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This study focuses on the opecoelid genus Podocotyle, particularly the species in the northern European seas (White, Barents and Pechora), with additional data from few isolates from the Far East. The research combines molecular analyses (28S, 5.8S+ITS2 rDNA, and cox1 mtDNA) and morphological examinations. Molecular analyses suggested that there are most likely four species of Podocotyle in the northern European seas and three more in the Far East. Morphological redescriptions are provided for three northern European species: P. atomon, P. reflexa, and P. odhneri, with the latter recognized as a valid species. The study also verified the life cycle of P. atomon and identified Lacuna vincta (Littorinidae) as the first intermediate host for P. reflexa. In the Sea of Okhotsk, L. turrita is the first intermediate host for two apparently undescribed Podocotyle species. The results also highlight the morphological variability of P. atomon, emphasizing the need for an integrative approach in the taxonomy and biodiversity studies., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Parasites belonging to the trematode family Clinostomidae have a global distribution. Freshwater fish in Bangladesh frequently serve as hosts for different clinostomid species. During the metacercaria stage, the digenetic trematode Euclinostomum heterostomum exhibits a specific preference for Channidae species, where it undergoes encystment within the liver, kidneys, and muscles of these hosts. The study aimed to identify E. heterostomum in Channa punctata through combined morphological and molecular analysis. Light and scanning electron microscopy were conducted to investigate the morphological characteristics of the species. The histological examination of the infected liver tissue revealed the presence of encysted flukes, inflammatory leukocyte infiltrates, and degeneration and loosening of hepatic tissue. In molecular analysis, the generated internal transcribed spacer 1 (ITS1), 5.8S ribosomal DNA and ITS2 regions sequence (GenBank accession no: OR591452) of 830 bp showed 100% identity with Euclinostomum heterostomum identified in India (MT785786). The phylogenetic reconstruction provided substantial evidence of genetic similarities (0-1% genetic distance) among different isolates of the genus Euclinostomum, suggesting that there is a shared heritage., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Scanning electron microscopy studies of three paratype specimens (two males and one female) of Ascarophis parupenei Moravec, Orecchia & Paggi, 1988, an intestinal parasite of the marine fish Parupeneus indicus (Shaw) in the Indian Ocean, made it possible to redescribe in detail the cephalic structures of this nematode as well as the morphology of the male caudal end. The presence of non-bilobed sublabia, phasmids in both males and females, bifurcated deirids, well-developed precloacal cuticular ridges (area rugosa) and a ventral median caudal protuberance in the male are reported in this species for the first time. The general morphology and measurements of A. parupenei somewhat resemble those of Rasheedia novaecaledoniensis Moravec & Justine, 2018 described from the same host species (P. indicus) from off New Caledonia, but both species clearly differ from each other by the shape and structure of pseudolabia and the anterior portion of the digestive tract, belonging thus to different nematode families (Cystidicolidae and Physalopteridae, respectively)., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

In a parasitological survey of fishes from Moreton Bay (southeastern Queensland, Australia), 169 teleost fishes, representing 54 species from 28 families, were examined for larval cestodes. Of these 54 species, 36 were found to be infected by metacestodes. Metacestodes were characterised by morphological and molecular data (the D1-D3 region of the 28S rDNA gene); these data were analysed in parallel to inform larval type allocation. Metacestodes collected represented eight morphological types, seven previously reported (Types I, II, IV, V, VI, VII, and X) and one novel type (Type XVI). Phylogenetic analyses were conducted to genetically match larval types to adult cestodes. Six of the eight larval types found were matched to adult forms: Type I metacestodes matched species of Phoreiobothrium Linton, 1889 (Onchobothriidae); Type II metacestodes matched species of Acanthobothrium van Beneden, 1849 (Onchobothriidae); Type IV metacestodes matched species of Scyphophyllidium Woodland, 1927 and Alexandercestus Ruhnke & Workman, 2013 (Phyllobothriidae); Type VI metacestodes matched species of Anthobothrium van Beneden, 1850 (Tetraphyllidea incertae sedis); Type X metacestodes matched species of Ambitalveolus Caira & Jensen, 2022 (Tetraphyllidea incertae sedis); and Type XVI metacestodes matched species of Platybothrium Linton, 1890 (Onchobothriidae). Based on phylogenetic topology, Type V metacestodes are inferred to match Pedibothrium Linton, 1909 (Balanobothriidae) and Type VII metacestodes are inferred to match Spongiobothrium Linton, 1889 (Rhinebothriidae). These findings support and extend the unified morphological type system proposed previously, but suggest that morphological types will ultimately be informative to identify metacestodes to a group of related genera rather than any distinct genus., (© 2024. The Author(s).)

The comparative analysis of records of Elthusa samariscii (Shiino, 1951) from Japan and India, alongside corresponding illustrations, indicates that the records of E. samariscii from Samaris cristatus Gray in India represent a distinct and previously undescribed species. This study introduces Sandythoa tiranga gen. and sp. nov., providing comprehensive descriptions of various lifecycle stages, including the female, male, transitional, premanca, and manca larvae. The following combinations of characters identify the genus: cephalon anterior margin with acute rostrum; pleonite 1 is distinctly narrow, not extending laterally; presence of a narrow gap between pleonites; antenna with more than 10 articles; maxilliped with oostegital lobe. Sandythoa tiranga sp. nov. is specifically identified along the southwest coast of India. Furthermore, we propose transferring the following species from Elthusa: Sandythoa arnoglossi (Trilles and Justine 2006) comb. nov.; Sandythoa parabothi (Trilles and Justine, 2004) comb. nov.; Sandythoa samariscii (Shiino, 1951) comb. nov.; Sandythoa moritakii (Saito and Yamauchi, 2016) comb. nov. A revised key to the global marine branchial cymothoid genera is provided., (© 2024. The Author(s).)

Myxosporean infection in marine water fishes has drawn less attention than in freshwater fishes, which resulted in a higher taxonomic variety in freshwater in Malaysia. This study aimed to address the gap by conducting a myxosporean survey on two commercially significant marine fish species, Nemipterus furcosus (Valenciennes) (Eupercaria incertae sedis: Nemipteridae) and Selar crumenophthalmus (Bloch) (Carangiformes: Carangidae), collected from the northeastern part of peninsular Malaysia. During the examination of the organs, two distinct Myxobolus Bütschli, 1882 species were discovered in the brain tissue of these fishes, despite the absence of any observable pathological signs. The two Myxobolus species were characterized through morphometry, morphology, and analysis of partial small subunit ribosomal RNA (18S rDNA) gene. As a result, Myxobolus acanthogobii Hoshina, 1952, which infects 2.3% of N. furcosus, is synonymous with a myxobolid species commonly found in Japanese waters, based on its morphological traits, tissue tropism, and molecular diagnostics. Furthermore, a novel species, Myxobolus selari n. sp., was described, infecting the brain of one (11%) individual S. crumenophthalmus. This unique species displayed distinctive features, placing it within a well-supported subclade primarily comprising brain-infecting myxobolids. Maximum likelihood analysis further revealed the close relationships among these brain-infecting myxobolids, underscoring the significance of tissue tropism and host taxonomy for myxobolids. This study represents the initial documentation of Myxobolus species within the southern South China Sea, shedding light on the potential diversity of marine myxosporean in this region. This article was registered in the Official Register of Zoological Nomenclature (ZooBank) as urn:lsid:zoobank.org:pub:7C400E35-7CB8-4DEE-92B7-F75FF3926441., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

A synopsis of Ortholinea Shulman, 1962 (Cnidaria: Myxosporea: Ortholineidae) is presented and identifies 26 nominal species presently allocated within this genus. Species morphological and morphometric features, tissue tropism, type-host, and type-locality are provided from original descriptions. Data from subsequent redescriptions and reports is also given. Accession numbers to sequences deposited in GenBank are indicated when available, and the myxospores were redrawn based on original descriptions. The information gathered shows that Ortholinea infect a wide taxonomic variety of freshwater and marine fish. Nonetheless, the broad host specificity reported for several species is not fully supported by morphological descriptions and requires molecular corroboration. The members of this genus are coelozoic and mainly parasitize the urinary system, with few species occurring in the gallbladder. Ortholinea visakhapatnamensis is the only exception, being histozoic in the visceral peritoneum. Molecular data of the small subunit ribosomal RNA gene (SSU rDNA) is available for about one third of Ortholinea species, with genetic interspecific variation ranging between 1.65% and 29.1%. Phylogenetic analyses reveal Ortholinea to be polyphyletic, with available SSU rDNA sequences clustering within the subclades of the highly heterogenous freshwater urinary clade of the oligochaete-infecting lineage. The life cycles of two Ortholinea species have been clarified based on molecular inferences and identify triactinomyxon actinospores as counterparts, and marine oligochaetes of the family Naididae as permissive hosts to this genus., (© 2024. The Author(s).)

Seven species belonging to Pennellidae are reported from marine teleosts caught off southern Africa. Additionally, complete re-descriptions are provided for Propeniculus stromatei and Sarcotretes scopeli. Examination of Lernaeenicus gonostomae, deposited in the Iziko South African Museum, indicated that it has the morphological features of Sarcotretes rather than Lernaeenicus and thus should be moved to Sarcotretes i.e. S. gonostomae n. comb. for which a re-description is also provided. Reports of new host records include those of Pennella instructa from Seriola lalandi; Propeniculus stromatei from Rhabdosargus holubi and Pomadasys commersonnii; Sarcotretes scopeli from Nansenia tenera, and Sarcotretes longirostris from Centrolophus niger. New geographical records include those of P. instructa, P. stromatei, S. scopeli, S. longirostris, and L. longiventris off southern Africa. Additionally, an attempt to estimate the evolutionary relationships amongst some genera is done from partial COI sequences deposited in Genbank., (© 2024. The Author(s).)

Brucethoa isro n. sp., a new species of deep-sea cymothoid is described and illustrated from the host fish Spinyjaw greeneye, Chlorophthalmus corniger Alcock, 1894, at depths of 265 to 458 metres from the southwest coast of India. Brucethoa isro n. sp. is recovered from the base of the gill cavity, facing the head towards the anterior, and the dorsal body closely adpressed against the gill, while the ventral brood presses against the inner wall of the operculum. Brucethoa isro n. sp., the second species of the genus, is characterized by: head weakly immersed in pereonite 1, very elongated body (3.15 times as long as wide); body dorsum not vaulted, almost flat; all coxae short, 0.5 times as the length of corresponding pereonites; sternite 7 with prominent posterior lobes. All adult life stages of the new species are described [including females (ovigerous and non-ovigerous), males, transitional, and juvenile. The species is currently known from the southwest coast of India and is the type locality. Additionally, this research provides valuable ecological insights into Brucethoa isro n. sp. and its habitat. As part of the taxonomic contributions, two species, Brucethoa alvaradoensis (Rocha-Ramírez, Chávez-López & Bruce, 2005) comb. n. and Brucethoa epinepheli (Trilles & Justine, 2010) comb. n., are transferred from the Elthusa genus to the Brucethoa genus., (© 2024. The Author(s).)

Between 2010 and 2023, a longitudinal study was undertaken to uncover the diversity of the parasite fauna of marine fishes in the Cat Ba Archipelago, a world biosphere reserve, in Vietnam. A total of 1,042 specimens representing 80 different fish species were collected and examined. Of these, 68 fish species, represented by 994 specimens (95.39%), were infected with parasites. A total of 162 parasitic species were discovered, including 54 trematodes, 37 monogeneans, 27 crustaceans, 15 myxozoans, 10 acanthocephalans, 10 nematodes, 7 cestodes, and 2 hirudineans. Over the course of the survey, twenty new species were described, including 7 acanthocephalans and 13 trematodes. Additionally, twenty species were recorded for the first time from the Cat Ba Archipelago and twenty-two species had new host records reported. The prevalence and mean intensity of parasite infection were found to be unaffected by season. These data on the parasitic fauna of Cat Ba Archipelago not only expand our knowledge of the diversity of Vietnam, but also provide strong baseline data for measuring future change resulting from environmental perturbations., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Examinations of some deep-sea hydrothermal vent fishes from the western and eastern regions of the Pacific Ocean revealed the presence of three new species of Ascarophis van Beneden, 1871 (Nematoda: Cystidicolidae), all gastrointestinal parasites, namely: A. justinei n. sp. from Thermarces cerberus Rosenblatt & Cohen (type host) and Thermichthys hollisi Cohen, Rosemblatt & Moser (both Zoarcidae, Perciformes) and A. globuligera n. sp. from T. cerberus from the Northern East Pacific Rise, and A. monofilamentosa n. sp. from Pyrolicus manusanus Machida & Hashimoto (Zoarcidae, Perciformes) from the Manus Basin near Papua New Guinea. Specimens are described and illustrated based on light and scanning electron microscopical examinations. In addition to other morphological differences, all the three new species differ from each other by the structure of eggs: eggs bearing a lateral superficial swelling (A. globuligera n. sp.), eggs with one conspicuously long filament on one pole (A. monofilamentosa n. sp.) and eggs smooth, without any filaments or swellings (A. justinei n. sp.). The egg morphology of the two first-named species is unique within all species of Ascarophis, which indicates that all the three newly described species of Ascarophis are probably endemic to the respective hydrothermal vents as their fish hosts., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Recent examinations of some marine fishes from off the southern coast of Iraq revealed the presence of two new species of Dichelyne (Dichelyne) Jägerskiöld, 1902 (Nematoda: Cucullanidae), both intestinal parasites, namely: D. (D.) lethrini n. sp. from the smalltooth emperor Lethrinus microdon Valenciennes (Lethrinidae, Acanthuriformes) and D. (D.) iraqiensis n. sp. from the humphead snapper Lutjanus sanguineus (Cuvier) (Lutjanidae, Acanthuriformes). Specimens are described and illustrated based on light and scanning electron microscopical examinations. Dichelyne (D.) lethrini n. sp. is mainly characterised by the length of spicules (522 µm), presence of a dorsal caecum, location of deirids at the level of the posterior end of oesophagus and the post-oesophageal position of the excretory pore, number (10 pairs) and distribution of caudal papillae in the male, and the presence of two minute terminal spines on the female tail tip. Dichelyne (D.) iraqiensis n. sp. differs from the species of the subgenus Dichelyne mainly based on the absence of caudal spines, the presence of a dorsal caecum, the length of spicules (789-884 µm), the location of deirids and the excretory pore approximately at the same level, and the size of eggs (72-78 × 42-51 µm). These new species infecting marine fishes in Iraq represent new geographic records of cucullanids of the subgenus Dichelyne from fishes in marine waters off Iraq., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

This paper provides an updated checklist of species-level identified myxosporeans from marine and freshwater fishes in Vietnam. The list includes 51 nominal species (38 marine and 13 freshwater) belonging to 9 genera: Myxobolus Bütschli, 1882 (26 species); Kudoa Meglitsch, 1947 (6 species); Henneguya Thélohan, 1892 (6 species); Thelohanellus Kudo, 1933 (5 species); Unicapsula Davis, 1924 (2 species); Ceratomyxa Thélohan, 1892 (2 species), Zschokkella Auerbach, 1909 (2 species); Auerbachia Meglitsch, 1960 (1 species), and Meglitschia Kovaleva, 1988 (1 species). For each parasite species, information on myxospore morphology, line drawings, fish hosts, infection sites, and collection locality in Vietnam are reported. Where available, we also provide GenBank accession numbers for nucleotide sequence data. In addition, taxonomic status of several species was discussed and Myxobolus eszterbaueri nom. nov. is proposed as a junior homonym for Myxobolus hakyi Baska, Voronin, Eszterbauer, Müller, Marton & Molnár 2009, which is preoccupied., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)

Members of the parasitic copepod family Pennellidae are highly transformed ecto- or mesoparasites infecting a wide array of marine teleosts. Currently, this family contains more than 20 valid genera. The pennellid genus Cardiodectes Wilson, 1917 is currently known to contain 15 nominal species. Some pennellids exhibit a complex life cycle involving an intermediate host; it is known that planktonic pteropod molluscs are intermediate hosts for Cardiodectes. Pennellid mesoparasites can be detected by the conspicuous female egg-carrying trunk on the host external surface. The copepod cephalothorax is deeply embedded in the host muscle tissue. Members of Cardiodectes have been reported from several teleost families, mainly Myctophidae and Engraulidae. From the parasitological examination of a juvenile individual of a scarid teleost collected in a reef lagoon of Roatan Island, Honduras, Central America, several ovigerous female individuals of a mesoparasitic pennellid copepod were found; these specimens were recognized as representative of an undescribed species of Cardiodectes Wilson, 1917. The new species, C. roatanensis n. sp., differs from its known congeners in several respects, including the presence of neck lobes, paired posterior protuberances of the trunk, trunk shape and proportions, structure of cephalothorax lobes, cephalothorax relative size, and number of legs. The new species from Roatan is the second member of this copepod genus to be reported from the Caribbean region, after C. boxshalli Bellwood, 1981 from off Jamaica (Bellwood 1981). It is also the second report of Cardiodectes on a parrotfish., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

A new cryptogonimid trematode, Siphoderina hustoni n. sp., is reported, collected off Lizard Island, Queensland, Australia, from the Maori snapper Lutjanus rivulatus (Cuvier). The new species is moderately distinctive within the genus. It is larger and more elongate than most other species of Siphoderina Manter, 1934, has the shortest forebody of any, a relatively large ventral sucker, a long post-testicular zone, and is perhaps most recognisable for the substantial space in the midbody between the ventral sucker and ovary devoid of uterine coils and vitelline follicles, the former being restricted to largely posterior to the ovary and the latter distributed from the level of the anterior testis to the level of the ovary. In phylogenetic analyses of 28S ribosomal DNA, the new species resolved with the other nine species of Siphoderina for which sequence data are available, all of which are from Queensland waters and from lutjanid and haemulid fishes. Molecular barcode data were also generated, for the ITS2 ribosomal DNA and cox1 mitochondrial DNA markers. The new species is the first cryptogonimid known from L. rivulatus and the first metazoan parasite reported from that fish in Australian waters., (© 2022. The Author(s).)

In 2014-2015 and 2019-2021, teleost fishes off Galindez Island (Antarctic Peninsula) were examined for trematodes. Combined morphological and molecular analyses revealed the presence of eight trematode species of four families (Hemiuridae, Lecithasteridae, Opecoelidae, Lepidapedidae) from five fish species. Only adult trematodes were found and all of them are Antarctic endemics with their congeners occurring on other continents. The hemiuroids, Elytrophalloides oatesi (Leiper & Atkinson, 1914), Genolinea bowersi (Leiper & Atkinson, 1914), and Lecithaster macrocotyle Szidat & Graefe, 1967 belong to the most common Antarctic species and together with Lepidapedon garrardi (Leiper & Atkinson, 1914) and Neolebouria georgiensis Gibson, 1976 they were recorded as the least host-specific parasites. The originally sub-Antarctic Neolepidapedon macquariensis Zdzitowiecki, 1993 is a new record for the Antarctic Peninsula and Parachaenichthys charcoti (Vaillant), is a new host record. Neolebouria terranovaensis Zdzitowiecki, Pisano & Vacchi, 1993 is considered a synonym of N. georgiensis because of identical morphology and dimensions. The currently known phylogenetic relationships within the studied families are supported, including the polyphyly of Macvicaria Gibson & Bray, 1982 with the future need to accommodate its Antarctic species in a new genus. The validity of M. georgiana (Kovaleva & Gaevskaja, 1974) and M. magellanica Laskowski, Jezewski & Zdzitowiecki, 2013 needs to be confirmed by further analyses. Genetic sequence data are still scarce from Antarctica, and more studies applying integrative taxonomic approaches and large-scale parasitological examinations of benthic invertebrates are needed to match sequences of larval stages to those of well-characterised adults and to elucidate trematode life-cycles., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

The family Pennellidae comprises ecto- and mesoparasitic copepods on marine fishes. Although a preliminary scheme of phylogenetic relationships of pennellids based on morphological characters exists, it is difficult to objectively define character states because of their highly modified bodies and reduced appendages. This molecule-based study analysed phylogenetic relationships among seven genera and 12 species of pennellids, using 18S and 28S ribosomal DNA sequences in order to infer evolutionary trends within the family. Our molecular analysis recovered three clades (Clade-I, Peniculus; Clade-II, Haemobaphes-Lernaeocera-Phrixocephalus-Exopenna-Lernaeenicus radiatus; and Clade-III, Pennella-Lernaeenicus spp.). This result was congruent with some of the morphology-based phylogenetic relationships previously proposed but did not support a sister group comprising Exopenna, Phrixocephalus and Pennella. The second and third offshoots after the divergence of Clade-I species are characterized by reduced body tagmosis and changes in lifestyle from ectoparasites to mesoparasites. In some gill parasites of Clade-II, their sigmoid-shaped bodies and coiled egg strings have likely evolved in adaptation to the limited available space within the gill cavities of the hosts. Phrixocephalus is an eye parasite in Clade-II, which also has coiled egg strings, may have descended from an ancestral gill parasite. All species of Clade-III are characterized by the possession of a head region with processes deeply embedded into the host tissues and functioning as an anchor., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Recent examinations of some marine fishes from off the southern coast of Iraq revealed the presence of two species of Philometra Costa, 1845 (Nematoda: Philometridae): P. parabrevicollis n. sp. (males and subgravid and nongravid females) from the ovary of the bigeye snapper Lutjanus lutjanus Bloch (Perciformes, Lutjanidae) and Philometra sp. (subgravid females) from the ovary of the bartail flathead Platycephalus indicus (Linnaeus) (Perciformes, Platycephalidae). Specimens of species are described and illustrated based on light and scanning electron microscopical examinations. Philometra parabrevicollis n. sp. is mainly characterised by the length of spicules (267-285 µm) and gubernaculum (159-168 µm), the gubernaculum/spicule length ratio (1:1.64-1.76), the structure of the gubernaculum distal tip and of the male caudal end, and the body length of males (4.03-4.90 mm). The description of this new species again confirms a high degree of host specificity of gonad-infecting species of Philometra in congeneric lutjanid hosts. Although Philometra sp. parasitising P. indicus in Iraqi waters was previously recorded, its subgravid females are described for the first time. A key to gonad-infecting species of Philometra parasitic in fishes of the family Lutjanidae is provided., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Gorgorhynchoides pseudocarangis n. sp. (Isthmosacanthidae), is described from the intestine of the white trevally Pseudocaranx dentex (Bloch & Schneider) (Carangiformes: Carangidae) collected in Moreton Bay, Queensland, Australia. The new species has a proboscis armature of 27-28 rows of 16-17 hooks. It is most similar morphologically to Gorgorhynchoides bullocki Cable & Marafachisi, 1970 and Gorgorhynchoides gnathanodontos Smales, 2014 but differs from the former in having a longer proboscis with more rows of hooks, ventral hooks 6/7-12 with notched tips and trunk spines which do not extend onto the anterior bulbous swelling, and from the latter in having a longer proboscis, ventral hooks 6/7-12 with notched tips, more circles of trunk spines, larger eggs and a proboscis armature with all hooks lacking manubria. Previous molecular phylogenetic analyses have shown that the genus Serrasentis Van Cleave, 1923 is sister to Gorgorhynchoides Cable & Linderoth, 1963, although some have failed to resolve these two lineages in separate monophyletic clades. We performed novel single-gene and concatenated phylogenetic analyses using cox1 mtDNA, 18S and 28S rDNA gene-sequences, resolving Gorgorhynchoides and Serrasentis in monophyletic sister clades and demonstrating that Gorgorhynchoides pseudocarangis n. sp. is phylogenetically distinct from related species for which molecular sequence data are available. We view the previous amendment of the Isthmosacanthidae to include the genera Golvanorhynchus Noronha, Fabio & Pinto, 1987, Gorgorhynchoides, Isthmosacanthus Smales 2014 and Serrasentis, and the transfer of the family to the Polymorphida, as the most satisfactory classification at present, although additional molecular evidence would provide greater stability., (© 2021. The Author(s), under exclusive licence to Springer Nature B.V.)

Thirteen species of sea lice (family Caligidae) are reported from a range of elasmobranch and actinopterygian fishes caught off South Africa or obtained from public aquaria in South Africa. Two new species of Caligus Müller, 1785 are described: C. linearis n. sp. from Pomatomus saltatrix (Linnaeus) and C. tumulus n. sp. from Chrysoblephus cristiceps (Valenciennes). A supplementary description is provided for both sexes of Caligus tetrodontis Barnard, 1948 taken from Amblyrhynchotes honckenii (Bloch) and previous records of this parasite from South African fishes are critically reviewed. It is concluded that Caligus material from Arothron hispidus Linnaeus was previously misidentified as C. tetrodontis and is in urgent need of re-examination. Morphological and molecular observations on Caligus furcisetifer Redkar, Rangnekar & Murti, 1949 indicate that this copepod is phenotypically and genetically identical to Lepeophtheirus natalensis Kensley & Grindley, 1973, and the latter becomes a junior subjective synonym of C. furcisetifer. We include new geographical distribution records for Caligus longipedis Bassett-Smith, 1898, C. rufimaculatus Wilson, 1905 and Lepeophtheirus spinifer Kirtisinghe, 1937, extending into South African waters, as well as both new distribution and host records for Alebion gracilis Wilson, 1905, Caligus dakari van Beneden, 1892 and Lepeophtheirus acutus Heegaard, 1943. The molecular analysis confirmed the monophyly of the genus Caligus. The South African species of Caligus did not cluster together, but the two included South African species of Lepeophtheirus were recovered as sister taxa., (© 2021. The Author(s).)

Tapeworms (Cestoda) of the Proteocephalus-species aggregate from cyprinoids, pike, eel, smelt and cavefish in the Nearctic region (North America) are reviewed, based on a critical examination of newly collected and museum specimens. For some species neither new nor museum specimens were available and only literature data were used for these taxa. Two species occur in North American cyprinoids: (i) Nearctic Proteocephalus buplanensis Mayes, 1976 in Semotilus atromaculatus (Mitchill) in the upper Mississippi River and Hudson Bay drainage basins, and (ii) Holarctic P. torulosus (Batsch, 1786) (syns. P. ptychocheilus Faust, 1919; P. cobraeformis Haderlie, 1953; and Ophiotaenia critica Mpoame & Landers, 1981, new synonym), which occurs in Ptychocheilus spp. and other leuciscids in the western part of North America. Proteocephalus pinguis La Rue, 1911 is a specific parasite of pike (Esox spp.), which is briefly redescribed here to establish its diagnostic morphological characteristics because the original description was based on a mixture of at least two species. In addition to P. pinguis, pike serve as postyclic hosts of several species of the Proteocephalus-aggregate typical of other fish, such as bass, perch and whitefish, namely P. fluviatilis Bangham, 1925, P. pearsei La Rue, 1919 and P. longicollis (Zeder, 1800). Cavefish (Amblyopsidae) in North America harbour two endemic species, P. chologasteri Whittaker & Hill, 1968 from Chologaster agassizii Putman and P. poulsoni Whittaker & Zober, 1978 from Amblyopsis spelaea DeKay, which have never been found since their original description and their validity should be confirmed based on new collections and molecular data. Two other species of the Proteocephalus-aggregate, P. macrocephalus (Creplin, 1825), a parasite of eels (Anguilla spp.), and P. tetrastomus (Rudolphi, 1810) from smelt (Osmeridae), have circumboreal (Holarctic) distribution. Molecular data are available only for three of the seven species treated herein, but they do not form a monophyletic group.

A new parasitic copepod, Ergasilus yandemontei n. sp., is described based on 10 adult females collected from the gills of the atherinid silverside Odontesthes hatcheri (Eigenmann), in Lake Pellegrini, Neuquén Province, Patagonia, Argentina. This new copepod species is characterized by having: (i) a 2-segmented endopod on leg 1; (ii) a semi pinnate seta on the terminal segment of the exopod of leg 1; (iii) a reduced leg 5 with a single seta; (iv) aesthetascs on antennule, 1 aesthetasc on the sixth segment and 1 on the fourth segment. Ergasilus yandemontei n. sp. represents the first species described from Patagonian freshwaters. Ergasilus sieboldi var. patagonicus Szidat, 1956 described from Lake Pellegrini, should be considered a synonym of the new species described herein.

A synopsis of the species of Zschokkella Auerbach, 1910 (Myxozoa: Bivalvulida: Myxidiidae) is presented, including 94 nominal species from piscine hosts and 3 additional nominal species from amphibian or reptilian hosts. The most relevant morphological and morphometric features of both myxospores and trophozoite stages (when available) are presented for each species in tabulated format.

The diclidophorid Flexophora ophidii Prost & Euzet, 1962, the type- and only species of the genus Flexophora Prost & Euzet, 1962, has never been redescribed neither reported since its original description. The latest lacked a diagnosis of the genus that remains unavailable to date. Flexophora ophidii is redescribed and illustrated based on examination of new material from the type-host Ophidion barbatum L. (Ophidiiformes: Ophidiidae) collected off the Algerian coast (new geographical record), southern Mediterranean. A diagnosis of the genus is provided.

The current status of the caligid copepods parasitic on marine fishes off Turkey is reviewed and an updated checklist comprising a total of 24 species, belonging to three different genera, Caligus O. F. Müller, 1785, Euryphorus H. Milne Edwards, 1840 and Lepeophtheirus von Nordmann, 1832, is presented together with habitus illustrations and a key to all 24 species. Two of the species of caligids listed herein constitute new records for Turkish waters. The first, Caligus quadratus Shiino, 1954, a well-known species of the genus, was collected from the common dolphin fish, Coryphaena hippurus Linnaeus. The second, Caligus scribae Essafi, Cabral & Raibaut, 1984, a very rare and poorly known member of the genus, was sampled from a new teleost host, the parrot fish, Sparisoma cretense (Linnaeus). Both fish species were caught in north-eastern Mediterranean waters off the Turkish coast. Caligus quadratus is only briefly described based on key diagnostic characters whereas a full re-description is provided for C. scribae, as the only description available for this species is incomplete and lacks detail. Sparisoma cretense is a new host record for C. scribae. In addition, this is the first report of C. quadratus from the Mediterranean.

The Monorchiidae Odhner, 1911 are well represented in tropical and subtropical marine fishes worldwide but rarely reported from the Lutjanidae, an important family of tropical fishes that prey mainly on demersal fishes, decapods and cephalopods. Here, we report the first monorchiid from a lutjanid in Australian waters, Retroporomonorchis pansho n. g., n. sp. in Lutjanus fulvus (Forster), off Lizard Island on the northern Great Barrier Reef. It is morphologically and phylogenetically distinct among known monorchiids, resolves within the Monorchiinae Odhner, 1911, and is characterised by a relatively large ventral sucker, a sinistral genital pore immediately posterior to the ventral sucker, unfilamented eggs, a single testis, and vitelline follicles restricted to the level of the gonads. We assessed all previous records of monorchiids from lutjanid fishes and found only one to be convincing, that of Infundiburictus overstreeti (Gupta & Gupta, 1990) Wee, Cutmore, Pérez-del-Olmo & Cribb, 2020 from Lutjanus monostigma (Cuvier) in the Bay of Bengal. Another, Monorcheides xishaensis Shen, 1985, from Lutjanus argentimaculatus (Forsskål) in the Paracel Islands, South China Sea, is here recognised as a cryptogonimid, and is synonymised with Siphoderina asiatica Gu & Shen, 1979. In the remaining reports, the identity of the host is either ambiguous or doubtful, or the identity of the worm is not supported with sufficient evidence.

A new species of deep-sea digenean, Steringophorus merretti n. sp., is described from the bythitid fish Cataetyx laticeps in deep waters of the Goban Spur, Northeastern Atlantic. It is distinguishable from other described members of the genus by its tiny eggs and large cirrus-sac. A phylogenetic tree, based on 28S rDNA sequences, indicates that this species is embedded within a clade of deep-sea species and is sister to the eurybathic species S. thulini Bray & Gibson, 1980. Steringotrema robertpoulini Pérez-Ponce de León, Anglade & Randhawa, 2018 falls within the Steringophorus Odhner, 1905 clade. In view of this the morphological and biological characteristics of species of Steringophorus and Steringotrema are discussed.

Chimaeras, or ratfishes, are the only extant group of holocephalan fishes and are the sole host group of gyrocotylidean cestodes, which represent a sister group of the true tapeworms (Eucestoda). These unique, non-segmented cestodes have been known since the 1850s and multiple species and genera have been erected despite a general agreement that the delineation of species on the basis of morphology is effectively impossible. Thus, in the absence of molecular studies, the validity of gyrocotylid taxa and their specific host associations has remained highly speculative. Here we report the presence of Gyrocotyle spp. from rarely-caught deep-sea chimaeras collected in the North-East Atlantic, and describe two new species: G. haffii n. sp. from the bent-nose chimaera, Harriota raleighana Goode & Bean, and G. discoveryi n. sp. from the large-eyed rabbit fish, Hydrolagus mirabilis (Collett). Nuclear ribosomal sequence data were generated for individual parasites taken from different host species collected on different dates and from different localities and were combined with previously published sequences. Phylogenetic analyses supported the recognition of independent lineages and clusters, indicative of species, but were indecisive in recovering the root of the tree in analyses that included non-gyrocotylid outgroup taxa. The molecular data reveal variation not reflected in morphology and point to a complex picture of genetic divergence shaped by both isolation and migration in the deep-sea environment.

Based on light and scanning electron microscopical studies, a new nematode parasite, Paracapillaria (Paracapillaria) gastrica n. sp. (Capillariidae), is described from the stomach of the marine fish (variegated lizardfish) Synodus variegatus (Lacépède) (Aulopiformes: Synodontidae) from off New Caledonia. This species is mainly characterised by the length of the spicule (267 µm), the proximal spicule end expanded to form a conspicuous folded, lobular rim, the presence of a well-developed caudal bursa supported by two lateral projections (rays) not adhering to the posterior border of body and by the size of eggs (54-60 × 24-27 µm) with non-protruding polar plugs. Paracapillaria gastrica n. sp. is the first known capillariid species parasitic in a host belonging to the fish order Aulopiformes and the first species of this genus reported from fishes in New Caledonian waters and the South Pacific Ocean.

We provide molecular data (cox1, 18S rDNA and 28S rDNA) for 17 acanthocephalan species and 20 host-parasite combinations from Australian marine teleosts collected from off Queensland, Australia. Fourteen of these acanthocephalans are characterised with molecular data for the first time and we provide the first molecular data for a species of each of the genera Heterosentis Van Cleave, 1931, Pyriproboscis Amin, Abdullah & Mhaisen, 2003 and Sclerocollum Schmidt & Paperna, 1978. Using 18S and 28S rDNA sequences, the phylogenetic position of each newly sequenced species is assessed with both single-gene and concatenated 18S+28S maximum likelihood and Bayesian inference analyses. Additional phylogenetic analyses focusing on the genus Rhadinorhynchus Lühe, 1912 and related lineages are included. Our phylogenetic results are broadly consistent with previous analyses, recovering previously identified inconsistencies but also providing new insights and necessitating taxonomic action. We do not find sufficient evidence to recognise the Gymnorhadinorhynchidae Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014 as distinct from the Rhadinorhynchidae Lühe, 1912. The family Gymnorhadinorhynchidae and its sole genus, Gymnorhadinorhynchus Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014, are here recognised as junior synonyms of Rhadinorhynchidae and Rhadinorhynchus, respectively. The two species currently assigned to Gymnorhadinorhynchus are recombined as Rhadinorhynchus decapteri (Braicovich, Lanfranchi, Farber, Marvaldi, Luque & Timi, 2014) n. comb. and Rhadinorhynchus mariserpentis (Steinauer, Garcia-Vedrenne, Weinstein & Kuris, 2019) n. comb. In all of our analyses, Rhadinorhynchus biformis Smales, 2014 is found basal to the Rhadinorhynchidae + Transvenidae Pichelin & Cribb, 2001, thus resulting in a paraphyletic Rhadinorhynchidae. It appears that R. biformis may require a new genus and family; however, morphological data for this species are currently insufficient to adequately distinguish it from related lineages, thus we defer the proposal of any new higher-rank names for this species. Species of the genus Sclerocollum, currently assigned to the Cavisomidae Meyer, 1932, are found nested within the family Transvenidae. We transfer the genus Sclerocollum to the Transvenidae and amend the diagnosis of the family accordingly. The genera Gorgorhynchoides Cable & Linderoth, 1963 and Serrasentis Van Cleave, 1923, currently assigned to the Rhadinorhynchidae, are supported as sister taxa and form a clade in the Polymorphida. We transfer these genera and Golvanorhynchus Noronha, Fabio & Pinto, 1978 to an emended concept of the Isthomosacanthidae Smales, 2012 and transfer this family to the Polymorphida. Lastly, Pyriproboscis heronensis (Pichelin, 1997) Amin, Abdullah & Mhaisen, 2003, currently assigned to the Pomphorhynchidae Yamaguti, 1939, falls under the Polymorphida in our analyses with some support for a sister relationship with the Centrorhynchidae Van Cleave, 1916. As this species clearly does not belong in the Pomphorhynchidae and is morphologically and molecularly distinct from the lineages of the Polymorphida, we propose the Pyriprobosicidae n. fam. to accommodate it.

The species diversity of Lepidapedon Stafford, 1904 (Lepidapediae) in the Western Mediterranean was assessed based on samples from five deep-sea gadiform fishes collected between the Balearic Islands and the Catalonian coast of Spain: Lepidion lepidion (Risso) and Mora moro (Risso) (both Moridae); Coelorinchus mediterraneus Iwamoto & Ungaro and Trachyrincus scabrus (Rafinesque) (both Macrouridae); and Phycis blennoides (Brünnich) (Phycidae). Integration of morphological and molecular evidence (28S rRNA gene and the mitochondrial nad1 gene) revealed that the deep-sea fishes in the Western Mediterranean share two species of Lepidapedon. Lepidapedon desclersae Bray & Gibson, 1995 was recovered in all five fish species of three families [Moridae (L. lepidion and M. moro); Macrouridae (C. mediterraneus and T. scabrus); and Phycidae (P. blennoides)] and L. guevarai Lopez-Roman & Maillard, 1973 was recovered in three fish species of three families [Phycidae (P. blennoides); Macrouridae (T. scabrus); and Moridae (L. lepidion)]. Therefore, both species are considered to be euryxenic but restricted to gadiforms. The voucher material for the two species from different fish hosts is described in detail and the host-related variability based on the morphometric data is assessed.

We isolated and re-investigated Nephrocystidium pickii Weißenberg, 1921 (Myxozoa: Bivalvulida: Variisporina) using light microscopy and phylogenetic analysis of the small-subunit (SSU) ribosomal RNA gene. This species is a parasite of the northern pike Esox lucius L. (Actinopterygii: Esocidae) which localizes in the endothelial cells of the glomerular capillary. The results of the phylogenetic analysis including this species clarify its taxonomic status and show that although it is the closest relative to Myxidium lieberkuehni Bütschli, 1882, the two organisms are not conspecific, contrary to the earlier hypotheses. The data obtained highlight the necessity of a profound taxonomic revision of the Myxozoa and the need to clarify species affiliation of extrasporogonic developmental stages of these organisms that occur in different organs of fish.

Three species of parasitic nematodes are redescribed based on light and scanning electron microscopical (SEM) examinations of newly collected specimens in fishes of South Carolina, USA: Dichelyne (Cucullanellus) bullocki Stromberg & Crites, 1972 from Fundulus heteroclitus (Linnaeus) (Fundulidae); Dichelyne (Dichelyne) diplocaecum Chandler, 1935 from Ictalurus furcatus (Valenciennes) (Ictaluridae); and Hysterothylacium pelagicum Deardorff & Overstreet, 1982 from Coryphaena hippurus Linnaeus (Coryphaenidae). For the first time, intraspecific variations in the number of intestinal caeca were observed in D. bullocki, as well as previously unknown males and gravid females of D. diplocaecum are described; this enabled to synonymise D. mexicanus Caspeta-Mandujano, Moravec & Salgado-Maldonado, 1999 with D. diplocaecum. Unlike most congeneric species, H. pelagicum has no double postanal papillae, as confirmed by SEM. A key to the species of Dichelyne Jägerskiöld, 1902 parasitic in freshwater and brackish-water fishes in North America is provided.

Two rhadinorhynchid acanthocephalans are described from marine fishes off the Pacific coast of Vietnam. Sclerocollum neorubrimaris n. sp. (Gorgorhynchinae Van Cleave & Lincicome, 1940) is described from the spine-foot rabbitfish Siganus guttatus (Bloch) (Siganidae) off Nha Trang. The new species is similar to the type-species, Sclerocollum rubrimaris Schmidt & Paperna, 1978 in most measurements and counts but has a posterior cephalic ganglion, a sub-ventral female gonopore, and one dorsal paravaginal filament bundle. In S. rubrimaris, the cephalic ganglion is near the middle of the receptacle, the female gonopore is terminal with two paravaginal filament bundles. The new species is distinguished from three other species of Sclerocollum Schmidt & Paperna, 1978 in proboscis hook formulas and the position of the female gonopore and cephalic ganglion. The issue of the importance of the position of the cephalic ganglion at the generic and sub-generic levels in the Acanthocephala is discussed. Females of Australorhynchus multispinosus n. sp. (Gorgorhynchinae) are described from the red cornetfish Fistularia petimba Lacépède off Nha Trang in the Pacific south. It is distinguished from the only other species of the genus, Australorhynchus tetramorphacanthus Lebedev, 1967, by having more trunk spines extending beyond the level of the proboscis receptacle and a smaller proboscis with considerably fewer hooks.

Opistholebetine opecoelids are reported following examination of 1,041 individual tetraodontiform fishes, comprising 60 species and seven families, collected in Australian waters between 1986 and 2018. Nine species consistent with Opistholebes Nicoll, 1915, Heterolebes Ozaki, 1935 or Maculifer Nicoll, 1915 were recovered. However, phylogenetic analysis of sequence data, generated for some of these species, suggested that five genera, not three, are required to adequately accommodate these taxa. Thus, the concept and composition for each is revised, Pseudoheterolebes Yamaguti, 1959 nec Gupta, 1968 is resurrected and Parallelolebes n. g. is proposed. Of the nine species examined, five are new. Four new species are from fishes endemic to subtropical and temperate Australian waters for which no trematodes have previously been reported: Pa. australis n. sp. and Ps. corazonae n. sp. from the slender-spined porcupinefish Diodon nicthemerus Cuvier (Diodontidae) off Stanley, Tasmania; Pa. virilis n. sp. from the horse-shoe leatherjacket Meuschenia hippocrepis (Quoy & Gaimard) (Monacanthidae) off Stanley; and Ps. stellaglobulus n. sp. from the threebar pocupinefish Dicotylichthys punctulatus Kaup (Diodontidae) in Moreton Bay, south-east Queensland. The fifth new species is M. diodontis n. sp., collected from the spotted porcupinefish Diodon hystrix Linnaeus and the blackblotched porcupinefish D. liturosus Shaw, in tropical waters on the Great Barrier Reef. Species reported previously include the type-species of Opistholebes, O. amplicoelus Nicoll, 1915 from the rough golden puffer Lagocephalus lunaris (Bloch & Schneider) (Tetraodontidae) and the common toadfish Tetractenos hamiltoni (Richardson) (Tetraodontidae) in Moreton Bay, and three species reported for the first time from fishes in Australian waters: H. maculosus Ozaki, 1935, Pa. elongatus Ozaki, 1937 n. comb. and Ps. diodontis (Cable, 1956) n. comb., each from both D. hystrix and D. liturosus on the Great Barrier Reef. Following the revisions, Opistholebes is recognised for two species, Heterolebes for five, Maculifer for eight, Pseudoheterolebes for five and Parallelolebes for three.

Eight species of the trematode family Bucephalidae Poche, 1907 are reported from teleost fishes in Moreton Bay, Queensland, Australia. Heterobucephalopsis yongi n. sp. is described from Gymnothorax eurostus (Muraenidae); the new form is distinguished from its congeners in the possession of a tiny cirrus-sac relative to body length, the length of the caecum, the position of the mouth and pharynx, and the position of the testes and ovary. Two known species of Dollfustrema Eckmann, 1934, D. durum Nolan, Curran, Miller, Cutmore, Cantacessi & Cribb, 2015 and D. gibsoni Nolan & Cribb, 2010, are reported from Gymnothorax pseudothyrsoideus (Bleeker) (Muraenidae); although both species were described from Australian waters, this represents the first reports from Moreton Bay and G. pseudothyrsoideus. Four species of Prosorhynchus Odhner, 1905 are reported, including one new, P. brayi n. sp., which is described from Epinephelus coioides (Hamilton) (Serranidae); P. brayi n. sp. is distinguished from its congeners in the possession of vitelline follicles in a confluent arc distinctly posterior to a conical rhynchus, uterine coils that do not extend anterior to the vitelline arc, contiguous testes, a cirrus-sac that reaches anteriorly to at least the level of the posterior testis and a short excretory vesicle. Three known species of Prosorhynchus are reported from Australia, for the first time: P. luzonicus Velasquez, 1959 and P. maternus Bray & Justine, 2006 from E. coioides and Prosorhynchus platycephali (Yamaguti, 1934) Srivastava, 1938 from Ambiserrula jugosa (McCulloch) and Inegocia japonica (Cuvier) (Platycephalidae). Skrjabiniella Issaitschikow, 1928 is re-recognised for new specimens of Skrjabiniella uniporus (Ozaki, 1924) n. comb. collected from Conger cinereus Rüppell (Congridae); three additional species of Prosorhynchus are considered members of this genus, two of which are synonymised with S. uniporus.

Two new species of parasitic copepods, Sagum gurukun n. sp. and S. bitaro n. sp. (Siphonostomatoida: Lernanthropidae), are described based on specimens collected from the gill filaments of the double-lined fusilier Pterocaesio digramma (Bleeker) (Actinopterygii: Perciformes: Caesionidae) and the five-lined snapper Lutjanus quinquelineatus (Bloch) (Actinopterygii: Perciformes: Lutjanidae), respectively, caught off Iriomote-jima Island, the Ryukyu Islands, East China Sea, Japan. The findings bring the number of species of Sagum to 14. The two new species are similar in the morphology of the head and the legs 3 and 4 to the three congeners, S. folium Ho, Liu & Liu, 2011, S. paracaesionis Izawa, 2014 and S. vietnamiensis Kazachenko, Kovaleva, Nguyen & Ngo, 2017. Sagum gurukun n. sp. is differentiated from the three congeners by the proportions of the caudal rami, the absence of leg 5, and the shape of the legs 1 and 2. Sagum bitaro n. sp. differs from the three congeners and S. gurukun n. sp. by the presence of the conical leg 5 armed with an apical seta. A key to the species of the genus Sagum, based on the available information on female morphology in previous publications and the present study, is provided. To date, a total of 19 species of lernanthropid copepods considered valid are known in Japanese waters.

During a research on gill ectoparasites of Peruvian marine fishes, four dactylogyrid (Monogenea) species, parasitising two teleost species, Bodianus diplotaenia (Gill) (Labridae) and Calamus brachysomus (Lockington) (Sparidae), were found. Euryhaliotrema luisae n. sp. ex C. brachysomus is differentiated from other congeneric species by the morphology of the male copulatory organ, which comprises a coil of nine counterclockwise rings, and by the morphology of the anchors and bars. Euryhaliotrema magnopharyngis n. sp. ex C. brachysomus can be distinguished from all other congeners by having a well-developed pharynx occupying much of the anterior region and by the ventral bar, which is V-shaped, with well-elongated, thin arms. In addition, E. luisae n. sp. and E. magnopharyngis n. sp. can be differentiated from all other members of Euryhaliotrema Kritsky & Boeger, 2002 by the presence of a glandular oval plate lying on peduncle. Haliotrema diplotaenia n. sp. ex B. diplotaenia is characterised by the structure of the male copulatory organ, comprising a tapered-shaped cirrus tube with twisted acute tip and a filament-shaped accessory piece with medial and distal expansions, and by the morphology of the ventral bar (inverted W-shaped, with short lateral ends and two anterior conical protuberances). Haliotrema saezae n. sp. ex B. diplotaenia differs from all other members of Haliotrema Johnston & Tiegs, 1922 by having a tubular copulatory organ with curved distal tip and a filament-shaped accessory piece without lateral expansions, and by the morphology of anchors and bars. The present findings are added to the other six marine dactylogyrids previously reported from Peru.

Two new genera and three new species of paramphistomoid digeneans are described in the family Cladorchiidae Fischoeder, 1901 from doradid, heptapterid, pimelodid and pseudopimelodid fishes in the Amazon River in Peru. Goeldamphistomum amazonum n. g., n. sp. (type-species) from Goeldiella eques (Müller & Troschel) (type-host) and Tenellus trimaculatus (Boulenger), and Goeldamphistomum peruanum n. g., n. sp. from Duopalatinus peruanus Eigenmann & Allen (type-host), Calophysus macropterus (Lichtenstein) and Microglanis sp. are placed in the Dadayiinae Fukui, 1929. Both species have an accessory acetabular sucker, which distinguishes the genus from all taxa previously reported from South American freshwater fishes. They differ from each other primarily in that G. amazonum has a prebifurcal genital pore and oblique, separated testes, the levels of which rarely overlap longitudinally, whereas G. peruanum has a postbifurcal genital pore and testes directly to obliquely tandem. Iquitostrema papillatum n. g., n. sp. (Kalitrematinae Travassos, 1933) from the intestine of Hassar orestis (Steindachner) differs from other members of the subfamily in the combination of a massive acetabulum with a papillate luminal surface and symmetrical testes which overlie the caeca close to the caecal arch. These are the first records of paramphistomes from the five host species studied here.

Two new species of Bacciger Nicoll, 1914 (Faustulidae) are described infecting clupeids collected from the waters off Queensland, Australia; Bacciger minor n. sp. is described from Herklotsichthys castelnaui (Ogilby) in Moreton Bay, southern Queensland and Bacciger major n. sp. is described from Herklotsichthys quadrimaculatus (Rüppell) collected off Lizard Island, on the northern Great Barrier Reef. The two species both differ from previously described species of Bacciger in the combination of their generally elongate bodies, an entire rather than deeply lobed ovary, vitelline follicles that reach to at least the intestinal bifurcation, instead of restricted to further posteriorly but principally distributed in the hindbody, and intestinal caeca extending posteriorly well past the ventral sucker. The two new species have non-overlapping size ranges and differ in their sucker ratios, the distribution of the vitelline follicles and in the shape of the cirrus-sac. ITS2 and 28S rDNA sequence data distinguish the two new species unambiguously. Phylogenetic analysis of available 28S data show they are most closely related to Pseudobacciger cheneyae Sun, Bray, Yong, Cutmore & Cribb, 2014, also recorded off Lizard Island. These are the first faustulids reported from species of Herklotsichthys Whitley, but overall members of the Clupeidae undoubtedly harbours the richest faustulid fauna of any fish family. Baccigeroides ovatus (Price, 1934) n. comb. is proposed for Bacciger ovatus (Price, 1934) Bray & Gibson, 1980 (syn. B. opisthonema Nahhas & Cable, 1964) based on the position of the genital pore being far anteriorly removed from the ventral sucker.

A survey of the trematode fauna of lutjanid fishes off the east coast of Queensland (QLD), Australia revealed the presence of two species of Neometadena Hafeezullah & Siddiqi, 1970 (Digenea: Cryptogonimidae). Neometadena paucispina n. sp. is described from the intestine and pyloric caeca of Lutjanus fulviflamma (Forsskål) and L. russellii (Bleeker) from Moreton Bay, in southeast QLD. Specimens of the type- and only other species, N. ovata (Yamaguti, 1952) Miller & Cribb, 2008, were recovered from L. carponotatus (Richardson), L. fulviflamma, L. fulvus (Forster), L. russellii, and L. vitta (Quoy & Gaimard) off Lizard Island, on the northern Great Barrier Reef (GBR). Neometadena paucispina is distinguished from N. ovata in having fewer oral spines (55-65 vs 67-80). Alignment of novel molecular data for these two taxa revealed that they differ consistently by 13 nucleotides (1.5%) over the partial large subunit (LSU), 34 nucleotides (6.6%) over the internal transcribed spacer 1 (ITS1), 0 nucleotides over the 5.8S, and 21 nucleotides (7.3%) over the ITS2 rDNA regions. Despite relatively large samples of L. carponotatus, L. fulviflamma and L. russellii from three distinct locations along the east coast of QLD (i.e. Moreton Bay in the south, Heron Island in central QLD and Lizard Island in northern QLD), these two species have been found at only one site each with neither species at Heron Island. These distributions are discussed in the context of the wide distribution of other cryptogonomid species in the same hosts elsewhere in the Indo-West Pacific.

An annotated list of larvae (metacestodes) of gryporhynchid tapeworms (Cestoda: Cyclophyllidea) from freshwater fishes in Africa is provided with numerous new host and geographical records. Newly collected materials from Burundi, Democratic Republic of the Congo, Kenya, Madagascar, Namibia, Senegal, South Africa, Sudan and Zimbabwe practically double the total number of species reported from African fish so far. We confirm the occurrence of 16 species (five unidentified to the species level and most likely representing new taxa) belonging to the genera Amirthalingamia Bray, 1974 (1 species), Cyclustera Fuhrmann, 1901 (2 species), Dendrouterina Fuhrmann, 1912 (1 species), Neogryporhynchus Baer & Bona, 1960 (1 species), Paradilepis Hsü, 1935 (4 species), Parvitaenia Burt, 1940 (5 species), and Valipora Linton, 1927 (2 species). Additionally, metacestodes of four unidentified species of Paradilepis and Parvitaenia are reported from fish for the first time. Rostellar hooks of all species are illustrated and their measurements are provided together with a host-parasite list. The molecular phylogenetic analysis based on partial LSU rDNA sequences offers the first insight into the internal phylogenetic relationships within the family. Together with the morphological observations, the present study provides a taxonomic baseline for future studies on this largely neglected, but widely distributed and relatively frequent, group of parasites of African fishes, including economically important cichlids like tilapias and cyprinids.

Despite morphological and ecological inconsistencies among species, all plagioporine opecoelids with a pedunculate ventral sucker are currently considered to belong in the genus Podocotyloides Yamaguti, 1934. We revise the genus based on combined morphological and phylogenetic analyses of novel material collected from haemulid fishes in Queensland waters that we interpret to represent species congeneric with the type-species, Pod. petalophallus Yamaguti, 1934, also known from a haemulid, off Japan. Our phylogenetic analysis demonstrates polyphyly of Podocotyloides; prompts us to resurrect Pedunculacetabulum Yamaguti, 1934; and suggests that Pod. brevis Andres & Overstreet, 2013, from a deep-sea congrid in the Caribbean, and Pod. parupenei (Manter, 1963) Pritchard, 1966 and Pod. stenometra Pritchard, 1966, from mullids and chaetodontids, respectively, on the Great Barrier Reef, may each represent a distinct genus awaiting recognition. Our revised concept of Podocotyloides requires a pedunculate ventral sucker, but also a uterine sphincter prior to the genital atrium, a petalloid cirrus appendage, restriction of the vitelline follicles to the hindbody, and for the excretory vesicle to reach to the level of the ventral sucker. Of about 20 nominal species, we recognise just three in Podocotyloides (sensu stricto): Pod. petalophallus, Pod. gracilis (Yamaguti, 1952) Pritchard, 1966 and Pod. magnatestes Aleshkina & Gaevskaya, 1985. We provide new records for Pod. gracilis, and propose two new species of Podocotyloides, Pod. australis n. sp. and Pod. brevivesiculatus n. sp., and one new Pedunculacetabulum species, Ped. inopinipugnus n. sp., all from haemulids. Podocotyloides australis is morphologically indistinguishable from Pod. gracilis, and exploits the same definitive host, but is genetically and biogeographically distinct. It is thus a cryptic species, the first such opecoelid to be formally named.

Three species of beloniform fishes were found infected with species of Monogenoidea Bychowsky, 1937 during a survey of the diversity of parasites infecting the fishes of Moreton Bay, Queensland, Australia. The diagnoses of Hareocephalus Young, 1969 and Hemirhamphiculus Bychowsky & Nagibina, 1969 (both Polyonchoinea Bychowsky, 1937: Dactylogyridae Bychowsky, 1933) were emended. Hareocephalus thiasae Young, 1969, type-species of the genus, was recorded and redescribed from the gill lamellae of the stout longtom Tylosurus gavialoides (Castelnau) (Belonidae), and six new species of Hemirhamphiculus were described from the gill lamellae of three host species: Hemirhamphiculus exserocephalus n. sp. from T. gavialoides; Hemirhamphiculus choanophallus n. sp. and Hemirhamphiculus flagrum n. sp. from the river garfish Hyporhamphus regularis (Günther) (Hemiramphidae); and Hemirhamphiculus perexiguus n. sp., Hemirhamphiculus krabsi n. sp., and Hemirhamphiculus imcomptus n. sp. from the southeastern snub-nose garfish Arrhamphus sclerolepis krefftii (Steindachner) (Hemiramphidae). An unidentified species of the Suborder Microcotylinea Lebedev, 1972 (Heteronchoinea Boeger & Kritsky, 2001) was found infecting single specimens of each of H. regularis and A. sclerolepis krefftii. Parahemirhamphiculus Bychowsky & Nagibina, 1969 is placed in junior subjective synonymy with Hemirhamphiculus, and its three species, Parahemirhamphiculus pinguis Bychowsky & Nagibina, 1969, Parahemirhamphiculus brevilamellatus Zhang, 2001, and Parahemirhamphiculus longilamellatus An & Zhang, 1988 are transferred to Hemirhamphiculus.

Acipensericola glacialis n. sp. infects the heart of lake sturgeon, Acipenser fulvescens (Rafinesque), in the Lake Winnebago System and differs from its only congener, Acipensericola petersoni Bullard, Snyder, Jensen & Overstreet, 2008, by having a dendritic intestine, deeply-lobed testes, a post-ovarian oötype, and a common genital pore that is medial to the dextral caecum. Acipensericola petersoni has a non-dendritic intestine, testes that are not deeply lobed, an oötype that is at level of the ovary (ventral to the ovary), and a common genital pore that is dorsal to the dextral caecum. Comparison of the large (28S) and small (18S) sub-unit ribosomal DNA and internal transcribed spacer 2 (ITS2) regions between specimens of A. glacialis n. sp. and A. petersoni revealed 13 (of 1,621 nt; 99.2% similarity in the 28S), 8 (of 1,841 nt; 99.9% similarity in the 18S), and 11 (of 442 nt; 97.5% similarity in the ITS2) nucleotide differences. Collectively, these results comprise an unexpectedly high degree of morphological and molecular similarity given the geographical (Mississippi River Basin vs Great Lakes Basin) and phylogenetic (Polyodontidae vs Acipenseridae) separation of these hosts but seemingly did not reject a previous hypothesis concerning lake sturgeon dispersal from the Mississippi Refugium following the Wisconsin glaciation ~18,000 years ago. The new species is the first nominal blood fluke described from a sturgeon.

Newly collected specimens of Procamallanus (Spirocamallanus) macaensis Vicente & Santos, 1972 from the intestine of Paralonchurus brasiliensis (Steindachner), off Rio de Janeiro, Brazil, are redescribed and genetically characterised. Additionally, all congeners deposited in the Coleção Helmintológica do Instituto Oswaldo Cruz (CHIOC) parasitic in marine fishes of the South Atlantic, including types of P. (S.) macaensis, were re-evaluated. The following features are described for the first time in P. (S.) macaensis: morphology and arrangement of cephalic structures, shape of deirids and location of phasmids. The position of the excretory pore, the number and arrangement of caudal papillae in males, the structure of the spicules and of tail end in both males and females are rectified. Most specimens deposited in the CHIOC identified as P. (S.) pereirai Annereaux, 1946 were transferred to P. (S.) macaensis and others were designated as Procamallanus (S.) sp. Procamallanus (S.) cruzi Guimarães, Cristófaro & Rodrigues, 1976 is considered a species inquirenda due to its poor description and the lack of match of its original description with the type-material re-examined. Moreover, several taxonomic problems were noted after observations of the specimens (mostly poorly preserved), including inadequate morphological reports as well as misidentifications. Phylogenies inferred using sequences of the SSU rDNA from camallanids (Nematoda: Camallanidae) mostly generated weakly supported clades; however, Camallanus Railliet & Henry, 1915 and Procamallanus Baylis, 1923 do not seem to be monophyletic. Based on the present results and the lack of molecular data, it would be pertinent to adopt the widely-used classification for the subgenera of Procamallanus.

A new microcotylid, Tinrovia mamaevi n. sp. (Monogenea: Polyopisthocotylea), is described from the gills of Notacanthus bonaparte Risso (Notacanthiformes: Notacanthidae), sampled in the Western Mediterranean and North East Atlantic. This species is allocated to the subfamily Syncoelicotylinae Mamaev & Zubchenko, 1978 due to the possession of a symmetrical haptor with two separate frills. The clamps in T. mamaevi n. sp. are of the "microcotylid" type, arranged in two distinct lateral haptoral frills; the genital atrium and the copulatory organ are armed and the vaginal pore is unarmed. The new species differs from the type- and only species of the genus, T. papiliocauda Mamaev, 1987, in having a shorter and narrower haptor with a smaller number of clamps. Clamps are also smaller in the new species, testes are more numerous, the genital atrium is smaller, divided into two lateral lobes (instead of five) with a smaller number of spines and the eggs have a short and a long filament (instead of two short filaments). The host species and locality of T. mamaevi n. sp. also differ as T. papiliocauda which was recorded in Notacanthus sexspinis Richardson from the South Pacific.

Three species of Heteromazocraes Mamaev, 1981 including two new taxa are described from the gills of three species of engraulid fishes Thryssa mystax (Bloch & Schneider), T. setirostris (Broussonet) and T. malabarica (Bloch) collected from the coastal waters off Visakhapatnam, Bay of Bengal. Heteromazocraes thryssaensis n. sp. differs from the closely related H. dodecacantha Mamaev, 1981 in the shape of the body and ovary, the number of testes and the number and shape of the genital hooks. Heteromazocraes engrauliae n. sp. differs from all the other species of the genus in the relative sizes of the haptoral clamps, in that the four closed clamps on the left side are larger than the two open clamps on the right side, in contrast to the situation in other species where the two open clamps on the anterior right side are markedly larger than the remaining clamps. Heteromazocraes kazikodiensis (Gupta & Khullar, 1967) Mamaev, 1981 regarded as a species inquirenda is redescribed with additional details and is reinstated as a valid species. A review of Heteromazocraes including a key for identification of the species is provided.

A new opecoelid trematode is reported from fishes of the Lethrinidae, Lutjanidae and Nemipteridae off Lizard Island on the northern Great Barrier Reef, Australia. The new species keys to Neolebouria Gibson, 1976 and shows strong similarity to several species of that genus, but is not consistent with the type-species, N. georgiensis Gibson, 1976, or others known from temperate/polar and/or deep-sea fishes. The new species is also phylogenetically distant from N. lanceolata (Price, 1934) Reimer, 1987, the only representative of the genus for which molecular data are available. A new genus, Trilobovarium n. g., is proposed for the new species, T. parvvatis n. sp. Eight morphologically similar species, previously recognised as belonging to Neolebouria, from shallow-water, mostly tropical/subtropical fishes, are transferred to Trilobovarium: T. diacopae (Nagaty & Abdel Aal, 1962) n. comb.; T. ira (Yamaguti, 1940) n. comb.; T. khalili (Ramadan, 1983) n. comb.; T. krusadaiense (Gupta, 1956) n. comb.; T. lineatum (Aken'Ova & Cribb, 2001) n. comb.; T. moretonense (Aken'Ova & Cribb, 2001) n. comb.; T. palauense (Machida, 2014) n. comb.; and T. truncatum (Linton, 1940) n. comb. Paramanteriella Li, Qiu & Zhang, 1988 is resurrected for five species of Neolebouria with a post-bifurcal genital pore: P. cantherini Li, Qiu & Zhang, 1988; P. capoori (Jaiswal, Upadhyay, Malhotra, Dronen & Malhotra, 2014) n. comb.; P. confusa (Overstreet, 1969) n. comb.; P. leiperi (Gupta, 1956) n. comb.; and P. pallenisca (Shipley & Hornell, 1905) n. comb. Neolebouria georgenascimentoi Bray, 2002, a species with an exceptionally long cirrus-sac, is transferred to Bentholebouria Andres, Pulis & Overstreet, 2004 as B. georgenascimentoi (Bray, 2002) n. comb., and N. maorum (Allison, 1966) Gibson 1976, an unusual species known from cephalopods, is designated a species incertae sedis. Eleven species are retained in a revised concept of Neolebouria.

Two new species of Cardicola Short, 1953 are described from the milkfish, Chanos chanos Forsskål (Gonorynchiformes: Chanidae), obtained from off Lizard Island on the northern Great Barrier Reef (GBR) and North Stradbroke Island in southeast Queensland. These are the first known blood flukes from this order of fishes. Cardicola suni n. sp. differs from all other Cardicola spp. by a combination of a large ovoid oral sucker surrounding a subterminal mouth, recurved tegumental spines up to 16 μm long, anterior caeca occupying 25.1-31.3% (28.7%) of total body length and a mostly-intercaecal ovary. Cardicola jiigurru n. sp. differs from C. suni n. sp. and all other species of Cardicola by a combination of a narrowly lanceolate body, weakly-muscularised and poorly-demarcated oral sucker, minute tegumental spines <1 µm in length, and anterior caeca occupying 15.9-22.0% (19.4%) of total body length, an almost entirely post-caecal ovary and the male genital pore terminal on a dorsolateral protuberance. A third species, closely resembling C. suni n. sp., was also discovered off Wangetti Beach, north Queensland, but is not described due to lack of material. Molecular phylogenetic analysis, based on both ITS2 and partial 28S rDNA regions, shows that these three species form a clade nested within that formed by existing species of Cardicola.