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The taxonomy of the enigmatic dark-mouth skate, Bathyraja arctowskii (Dollo, 1904), from the Southern Ocean was finally resolved after more than 100 years of ambiguity in 2021. This species is the smallest known species of the species-rich deep-water skate genus Bathyraja Ishiyama, 1958, which attains a total length of only about 61 cm and appears to be a wide-ranging and locally common species in the Southern Ocean. It differs from its congeners in the small adult size, dark-pigmented mouth cavity and underside of nasal curtain, lack of thorns on upper disc, as well as small and slender egg cases. Although the identity of this species was unambiguously clarified, the syntype egg cases could not be examined due to the COVID-19 pandemic. This examination has now become possible, and detailed data of the syntypes are provided in the present paper for the first time, together with hitherto unknown details of tooth, dermal denticle and thorn morphology. Furthermore, a lectotype and two paralectotypes are designated from the syntypes.

Two new species of Guidus are herein described based on detailed morphology of adult worms using light and scanning electron microscopy (SEM), and histological sections. Worms prepared for scanning electron microscopy (SEM) were hydrated in a graded ethanol series, post-fixed in 1% osmium tetroxide overnight at room temperature, dehydrated in a graded ethanol series, and dried using hexamethyldisilazane. After drying, the specimens were mounted on stubs with carbon tape, coated with c. 40 nm of gold/palladium with a Thermo VG Scientific Polaron SC 7630 and examined in either a Philips XL 30 or a Carl Zeiss NTS-SUPRA 40 scanning electron microscope. RESULTS Guidus francoi sp. n. Figs. 1-3 ZooBank number for species: urn:lsid:zoobank.org:act:1A016D65-7CA8-40A3-A2C6-818D397EC5E0 Description (based on 13 mature and 21 gravid whole worms, two mature and one gravid specimens examined with SEM, and cross sections of mature proglottids).

— First information on the Arctoraja sexoculata frequency of occurrence, ecology, and biology, from the area off the middle Kuril Islands has been provided. It is estimated that the Arctoraja sexoculata is a common bycatch species in trawl fishing for the commander squid Berryteuthis magister in this water area. The locations of catch events for this species were localized off the Ketoy and Simushir Islands and in the Diana Strait at the depths of 250–490 m at a water temperature near the bottom of 1.8–2.5°С. It is supposed that the species belongs to the mesobenthal ichthyocene. In the catches, A. sexoculata represented by individuals of 26–90 cm length and 0.1–5.6 kg body mass. The species probably reaches the age of maturity for the first time at 8–9 years old and over. Its highest life expectancy is 16 years. The individuals of 50–90 cm length become predators consuming predominantly cephalopods and fishes, in the same time isopods and ctenophores among the food items were rarely recorded.

Egg capsules of the multispine skate, Bathyraja multispinis (Norman, 1937 ), described here for the first time, are larger (180 mm in length without horns) than those of any Bathyraja species from the South-west Atlantic Ocean (SWA). The capsule’s surface texture is relatively smooth by the presence of woven-like fibres. However, below the fibres, it is rough to the touch by the presence of longitudinal ridges and prickles of different shapes and sizes, ending in two or more digitiform projections. An identification key to all described Bathyraja egg capsules occurring in the SWA from 34° to 55°S is provided.

— Based on the materials of bottom trawl surveys, the data are presented on the features of distribution, thermal conditions of habitats and the size composition of the white-blotched skate Bathyraja maculata in the northeastern Sea of Okhotsk during the hydrological summer of 1998–2019. The main aggregations of the species were found in the area of the eastern slope of the TINRO depression north of 56° N. The vertical distribution area covered depths of 60–874 m. The temperature range of the near-bottom layer of water at which the species was encountered was 0–3.0°С. High values of relative abundance were typical for depths of 401–500 and 601–700 m, for relative biomass, up to 500 m. Juveniles of white-blotched skate were found near the lower boundary of the habitat (> 600 m), and large individuals inhabited the shelf and adjacent areas of the continental slope. Presumably, one of the spawning grounds of the species is located on the eastern slope of the TINRO depression.

— A complete annotated list of fresh and brackish waters ichthyofauna of the Russian Federation and adjacent areas, based on a critical analysis of scientific publications of the last 200 years, and on the data of the authors’ research, is the aim of this study. The taxonomic composition of the freshwater and brackish water fish fauna of Russia remains insufficiently studied. This may result incorrect data on the true number of fish species of this category, not only for the waters of Russia, but also in the modern system of the world ichthyofauna as a whole, and also does not give a complete idea of the range, degree of endemism, abundance, conservation status, commercial value, and others important aspects. Until the present study, according to various sources, the Russian freshwater and brackish water ichthyofauna was estimated to amount from 351 to 486 species, respectively. However, based on our ongoing research, these numbers are too low and need to be revised. The total species number in all categories should include at least 800 species also including the introduced non-native species, as well as species not yet recorded from Russian waters, but suggested to be found in the future. In this first part of our updated checklist, we provide a basic historical review of ichthyological research in Russia, together with the first 77 species belonging to three classes (Petromyzonti, Elasmobranchii and Actinopteri), ten orders (Petromyzontiformes, Lamniformes, Carcharhiniformes, Squaliformes, Rajiformes, Myliobatiformes, Acipenseriformes, Elopiformes, Anguilliformes and Clupeiformes), nineteen families (Petromyzontidae, Alopiidae, Lamnidae, Triakidae, Carcharhinidae, Sphyrnidae, Somniosidae, Squalidae, Rajidae, Arhynchobatidae, Dasyatidae, Acipenseridae, Polyodontidae, Megalopidae, Anguillidae, Muraenesocidae, Clupeidae, Engraulidae and Pristigasteridae) and 38 genera. For each species, the following details are presented: scientific and English common names, taxonomic position with comments and synonyms (if necessary), conservation status, world distribution, zoogeographic characteristics, distribution in Russian waters and adjacent areas, abundance, and commercial value.

The complete mitochondrial genome of Eaton's skate Bathyraja eatonii was studied using the long-read technology, PacBio Sequel System. The complete mitochondrial genome form of B. eatonii was 16,698 bp and it's comprised of 13 protein-coding genes, 22 tRNA and 2 rRNA. The base composition of B. eatonii is analyzed 31.94% for A, 33.94% for T, 13.49% for G, 20.64% for C, the result of GC content was 33.94%. Phylogenetic analysis showed that B. eatonii was closely related to Bathyraja meridionalis in Arhynchobatidae family, and this first mitochondrial genome of Antarctic skate would provide fundamental information to the evolutional relationship of Antarctic fishes

During a survey on the myxosporean fauna of Rajiformes from the Atlantic coast of Argentina, in waters off Buenos Aires Province (34°–42°S; 53°–62°W), the gall bladders of 217 specimens belonging to seven species of skates, representatives of two families, were examined. As a result, three species of Chloromyxum Mingazzini, 1890, namely C. atlantoraji n. sp., C. zearaji n. sp. and C. riorajum Azevedo, Casal, Garcia, Matos, Teles-Grilo and Matos, 2009 were found infecting three endemic host species, the spotback skate Atlantoraja castelnaui (Arhynchobatidae), the yellownose skate Zearaja chilensis (Rajidae) and the Rio skate Rioraja agassizii (Arhynchobatidae), respectively. These species were described based on myxospore morphology and morphometry characterization, as well as by providing their small subunit ribosomal DNA (SSU rDNA) sequences. The SSU rDNA-based phylogenetic analyses showed that these three species constituted a well-established monophyletic subclade within the marine Chloromyxum clade, while branches subtending the other Chloromyxum species were poorly resolved or unresolved, independently of the host taxonomic identities (Carchariniformes, Myliobatiformes, Orectolobiformes, Pristiophoriformes, Rajiformes, Squaliformes and Torpediniformes) and/or host geographic distribution (Atlantic coast of Portugal, Atlantic coast of the USA, Australian waters or Mediterranean Sea). The possible causes of these discrepancies are discussed, providing new insights into the phylogeny of the marine Chloromyxum clade. Lors d’une étude de la faune des Myxozoaires des Rajiformes de la côte atlantique argentine, dans les eaux situées au large de la province de Buenos Aires (34°–42°S; 53°–62°O), les vésicules biliaires de 217 spécimens appartenant à sept espèces, représentants deux familles, ont été examinés. En conséquence, trois espèces de Chloromyxum Mingazzini, 1890, à savoir C. atlantoraji n. sp., C. zearaji n. sp. et C. riorajum Azevedo, Casal, Garcia, Matos, Teles-Grilo et Matos, 2009 ont été trouvées, infectant trois espèces hôtes endémiques, Atlantoraja castelnaui (Arhynchobatidae), Zearaja chilensis (Rajidae) et Rioraja agassizii (Arhynchobatidae), respectivement. Ces espèces sont décrites sur la base de la morphologie et de la morphométrie des myxospores, ainsi qu’en fournissant leurs petites séquences d’ADN ribosomal (SSU ADNr). Les analyses phylogénétiques basées sur l’ADNr SSU ont montré que ces trois espèces constituaient un sous-clade monophylétique bien établi dans le clade des Chloromyxum marins, tandis que les branches sous-jacentes aux autres espèces de Chloromyxum étaient mal ou non résolues, indépendamment des identités taxonomiques hôtes (Carchariniformes, Myliobatiformes, Orectolobiformes, Pristiophoriformes, Rajiformes, Squaliformes et Torpediniformes) et/ou de la répartition géographique de l’hôte (côte atlantique du Portugal, côte atlantique des États-Unis, eaux australiennes ou mer Méditerranée). Les causes possibles de ces divergences sont discutées, fournissant de nouvelles informations sur la phylogénie du clade des Chloromyxum marins.

This study quantifies and describes the diet composition and variability, and the trophic ecology of Sympterygia bonapartii (Batoidea: Arhynchobatidae) in the San Matías Gulf, northern Patagonia, Argentina. A total of 1,047 stomachs were analyzed and 98 % of them contained food. The low proportion of empty stomachs recorded and the presence of prey in different stages of digestion suggested that this skate was a continuous feeder. A total of 81 prey items were identified. However, the diet was mainly composed of crabs. Other important groups in its diet were teleost fishes, shrimps and prawns, bivalves and worms. At the species level, the crab Peltarion spinosulum accounted for the highest contribution and the anchovy Engraulis anchoita ranked second in importance. By analyzing its diet composition, it was possible to classify S. bonapartii as a benthic predator, as are other skates reaching a similar maximum size. In addition, it was placed in the functional group of species that mainly feeds on decapod crustaceans. Trophic level was estimated at 3.61, indicating that the species was a secondary consumer. Significant differences were found in the diet according to sex, size class and season. These differences may be due to extrinsic and intrinsic factors that could be operating together.

Recent deep-water surveys of the continental slope in the Bering Sea and the eastern North Pacific, conducted by the US National Marine Fisheries Service, Alaska Fisheries Science Center, and Fisheries and Oceans Canada, have broadened our understanding of the ichthyofauna in the region. Herein, we report significant new records of 2 species of skates based on morphological and molecular data. For Bathyraja spinosissima, the White Skate, we describe 2 specimens: a neonate male that constitutes a northern range extension for the species to Alaska in the Bering Sea; and an adult male representing a new record for the species in British Columbia. For B. microtrachys, the Fine-spined Skate, we describe 5 males taken in a single haul that represent the 1st record of the species in British Columbia. These specimens had been previously misidentified as B. violacea, the Okhotsk Skate, a species known only from the western Aleutian Islands and the western North Pacific.