Digenean parasites of deep-sea teleosts: a review and case studies of intrageneric phylogenies

Lepocreadiidae (Trematoda) associated with gelatinous zooplankton (Cnidaria and Ctenophora) and fishes in Australian and Japanese waters

We examined gelatinous zooplankton from off eastern Australia for lepocreadiid trematode metacercariae. From 221 specimens of 17 species of cnidarian medusae and 218 specimens of four species of ctenophores, infections were found in seven cnidarian and two ctenophore species. Metacercariae were distinguished using cox1 mtDNA, ITS2 rDNA and morphology. We identified three species of Prodistomum Linton, 1910 [P. keyam Bray & Cribb, 1996, P. orientale (Layman, 1930), and Prodistomum Type 3], two species of Opechona Looss, 1907 [O. kahawai Bray & Cribb, 2003 and O. cf. olssoni], and Cephalolepidapedon saba Yamaguti, 1970. Two species were found in cnidarians and ctenophores, three only in cnidarians, and one only in a ctenophore. Three Australian fishes were identified as definitive hosts; four species were collected from Scomber australasicus and one each from Arripis trutta and Monodactylus argenteus. Transmission of trematodes to these fishes by ingestion of gelatinous zooplankton is plausible given their mid-water feeding habits, although such predation is rarely reported. Combined morphological and molecular analyses of adult trematodes identified two cox1 types for C. saba, three cox1 types and species of Opechona, and six cox1 types and five species of Prodistomum of which only two are identified to species. All three genera are widely distributed geographically and have unresolved taxonomic issues. Levels of distinction between the recognised species varied dramatically for morphology, the three molecular markers, and host distribution. Phylogenetic analysis of 28S rDNA data extends previous findings that species of Opechona and Prodistomum do not form monophyletic clades.

The oceanic pleuston community as a potentially crucial life-cycle pathway for pelagic fish-infecting parasitic worms

Pleustonic organisms form an important part of pelagic ecosystems by contributing to pelagic trophic chains and supporting connectivity between oceanic habitats. This study systematically analysed the trematode community harboured by pleustonic molluscs and cnidarians from offshore Queensland, Australia. Four mollusc and three cnidarian species were collected from beaches of North Stradbroke Island, Queensland. Two mollusc species and all three cnidarians harboured large numbers of hemiuroid metacercariae (Trematoda: Hemiuroidea). Eight taxa from four hemiuroid families (Accacoeliidae, Didymozoidae, Hemiuridae and Sclerodistomidae) were distinguished via molecular sequencing. Four of those taxa were identified to species. All trematode taxa except one didymozoid were shared by two or more host species; five species occurred in both gastropods and cnidarians. It is hypothesised that the life-cycles of these hemiuroids are highly plastic, involving multiple opportunistic pathways of metacercarial transmission to the definitive hosts. Transmission and the use of pleuston by hemiuroids likely varies with sea surface use and ontogenetic trophic shifts of apex predators. The small number of trematode species found in pleuston is consistent with significant ecological specificity, and the inference that other pelagic trematodes use alternative pathways of transmission that do not involve pleustonic organisms. Such pathways may involve i) pelagic hosts exclusively; ii) benthic or demersal hosts exclusively, consumed by apex predators during their dives; or iii) both benthic and pelagic hosts in transmission chains dependent on vertical migrations of prey. The influence of the connectivity of open-ocean ecosystems on parasite transmission is identified as an area in critical need of research.

Proposal of a new genus, Doorochen (Digenea: Lepocreadioidea), for reef-inhabiting members of the genus Postlepidapedon Zdzitowiecki, 1993

A new genus, Doorochen n. gen., is erected for four species of Postlepidapedon Zdzitowiecki, 1993, all of which inhabit members of the labroid genus Choerodon Bleeker, the tuskfishes, and which molecular phylogenies have indicated are not congeneric with the type-species, P. opisthobifurcatum (Zdzitowiecki, 1990) Zdzitowiecki, 1993. Doorochen secundum (Durio & Manter, 1968) n. comb. from Choerodon graphicus (De Vis), the Graphic tuskfish, from the Great Barrier Reef (GBR) and New Caledonia is designated the type-species of the new genus. Other species recognised are Doorochen spissum (Bray, Cribb & Barker, 1997) n. comb. from C. venustus (De Vis), the Venus tuskfish, C. cyanodus (Richardson), the Blue tuskfish, and C. graphicus from the GBR; D. uberis (Bray, Cribb & Barker, 1997) n. comb. from C. schoenleinii (Valenciennes), the Blackspot tuskfish, and C. venustus from the GBR and Moreton Bay; and D. philippinense (Machida, 2004) n. comb. from C. anchorago (Bloch), the Orange-dotted tuskfish, from Philippine waters. In addition to these four species, two new species are described: D. zdzitowieckii n. sp. from C. fasciatus (Günther), the Harlequin tuskfish, and C. graphicus from the GBR; and D. goorchana n. sp. from C. anchorago from the GBR and Palau. The genus Postlepidapedon is now considered to comprise just two species, P. opisthobifurcatum and P. quintum Bray & Cribb, 2001. The relationships of Doorochen, Postlepidapedon, Myzoxenus Manter, 1934 and Intusatrium Durio & Manter, 1968 in the family Lepidapedidae Yamaguti, 1958 are discussed.

Marine fish parasites of Vietnam: a comprehensive review and updated list of species, hosts, and zoogeographical distribution

With a long coastline stretching from tropical to subtropical climate zones, and an immense exclusive economic zone with over 4000 islands, the Vietnamese marine waters support a rich and biodiverse parasite fauna. Although the first parasitological record was in 1898, systematic studies of the parasite fauna have increased during the last 50 years. This comprehensive review covers the current state of knowledge of marine fish parasites in Vietnam and lists 498 species found in 225 fish species, and their geographical distribution. In addition, 251 marine parasite species have newly been added to the already known fauna of 247 species since 2006 (more than two-fold increase). The most speciose group was the Digenea, which accounted for 43% of the total parasite species biodiversity, followed by Monogenea (23.5%), Crustacea (11.6%), Nematoda, and Acanthocephala (8.0% each). The shallow and muddy Gulf of Tonkin showed a rich parasite fauna, accounting for 66.3% of the whole marine parasite fauna of Vietnam, with Digenea accounting for 51% of the regional total parasite richness, followed by Monogenea (27%), Acanthocephala (8.8%), and Nematoda (5.8%). Only a few species belonged to Hirudinea, Myxozoa, and Cestoda, suggesting that these taxa may be understudied. Despite significant progress in studies of marine fish parasites in Vietnam since 2006, only about 12% and 13% of the total fish species have been examined for parasites in the whole country and the Gulf of Tonkin, respectively.

A new species, new host records and life cycle data for lepocreadiids (Digenea) of pomacentrid fishes from the Great Barrier Reef, Australia

A new species of lepocreadiid, Opechonoides opisthoporus n. sp., is described infecting 12 pomacentrid fish species from the Great Barrier Reef, Australia, with Abudefduf whitleyi Allen & Robertson as the type-host. This taxon differs from the only other known member of the genus, Opechonoides gure Yamaguti, 1940, in the sucker width ratio, cirrus-sac length, position of the testes, position of the pore of Laurer's canal, and relative post-testicular distance. The new species exhibits stenoxenic host-specificity, infecting pomacentrids from seven genera: Abudefduf Forsskål, Amphiprion Bloch & Schneider, Neoglyphidodon Allen, Neopomacentrus Allen, Plectroglyphidodon Fowler & Ball, Pomacentrus Lacépède and Stegastes Jenyns. Phylogenetic analyses of 28S rDNA sequence data demonstrate that O. opisthoporus n. sp. forms a strongly supported clade with Prodistomum orientale (Layman, 1930) Bray & Gibson, 1990. The life cycle of this new species is partly elucidated on the basis of ITS2 rDNA sequence data; intermediate hosts are shown to be three species of Ctenophora. New host records and molecular data are reported for Lepocreadium oyabitcha Machida, 1984 and Lepotrema amblyglyphidodonis Bray, Cutmore & Cribb, 2018, and new molecular data are provided for Lepotrema acanthochromidis Bray, Cutmore & Cribb, 2018 and Lepotrema adlardi (Bray, Cribb & Barker, 1993) Bray & Cribb, 1996. Novel cox1 mtDNA sequence data showed intraspecific geographical structuring between Heron Island and Lizard Island for L. acanthochromidis but not for L. adlardi or O. opisthoporus n. sp.

New trematode species Lecithostaphylus halongi n. sp. (Zoogonidae, Microphalloidea) and Gymnotergestia strongyluri n. sp. (Fellodistomidae, Gymnophalloidea) from beloniform fishes in Vietnam

In this study we described two new trematode species, Lecithostaphylus halongi n. sp. (Zoogonidae, Lecithostaphylinae) and Gymnotergestia strongyluri n. sp. (Fellodistomidae, Tergestiinae), on the basis of morphological and molecular data. Adult worms of these two species were collected from, respectively, Hemiramphus spp. (Hemiramphidae) and Strongylura strongylura (Belonidae) caught in the coastal waters of Vietnam. Adult worms of L. halongi n. sp. are morphologically close to Lecithostaphylus gibsoni Cribb, Bray & Barker, 1992 ex Abudefduf whitleyi from Heron Island and Lecithostaphylus depauperati Yamaguti, 1970 ex Hemiramphus depauperatus from Hawaii, but differ from these species in having a larger cirrus sac and a different arrangement of vitelline fields. They also differ from Lecithostaphylus brayi Cabañas-Granillo, Solórzano-García, Mendoza-Garfias & Pérez-Ponce de León, 2020 in the 28S ribosomal DNA (rDNA) sequence data at the interspecific level. Adult worms of G. strongyluri n. sp. ex S. strongylura are morphologically similar to Gymnotergestia chaetodipteri, the only previously known species of this genus, described from Chaetodipterus faber in Jamaica. The new species differs from G. chaetodipteri in body shape, testicular arrangement and the size of the pharynx and eggs. The 28S rDNA-based phylogenetic analysis indicates that G. strongyluri n. sp. is closely related to Tergestia spp., rendering Tergestia paraphyletic. Genetic divergence values between G. strongyluri n. sp. and Tergestia spp. are similar to those among species in the genera Tergestia, Steringophorus and Proctoeces. Our molecular results indicate that G. strongyluri n. sp. and Tergestia spp. may belong the same genus, but additional molecular data are needed for the final conclusion.

A paradigm for the recognition of cryptic trematode species in tropical Indo-west Pacific fishes: the problematic genus Preptetos (Trematoda: Lepocreadiidae)

Molecular data have transformed approaches to trematode taxonomy by providing objective evidence for the delineation of species. However, although the data are objective, the interpretation of these data regarding species boundaries is subjective, especially when different markers conflict. Conserved markers can lead to an underestimation of richness and those used for finer species delineation have the capacity to inflate species recognition, perhaps unrealistically. Here we examine molecular and morphological evidence for species recognition in an especially confusing system, the lepocreadiid genus Preptetos Pritchard, 1960 in acanthuriform fishes of the tropical Indo-west Pacific. We consider species boundaries within this genus based on combined data (ITS2 and 28S rDNA; cox1 mtDNA and morphometrics) for substantial new collections. Delineation of species using only morphological data suggest fewer species than analysis of the sequence data; the latter suggests the presence of potential cryptic species and analysis of different markers suggests the presence of differing numbers of species. We conclude that an integrative interpretation creates the most satisfying taxonomic hypothesis. In the light of the new data, we have chosen and propose a model of trematode species recognition that demands reciprocal monophyly in the most discriminating available molecular marker plus distinction in morphology or host distribution. By invoking these criteria, we distinguish eight species in our new tropical Indo-west Pacific collections. Six of these are new (Preptetos allocaballeroi n. sp., Preptetos paracaballeroi n. sp., Preptetos pearsoni n. sp., Preptetos prudhoei n. sp., Preptetos quandamooka n. sp. and Preptetos zebravaranus n. sp.) and we continue to recognise Preptetos cannoni Barker, Bray & Cribb, 1993 and Preptetos laguncula Bray and Cribb, 1996. Notably; two of the new species, P. allocaballeroi n. sp. and P. paracaballeroi n. sp., are morphologically cryptic relative to each other. Our criteria lead us to recognise, as species, populations with unvarying morphology and similar host relationships but which may have a complex population structure over their range. In our view, this paradigm has the capacity to render tractable the interpretation of the species status of the huge trematode fauna of the tropical Indo-west Pacific.

Eight species of Lintonium Stunkard & Nigrelli, 1930 (Digenea: Fellodistomidae) in Australian tetraodontiform fishes

We report eight species of Lintonium from tetraodontiform fishes from Australian waters and describe six of them as new. Two species are described from tetraodontids from the Great Barrier Reef (GBR): Lintonium kostadinovae n. sp. from Arothron nigropunctatus (Bloch & Schneider) and Arothron hispidus (Linnaeus); and Lintonium droneni n. sp. from A. nigropunctatus. Two species are described from temperate monacanthids: Lintonium crowcrofti n. sp. from Meuschenia hippocrepis (Quoy & Gaimard) and Meuschenia freycineti (Quoy & Gaimard) off Tasmania and from M. hippocrepis off Glenelg, South Australia and off Fremantle, Western Australia; and Lintonium blendi n. sp. from M. hippocrepis off Stanley, Tasmania. The final two new species are described from tropical monacanthids: Lintonium currani n. sp. from Cantherhines pardalis (Rüppell) from Ningaloo Reef, Western Australia; and Lintonium madhaviae n. sp. from Amanses scopas (Cuvier) from the southern GBR. Two previously described species are reported from tetraodontids: Lintonium pulchrum (Johnston, 1913) Yamaguti, 1954 from Arothron stellatus (Anonymous), A. hispidus, A. manilensis (Marion de Procé) and Lagocephalus lunaris (Bloch & Schneider) from the GBR and southern Queensland; and Lintonium consors (Lühe, 1906) Crowcroft, 1950 from A. nigropunctatus from the southern GBR. Sequence data for three markers (ITS2 and 28S rDNA and cox1 mtDNA) for six of the eight species (L. crowcrofti n. sp., L. currani n. sp., L. droneni n. sp., L. kostadinovae n. sp., L. madhaviae n. sp. and L. pulchrum) are the first for the genus and distinguish each species unambiguously. Many records of species of Lintonium, especially widespread records of the type species, L. vibex (Linton, 1900) Stunkard & Nigrelli, 1930, remain to be clarified. A key finding of the present study is that three fish species (A. hispidus, A. nigropunctatus and M. hippocrepis) are identified as harbouring either two or three species of Lintonium at individual localities.

Contrasting Host-Parasite Population Structure: Morphology and Mitogenomics of a Parasitic Flatworm on Pelagic Deepwater Cichlid Fishes from Lake Tanganyika

Little phylogeographic structure is presumed for highly mobile species in pelagic zones. Lake Tanganyika is a unique ecosystem with a speciose and largely endemic fauna famous for its remarkable evolutionary history. In bathybatine cichlid fishes, the pattern of lake-wide population differentiation differs among species. We assessed the congruence between the phylogeographic structure of bathybatine cichlids and their parasitic flatworm Cichlidogyrus casuarinus to test the magnifying glass hypothesis. Additionally, we evaluated the use of a PoolSeq approach to study intraspecific variation in dactylogyrid monogeneans. The lake-wide population structure of C. casuarinus ex Hemibates stenosoma was assessed based on a portion of the cox1 gene combined with morphological characterisation. Additionally, intraspecific mitogenomic variation among 80 parasite samples from one spatially constrained metapopulation was assessed using shotgun NGS. While no clear geographic genetic structure was detected in parasites, both geographic and host-related phenotypic variation was apparent. The incongruence with the genetic north-south gradient observed in H. stenosoma may be explained by the broad host range of this flatworm including eupelagic bathybatine host species that form panmictic populations across the lake. In addition, we present the first parasite mitogenome from Lake Tanganyika and propose a methodological framework for studying the intraspecific mitogenomic variation of dactylogyrid monogeneans.

OPECHONA CHLOROSCOMBRI AND OPECHONA CORKUMI N. SP. (DIGENEA: LEPOCREADIIDAE) FROM THE NORTHERN GULF OF MEXICO WITH PHYLOGENETIC ANALYSIS BASED ON 28S RDNA

This study investigated the identity of 2 lepocreadiid digenean species belonging in the genus Opechona Looss, 1907 that infect littoral fishes of the northern Gulf of Mexico. Opechona chloroscombriNahhas and Cable, 1964, a species previously known only from the Caribbean Sea and the Atlantic Ocean off Brazil, is reported herein from the Atlantic bumper, Chloroscombrus chrysurus (L.), in the northern Gulf of Mexico. A second species infects the gulf butterfish, Peprilus burti Fowler, and the American harvestfish, Peprilus paru (L.), and it is described as a new species that occurs in coastal waters of the north-central and northeastern Gulf of Mexico. Metacercariae infecting the mesoglea of pelagic jellyfishes (Bougainvillia carolinensis [McCady], Chrysaora quinquecirrha [Desor], and Stomolophus meleagris Agassiz) and pelagic comb jellies (Mnemiopsis leidyi Agassiz and Beroe ovata Bruguière) were collected that resemble the new species but require further study to identify. Newly generated sequence fragments (28S rDNA) from both species of Opechona plus 2 other lepocreadiids collected during the study were aligned with publicly available sequences from 18 other lepocreadiids, 6 species of Aephnidiogenidae Yamaguti, 1934, and 2 species of Gorgocephalidae Manter, 1966. The alignment was subjected to Bayesian inference analysis rooted using a gorgocephalid. The resulting tree estimated the positions of both Opechona spp. as being unresolved within a group of taxa that included all available species of Opechona plus available species from the morphologically similar genera ProdistomumLinton, 1910, Preptetos Pritchard, 1960, and Clavogalea Bray, 1985. Although relatively similar in morphology, the 2 studied species of Opechona were surprisingly not closely related. Opechona cablei (Stunkard, 1980) Bray and Gibson, 1990 is herein considered to be a junior synonym of Opechona pyriformis (Linton, 1900) Bray and Gibson, 1990.

Description of a metacercaria of a zoogonid trematode Steganoderma cf. eamiqtrema Blend and Racz, 2020 (Microphalloidea: Zoogonidae), with notes on the phylogenetic position of the genus Steganoderma Stafford, 1904, and resurrection of the subfamily Lecithostaphylinae Odhner, 1911

Metacercariae of the zoogonid trematode Steganoderma cf. eamiqtrema ex crab Chionoecetes bairdi caught in the Sea of Okhotsk were described using morphological and molecular-genetic (ITS2 region, 28S rRNA and nd1 genes) data. These are the first molecular-genetic data for the genus Steganoderma. The studied trematodes differed from S. eamiqtrema in having a much larger body size. The phylogenetic analysis based on the 28S rRNA gene supported neither the current taxonomic hypothesis that Steganoderma belongs to the subfamily Lepidophyllinae nor the earlier views that the Steganodermatinae and the Lecithostaphylinae are synonymous. The topology of the phylogenetic tree shows that the Steganodermatinae and the Lecithostaphylinae are independent subfamilies. However, morphological differences between them are obscure. Until morphological evidence for the Steganodermatinae is found, we propose to distinguish the subfamily Lepidophyllinae sensu stricto with the genera Lepidophyllus and Urinatrema, and the subfamily Lecithostaphylinae sensu lato uniting all the other former lepidophyllines. Thus, for now, we propose to consider the Steganodermatinae as a conditional synonym for Lecithostaphylinae sensu lato.

Molecular characterization of European Pygorchis Looss, 1899

Adult trematodes of the genus Pygorchis Looss, 1899 (Trematoda: Philophthalmidae) parasitize the cloaca of birds. The genus contains three species, all of which are rarely reported and molecular phylogenetics of which have not been applied. The absence of reference DNA sequences limit studies of their indistinct larval forms. Based on the materials that were obtained from birds of the Czech origin, we performed a molecular characterization of both currently known Pygorchis spp., which are known from the Palearctic, the type species Pygorchis affixus Looss, 1899 and Pygorchis alakolensis Zhatkanbaeva, 1967, and provided morphological description of the examined P. alakolensis specimen. We found that the two species were of similar dimensions; the only difference was in the position of testes and in the extent of vitelline follicles. However, the position of testes in P. affixus was variable, and approximately 10% of examined P. affixus individuals had testes positioned obliquely. The second feature that allows differential diagnostic, the extent of vitelline follicles, was more reproducible as the vitelline follicles of P. affixus did not extend beyond the intestinal caeca, or, in exceptional cases, they extended them at only one side. In the examined P. alakolensis individual, the testes were positioned obliquely, and the vitelline follicles extended beyond the intestinal caeca. We reported P. alakolensis for the first time from Europe; previously, it was known only from Central Asian lakes and rivers. We confirmed the classification of Pygorchis into Philophtalmidae.

Gaharitrema droneni n. gen., n. sp. (Digenea: Zoogonidae) from the Pudgy Cuskeel, Spectrunculus grandis (Ophidiiformes: Ophidiidae), from Deep Waters Off Oregon, with Updated Keys to Zoogonid Subfamilies and Genera

Gaharitrema droneni n. gen., n. sp. (Digenea: Zoogonidae: Lepidophyllinae) is described from the intestine of the pudgy cuskeel, Spectrunculus grandis (Günther, 1877) (Ophidiiformes: Ophidiidae), collected at 2,800 m depth from the northeastern Pacific Ocean off Oregon. The new genus is distinguished from BrachyenteronManter, 1934 and SteganodermaStafford, 1904, the 2 closest lepidophylline genera, and from 4 other zoogonid genera erected since 2007, the last major revision of the family, by a combination of diagnostic features including a pyriform or spindle-shaped body, smooth testes and ovary, narrow ceca that reach with the vitellarium into the hindbody, an unspecialized ventral sucker, non-filamented eggs, a claviform cirrus pouch, and an unpocketed ejaculatory duct and metraterm, and the new genus lacks circumoral spines. We present updated keys to the 3 subfamilies of the Zoogonidae Odhner, 1902, as well as to the genera of the Cephaloporinae Yamaguti, 1934 and the Lepidophyllinae Stossich, 1903. A listing of the parasites known from S. grandis also is presented. This study documents the third family of digeneans (Zoogonidae) known to parasitize S. grandis, and it is a new host record (i.e., the first zoogonid reported from this host species). We discuss the relatively impressive presence of the Zoogonidae and their hosts within the deep sea. Specifically, of the 35 genera we recognize within this digenean family, 14 (40%) have deep-sea representatives. At least 37 species within 27 genera and 19 families within 11 orders of deep-sea fish are known to harbor zoogonids. Furthermore, of the 37 known deep-sea fish species parasitized by zoogonids, only 5 (13.5%) harbor 2 or more zoogonid species; the remaining 32 (86.5%) harbor only 1 parasite species each, indicating strong host specificity. Finally, the dietary ecology of S. grandis is presented, allowing us to speculate that Gaharitrema droneni may be utilizing gastropods and polychaetes as well as S. grandis to complete its life cycle in the deep sea.

Steringophorus merretti n. sp. (Digenea: Fellodistomidae) from the deep-sea fish Cataetyx laticeps Koefoed (Ophidiiformes: Bythitidae) from the Goban Spur, Northeastern Atlantic Ocean

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.

New data on life cycles for three species of Fellodistomidae (Digenea) in the White Sea

Few digeneans of the family Fellodistomidae are known from the Russian Arctic seas. The taxonomic status of these species, their life cycles and host range raised recurrent questions, some of which remain unanswered. To revise the species composition and life cycles of fellodistomids in the White Sea, we searched for them in several known and suspected hosts: wolffish, flatfishes (definitive), gastropods of the family Buccinidae (second intermediate) and protobranch bivalves (first intermediate). Species identification was based both on morphology and 28S ribosomal RNA gene sequences. We found Fellodistomum agnotum in the White Sea for the first time. Buccinum undatum was proved to be intermediate host of both F. agnotum and Fellodistomum fellis, and metacercariae of F. fellis were registered from two more buccinid species: Buccinum scalariforme and Neptunea despecta. We also found metacercariae of F. agnotum and F. fellis producing eggs in the second intermediate host. Two fellodistomids were found in protobranch bivalves: sporocysts and cercariae of Steringophorus furciger in Nuculana pernula, and sporocysts with large furcocercous cercariae in Ennucula tenuis. The latter were identified as F. agnotum by molecular analysis; thus, the entire life cycle of this species was reconstructed.

Digenean parasites of deep-sea teleosts: A progress report

The developments in the study of digeneans of deep-sea fish in the 21st Century are documented and discussed. Most recent work has been on the bathyal fauna (i.e. 1,000m-2,999 m depth), with virtually nothing on the abyssal fauna (i.e. deeper than 3,000 m). The one study on hydrothermal vent digeneans has indicated that these regions probably harbour a distinctive fauna. The demarcation of the deep-sea fauna is blurred at the poles, where the cold-adapted fauna appears similar to the shallower bathyal fauna. The abyssal fauna, however, appears distinct, possibly due to adaptations to variable or ultra-high pressures. The digenean fauna of bathypelagic fishes is depauperate. Recent phylogenetic studies reinforce the view that the typical deep-sea fauna has radiated in the deep-sea. Encroachment into the deep from shallow water is relatively rare. Overall, the digenean fauna in the deep-sea is distinctly less diverse that the equivalent fauna in shallow waters. A major conclusion is that our understanding of the deep-sea digenean fauna is poor, and that much further work over a much wider area is needed.

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Sampling effort in the deep-sea is poor and restricted to a few areas.

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Deep-sea digenean diversity is distinctly lower than in shallow water.

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Much of the deep-sea digenean fauna appears to have radiated in the deep-sea.

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Encroachment into the very deep sea from shallow waters is rare.

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Adaptation to cold temperature appears to be a major factor in deep-sea digeneans.

Air sac trematodes: Morishitium polonicum as a newly identified cause of death in the common blackbird (Turdus merula)

Necropsy of two free-ranging common blackbirds (Turdus merula) found dead in central Italy revealed the presence of a high number of cyclocoelid flukes in the coelomatic cavity. Cyclocoelid flukes primarily infect avian respiratory system. Histologically, air sac walls were covered with a fibrinous exudate containing degenerate heterophils, many trematodes and some colonies of Gram-positive cocci. The superficial bronchi and parabronchi were markedly distended, and the adjacent pulmonary parenchyma was congested and collapsed. Trematodes, surrounded by a mild suppurative to pyogranulomatous inflammatory reaction, were also observed on the pericardial, intestinal, kidney and hepatic serosal surfaces. The death of the two examined birds was likely due to the high parasite load and associated severe lesions. At parasitological examination, flukes showed a tongue-shaped elongate body, tapered anteriorly and rounded posteriorly, of 2,088-2,314 μm in width and 8,268-11,830 μm in length. The mouth was slightly oval and sub-terminal, with a small oral sucker. The oval pharynx measured 250-309 μm, and the two caeca joined posteriorly. Two large (550-702 μm × 450-520 μm) globular testes were situated obliquely to each other, whereas an oval (250 × 300 μm in mean) or round (about 334 μm in diameter) intertesticular ovary was placed in a longitudinal straight line with the testes. The ootype was about 110 μm in diameter, while the brown-yellow eggs measured 131.5 × 73.9 μm in mean. The genital pore was post-pharyngeal, while the symmetrically arranged vitelline glands were not confluent posteriorly. Morphoflogical diagnosis led to the identification of Morishitium polonicum, a cyclocoelid fluke species that typically inhabits the air sacs of blackbirds. The morphological diagnosis was corroborated by molecular phylogenetic analysis of the mitochondrial (CO1, ND1) DNA loci. The present study provides the first report of pathological lesions and death caused by M. polonicum in birds.

Molecular identification and histological aspects of Renicola sloanei (Digenea: Renicolidae) in Puffinus puffinus (Procellariiformes): a first record

Abstract Renicolids are parasites that inhabit the renal tubules and ureters of molluscivorous and piscivorous birds. Puffinus puffinus is a migratory seabird that was identified as the definitive host of Renicola spp. Studies focusing on the renicolid species and the resulting renal lesions are valuable for their association with causes of stranding in seabirds. The aim of this study was to identify the renicolid trematodes and evaluate the histological findings in two P. puffinus stranded on the coast of Paraná state, Brazil. The parasites were evaluated by histologic, ultrastructural and molecular assays, while tissue changes were analyzed by histologic methods. The morphological and morphometrical characteristics of the parasites, along with polymerase chain reaction and sequencing assays (ribosomal and mitochondrial regions), identified the species as Renicola sloanei. The results also suggest that this helminth can be the adult form of Cercaria pythionike. The dilation of collecting ducts was the main histological finding in the kidneys. In conclusion, R. sloanei was identified, and for the first time, P. puffinus was described as a host of this digenean inducing mild renal changes.

Species of Lepidapedon Stafford, 1904 (Digenea: Lepidapedidae) from deep-sea fishes in the Western Mediterranean: molecular and morphological evidence

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.

Phylogenetic Position of Pseudosellacotyla lutzi (Freitas, 1941) (Digenea: Cryptogonimidae), A Parasite of Hoplias malabaricus (Bloch) in South America, through 28S rDNA Sequences, and New Observations of the Ultrastructure of Their Tegument

The freshwater fish digenean Pseudosellacotyla lutzi ( Freitas, 1941 ) Yamaguti, 1954 has had an unsettled taxonomic history, and has at various times been classified as a member of Nanophyetidae, Heterophyidae, Microphallidae, Faustulidae, and Cryptogonimidae. Nine individual specimens of the trahira, Hoplias malabaricus (Bloch, 1794), were sampled in the Paraná River basin, Paraná State, Brazil; 22 specimens of P. lutzi were collected. One specimen of P. lutzi was used to obtain a sequence of the domains D1-D3 of the 28S rRNA gene, and to perform a phylogenetic analysis to assess their position and classification within Plagiorchiida. The resulting tree unequivocally shows that the species, along with acanthostomines, belong to the Cryptogonimidae, corroborating recent findings based on the morphology of the cercariae, and in the characteristics of the life cycle. In addition, the study of the ultrastructure of the tegumental spines through scanning electron microscopy allowed us to characterize them as pectinate spines possessing 3 to 8 digitiform projections at their distal end and extending from the anterior to the posterior extremity of the body. This study also provides the first molecular data for a cryptogonimid from South America.

Central European Strigeidae Railliet, 1919 (Trematoda: Strigeidida): Molecular and comparative morphological analysis suggests the reclassification of Parastrigea robusta Szidat, 1928 into Strigea Abildgaard, 1790

Strigeidae Railliet, 1919 are digenean parasites of birds and mammals that are characteristic by their cup-shaped forebody and bilobed holdfast organ. Despite that the family is taxonomically unsettled, particularly due to a very limited number of visible autapomorphic identification features, molecular phylogenetics have never been applied to analyze the relationships among European members of Strigeidae except for the genus Ichthyocotylurus. Here, we analyze the Strigeidae found during the examination of Czech birds performed from 1962 to 2017, and we provide comparative measurements and host spectra, including prevalence and intensity; we also provide and analyze sequences of four DNA loci of 12 of the Strigeidae species. We suggest the reclassification of Parastrigea robusta Szidat, 1928 as Strigea robusta (Szidat, 1928) Heneberg and Sitko, 2018 comb. n. The genera Strigea Abildgaard, 1790 and Parastrigea Szidat, 1928 appear paraphyletic, and morphological diagnostic features of genera within Strigeini Dubois, 1936 are invalid. The mute swan Cygnus olor hosts two Cotylurus spp., Cotylurus syrius Dubois, 1934 and a second species with molecular identification features shared in part with Cotylurus cornutus (Rudolphi, 1808) and Cotylurus gallinulae Lutz, 1928. New host records are provided for seven species. Analyses of non-European genera of the Strigeidae are needed to provide an updated key to Strigeini.

New Data on the Morphology and Phylogenetic Connections of Postlepidapedon Opisthobifurcatum (Trematoda, Lepocreadioidea: Lepidapedidae), a Parasite of Antarctic and Sub-Antarctic Fishes

The trematode Postlepidapedon opisthobifurcatum (Zdzitowiecki, 1990) is a common intestinal parasite of the gadiform fishes of the Southern Ocean. In this work, we supplement the description of the species with the anatomy of the terminal part of the reproductive system and with molecular data. The male terminal genitalia are characterised by the presence of the external seminal vesicle and cirrus-sac. The external seminal vesicle is surrounded by aciniform groups of outer prostatic cells. Groups of outer prostatic cells and proximal parts of their ducts are associated with a thin-walled membrane that is connected to the proximal edge of the сirrus-sac. The cirrus-sac is claviform, with a long proximal part accommodating the tubular, thin-walled internal seminal vesicle and ducts of outer prostatic cells. The female terminal genitalia are represented by a thick-walled metraterm, which is surrounded by aciniform groups of glandular cells. Phylogenetic analysis based on 28S rDNA partial sequences data placed P. opisthobifurcatum into the monophyletic group Lepidapedidae, including the species Myzoxenus insolens (Crowcroft, 1945), Intusatrium robustum Durio et Manter, 1968, and Postlepidapedon uberis Bray, Cribb et Barker, 1997. However, we were unable to detect direct phylogenetic connections between P. opisthobifurcatum and P. uberis.

A new species of Steringotrema Odhner, 1911 (Trematoda: Fellodistomidae) from the New Zealand sole Peltorhamphus novaezeelandiae Günther off Kaka point in the Catlins, South Island, New Zealand

As a part of a comprehensive survey of macroparasites of commercially exploited fish species off the coast of Otago, New Zealand, the parasite fauna of the New Zealand sole Peltorhamphus novaezeelandiae Günther was recently studied. Steringotrema robertpoulini n. sp. is described from this host and compared with known species of Steringotrema Odhner, 1911. The new species is readily distinguished from all of its congeners, except for S. divergens (Rudolphi, 1809) Odhner, 1911, by having the follicular vitellarium divided in four zones rather than two, and can be differentiated from S. divergens mainly by the posterior extent of the intestinal caeca in the hindbody, as well as by host association and geographical distribution. DNA sequences of the 28S ribosomal gene were generated and phylogenetic analyses were undertaken using maximum likelihood and Bayesian inference to assess the phylogenetic position of the new species within the family Fellodistomidae Nicoll, 1909. Analyses included the available sequences for 14 species of the family distributed among eight genera, along with nine species of other members of the order Plagiorchiida La Rue, 1957 as outgroups. The resulting topology shows that the new species of Steringotrema is nested as the sister species of Steringophorus dorsolineatus (Reimer, 1985) Bray, 1995. However, low nodal support indicates that relationships among these species are not fully resolved and require further revision and denser taxon sampling for more detailed molecular work. More information is required to draw further conclusions about the taxonomic status of the genera Steringotrema and Steringophorus Odhner, 1905.

Two new and one known species of Tergestia Stossich, 1899 (Trematoda: Fellodistomidae) with novel molecular characterisation for the genus

Combined morphological and molecular analyses are employed to characterise three species of Tergestia Stossich, 1899 (Digenea: Fellodistomidae) from fishes of Moreton Bay, Queensland, Australia. Tergestia clonacantha Manter, 1963 is reported here for the first time from the halfbeak (Beloniformes: Hemiramphidae) species Arrhamphus sclerolepis krefftii (Steindachner), Hyporhamphus australis (Steindachner), H. quoyi (Valenciennes) and H. regularis ardelio (Whitley). Two new species, both infecting trevally (Perciformes: Carangidae) species, are described: T. maryae n. sp. from Alepes apercna Grant and T. henryi n. sp. from Pantolabus radiatus (MacLeay). Complete ITS2 and partial 28S ribosomal DNA data were generated for each of the new taxa. The three species differ from each other by 47-58 base pairs (bp) in the ITS2 rDNA region. Phylogenetic analysis of 28S rDNA supports Tergestia as a reliable generic concept, with our analyses showing that some species of the genus form a well-supported clade to the exclusion of all other fellodistomids for which sequence data are available.

A new species of Tinrovia Mamaev, 1987 (Monogenea: Microcotylidae) from the deep-sea fish Notacanthus bonaparte Risso (Notacanthiformes: Notacanthidae) in the Western Mediterranean and the North East Atlantic

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.

Acanthocotyle gurgesiella n. sp. (Monogenea: Acanthocotylidae) from the deep-sea skate Gurgesiella furvescens (Rajidae) in the south-eastern Pacific

Little is known about the diversity of parasites of the deep-sea fish of the world's oceans. Here, a new species of monogenean parasite of the deep-sea skate Gurgesiella furvescens is described. Specimens of parasites were obtained from the skin of two specimens of the dusky finless skate, G. furvescens (Rajidae), in the vicinity of Valparaiso (33°S, 72°W), central Chile, from midwater trawl fishing at depths of 350–450 m. Both morphological and molecular analyses were conducted to provide a full description of the new species, named Acanthocotyle gurgesiella. For the molecular analyses, nuclear large subunit (LSU) rDNA and the mitochondrial gene cytochrome c oxidase 1 (COI) were used. From the morphological analysis and a comparison with the known species of the genus, A. gurgesiella can be identified by a combination of morphological characteristics, including the number of testes, number of radial rows of sclerites in the pseudohaptor, aperture of the genital pore and shape of the vitelline follicles. The results from the DNA analysis indicated that A. gurgesiella has a genetic divergence of 3.2–3.7% (LSU rDNA gene) from A. urolophi, the only congener species for which molecular data are available.

Central European parasitic flatworms of the Cyclocoelidae Stossich, 1902 (Trematoda: Plagiorchiida): molecular and comparative morphological analysis suggests the reclassification of Cyclocoelum obscurum (Leidy, 1887) into the Harrahium Witenberg, 1926

Cyclocoelidae Stossich, 1902 are medium-sized to large digenean bird parasites. Although these parasites bear few visible autapomorphic signs, and their diagnostic characters are unstable in response to the pressure applied during preparation, the numerous hitherto suggested re-classifications within the family have not been supported by any molecular analysis. We analyse here cyclocoelids found during the extensive examination of central European birds performed from 1962 to 2016, provide comparative measurements, host spectra, prevalence and intensity, and provide and analyse sequences of four DNA loci of five of the cyclocoelid species. Cyclocoleum Brandes, 1892 appears paraphyletic; thus we suggest the re-classification of Cyclocoleum obscurum (Leidy, 1887) as Harrahium obscurum (Leidy, 1887) Sitko and Heneberg comb. n. Molecular phylogenetics questioned also the validity of Cyclocoelinae Stossich, 1902 and Hyptiasminae Dollfus, 1948, which formed a single clade, whereas Allopyge Johnston, 1913, Prohyptiasmus Witenberg, 1923 and Morishitium Witenberg, 1928 formed another clade. Haematotrephinae Dollfus, 1948 are newly characterized as having a pretesticular or intertesticular ovary that forms a triangle with the testes. Analyses of non-European genera of the Cyclocoelidae and an examination of the position of families within Echinostomata La Rue, 1926 are needed.

Central European parasitic flatworms of the family Renicolidae Dollfus, 1939 (Trematoda: Plagiorchiida): molecular and comparative morphological analysis rejects the synonymization of Renicola pinguis complex suggested by Odening

The Renicolidae are digenean parasites of piscivorous and molluscivorous birds. Although they exhibit few morphological autapomorphies and are highly variable, the numerous suggested re-classifications within the family have never been supported by any molecular analyses. We address the possible synonymization of species within the Renicola pinguis complex suggested previously by Odening. We provide and analyse sequences of two nuclear (ITS2, 28S rDNA) and two mitochondrial (CO1, ND1) DNA loci of central European species of the Renicolidae, namely Renicola lari, Renicola pinguis and Renicola sternae sp. n., and we also provide first sequences of Renicola sloanei. The combined molecular and comparative morphological analysis confirms the previously questioned validity of the three Renicola spp. of highly similar morphology, which display strict niche separation in terms of host specificity and selectivity. We identify two previously unreported clades within the genus Renicola; however, only one of them is supported by the analysis of adult worms. We also provide comparative measurements of the three examined closely related central European renicolids, and describe the newly proposed tern-specialized species Renicola sternae sp. n., which was previously repeatedly misidentified as Renicola paraquinta. Based on the extensive dataset collected in 1962-2015, we update the host spectrum of Renicolidae parasitizing central European birds (Renicola bretensis, R. lari, Renicola mediovitellata, R. pinguis, Renicola secunda and R. sternae sp. n.) and discuss their host-specific prevalence and intensity of infections.

Knowledge of marine fish trematodes of Atlantic and Eastern Pacific Oceans

A brief summary of the early history of the study of Atlantic Ocean marine fish digeneans is followed by a discussion of the occurrence and distribution of these worms in the Atlantic Ocean and adjacent Eastern Pacific Ocean, using the Provinces of the ‘Marine Ecoregions’ delimited by Spalding et al. (Bioscience 57:573–583, 2007). The discussion is based on a database of 9,880 records of 1,274 species in 430 genera and 45 families. 8,633 of these records are from the Atlantic Ocean, including 1,125 species in 384 genera and 45 families. About 1,000 species are endemic to the Atlantic Ocean Basin. The most species-rich families in the Atlantic Ocean are the Opecoelidae Ozaki, 1925, Hemiuridae Looss, 1899 and Bucephalidae Poche, 1907, and the most wide-spread the Opecoelidae, Hemiuridae, Acanthocolpidae Lühe, 1906, Lepocreadiidae Odhner, 1905 and Lecithasteridae Odhner, 1905. A total of 109 species are shared by the Atlantic Ocean and the Eastern Pacific, made up of cosmopolitan, circum-boreal, trans-Panama Isthmus and Magellanic species. The lack of genetic evaluation of identifications is emphasised and the scope for much more work is stressed.

Molecular and comparative morphological analysis of central European parasitic flatworms of the superfamily Brachylaimoidea Allison, 1943 (Trematoda: Plagiorchiida)

The Brachylaimoidea are digenean parasites of vertebrates, including humans, domestic animals, poultry and wild game. Numerous Brachylaimoidea, particularly adults ofBrachylaimaandLeucochloridium, are difficult to identify to species. We provide and analyse sequences of two nuclear (18S rDNA, ITS2) and two mitochondrial (CO1, ND1) DNA loci of central European species of the Brachylaimoidea, namelyLeucochloridium holostomum, Leucochloridium paradoxum, Leucochloridium perturbatum, Leucochloridium subtilis, Leucochloridium vogtianum, Urotocus rossitensis, Urogonimus macrostomus, Michajlovia migrata, Leucochloridiomorpha lutea, Brachylaima arcuatus, Brachylaima fuscataandBrachylaima mesostoma. We identified three clades in the genusLeucochloridium, which do not correspond to the previously suggested subgeneraNeoleucochloridium, PapilloleucochloridiumandLeucochloridium. We reject classification ofUrotocusandUrogonimusin Leucochloridiinae, and, instead, re-establish the subfamilies Urotocinae and Urogoniminae. We synonymize the genusRenylaimawith the genusBrachylaima. We rejectM. migrataas a member of Leucochloridiinae sensu stricto or Brachylaimidae suggested by some previous authors. We found that the previously sequencedGlaphyrostomumsp. does not cluster with any hitherto sequenced Brachylaimidae. We also provide comparative measurements of the examined central European Brachylaimoidea, address the the specificity of their localization in the host and discuss their host-specific prevalence and intensity of infections based on the extensive dataset of birds examined in 1962–2015.

Description of a new species of Podocotyle Dujardin, 1845 (Digenea: Opecoelidae: Plagioporinae) from the cusk-eel, Luciobrotula corethromycter Cohen, 1964 (Ophidiiformes: Ophidiidae), from the Gulf of Mexico and Caribbean Sea

Podocotyle bathyhelminthos n. sp. (Opecoelidae: Plagioporinae) is described from the cusk-eel, Luciobrotula corethromycter Cohen, 1964 (Ophidiiformes: Ophidiidae), collected at depths of 622-1,280 m in the northern Gulf of Mexico and Caribbean Sea off Colombia. The new species is distinguished by possessing a combination of the following features: an elongate oval body shape, a sucker width ratio of 1:1.4-1.9, deeply lobed and irregularly-shaped testes, a cirrus-sac that extends just in to the hindbody, a trilobed ovary and vitellarium that extend to the ventral sucker level. Several unique features in P. bathyhelminthos n. sp. were not present in all, or almost all, recognized species of Podocotyle including a conspicuous deep cleft at the posterior end of the worm, a small transverse ridge on the ventral surface immediately anterior to the ventral sucker, uterine loops extending ventral to the caeca and, at times, lateral to the caeca, a thick-walled metraterm extending 1/3 to 1/2 the length of the cirrus-sac and P. bathyhelminthos n. sp. parasitizes a deep water piscine host. Podocotyle etheostomae Aliff, 1973 is declared a nomen nudum. A brief discussion of Podocotyle Dujardin, 1845 in deep waters is presented, and a gastropod, caridean shrimp and cusk-eel are hypothesized as hosts in the life cycle of P. bathyhelminthos n. sp. in the deep sea.

New genus of opecoelid trematode from Pristipomoides aquilonaris (Perciformes: Lutjanidae) and its phylogenetic affinity within the family Opecoelidae

Bentholebouria colubrosa gen. n. et sp. n. (Digenea: Opecoelidae) is described in the wenchman, Pristipomoides aquilonaris (Goode et Bean), from the eastern Gulf of Mexico, and new combinations are proposed: Bentholebouria blatta (Bray et Justine, 2009) comb. n., Bentholebouria longisaccula (Yamaguti, 1970) comb. n., Bentholebouria rooseveltiae (Yamaguti, 1970) comb. n., and Bentholebouria ulaula (Yamaguti, 1970) comb. n. The new genus is morphologically similar to Neolebouria Gibson, 1976, but with a longer cirrus sac, entire testes, a rounded posterior margin with a cleft, and an apparent restriction to the deepwater snappers. Morphologically, the new species is closest to B. blatta from Pristipomoides argyrogrammicus (Valenciennes) off New Caledonia but can be differentiated by the nature of the internal seminal vesicle (2-6 turns or loops rather than constrictions), a longer internal seminal vesicle (occupying about 65% rather than 50% of the cirrus sac), a cirrus sac that extends further into the hindbody (averaging 136% rather than 103% of the distance from the posterior margin of the ventral sucker to the ovary), and a narrower body (27% rather than 35% mean width as % of body length). A Bayesian inference analysis of partial sequence of the 28S rDNA from Neolebouria lanceolata (Price, 1934), Cainocreadium lintoni (Siddiqi et Cable, 1960), Hamacreadium mutabile Linton, 1910, Opecoeloides fimbriatus (Linton, 1910), Podocotyloides brevis Andres et Overstreet, 2013, the new species, and previously published comparable sequences from 10 opecoelid species revealed two clades. One clade includes deep-sea (> or = 200 m) and freshwater fish opecoelids + Opecoeloides Bremser in Rudolphi, 1819, and a second clade included those opecoelids from shallow-water marine, perciform fishes.

Active chi-like sequences are present in the ITS1 region of polyembryonic adult Collyriclum faba trematodes encysted in pairs

Collyriclum faba (Plagiochiida: Collyriclidae) adults occur in pairs within subcutaneous cysts. Here, we tested the extensive C. faba infrapopulation for five DNA loci known to display variability among Central European C. faba individuals. The infrapopulation tested shared 100% similarity in four of the five mitochondrial and nuclear DNA loci tested. Contrariwise, the internal transcribed spacer 1 (ITS1) loci in all but one individual differed from each other. We found only 0.0-1.5 base substitutions per 1,000 sites within the cysts, while we found 0.7-9.0 substitutions between the cysts of the single host and 3.0-9.0 substitutions when comparing C. faba individuals isolated from different host individuals. We observed the most of the ITS1 variability within 48 bp repetitive sequences featured by the chi-like sequence 5'-GCTTGTCTGCC-3' at their beginning. Similarly to the extensive C. faba infrapopulation examined, we determined the presence of highly variable number of repetitive sequences within the ITS1 locus of C. faba isolated from multiple host species and from various geographic locations. While similar variability was observed earlier in mutually unrelated specimens of several Schistosomatidae and Microphallidae species, here, we for the first time document it among multiple individuals of a single infracommunity possessing single mitochondrial haplotype. Lower ITS1 evolutionary divergence rates observed between individuals within the cysts when compared to those between the cysts suggest that the recombination occurs at multiple stages of the life cycle. We propose DNA recombination involving chi-like sequences to serve as a general feature shared by multiple families of digenetic trematodes to increase genetic diversity of their polyembryonic populations infecting their definitive hosts.

Pseudobacciger cheneyae n. sp. (Digenea: Gymnophalloidea) from Weber's chromis (Chromis weberi Fowler & Bean) (Perciformes: Pomacentridae) at Lizard Island, Great Barrier Reef, Australia

A new species of digenean, Pseudobacciger cheneyae n. sp., is described from the intestines of Weber's chromis (Chromis weberi Fowler & Bean) from off Lizard Island, Great Barrier Reef, Australia. This species differs from the three described species of Pseudobacciger Nahhas & Cable, 1964 [P. cablei Madhavi, 1975, P. harengulae Yamaguti, 1938 and P. manteri Nahhas & Cable, 1964] in combinations of the size of the suckers and the length of the caeca. The host of the present species is a perciform (Family Pomacentridae) which contrasts with previous records of the genus which are almost exclusively from clupeiform fishes. The genus Pseudobacciger is presently recognised within the family Faustulidae (Poche, 1926) but phylogenetic analyses of 28S and ITS2 rDNA show that the new species bears no relationship to species of four other faustulid genera (Antorchis Linton, 1911, Bacciger Nicoll, 1924, Paradiscogaster Yamaguti, 1934 and Trigonocryptus Martin, 1958) but that instead it is nested within the Gymnophalloidea (Odhner, 1905) as sister to the Tandanicolidae (Johnston, 1927). This result suggests that the Faustulidae is polyphyletic.

Lepidapedon sereti n. sp. (Digenea: Lepidapedidae) in Coelorinchus sereti (Gadiformes: Macrouridae) from deep waters off Vanuatu

Lepidapedon sereti n. sp. is described from the macrourid Coelorinchus sereti from the deep water off Vanuatu. It is placed in the Elongatum group and Elongatum subgroup. It differs from the other species described in this subgroup by the distinctly dorsally subterminal excretory pore. It also differs from other species in combinations of size, excretory vesicle length, proportions of forebody, post-testicular region and other metric features. This constitutes the first record of a Lepidapedon (sensu stricto) from the Central Western Pacific Ocean.

Morphometric and molecular characterisation of specimens of Lepidapedon Stafford, 1904 (Digenea: Lepidapedidae) from the deep-sea fish Mora moro (Risso) (Teleostei: Moridae) in the western Mediterranean

In a study of the parasites of the deep-sea fish Mora moro (Risso) (Gadiformes: Moridae) off the Mediterranean coasts of Catalonia and the Balearic Islands (Spain), we were able to distinguish two morphs of specimens belonging to Lepidapedon Stafford, 1904 (Digenea: Lepidapedidae). This material is herein described and illustrated. Comparative sequence analyses using partial mitochondrial nad1 sequences revealed that the material assigned to one of these morphs can be considered conspecific with the material identified as Lepidapedon desclersae Bray & Gibson, 1995 from the same host. However, the published nad1 sequence for L. desclersae was generated from a specimen ex M. moro from the North East Atlantic. Examination of the voucher specimens associated with this sequence revealed that both the North East Atlantic and the Mediterranean specimens ex M. moro differ from L. desclersae as described from its type-host, Lepidion eques (Günther), in the anterior extent of the vitelline fields which is further posterior, reaching only to the posterior margin of the external seminal vesicle in L. desclersae, versus being at the mid-level of this organ and reaching the posterior margin of the ventral sucker. Therefore, we have tentatively assigned the material characterised here, both morphologically and molecularly as Lepidapedon sp. Acquisition of additional sequences for both nad1 mitochondrial and 28S rRNA genes of L. desclersae from material ex Lepidion spp. is required in order to determine whether the observed morphometric variation reflects host-related or inter-specific differences. The second morph of Lepidapedon from M. moro is described and distinguished on morphometric grounds, such as the position of the most anterior vitelline follicles, which reach to the anterior margin of the ventral sucker. Its identity is commented upon, but, in view of the fact that there were few specimens and no molecular data available, it is not named.

Phylogenetic relationships of the Gorgoderidae (Platyhelminthes: Trematoda), including the proposal of a new subfamily (Degeneriinae n. subfam.)

Phylogenetic analyses of a range of gorgoderid trematodes based on ITS2 and partial 28S rDNA data lead us to propose the Degeneriinae n. subfam. for the genus Degeneria in recognition of its phylogenetic isolation and distinctive morphology and biology. The current concepts of the subfamilies Anaporrhutinae and Gorgoderinae were supported. Within the Gorgoderinae, the large genus Phyllodistomum is shown to be paraphyletic relative to Pseudophyllodistomum and Xystretrum. Notably, the clade of marine Phyllodistomum does not form a clade with the other marine genus, Xystretrum. Distinct clades within the Gorgoderinae correspond variously to identity of first intermediate host, form of cercaria and their marine or freshwater habitat. We are not yet in a position to propose separate genera for these clades.

Gastrointestinal helminth communities of the blackspot seabream Pagellus bogaraveo (Teleostei: Sparidae) from Portuguese north-east Atlantic waters

A study was carried out on the gastrointestinal helminth communities of blackspot seabream, Pagellus bogaraveo, from the Portuguese mainland and island waters. Fifteen helminth parasite species were detected, including the following new records in this host: the digeneans Accacladocoelium petasiporum, Brachyenteron helicoleni, Glomericirrus macrouri, Lecithocladium excisum, Lepocreadium album and Pachycreadium carnosum; the nematode Camallanus sp. and the acanthocephalan Rhadinorhynchus pristis. Infection levels were generally low. Samples from mainland waters had a significantly higher prevalence of digeneans than those from the islands, probably due to the greater availability of invertebrate intermediate hosts on the continental slope. The helminth community of P. bogaraveo from Azores was diverse but mostly composed of species that infected no more than a single host, whereas in Madeira the helminth community was very depauperate. Most helminth species exhibited niche preferences within the gastrointestinal tract of the host. Higher functional richness and evenness were obtained in helminth communities of P. bogaraveo from mainland waters, indicating a balanced use of available resources, which is suggestive of more stable gastrointestinal helminth communities in these waters.

Macrourimegatrema gadoma n. sp. (Digenea: Opecoelidae) from the doublethread grenadier Gadomus arcuatus (Goode & Bean) (Macrouridae) in the Gulf of Mexico and Caribbean Sea

Macrourimegatrema gadoma n. sp. (Digenea: Opecoelidae: Plagioporinae) is described from the pyloric caeca and intestine of the doublethread grenadier Gadomus arcuatus (Goode & Bean) (Macrouridae) collected from the northeastern Gulf of Mexico and off Venezuela. The new species differs from Macrourimegatrema brayi Blend, Dronen & Armstrong, 2004, the type and only species in the genus, in the distribution of the vitelline follicles and gonads, a larger body size, and the presence of highly-folded caeca with numerous outpocketings or pouches. It is suggested that species of Macrourimegatrema Blend, Dronen & Armstrong, 2004 probably infect their piscine hosts through the ingestion of a benthopelagic crustacean.