Helminths of three species of White Sea fishes.

Parasitic fauna of the White Sea cod, Gadus morhua marisalbi; the navaga, Eleginus nawaga; and the shorthorn sculpin, Myoxocephalus scorpius, in the White Sea was repeatedly studied, but no large-scale parasitological surveys have been made in the recent three decades. To fill this gap, we conducted a survey of the helminths of these three fish species at the White Sea Biological Station (Karelia, Russia) of the Lomonosov Moscow State University in August 2021. The navaga (50 specimens studied) was found to be infected with 13 species of helminths; the White Sea cod (50 specimens), with 12 species; and the shorthorn sculpin (21 specimens), with 13 species. Plerocercoids of Diphyllobothrium schistochilus and third-stage juveniles of Pseudoterranova bulbosa were recorded in the White Sea for the first time. The helminth infracommunities of the navaga and the White Sea cod were closer in structure to each other than to those of the shorthorn sculpin. In general, the levels of helminth infection of the White Sea cod, the navaga, and shorthorn sculpin have been consistently high over 85 years of observations in the White Sea, but long-term trends in the abundance of some helminth species were multidirectional.

Onchobothrium malakhovi n. sp. (Cestoda: Onchoproteocephalidea) ex Bathyraja (Arctoraja) sexoculata (Rajiformes: Arhynchobatidae) from Kuril Islands (Russia), with comments on the status of the genus Onchobothrium.

Onchobothrium malakhovin. sp. was found in the spiral valve of the softnose skate Bathyraja (Arctoraja) sexoculata off the Simushir Island (Kuril Islands, Russia). The new species has bothridia with three loculi and no additional suckers on bothridia, single-toothed hooks unconnected by their bases, no spines at the bases of the hooks, dense matrix around the hook bases shaped as an unpaired butterfly wing, and a short and wide ovary. Onchobothrium malakhovin. sp. differs from O. antarcticum and O. magnum in having a smaller total length, cirrus sac and ovary, smaller testes and eggs. Additionally, the new species differs from O. antarcticum by the absence of a vaginal sphincter and shorter bothridia; differs from O. magnum in having fewer proglottids and smaller vitelline follicles. It differs from O. farmeri, O. convolutum, and O. pseudouncinatum, by the absence of a small spine at the base of the hooks and the absence of accessory suckers on bothridia; from O. pseudouncinatum, additionally, by unconnected hooks; from O. schizacanthium, by the number of testes and by the presence of a postvaginal group of testes. Onchobothrium malakhovin. sp. was placed among other members of the Onchoproteocephalidea with a high support based on the sequence data for the D1-D3 region of the 28S rDNA and cox1 gene. The phylogenetic position of the genus Onchobothrium sensu lato remains ambiguous. We suggest that Onchobothrium sensu lato is a complex genus containing at least two morphologically different groups of species. Onchobothrium farmer, O. convolutum, O. schizacanthium, and O. pseudouncinatum, for which there are no molecular genetic data, are considerably different morphologically from O. malakhovin. sp., O. antarcticum, and O. magnum. A new genus might have to be established for the latter three species after the accumulation of genetic data.

First Description of the Metacercaria of Nematostrigea serpens serpens (Nitzsch, 1819) (Trematoda, Strigeidae) and Phylogenetic Affiliation of Nematostrigea vietnamiensis Zhokhov & Mishina, 2011.

BACKGROUND: The genus Nematostrigea comprises trematodes parasitising in fish-eating birds of Europe, Africa, and North America. Their life cycle is unknown. PURPOSE: To provide the first description of metacercariae of Nematostrigea serpens serpens, a nominative subspecies of the type species of Nematostrigea, and to record metacercaria of Nematostrigea vietnamiensis, with molecular data. METHODS: Encysted metacercariae of N. serpens serpens and N. vietnamiensis were collected from fish in Russia and Vietnam, respectively, and were processed, identified, and documented using standard morphological techniques. The 28S rRNA gene of metacercariae of both species and the cox1 gene of metacercariae an earlier studied adult of N. serpens serpens were sequenced and used for phylogenetic analysis. RESULTS: Metacercaria of N. serpens serpens have a spatulate body with a foliate forebody and a short hindbody, two long lateral rectilinear pseudosuckers, and the holdfast organ with bifurcated anterior and entire posterior external lobes. The analysis of the cox1and 28S rRNA gene sequences unequivocally showed the conspecificity of metacercariae and adult stage of N. serpens serpens. Based on the 28S rRNA gene sequence-based phylogenetic analysis, the genus Nematostrigea is a sister taxon to the group of strigeid genera Cotylurus + Ichthyocotylurus. Morphological and phylogenetic data demonstrated that N. vietnamiensis does not belong to the genus Nematostrigea and is possibly be affiliated with the crassiphialine trematodes. CONCLUSION: This is the first record of metacercariae of N. serpens serpens. N. vietnamiensis, renamed Prodiplostomulum vietnamiense comb. nov., must be moved to the crassiphialine 'Prodiplostomulum'-type metacercariae group.

Bathyraja (Arctoraja) sexoculata sp. nov., a new softnose skate (Rajiformes: Arhynchobatidae) from Simushir Island, Kuril Islands (western North Pacific), with special reference to geographic variations in Bathyraja (Arctoraja) smirnovi.

A new species of softnose skate (Arhynchobatidae), Bathyraja sexoculata Misawa, Orlov, Orlova, Gordeev and Ishihara is described on the basis of five specimens collected from off the east coast of Simushir Island, Kuril Islands, located in the western North Pacific. The specimens conformed to the genus Bathyraja by having the anteriormost pectoral-fin skeleton almost reaching the snout tip, and a slender unsegmented rostral cartilage. Within Bathyraja, the new species belongs to the subgenus Arctoraja (currently with four valid species) due to the relatively short tail (79-86% of disc width), high count of predorsal caudal vertebrae (more than 86), and large strong nuchal and scapular thorns. It is most similar to Bathyraja (Arctoraja) smirnovi, distributed in the Seas of Japan and Okhotsk, in having tail thorns not extending to the nuchal area, median thorns discontinuous from the nape to the tail, and no mid-dorsal thorns. However, B. sexoculata can be distinguished from B. smirnovi by the following characters: three pairs of white blotches on the dorsal disc surface (vs. blotches absent, or a pair of white or dark blotches in B. smirnovi), dark blotch around cloaca, dark bands along mid ventral line of tail (vs. dark blotch and band usually absent ventral disc surface in B. smirnovi), 86-93 predorsal caudal vertebrae (vs. 80-87 in B. smirnovi), and a unique mitochondrial DNA cytochrome c oxidase subunit I sequence. Proportional measurements, including disc width, disc length, head length, preoral length, prenarial length, internarial distance, eye diameter, and tail length, also differ between the two species. For the referential purpose, geographical variations of B. smirnovi distributed in the Seas of Japan and Okhotsk are analyzed and clarified based on morphological and genetic data. Significant morphological and genetic differences were found between local populations in the Seas of Japan and Okhotsk.

Phylogenetic position of deep-sea opecoelid digenean Tellervotrema beringi (Mamaev, 1965) (Trematoda: Opecoelidae) based on novel genetic data.

Adult opecoelid digeneans consistent with Tellervotrema beringi (Mamaev, 1965) were found in the intestine of the deep-water fish Antimora microlepis Bean collected off the northern Kuril Islands (Russia). Earlier, T. beringi was recorded only in macrourid fish. This is the first record of a species of Tellervotrema Gibson & Bray, 1982 from fishes of the family Moridae (Gadiformes). A partial 28S rRNA gene sequence was obtained for this species and was compared with the available sequences on GenBank from other opecoelids. The phylogenetic analysis did not support the current taxonomic hypothesis that the genus Tellervotrema belongs to the subfamily Podocotylinae Dollfus, 1959. Our results demonstrated that species of this genus formed a clade with those of the genera Mesobathylebouria Martin, Huston, Cutmore & Cribb, 2019 and Abyssopedunculus Martin, Huston, Cutmore & Cribb, 2019. The morphological synapomorphies of the Tellervotrema + (Mesobathylebouria + Abyssopedunculus) clade are currently unclear, and this group does not have an adequate subfamilial classification.

Helminths of Fedorov's lumpsucker Eumicrotremus fedorovi Mandrytsa, 1991 (Actinopterygii: Cyclopteridae) in the Simushir Island area (Pacific Ocean).

Fedorov's lumpsucker, Eumicrotremus fedorovi Mandrytsa, 1991, is native to the Kuril Islands area. Two sets of 69 and 30 adult specimens of E. fedorovi caught on the continental shelf and slope of Simushir Island in the Pacific Ocean were dissected and studied for macroparasites. The studied specimens were heavily infected with plerocercoids of Nybelinia surmenicola and Ascarophis pacifica. For the first time, 15 parasite taxa were recorded for E. fedorovi. None of the parasites found are solely specific to the E. fedorovi or to the representatives of the family Cyclopteridae. The infection of E. fedorovi could be dramatically different in different parts of the Simushir Island area in terms of parasite species composition and intensity of infection.

Asaccotrema vietnamiense n. gen.; n. sp. (Trematoda: Monorchioidea), a new aberrant representative of lissorchiid trematodes from the sidestripe rasbora, Rasbora paviana Tirant (Actinopterygii: Cyprinidae), Vietnam.

In this paper we erect Asaccotrema n. gen. of Lissorchiidae Magath, 1917 (Trematoda, Monorchioidea) and provide a description of Asaccotrema vietnamiense n. sp., that infects freshwater fish in Vietnam. The morphology of Asaccotrema n. gen. is significantly different from that of other lissorchiid genera due to the absence of the cirrus-sac, and position of the genital pore sublaterally, near the middle level of the esophagus. The male terminal genitalia are characterized by the presence of the seminal vesicle, which is surrounded by prostate gland-cells, a tubular pars prostatica and a long unarmed ejaculatory duct. The terminal portion of the cluster of prostate gland-cells, which surrounds pars prostatica and the distal end of seminal vesicle, is covered with a thin-walled open-ended membrane, and the other constituents of the male terminal genitalia are naked. Asaccotrema vietnamiense n. sp. specimens are found as progenetic metacercariae on the liver of the sidestripe rasbora, Rasbora paviana Tirant (Actinopterygii: Cyprinidae). A partial sequence was obtained for the 28S rRNA gene (rDNA) of A. vietnamiense n. sp. The 28S rDNA-based phylogenetic analyses support the integration of A. vietnamiense n. sp. into the Lissorchiidae clade, which also includes Lissorchis kritskyi Barnhart Powell, 1979 and Asymphylodora perccotti Besprozvanykh, Ermolenko Atopkin, 2012. This is the second record of a lissorchiid species in fish in Vietnam.

Phylogenetic analysis of the superfamily Hemiuroidea (Platyhelminthes, Neodermata: Trematoda) based on partial 28S rDNA sequences.

In the present paper, the phylogenetic relationships between genera, subfamilies and families of the Hemiuroidea are explored. Twelve new sequences of 28 rDNA and data taken from GenBank (NSBI) on 43 species affiliated to 34 genera were included in the analysis. Most of the hemiuroidean trematodes form two highly supported clades (A and B), which are sister groups to each other. Hemipera manteri joined with Gonocerca spp. with moderate statistical support. This clade is basal relative to the clades A and B. Сlade A is polytomic and contains representatives of the families Accacoeliidae, Syncoeliidae, Didymozoidae, Hirudinellidae and Sclerodistomidae, and derogenid subfamilies Derogeninae and Halipeginae. At the same time, the Syncoeliidae, Hirudinellidae and Accacoeliidae form a well-supported monophyletic group. The phylogenetic relationship between Derogeninae and Halipeginae is poorly resolved. Сlade B unites the isoparorchiid, bunocotylid, lecithasterid and hemiurid trematodes. Our data re-establishes the family Bunocotylidae, which consists of two subfamilies, Opisthadeninae and Bunocotylinae, and the Machidatrema chilostoma + Hysterolecithoides frontilatus group. The Bunocotylidae is the sister group to the Hemiuridae + Lecithasteridae group and the Isoparorchiidae is a basal relative to the representatives of these three hemiuroid families.

Phylogenetic position of the genus Gonocerca Manter, 1925 (Trematoda, Hemiuroidea), based on partial sequences of 28S rRNA gene and a reconsideration of taxonomic status of Gonocercinae Skrjabin et Guschanskaja, 1955.

Adult trematodes of the genus Gonocerca Manter, 1925, are parasites of marine fishes. Identification of the phylogenetic positions and a revision of the taxonomic status of the subfamily Gonocercinae Skrjabin et Guschanskaja, 1955 (Derogenidae) are the main purposes of this research article. Four Gonocerca species were used in the study, including the type-species G. phycidis Manter, 1925. Molecular phylogenetic analysis, based on partial sequences of 28S rRNA gene, revealed that Gonocerca spp. are phylogenetically distant from other hemiuroid trematodes, including Derogenes varicus (Müller, 1784), representative of the type-genus of the family Derogenidae. The taxonomic rank of Gonocercinae should be raised to the family level. The generic composition of the family Gonocercidae Skrjabin et Guschanskaja, 1955 stat. nov., requires further clarification as the molecular data do not support the inclusion of the genus Hemipera Nicoll, 1913, in this family.

Where are the sensory organs of Nybelinia surmenicola (Trypanorhyncha)? A comparative analysis with Parachristianella sp. and other trypanorhynchean cestodes.

The sensory organs in tegument of two trypanorhynchean species--Nybelinia surmenicola (plerocercoid) and adult Parachristianella sp. (Cestoda, Trypanorhyncha)--were studied with the aim of ultrastructural description and a comparative analysis. The Nybelinia surmenicola plerocercoid lacks papillae with sensory cilia on the bothria adhesive surface. We found an unciliated sensory organ within the median bothria fold. This unciliated free nerve ending contains the central electron-dense disc, three dense supporting rings, and broad root. The nerve ending locates in the basal matrix under the tegument. The tegument of N. surmenicola has a number of ultrastructural features which make it significantly different from other Trypanorhyncha: (i) the tegumental cytoplasm has a plicated constitution in a form of high apical and deep basal folds, (ii) numerous layers of the basal matrix are presented in the subtegument, and (iii) the squamiform and bristlelike microtriches N. surmenicola lack the base and the basal plate. In contrast, numerous ciliated and unciliated receptors were found in Parachristianella sp.: six types on the bothria and one type in the strobila tegument. Ultrastructural constitution of sensory organs in the form of ciliated free nerve endings as well as unciliated basal nerve endings of Parachristianella sp. has many common features inside Eucestoda. In comparison with other Trypanorhyncha, all Nybelinia species studied have less quantity of the bothrial sensory organs. This fact may reflect behavioral patterns of Nybelinia as well as phylogenetic position into Trypanorhyncha. Our observations of living animals conventionally demonstrate the ability of N. surmenicola plerocercoids to locomote in forward direction on the Petri dish surface. The participation of the bothrial microtriches in a parasite movement has been discussed.