Coevolution of Retrovarium n. gen. (Digenea: Cryptogonimidae) in Lutjanidae and Haemulidae (Perciformes) in the Indo-West Pacific

Neohexangitrema spp. (Trematoda: Microscaphidiidae) in Indo-West Pacific Acanthuridae: Richness, distribution, diet and contemporary naming issues

Examination of hundreds of individuals of 32 species of Acanthuridae from the Indo-West Pacific resulted in the collection of trematodes consistent with the genus Neohexangitrema Machida, 1984 from the northern and southern Great Barrier Reef (GBR, Queensland, Australia), Ningaloo Reef (Western Australia), Okinawa (Japan), New Caledonia, and Mo'orea and Rangiroa in French Polynesia. Specimens of Neohexangitrema spp. were primarily collected from two species of Zebrasoma, Z. scopas (Cuvier) and Z. velifer (Bloch), and less frequently from three species of Acanthurus. Specimens from Z. scopas and A. nigricans (Linnaeus) from French Polynesia are morphologically and genetically distinct and here described as N. blairi n. sp. This species appears to represent an unusual case of parasite endemism in French Polynesia. Two other morphotypes occurred, often together, in fishes from at least one of the other localities but not in French Polynesia. The first of these, from Ningaloo Reef, Okinawa, GBR and New Caledonia, is clearly morphologically and genetically distinct and is described as N. phytophagum n. sp. This species frequently has large amounts of undigested algae in the digestive tract and appears to be a herbivore in a herbivore. The second widespread morphotype comprised specimens from Z. scopas and Z. velifer consistent with N. zebrasomatis Machida, 1984 as originally described from Z. velifer from off southern Japan. Molecular analyses (cox1 mtDNA and ITS2 and 28S rDNA) consistently suggest that these new specimens represent two morphologically cryptic species, both infecting Z. scopas and Z. velifer, one only at Ningaloo Reef and the other from the GBR. Neither of these species can presently be positively identified as N. zebrasomatis given the lack of molecular data from the type-locality. We here propose new names for both taxa, N. obscurum n. sp. for the species from the GBR and New Caledonia and N. crypticum n. sp. for the species from Ningaloo Reef. This proposal is made with the explicit understanding that one of the two may well (but will not necessarily) prove a synonym of N. zebrasomatis. This approach draws attention to the developing issue of the management of the names of combinations of cryptic trematode species.

Challenges in the recognition of trematode species: Consideration of hypotheses in an inexact science

The description and delineation of trematode species is a major ongoing task. Across the field there has been, and currently still is, great variation in the standard of this work and in the sophistication of the proposal of taxonomic hypotheses. Although most species are relatively unambiguously distinct from their congeners, many are either morphologically very similar, including the major and rapidly growing component of cryptic species, or are highly variable morphologically despite little to no molecular variation for standard DNA markers. Here we review challenges in species delineation in the context provided to us by the historical literature, and the use of morphological, geographical, host, and molecular data. We observe that there are potential challenges associated with all these information sources. As a result, we encourage careful proposal of taxonomic hypotheses with consideration for underlying species concepts and frank acknowledgement of weaknesses or conflict in the data. It seems clear that there is no single source of data that provides a wholly reliable answer to our taxonomic challenges but that nuanced consideration of information from multiple sources (the 'integrated approach') provides the best possibility of developing hypotheses that will stand the test of time.

Revision of Cryptogonimus Osborn, 1903 and Caecincola Marshall et Gilbert, 1905 (Digenea: Cryptogonimidae), supplemental description of Cryptogonimus chili Osborn, 1903, and description of a new species of Caecincola infecting basses (Centrarchiformes: Centrarchidae) in Tennessee and Alabama rivers

We provide a supplemental description of the type species for Cryptogonimus Osborn, 1903 (Digenea: Cryptogonimidae), Cryptogonimus chili Osborn, 1903, based on newly-collected, heat-killed, formalin-fixed specimens infecting rock bass, Ambloplites rupestris (Rafinesque), and smallmouth bass, Micropterus dolomieu Lacepède (both Centrarchiformes: Centrarchidae), from the Duck River, Tennessee (USA). We emend Cryptogonimus to include features observed in the present specimens of its type species and in the descriptions of its congeners: a broad (wider than long) oral sucker, an intestine that bifurcates in the posterior half of the forebody, a bipartite seminal vesicle, a hermaphroditic duct that is dorsal to the ventral sucker, a preovarian seminal receptacle, and a Laurer's canal that opens dorsally at the level of the anterior testis. We describe Caecincola duttonae sp. n. (Cryptogonimidae) infecting largemouth bass, Micropterus salmoides (Lacepède), from Neely Henry Reservoir (Coosa River, Alabama, USA). The new species differs from its congeners by having a combination of a less elongate body, an intestine that bifurcates at the level of the ventral sucker, caeca that terminate at the level of the testes, diagonal testes in the middle of the hindbody, and a vitellarium predominantly distributed in the hindbody. We emend Caecincola Marshall et Gilbert, 1905 (type species Caecincola parvulus Marshall et Gilbert, 1905) to include features of the new species and recently-described congeners: an elongate body, an intestine that bifurcates in the posterior half of the forebody, caeca that extend posteriad beyond the testes, tandem testes, and a vitellarium that is wholly or primarily in the hindbody. Our 28S and ITS2 phylogenetic analyses recovered Caecincola and Cryptogonimus as sister taxa; Caecincola was recovered as paraphyletic with 28S but monophyletic with ITS2. This is the first phylogenetic study of Cryptogonimidae that includes a nucleotide sequence for a species of the type genus Cryptogonimus. We regard Cryptogonimus diaphanus (Stafford, 1904) Miller, 1941 as a species inquirenda.

A new species of Siphoderina Manter, 1934 (Digenea: Cryptogonimidae) infecting the Dory Snapper Lutjanus fulviflamma (Teleostei: Lutjanidae) from the east coast of South Africa

Parasitological assessment of marine fishes at Sodwana Bay in the iSimangaliso Marine Protected Area on the east coast of South Africa revealed a new species of cryptogonimid trematode infecting the pyloric caeca of the Dory Snapper, Lutjanus fulviflamma (Forsskål) (Lutjanidae). The new species is morphologically consistent with the concept of the large genus Siphoderina Manter, 1934; its phylogenetic position within this genus was validated through molecular sequencing of the ITS2 and partial 28S ribosomal DNA sub-regions. We name this species Siphoderina nana n. sp. and comment on the current state of understanding for this genus of cryptogonimids.

Siphoderina hustoni n. sp. (Platyhelminthes: Trematoda: Cryptogonimidae) from the Maori snapper Lutjanus rivulatus (Cuvier) on the Great Barrier Reef

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.

A review of molecular identification tools for the opisthorchioidea

The superfamily Opisthorchioidea encompasses the families Cryptogonimidae, Opisthorchiidae and Heterophyidae. These parasites depend on the aquatic environment and include marine and freshwater species. Some species, such as Clonorchis sinensis and Opisthorchis viverrini, have a high impact on public health with millions of infected people worldwide and have thus been the object of many studies and tool developments. However, for many species, tools for identification and detection are scarce. Although morphological descriptions have been used and are still important, they are often not efficient on the immature stages of these parasites. Thus, during the past few decades, molecular approaches for parasite identification have become commonplace. These approaches are efficient, quick and reliable. Nonetheless, for some parasites of the superfamily Opisthorchioidea, reference genomic data are limited. This study reviews available genetic data and molecular tools for the identification and/or the detection of this superfamily. Molecular data on this superfamily are mostly based on mitochondrial and ribosomal gene sequence analyses, especially on the cytochrome c oxidase subunit 1 gene and internal transcribed spacer regions respectively.

Stemmatostoma cribbi n. sp. (Digenea: Cryptogonimidae) from Freshwater Fishes in the Wet Tropics Bioregion of Queensland, Australia

A survey of the parasite fauna of freshwater fishes from the Wet Tropics Bioregion in Queensland, Australia, revealed the presence of a new species of Stemmatostoma Cribb, 1986 (Digenea: Cryptogonimidae). Stemmatostoma cribbi n. sp. is described from the intestine and pyloric caeca of 2 species of grunter (Terapontidae), Hephaestus fuliginosus (Macleay) and Hephaestus tulliensis (De Vis), and the Jungle perch (Kuhliidae), Kuhlia rupestris (Lacepède), collected from the Barron and Mulgrave-Russell River drainage divisions in tropical north Queensland, Australia. Stemmatostoma cribbi is primarily distinguished morphologically from the type and only other species in the genus, Stemmatostoma pearsoni Cribb, 1986, in having consistently fewer oral spines (14 in S. cribbi vs. 16 in S. pearsoni). Alignment of novel molecular data for S. cribbi and S. pearsoni revealed that they differ genetically by 26 nucleotides (2.1%) over the 1,258 bp partial large subunit (LSU) region, 1 nucleotide (0.8%) over the 121 bp partial 5.8S region, and 23 nucleotides (7.2%) over the entire 318 bp ITS2 rDNA region. Bayesian inference and maximum likelihood phylogenetic analyses of the partial LSU region for the species of Stemmatostoma sequenced here were used to explore the relationships of these species to other cryptogonimid species reported from freshwater ecosystems.

DNA sequencing demonstrates the importance of jellyfish in life cycles of lepocreadiid trematodes

Sequence data were combined with morphological analyses to identify two lepocreadiid trematode species from jellyfishes and fishes. Three species of jellyfish were captured within Port Phillip Bay, Australia, and three species of fish that feed on jellyfish were obtained from Moreton Bay (Queensland) and Port Phillip Bay and Portland (Victoria). The digeneans were distributed throughout most parts of the jellyfish. Opechona cf. kahawai Bray & Cribb, 2003 parasitized the scyphozoan jellyfish Aequorea eurodina and the scombrid fish Scomber australasicus. Cephalolepidapedon warehou Bray & Cribb, 2003 parasitized the scyphozoans Pseudorhiza haeckeli and Cyanea annaskala, and the centrolophid fishes Seriolella brama and Seriolella punctata. Intensities ranged from four to 96 in the jellyfish, and one to 30 in the fish. For both trematode species, internal transcribed spacer 2 of ribosomal DNA sequences from mature adults in the fishes matched those from metacercariae from the jellyfish. This is the first record of larval stages of C. warehou and O. cf. kahawai, and the first use of DNA sequencing to identify digenean trematode metacercariae from jellyfish. Three new host records are reported for C. warehou and two for O. cf. kahawai.

Uncharted digenean diversity in Lake Tanganyika: cryptogonimids (Digenea: Cryptogonimidae) infecting endemic lates perches (Actinopterygii: Latidae)

BACKGROUND

Lake Tanganyika is considered a biodiversity hotspot with exceptional species richness and level of endemism. Given the global importance of the lake in the field of evolutionary biology, the understudied status of its parasite fauna is surprising with a single digenean species reported to date. Although the most famous group within the lake's fish fauna are cichlids, the pelagic zone is occupied mainly by endemic species of clupeids (Actinopterygii: Clupeidae) and lates perches (Actinopterygii: Latidae, Lates Cuvier), which are an important commercial source for local fisheries. In this study, we focused on the lake's four lates perches and targeted their thus far unexplored endoparasitic digenean fauna.

METHODS

A total of 85 lates perches from four localities in Lake Tanganyika were examined. Cryptogonimid digeneans were studied by means of morphological and molecular characterisation. Partial sequences of the nuclear 28S rRNA gene and the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene were sequenced for a representative subset of the specimens recovered. Phylogenetic analyses were conducted at the family level under Bayesian inference.

RESULTS

Our integrative approach revealed the presence of six species within the family Cryptogonimidae Ward, 1917. Three out of the four species of Lates were found to be infected with at least one cryptogonimid species. Two out of the three reported genera are new to science. Low interspecific but high intraspecific phenotypic and genetic diversity was found among Neocladocystis spp. Phylogenetic inference based on partial 28S rDNA sequences revealed a sister group relationship for two of the newly erected genera and their close relatedness to the widely distributed genus Acanthostomum Looss, 1899.

CONCLUSIONS

The present study provides the first comprehensive characterisation of the digenean diversity in a fish family from Lake Tanganyika which will serve as a baseline for future explorations of the lake's digenean fauna. Our study highlights the importance of employing an integrative approach for revealing the diversity in this unique host-parasite system.

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.

Two species of Neometadena Hafeezullah & Siddiqi, 1970 (Digenea: Cryptogonimidae) from Moreton Bay, Australia, including the description of Neometadena paucispina n. sp. from Australian Lutjanidae

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.

A molecular phylogenetic appraisal of the acanthostomines Acanthostomum and Timoniella and their position within Cryptogonimidae (Trematoda: Opisthorchioidea)

The phylogenetic position of three taxa from two trematode genera, belonging to the subfamily Acanthostominae (Opisthorchioidea: Cryptogonimidae), were analysed using partial 28S ribosomal DNA (Domains 1-2) and internal transcribed spacers (ITS1-5.8S-ITS2). Bayesian inference and Maximum likelihood analyses of combined 28S rDNA and ITS1 + 5.8S + ITS2 sequences indicated the monophyly of the genus Acanthostomum (A. cf. americanum and A. burminis) and paraphyly of the Acanthostominae. These phylogenetic relationships were consistent in analyses of 28S alone and concatenated 28S + ITS1 + 5.8S + ITS2 sequences analyses. Based on molecular phylogenetic analyses, the subfamily Acanthostominae is therefore a paraphyletic taxon, in contrast with previous classifications based on morphological data. Phylogenetic patterns of host specificity inferred from adult stages of other cryptogonimid taxa are also well supported. However, analyses using additional genera and species are necessary to support the phylogenetic inferences from this study. Our molecular phylogenetic reconstruction linked two larval stages of A. cf. americanum cercariae and metacercariae. Here, we present the evolutionary and ecological implications of parasitic infections in freshwater and brackish environments.

Three members of Opisthomonorcheides Parukhin, 1966 (Digenea: Monorchiidae) from carangid fishes (Perciformes) from Indonesia, with a review of the genus

Three species of Opisthomonorcheides Parukhin, 1966 are reported for the first time from Indonesian waters: O. pampi (Wang, 1982) Liu, Peng, Gao, Fu, Wu, Lu, Gao & Xiao, 2010 and O. ovacutus (Mamaev, 1970) Machida, 2011 from Parastromateus niger (Bloch), and O. decapteri Parukhin, 1966 from Atule mate (Cuvier). Both O. pampi and O. ovacutus can now be considered widespread in the Indo-Pacific region, with earlier records of these species being from Fujian Province, China and Penang, Malaysia, respectively. We redescribe O. decapteri from one of its original hosts, Atule mate, off New Caledonia, and report this species from Jakarta Bay, Indonesia, extending its range throughout the Indian Ocean into the south-western Pacific. All three species possess a genital atrium that is long, sometimes very long, and a genital pore that is located in the forebody. This validates the interpretation that the original description was erroneous in reporting the genital pore in the hindbody, well posterior to the ventral sucker. These observations verify the synonymy of Retractomonorchis Madhavi, 1977 with Opisthomonorcheides. A major discrepancy between the species of Opisthomonorcheides is that some are described with the uterus entering the terminal organ laterally and some with it entering terminally; this feature needs further analysis. Based on the length of the genital atrium and the posterior extent of the vitellarium, the 27 species of Opisthomonorcheides considered valid can be divided into four groups. Among the 53 host records analysed, the families Carangidae (53% of records), Stromateidae (17%) and Serranidae (5.7%) are the most common; the reports are overwhelmingly from members of the Perciformes (91%), with further records in the Clupeiformes (5.7%), Gadiformes (1.9%) and Pleuronectiformes (1.9%). Two fish genera (Parastromateus Bleeker and Pampus Bonaparte) dominate the recorded hosts, with the black pomfret Parastromateus niger harbouring six species, the silver pomfret Pampus argenteus (Euphrasen) harbouring six, and the Chinese silver pomfret P. chinensis (Euphrasen) two. A host-parasite checklist is presented. We discuss the host-specificity of members of the genus, questioning some records such as that of O. decapteri in a deep-sea macrourid. We also comment on the morphological similarity, but phylogenetic distance, between the various Pomfret species, advancing the possibility that a series of host misidentifications has occurred. Sequences of the ITS2 rDNA gene generated for O. pampi and O. ovacutus are briefly discussed and molecular data are lodged in the GenBank database.

Neopsilotrema n. g. (Digenea: Psilostomidae) and three new species from ducks (Anseriformes: Anatidae) in North America and Europe

Neopsilotrema n. g. (Digenea: Psilostomidae) and three new species of psilostomid digeneans are described from birds in North America and Europe: Neopsilotrema lakotae n. sp. from Aythya americana (Eyton) in North Dakota, USA, Neopsilotrema affine n. sp. from Aythya affinis (Eyton) in Minnesota, USA and Neopsilotrema lisitsynae n. sp. from Anas crecca L. in Kherson Region, Ukraine. Neopsilotrema n. g. shares a bipartite seminal vesicle with only three genera within the Psilostomidae, Psilotornus Byrd & Prestwood, 1969, Psilostomum Looss, 1899 and Grysoma Byrd, Bogitsh & Maples, 1961. The new genus differs from Psilotornus in the presence of a muscular pharynx and a massive ventral sucker; the location of the cirrus-sac in relation to the ventral sucker and more posterior location of ovary; the nature of the vitellarium (i.e. comprising large, compact follicles with small vitelline cells vs weakly defined follicles with large vitelline cells); a proportionately shorter forebody; and in parasitisation in anseriform (vs passeriform) birds. Differences between the new genus and Psilostomum comprise the shape of the body, the relative size of the suckers, somewhat longer forebody and a more anterior location of the testes. Neopsilotrema n. g. differs from Grysoma in the relative size of the suckers, the degree of development of prostatic cells, the nature of the vitellarium and the size of the eggs in relation to body length. The European species Neopsilotrema lisitsynae n. sp. is distinguished from its congeners in having a longer, narrower and distinctly more elongate body with a longer post-testicular region and anterior limits of the vitelline fields posterior to ventral sucker. The two North American forms, Neopsilotrema lakotae n. sp. and Neopsilotrema affine n. sp., are cryptic species with largely overlapping metrical data; these are distinguished by comparing genetic data. The phylogenetic hypotheses for the Psilostomidae developed from sequence data analyses based on partial 28S rDNA support the erection of the new genus and the distinction of the three new species. Grysoma marilae (Price, 1942) agrees more closely with the generic diagnosis of Neopsilotrema, especially in relation to the size and shape of the body, the relative length of the forebody and post-testicular field, the structure of the vitellarium, the location of the reproductive organs and the sucker ratio. Consequently, it is here transferred to the new genus as Neopsilotrema marilae (Price, 1942) n. comb.

Trematodes of fishes of the Indo-west Pacific: told and untold richness

The Indo-west Pacific is a marine bioregion stretching from the east coast of Africa to Hawaii, French Polynesia and Easter Island. An assessment of the literature from the region found reports of 2,582 trematode species infecting 1,485 fish species. Reports are concentrated in larger fishes, undoubtedly reflecting the tendency for larger hosts to be infected by more species of parasites as well as a collecting bias. Many hundreds of fish species, including many from families known to be rich in trematodes, have yet to be reported as hosts. Despite some areas (the Great Barrier Reef, Hawaii and the waters off China, India and Japan) receiving sustained attention, none can be considered to be comprehensively known. Several regions, most importantly in East Africa, French Polynesia and the Coral Triangle, are especially poorly known. The fauna of the Indo-west Pacific has been reported so unevenly that we consider it impossible to predict the true trematode richness for the region. We conclude that the greatest gap in our understanding is of the geographical distribution of species in the Indo-west Pacific. This is highlighted by the fact that 87% of trematodes in the region have been reported no more than five times. The reliable recognition of species is a major problem in this field; molecular approaches offer prospects for resolution of species identification but have been little adopted to date.

Echinostoma 'revolutum' (Digenea: Echinostomatidae) species complex revisited: species delimitation based on novel molecular and morphological data gathered in Europe

BACKGROUND

The systematics of echinostomes within the so-called 'revolutum' group of the genus Echinostoma, which encompasses the type-species E. revolutum and a number of morphologically similar species, has long been controversial. Recent molecular studies indicate the existence of more species than previously considered valid, thus stressing the need for wider taxon sampling from natural host populations. This is especially true for Europe where morphological evidence indicates higher species diversity than previously thought, but where molecular data are virtually lacking. This gap in our knowledge was addressed in the present study through an integration of morphological and molecular approaches in the investigation of a dataset with larger taxonomic and geographical coverage.

METHODS

More than 20,000 freshwater snails belonging to 16 species were collected during 1998-2012 from various localities in eight countries in Europe. Snail screening provided representative larval isolates for five species of the 'revolutum' group, identified by their morphology. Adult isolates for four species recovered from natural and experimental infections were also identified. Partial fragments of the mitochondrial nad1 and 28S rRNA genes were amplified for 74 and 16 isolates, respectively; these were analysed together with the sequences of Echinostoma spp. available on GenBank.

RESULTS

Delineation of the European Echinostoma spp. was carried out based on molecular, morphological and ecological data. The large-scale screening revealed infections with five Echinostoma spp., including one new species: E. revolutum (sensu stricto), E. miyagawai, E. paraulum, E. bolschewense and Echinostoma n. sp. The newly-generated nad1 sequences from Europe fall into six distinct, well-supported, reciprocally monophyletic lineages corresponding to the species identifications based on morphology; this was corroborated by the 28S rDNA sequences. The analyses of the total nad1 dataset provided evidence for 12 monophyletic groups and five singletons, which represent seven described/named species and ten cryptic species-level lineages of Echinostoma.

CONCLUSION

We conclude that nad1 should be the first choice for large-scale barcode-based identification of the species of the 'revolutum' group. Our study provides a comprehensive reference library for precisely identified isolates of the European species and highlights the importance of an integrative approach for species identification linking molecular, morphological and biological data.

A new brachycladiid species (Digenea) from Gervais' beaked whale Mesoplodon europaeus in north-western Atlantic waters

A new species of the digenean family Brachycladiidae Odhner, 1905 is described from the bile ducts of a Gervais' beaked whale Mesoplodon europaeus Gervais (Ziphiidae) stranded on the North Atlantic coast of Florida. These parasites were assigned to Brachycladium Looss, 1899 and differed from other species of the genus in the relative size of the oral and ventral suckers, the form and size of the eggs and their extremely small body size. A canonical discriminant analysis was used to examine differences between these specimens and the smallest available individuals of B. atlanticum (Abril, Balbuena and Raga, 1991) Gibson, 2005, considered the morphologically closest species. The overall results exhibited significant differences between the two samples and a jack-knife classification showed that 96.2% of the specimens were correctly classified to their group. In view of evidence from morphological data, the specimens from M. europaeus are considered as new to science and are designated as Brachycladium parvulum n. sp.

A review of molecular approaches for investigating patterns of coevolution in marine host-parasite relationships

Parasites and their relationships with hosts play a crucial role in the evolutionary pathways of every living organism. One method of investigating host-parasite systems is using a molecular approach. This is particularly important as analyses based solely on morphology or laboratory studies of parasites and their hosts do not take into account historical evolutionary interactions that can shape the distribution, abundance and population structure of parasites and their hosts. However, the predominant host-parasite coevolution literature has focused on terrestrial hosts and their parasites, and there still is a lack of studies in marine environments. Given that marine systems are generally more open than terrestrial ones, they provide fascinating opportunities for large-scale (as well as small-scale) geographic studies. Further, patterns and processes of genetic structuring and systematics are becoming more available across many different taxa (but especially fishes) in many marine systems, providing an excellent basis for examining whether parasites follow host population/species structure. In this chapter, we first highlight the factors and processes that challenge our ability to interpret evolutionary patterns of coevolution of hosts and their parasites in marine systems at different spatial, temporal and taxonomic scales. We then review the use of the most commonly utilized genetic markers in studying marine host-parasite systems. We give an overview and discuss which molecular methodologies resolve evolutionary relationships best and also discuss the applicability of new approaches, such as next-generation sequencing and studies utilizing functional markers to gain insights into more contemporary processes shaping host-parasite relationships.

Are cryptic species a problem for parasitological biological tagging for stock identification of aquatic organisms?

The effective use of biological tags in stock assessment relies on the reliable identification of the parasites concerned. This may be compromised if cryptic species are not recognized. Here we review what is known about cryptic species in aquatic hosts and its potential importance in this respect. Although strictly cryptic species may be considered as species which can be distinguished only by molecular data, we accept the far looser but more practical definition of species that cannot be readily distinguished morphologically. Cryptic species appear to have been identified most frequently as occurring in separate host species; this is heartening in that this has no significant impact on tagging studies. But cryptic species have occasionally been identified in single hosts sympatrically and are relatively common in geographically distinct populations of the same host species. Ignorance of both kinds of occurrences has the capacity to undermine the reliability of tagging analysis. We review in detail what is known of intra- and interspecific genetic variation over geographical ranges in the trematodes, based on recent molecular studies. Although the existence of cryptic species and evidence of intraspecific variability may appear daunting, we suspect that these complexities will add, and indeed have already added, to the sophistication of the information that can be derived from tagging studies.

Evidence for extensive cryptic speciation in trematodes of butterflyfishes (Chaetodontidae) of the tropical Indo-West Pacific

Molecular data from the cytochrome c oxidase subunit I (cox1) mitochondrial DNA gene and the second internal transcribed spacer (ITS2) nuclear rDNA region were used to test the current morphologically-based taxonomic hypothesis regarding species of Monorchiidae (Hurleytrematoides) from chaetodontid and tetraodontid fishes from six sites in the tropical Indo-West Pacific (TIWP): Heron and Lizard Islands off the Great Barrier Reef (GBR, Australia), Moorea (French Polynesia), New Caledonia, Ningaloo Reef (Australia) and Palau. The 16 morphospecies analysed differed from each other by a minimum of 55bp (9.1%) over the mitochondrial cox1 and 8bp (1.6%) over the ITS2 DNA regions. For two species, Hurleytrematoides loi and Hurleytrematoides sasali, specimens from the same host species in sympatry differed at levels comparable to those between pairs of distinct morphospecies for both cox1 and ITS2 sequences. We take this as evidence of the presence of combinations of cryptic species; however, we do not propose new species for these taxa because we lack identified morphological voucher specimens. For seven species, Hurleytrematoides coronatum, Hurleytrematoides deblocki, Hurleytrematoides faliexae, H. loi, Hurleytrematoides morandi, H. sasali and Hurleytrematoides sp. A, samples from some combinations of localities had base pair differences that were equal to or greater than differences between some pairs of distinct morphospecies for one or both cox1 and ITS2 sequences. For three species, H. coronatum, H. loi and H. morandi, one haplotype differed from every other haplotype by more than the morphospecies benchmark. In these cases morphological specimens could not be distinguished by morphology. These data suggest extensive cryptic richness in this genus. For the present we refrain from dividing any of the morphospecies. This is because there is a continuum of levels of intra- and interspecific genetic variation in this system, so that distinguishing the two would be largely arbitrary.

A new species of Parspina Pearse, 1920 (Digenea: Cryptogonimidae) from Pimelodella gracilis (Valenciennes) (Siluriformes: Heptapteridae) in the Paraná River basin, Argentina, and a key to the genus

A new species of cryptogonimid belonging to the genus Parspina Pearse, 1920 is described from the intestine of Pimelodella gracilis (Valenciennes) in the Paraná River basin, Argentina. Parspina pimelodellae n. sp. is characterised by having: (i) a body length/width ratio of 1:3.6-5.3 at the level of the ventral sucker; (ii) 21 oral spines; (iii) an oral sucker larger than the ventral sucker, with a sucker width ratio of 1:0.6-0.7; (iv) a postcaecal region of 16-19% of the body-length; (v) a compact, transversely elongate ovary, anterior to and well separated from the testes; (vi) small, branched vitelline follicles, extending from the level of the ventral sucker to the anterior margin of the ovary; and (vii) a large seminal vesicle situated posterodorsal to the ventral sucker. A key to the species of Parspina is presented.

An annotated list of fish parasites (Isopoda, Copepoda, Monogenea, Digenea, Cestoda, Nematoda) collected from Snappers and Bream (Lutjanidae, Nemipteridae, Caesionidae) in New Caledonia confirms high parasite biodiversity on coral reef fish

BACKGROUND

Coral reefs are areas of maximum biodiversity, but the parasites of coral reef fishes, and especially their species richness, are not well known. Over an 8-year period, parasites were collected from 24 species of Lutjanidae, Nemipteridae and Caesionidae off New Caledonia, South Pacific.

RESULTS

Host-parasite and parasite-host lists are provided, with a total of 207 host-parasite combinations and 58 parasite species identified at the species level, with 27 new host records. Results are presented for isopods, copepods, monogeneans, digeneans, cestodes and nematodes. When results are restricted to well-sampled reef fish species (sample size > 30), the number of host-parasite combinations is 20-25 per fish species, and the number of parasites identified at the species level is 9-13 per fish species. Lutjanids include reef-associated fish and deeper sea fish from the outer slopes of the coral reef: fish from both milieus were compared. Surprisingly, parasite biodiversity was higher in deeper sea fish than in reef fish (host-parasite combinations: 12.50 vs 10.13, number of species per fish 3.75 vs 3.00); however, we identified four biases which diminish the validity of this comparison. Finally, these results and previously published results allow us to propose a generalization of parasite biodiversity for four major families of reef-associated fishes (Lutjanidae, Nemipteridae, Serranidae and Lethrinidae): well-sampled fish have a mean of 20 host-parasite combinations per fish species, and the number of parasites identified at the species level is 10 per fish species.

CONCLUSIONS

Since all precautions have been taken to minimize taxon numbers, it is safe to affirm than the number of fish parasites is at least ten times the number of fish species in coral reefs, for species of similar size or larger than the species in the four families studied; this is a major improvement to our estimate of biodiversity in coral reefs. Our results suggest that extinction of a coral reef fish species would eventually result in the coextinction of at least ten species of parasites.

Taxonomic approaches to and interpretation of host specificity of trematodes of fishes: lessons from the Great Barrier Reef

The taxonomy of trematodes of Great Barrier Reef (GBR) fishes has been studied in some detail for over 20 years. Understanding of the fauna has been informed iteratively by approaches to sampling, understanding of morphology, the advent of molecular methodology and a feed-back loop from the emergent understanding of host specificity. Here we analyse 658 host-parasite combinations for 290 trematode species, 152 genera and 28 families from GBR fishes. These are reported from 8 orders, 38 families, 117 genera and 243 species of fishes. Of the 290 species, only 4 (1·4%) have been reported from more than one order of fishes and just 23 (7·9%) infect more than one family; 77·9% of species are known from only one genus, and 60% from only one species of fish. Molecular studies have revealed several complexes of cryptic species and others are suspected; we conclude that no euryxenous host distribution should be accepted on the basis of morphology only. The occurrence of individual trematode species in potential hosts is patchy and difficult to predict reliably a priori or explain convincingly a posteriori. These observations point to the need for a vigorous iterative interaction between the accretion of host specificity data and its interpretation.

Trematode families and genera: have we found them all?

The proposal of new trematode families has almost stopped. Many new genera are still being proposed, but the number has fallen below historical rates. For most of the history of description of trematodes there have been more genera known from tetrapods than from fishes, but this pattern has reversed recently. These reductions are argued to be more of a reflection of the law of diminishing returns than diminution of effort. Thus, at the family level the classification of trematodes is becoming mature, and at the genus level we are seeing the 'beginning of the end' of the discovery of diversity. However, work for generations of scientists remains in other aspects of trematode biodiversity research, especially in life cycles, phylogeny and biogeography.

Taxonomy, host-specificity and biogeography of Symmetrovesicula Yamaguti, 1938 (Digenea: Fellodistomidae) from chaetodontids (Teleostei: Perciformes) in the tropical Indo-west Pacific region

Combined molecular and morphological data demonstrate the presence of two species of Symmetrovesicula Yamaguti, 1938 in chaetodontid fishes from Australian waters. A total of 2,462 individuals of 46 species of chaetodontid at eight localities were dissected. Analysis of the rDNA ITS2 revealed the presence of three genotypes, two separated by a single base difference and the third differed from the other two by 10-11 base differences. Subsequent morphological examination identified a number of variations that supported the presence of two species; however, we found no additional evidence to support the presence of a third species corresponding to the single base variation. Thus, we take the conservative approach of recognising two species of Symmetrovesicula within Australian waters, S. chaetodontis Yamaguti, 1938 from off Ningaloo Reef, Western Australia and S. gracilis n. sp. from off Ningaloo Reef, the Great Barrier Reef, Queensland and New Caledonia. Both species exhibit distinct restrictions to certain clades of chaetodontids.

Staphylorchis cymatodes (Gorgoderidae: Anaporrhutinae) from carcharhiniform, orectolobiform and myliobatiform elasmobranchs of Australasia: low host specificity, wide distribution and morphological plasticity

Anaporrhutine gorgoderids (Digenea: Gorgoderidae: Anaporrhutinae) found in the body cavity of six species of elasmobranchs from the orders Carcharhiniformes, Myliobatiformes and Orectolobiformes from Australian waters were found to belong to the genus Staphylorchis. Although these specimens were morphologically variable, sequences of ITS2 and 28S ribosomal DNA from specimens from three host families and two host orders were identical. Based on morphological and molecular data these specimens were identified as the type-species of the genus, Staphylorchis cymatodes. New measurements are provided for S. cymatodes, and for the first time genetic data are presented for this species. In addition to providing new morphological and molecular data for S. cymatodes, the previously described species S. gigas, S. parisi and S. scoliodonii, are here synonymised with S. cymatodes. This implies that S. cymatodes, as conceived here, has remarkably low host-specificity, being recorded from eight elasmobranch species from four families and three orders, has a wide geographical distribution in the Indo-west Pacific from off India, in the Bay of Bengal, to Moreton Bay in the Coral Sea, and is morphologically plastic, with body size, size of specific organs and body shape differing dramatically between specimens from different host species. The genus Staphylorchis now contains only two valid species, S. cymatodes and S. pacifica.

Molecular evidence confirms that Proctoeces humboldti and Proctoeces chilensis (Digenea: Fellodistomidae) are the same species

Two species of Proctoeces Odhner, 1911 have been described in marine organisms from Chile: P. humboldti George-Nascimento & Quiroga (1983), parasitizing the gonads of keyhole limpets (Fissurella spp.), and P. chilensis Oliva (1984), an intestinal parasite of Sicyases sanguineus (Teleostei); both species were subsequently considered as P. lintoni Siddiqi & Cable (1960). To assist in the resolution of the taxonomic identification of Proctoeces species in marine organisms from Chile, phylogenetic studies using DNA sequences from the V4 region of the SSU rRNA gene were performed. Several specimens of P. lintoni were isolated from keyhole limpets (Fissurella spp.) and clingfish (S. sanguineus) from Bahia San Jorge (23°40′S) and Bahia Concepción (36°50′S). Phylogenetic analyses were conducted using three different approaches: a neighbour-joining (NJ), a maximum likelihood (ML) and Bayesian inference (BI). The phylogenetic analysis confirms that specimens of Proctoeces obtained from keyhole limpets and those specimens from the clingfish are in fact the same species. We prefer to consider our specimens as Proctoeces cf. lintoni, as the morphology of Proctoeces appears to be of doubtful value and genetic information about P. lintoni Siddiqi & Cable (1960) is not available. In addition, our results strongly suggest that there are at least three species in this genus.

Molecules and morphology reveal cryptic variation among digeneans infecting sympatric mullets in the Mediterranean

We applied a combined molecular and morphological approach to resolve the taxonomic status of Saccocoelium spp. parasitizing sympatric mullets (Mugilidae) in the Mediterranean. Eight morphotypes of Saccocoelium were distinguished by means of multivariate statistical analyses: 2 of Saccocoelium obesum ex Liza spp.; 4 of S. tensum ex Liza spp.; and 2 (S. cephali and Saccocoelium sp.) ex Mugil cephalus. Sequences of the 28S and ITS2 rRNA gene regions were obtained for a total of 21 isolates of these morphotypes. Combining sequence data analysis with a detailed morphological and multivariate morphometric study of the specimens allowed the demonstration of cryptic diversity thus rejecting the hypothesis of a single species of Saccocoelium infecting sympatric mullets in the Mediterranean. Comparative sequence analysis revealed 4 unique genotypes, thus corroborating the distinct species status of Saccocoelium obesum, S. tensum and S. cephali and a new cryptic species ex Liza aurata and L. saliens recognized by its consistent morphological differentiation and genetic divergence. However, in spite of their sharp morphological difference the 2 morphotypes from M. cephalus showed no molecular differentiation and 4 morphotypes of S. tensum were genetically identical. This wide intraspecific morphological variation within S. tensum and S. cephali suggests that delimiting species of Saccocoelium using solely morphological criteria will be misleading.

Gynichthys diakidnus n. g., n. sp. (Digenea: Cryptogonimidae) from the grunt Plectorhinchus gibbosus (Lacépède, 1802) (Perciformes: Haemulidae) off the Great Barrier Reef, Australia

Gynichthys diakidnus n. g., n. sp. (Digenea: Cryptogonimidae) is described from the fish Plectorhinchus gibbosus (Lacépède) (Perciformes: Haemulidae) off Heron and Lizard Islands on the Great Barrier Reef, Australia. The monotypic Gynichthys n. g. is distinguished from all other cryptogonimid genera by the combination of a fusiform body, the lack of oral spines, a forebody that occupies approximately half or more of the body length, a deeply lobed ovary, opposite to slightly oblique testes, a seminal vesicle that is confined mainly in the forebody and the presence of multiple gonotyls in the form of two small slightly muscular pores or pseudosucker-like structures in the mid-line well anterior to the ventral sucker. Bayesian inference analysis of LSU rDNA data revealed that G. diakidnus n. sp. grouped relatively distant to species of the cryptogonimid genus Oligogonotylus Watson, 1976, which also have multiple gonotyls, suggesting that the presence of multiple gonotyls is homoplasious and has thus at least evolved twice in the family. The secondary structure of the internal transcribed spacer 2 (ITS2) rDNA region was inferred for G. diakidnus using minimum free energy and homology modelling algorithms. A four helix model was inferred with helices I and IV being relatively short (<30 nucleotides) and helix three being the longest; this structure is homologous with that observed for other digeneans and eukaryotes in general.

Sympatric species of Deretrema Linton, 1910: D. combesae n. sp. and D. combesorum n. sp. (Digenea: Zoogonidae) from the manybar goatfish Parupeneus multifasciatus (Quoy & Gaimard, 1824) (Perciformes: Mullidae) from New Caledonia

Two sympatric species of Deretrema, D. combesae n. sp. and D. combesorum n. sp. are described from the manybar goatfish Parupeneus multifasciatus from off New Caledonia, South Pacific. D. combesae n. sp. does not fit any of the described Deretrema subgenera. The combination of the characters, tegumental spines, caeca reaching past the testes, the vitellarium reaching into the hindbody, much of the uterus at the level of and anterior to the gonads, a long oesophagus, testes in the hindbody and the pre-testicular ovary are not found in any of the described subgenera. D. combesorum n. sp. fits into the subgenus Deretrema (Deretrema), but differs from the described species in the sucker-ratio, eggs size, elongate shape and contiguous testes. The sympatry of these dissimilar species of Deretrema casts doubt on the value of the subgenera in Deretrema.

Two new cryptogonimid genera (Digenea, Cryptogonimidae) from Lutjanus bohar (Perciformes, Lutjanidae): analyses of ribosomal DNA reveals wide geographic distribution and presence of cryptic species

We describe three new species of Cryptogonimidae belonging to two new genera, Caulanus gen. nov. and Latuterus gen. nov., from the large piscivorous reef fish Lutjanus bohar Forsskål, 1775, recovered from Heron and Lizard Islands off the Great Barrier Reef and Rasdhoo Atoll, Maldives. To support our morphologically based taxonomic approach, three nuclear ribosomal DNA regions (28S, ITS1 and ITS2) were sequenced and analysed to explore the geographic distribution and integrity of the putative species recovered from these widespread localities. Sequencing of the rDNA regions included multiple replicates and revealed three distinct genotypes. Two of the observed genotypes were associated with phenotypically similar specimens of Latuterus, but were each restricted to a single locality, Lizard Island, GBR or Rasdhoo Atoll, Maldives. A posteriori analysis of the associated morphotypes revealed distinct morphological differences and these consistent differences, in combination with the consistent genetic differences led to the recognition of two distinct species in the system. Caulanus is distinguished by having oral spines, caeca which open via ani at the posterior end of the body, tandem testes and uterus that extends from the posterior end of the body to the pharynx. Latuterus is distinguished by lacking oral spines, having multiple/follicular testes, a uterus that is extensive in both fore-and hindbody and vitelline follicles which are confined to the region from the pharynx to oral sucker. Caulanus thomasi sp. nov. had identical sequences for all of the rDNA regions examined from specimens recovered from all three localities, indicating that this species has a wide Indo-Pacific distribution. The species reported here are evidently restricted to Lutjanus bohar because they were never found in large numbers of other lutjanid species sampled at the same localities.