest Atlantic, based on the genetic variability of the ITS region. The most species-specific ITS1 region was identical in both species. The differences in the ITS2 secondary structure and compensatory base changes in its hairpins between G. alviga and G. pterygialis were not observed. Morphometric comparison of G. alviga and G. pterygialis also showed no significant differences. On this basis, G. alviga is synonymised with G. pterygialis and a redescription of the latter is presented, including G. alviga new syn. Findings of this species in the White and Bering Seas, and possibly off the northeastern coast of North America, require confirmation based on both morphological and molecular data. The results of this study show that G. pterygialis has a wider distribution than previously known. The good concordance of the secondary structure of the first ITS2 hairpin with the phylogenetic reconstruction of Gyrodactylus species based on the whole ITS region was revealed, which is of interest for further studies on the phylogenetic systematics of Gyrodactylus.

Monogenean parasitic flatworms

Vanhove and colleagues introduce monogenean parasitic flatworms, a species-rich group of ectoparasitic flatworms that are mostly found on the skin, gills, or fins of fish and have a life cycle involving a single host.

Description of three new species of Gyrodactylus von Nordmann, 1832 (Monopisthocotylea: Gyrodactylidae) on Triplophysa species (Nemacheilidae) from Qinghai-Tibet Plateau

Three new species of Gyrodactylus were identified from the body surface of the Triplophysa species from the Qinghai-Tibet Plateau, Gyrodactylus triplorienchili n. sp. on Triplophysa orientalis in northern Tibet, G. yellochili n. sp. on T. sellaefer and T. scleroptera and G. triplsellachili n. sp. on T. sellaefer and T. robusta in Lanzhou Reach of the Yellow River. The three newly identified species share the nemachili group species' characteristic of having inturning hamulus roots. Gyrodactylus triplorienchili n. sp. shared a quadrate sickle heel and a thin marginal hook sickle, two morphological traits that set them apart from G. yellochili n. sp. However, they may be identified by the distinct shapes of the sickle base and marginal hook sickle point. Gyrodactylus triplsellachili n. sp. had much larger opisthaptoral hard part size than the other two species. The three new species show relatively low interspecific differences of 2.9-5.3% p-distance for ITS1-5.85-ITS2 rDNA sequences. Phylogenetic analysis indicated that the three new species formed a well-supported monophyletic group (bp = 99) with the other nemachili group species.

Gyrodactylus serrai n. sp. (Gyrodactylidae), from the Near-Threatened Clanwilliam Sawfin, Cheilobarbus serra (Peters) (Cyprinidae, Smilogastrinae), in the Cape Fold Ecoregion, South Africa

A new species of Gyrodactylus is described from the gills of the near-threatened Clanwilliam sawfin, Cheilobarbus serra (Smiliogastrinae) collected from the Matjies River, Cape Fold Ecoregion, Western Cape Province, South Africa. Morphometry and morphology of the haptoral hard parts (hamuli, bars and marginal hooks) of Gyrodactylus serrai n. sp. differ from the other known species of the genus in the smaller size of hamuli and the shape and size of marginal hooks. Furthermore, ITS rDNA for the new species is unique among available Gyrodactylus spp. data in GenBank. Based on the uncorrected p-distances, G. serrai n. sp. is genetically most closely related to Gyrodactylus moroccensis Rahmouni, 2023 and Gyrodactylus pseudomoroccensis Rahmouni, 2023 from two species of Luciobarbus (Barbinae) from northern Africa, with interspecific divergence of 8.7% and 8.8%, respectively. The presence of a median ridge in the terminal part of the ventral bar membrane at G. serrai n. sp. most probably represents a morphological link to the North African Gyrodactylus spp. that suggests a morphogenetic association across the African continent as a result of ancient waterways that facilitated the dispersion of cyprinids and their parasite fauna or an independent evolution event retaining similarities from a common ancestor. The description of Gyrodactylus serrai n. sp. represents only the second species of Gyrodactylus described from an endemic South African cyprinid host, underscoring the need for focused research on this group of fishes to provide a sound understanding of the parasitic communities of these highly threatened and poorly studied hosts.

Revision of the Most Primitive Taxa of the Family Gyrodactylidae (van Beneden et Hesse, 1864) (Platyhelminthes, Monopisthocotyla) Based on ITS rDNA Phylogeny

BACKGROUND

For the past 25 years, the ITS rDNA (ITS1-5.8S-ITS2) of Gyrodactylidae has been crucial for species identification, description, and phylogeny. This family includes 25 genera parasitizing marine and freshwater fish, initially distinguished by morphological differences in attachment and/or male copulatory organs. Gyrodactylus Nordmann, 1832, the most species-rich genus, has approximately 500 described species and an additional 25,000 species suspected. The genus is not monophyletic, and the functionally adaptive nature of morphological diagnostic characters complicates the delimitation of new genera.

METHODS

A phylogeny based on ITS rDNA was proposed to address these challenges, using only complete sequences of primitive taxa. Fifty-four sequences were aligned with the MUSCLE v5.1 algorithm, creating a 1590 ps long matrix. Maximum Likelihood (ML) and Bayesian Inference (BI) methods with the models TVM+F+G4 and SYM+G4 for ITS1-ITS2 and 5.8S, respectively, were inferred using IQ-TREE v2.3.5 and BEAST v2.7.6.0.

RESULTS

The findings revealed eleven main lineages. Four of them are proposed for classification into new genera: Cichlidarus gen. nov., Iraqemembranatus gen. nov., Macracanthus gen. nov., and Rysavyius gen. nov. Elevating the subgenus G. (Gyrodactylus) to genus rank was supported.

CONCLUSIONS

The presented phylogeny provides a foundation for developing a classification system within Gyrodactylidae that is both reasonable and comprehensive.

Parasite and genetic diversity of big-scale sand smelt (Atherina boyeri Risso, 1810) populations in their natural and expansion ranges in Ukraine

The big-scale sand smelt (Atherina boyeri) is an Atlanto-Mediterranean amphidromous fish species found within the Black Sea. Here, we assess differences in the parasite fauna of big-scale sand smelt populations from their natural range in the northwestern Black Sea and from their expansion range in the Lower and Middle River Dnipro. In addition, we undertook a microsatellite analysis to assess the genetic similarity of fish from the different locations. We found that the parasite community of fish in their natural range was wider than that from their expansion range. While the Gulf of Odesa was most distant from all other localities by parasite community composition and the Dnipro Reservoir was characterised by an absence of parasites (newest and most distant expansion locality), only fish from the Danube Delta showed a significant genetic difference. Our results suggest that the parasite community of big-scale sand smelt is primarily influenced by environmental factors, such as habitat type, water salinity and/or prey composition. Both microsatellite analysis and parasite community species composition (e.g. the presence of the marine Telosentis exiguus in the Kakhovka Reservoir and freshwater Raphidascaris sp. in the Gulf of Odesa) confirmed that populations in the River Dnipro reservoirs had, at some time, been connected with native marine populations, thus also confirming the species' amphidromous nature.

Morphological and genetic variability of the cryptic Gyrodactylus sphinx and Gyrodactylus gerasevi n. sp. (Platyhelminthes: Monogenea) from the Mediterranean Sea and Black Sea: two new members of the cross-ocean distributed Gyrodactylus orecchiae species group

Gyrodactylus sphinx Dmitrieva & Gerasev, 2000 is the only species of Gyrodactylus originally described from Aidablennius sphynx (Valenciennes) in the Black Sea. In the present study, monogeneans similar to G. sphinx are reported from the same host and from two other species of Blenniidae from the Black Sea, as well as from the Mediterranean Sea. This study aims to verify the taxonomic status of the specimens found in different hosts and localities, other than the type ones of G. sphinx. Twenty-two measurements of the haptoral structures of 169 gyrodactylids were used for the morphological study. Morphometric variability between different samples was analysed using analysis of variance, multivariate analysis of variance (MANOVA) and principal component analysis (PCA). Molecular studies were carried out using the nuclear internal transcribed spacer 2 and 5.8S ribosomal DNA regions. Network, Bayesian phylogenetic and species delimitation analyses were performed to infer the number of taxonomic units and the phylogeographic relationships occurring within and among them. MANOVA revealed a significant dependence of the morphometry of hamuli and marginal hooks on host species and regions, but a clear differentiation between samples was not confirmed by PCA. Moreover, the ranges of all dimensions overlapped between samples. However, molecular analyses suggested the occurrence of at least two taxonomic entities. The most common entity was present in individuals of the Black and Mediterranean seas, and is described here as Gyrodactylus gerasevi n. sp., whereas a second entity recognized as a G. sphinx was found only in individuals from two localities off Crimea. The monophyletic cluster grouping of these two species was placed within a large clade that also included a separate sister cluster with seven other species of the Gyrodactylus orecchiae cross-ocean species group.