Phylogenetics of the Monogenea--evidence from a medley of molecules

Checklist of monogeneans from Egyptian marine fishes, including some newly collected species

A checklist of 113 monogenean species parasitizing marine fishes (60 species) from different localities in Egypt is provided. The list is supplemented by eight newly collected monogenean species from Red Sea fishes, off Safaga and El-Quseir. Five of these species are new Egyptian records: Calydiscoides euzeti Justine, 2007, Calydiscoides rohdei Oliver, 1984, Lethrinitrema austrosinense (Li & Chen, 2005) Sun, Li & Yang, 2014, Pseudohaliotrema sphincteroporus Yamaguti, 1953, and Pentatres sphyraenae Euzet & Razarihelisoa, 1959. Furthermore, Lutjanus ehrenbergii (Peters), Lethrinus nebulosus (Forsskål), Lethrinus mahsena (Forsskål), Siganus stellatus (Forsskål), and Sphyraena flavicauda Rüppell represent new host records. The current study also lists nine monogenean species from the Gulf of Aqaba for which the coordinates of the sampling localities were not clearly defined, but which could also belong to the Egyptian fauna as the gulf is part of the Red Sea basin. Dactylogyrus aegyptiacus Ramadan, 1983 is transferred to Ecnomotrema Kritsky, 2023 as E. aegyptiacum (Ramadan, 1983) n. comb. Entobdella aegyptiacus Amer, 1990, Polylabroides aegyptiacus Mahmoud & Shaheed 1998, Gotocotyla sigani Abdel Aal, Ghattas & Badawy, 2001, Neohexostoma epinepheli Abdel Aal, Ghattas & Badawy, 2001, Neothoracocotyle commersoni Abdel Aal, Ghattas & Badawy, 2001, Acleotrema maculatum Morsy, El Fayoumi & Fahmy, 2014, Diplectanum harid Morsy, El Fayoumi, Al Shahawy & Fahmy, 2014, and Pseudorhabdosynochus chlorostigma Morsy, El Fayoumi, Al Shahawy & Fahmy, 2014, are considered species inquirendae. Paranaella diplodae Bayoumy, Abd El-Hady & Hassanain, 2007 is considered incertae sedis. Allencotyla lutini El-Dien, 1995 and Lamellodiscus diplodicus Bayoumy, 2003 are regarded as nomina nuda.

"Something old, something new, something borrowed, and the oioxeny is true": description of Plectanocotyle jeanloujustinei n. sp. (Polyopisthocotylea, Plectanocotylidae) from the MNHN Helminthology collection with novel molecular and morphological data for P. gurnardi (Van Beneden & Hesse, 1863) (sensu stricto) from Sweden

Natural history museums worldwide house billions of apposite specimens, offering the potential for cost-free parasitological datasets. Herein, we provide novel morphological and molecular data (28S and cox1) for the polyopisthocotylean Plectanocotyle gurnardi sensu stricto from the type-host Eutrigla gurnardus from Sweden based on newly collected specimens from the Northeast Atlantic, and specimen from T. Odhner's collections at the Swedish Museum of Natural History (Stockholm, Sweden). The newly generated 28S sequences of P. gurnardi from E. gurnardus from the Northeast Atlantic were identical to those from the Western Mediterranean, and nested in a single clade, suggesting the presence of a single species. A 28S sequences of P. gurnardi sensu stricto from Sweden and those from the U.K. (type locality for P. caudata) were identical; we confirm that P. caudata and P. gurnardi are conspecific and formally synonymize them. A single 28S sequence of Plectanocotyle sp. from Chelidonichthys lastoviza off France differed from P. gurnardi from the Northeast Atlantic by 3-4 % and from P. gurnardi from France by 3%. Plectanocotyle sp. ex C. lastoviza off France is clearly not P. gurnardi, suggesting an oioxenic specificity of P. gurnardi to E gurnardus. Careful re-examination of Plectanocotyle cf. gurnardi from C. lastoviza from the Western Mediterranean from the Helminthology collection of Muséum national d'Histoire naturelle (Paris, France) revealed that it differs from all congeners by morphometry (size of clamps, of terminal lappet and its hamuli and uncinuli, and size of atrial spines). The cox1 divergences between P. cf. gurnardi and P. major, P. lastovizae, and P. gurnardi sensu stricto were 10-11 %, 10-11 % and 8 % respectively, falling within the interspecific variations range. Plectanocotyle from the Mediterranean is described as a new species, P. jeanloujustinei n. sp. We apprise nomenclature problems in Plectanocotyle and consider P. elliptica a species inquirenda.

Description of a new species, Pseudodiscocotyla mikiae n. sp. (Monogenea: Discocotylidae) parasitic on gills of Pristipomoides filamentosus from off Okinawa-jima island in Japan, with redescription of Pseudodiscocotyla opakapaka

Two species of Pseudodiscocotyla Yamaguti, 1965 (Monogenea: Discocotylidae) were collected from crimson jobfish Pristipomoides filamentosus (Valenciennes) (Perciformes: Lutjanidae) off Okinawa-jima island, southern Japan. Pseudodiscocotyla opakapaka is redescribed and represents the first Japanese record. A new species, Pseudodiscocotyla mikiae n. sp., differs from Ps. opakapaka in the absence of spines around the male genital pore, the shape of the vaginal pore, the presence of spines inside the vaginal pore, and the shape of the clamp. The locations of the male genital atrium and the vaginal pore in both species were similar, and the observed armament differences of the male copulatory organ are therefore presumed to establish reproductive isolation. The phylogenetic trees for the Mazocraeidea based on the partial 28S rDNA sequences were created using new sequences of Pseudodiscocotyla mikiae n. sp., and Discocotylidae formed a sister group with the species Diclidophoridae, Macrovalvitrematidae, and Plectanocotylidae. Pristipomoides filamentosus is widely distributed across the Indo-Pacific, and Pseudodiscocotyla mikiae n. sp. could share the distribution of the host.

New species of Protomicrocotyle (Monogenea: Protomicrocotylidae), and new information on P. mirabilis, parasites of Caranx spp. from Veracruz, México

During a study of the helminth parasites of carangid fish of the Gulf of Mexico, Protomicrocotyle mirabilis and a new member of that genus were found. The aim of the present study is to provide new morphological and sequences of 28s rDNA and CO1 mtDNA for P. mirabilis and describe the new species. Between 2005-2022, 73 specimens of Caranx spp. were purchased from local fishermen of the littoral waters of the Gulf of Mexico. Protomicrocotyle veracruzensis sp. nov. is most similar to P. mirabilis than to P. ivoriensis, the only members of the genus known from the Greater Atlantic Ocean Basin. Protomicrocotyle veracruzensis sp. nov. can be distinguished from those two species by the arrangement and number of testes. Measurement data on the haptoral armature for the new species is provided and the potential value and need for comparative data from these structures of other members of the genus is discussed. The results of the molecular analysis and the morphometric analysis of 91 characters confirmed that this new species belongs to Protomicrocotyle.

Morphological and molecular characterization of Encotyllabe vallei Monticelli, 1907 (Monopisthocotylea, Monogenea) from the gilthead seabream Sparus aurata Linnaeus (Teleostei, Sparidae) from the southwestern Mediterranean and notes on host specificity of the genus Encotyllabe Diesing, 1850

Incomplete original descriptions, the unavailability or poor conditions of specimens and the lack of detailed redescriptions have caused the validity of several species of the genus Encotyllabe Diesing, 1850 to be questioned. To date, seven of the recognized species were described upon one or two specimens, hindering study of intraspecific variations. This was made worse by considering few morphoanatomical differences sufficient to erect new species. Among Encotyllabe spp. occurring in Mediterranean waters, E. vallei was first described from the gilt-head bream Sparus aurata (Sparidae) off Italy. Although beautifully illustrated for a paper from that century, morphometric data for E. vallei from the type-host S. aurata remain unavailable. Previous records of E. vallei provided either morphometrical or molecular data, and its validity was questioned. We provide a redescription of E. vallei based on newly collected specimens from the S. aurata from the southwestern Mediterranean (off Algeria) using integrative taxonomy. Analysis of cox1 sequences of E. vallei from S. aurata, compared to sequences from other sparid hosts, mainly Pagellus bogaraveo, revealed a divergence not exceeding 2%, suggesting a stenoxenic specificity for this monogenean. Given that P. bogaraveo is the type-host for Encotyllabe pagelli, we were tempted to suggest a synonymy between E. vallei and E. pagelli. We refrained from doing so because E. pagelli was first described from the Atlantic coast off Brest, France. Morphological data for Encotyllabe from P. bogaraveo are warranted assessing the host specificity of E. vallei and whether there might be a species complex within individual sparid fish species.

Variation in the parasite communities of three co-occurring herbivorous coral reef fishes

Parasites are important, diverse, and abundant components of natural ecosystems and can influence the behaviour and health of their hosts, inter- and intraspecific interactions, and ultimately community structure. Coral reefs are one of the world's most biodiverse ecosystems, yet our understanding of the abundance, diversity, and composition of parasite communities of coral reef fishes is limited. Here, the authors aimed to compare the abundance, richness and composition of parasite communities among three co-occurring herbivorous coral reef fishes (the barred rabbitfish Siganus doliatus, Ward's damsel Pomacentrus wardi and the obscure damsel Pomacentrus adelus) from an inshore reef of the Great Barrier Reef (GBR). In total, 3978 parasites (3869 endoparasites and 109 ectoparasites) from 17 families were recovered from 30 individuals of each of the three fish species (mean = 44 ± 22 s.e. parasites per fish; range = 0-1947 parasites per fish). The parasite communities of P. wardi and P. adelus were characterised by pennellid copepods, derogenid and lecithasterid digeneans and were distinct from those of S. doliatus that were characterised by a higher abundance of atractotrematid and gyliauchenid digeneans. The abundance and family richness of all parasites were greatest in S. doliatus (abundance: 22.1 ± 5.0 parasites per fish; richness: 3.2 ± 0.3 families per fish), intermediate in P. wardi (abundance: 4.8 ± 1.1 parasites per fish; richness: 2.3 ± 0.3 families per fish) and lowest in P. adelus (abundance: 1.4 ± 0.4 parasites per fish; richness: 0.9 ± 0.2 families per fish). Similarly, the abundance of endoparasites was greatest in S. doliatus (19.7 ± 5.1 endoparasites per fish), intermediate in P. wardi (2.6 ± 0.7 endoparasites per fish) and lowest in P. adelus (1.2 ± 0.4 endoparasites per fish). Ectoparasite abundances were also lowest for P. adelus (0.2 ± 0.1 ectoparasites per fish), and S. doliatus and P. wardi had comparable abundances of ectoparasites (1.3 ± 0.3 and 2.1 ± 0.5 parasites per fish, respectively). Similarities between the parasite assemblages of the two pomacentrids may be related to their similar behaviours and/or diets vs. those of the larger-bodied and more mobile rabbitfish. Investigating the causes and consequences of variation in parasite communities across a broader range of fish species will be critical to understand the potential role of parasites in coral reef ecosystems.

A Monogenean Gill Parasite within the Genus Haliotrema (Ancyrocephalidae) Infecting Argyrops filamentosus Fish: Morphology and Molecular Studies

Due to the presence of different parasite taxa and other disease-causing agents, all fish species are extremely prone to dangers. As a result, the current study focused on some of the monogenean parasites that infect one of the economically important fish species, the soldier bream Argyrops filamentosus, from the Red Sea coast of Jeddah, Saudi Arabia. Following that, thirty A. filamentosus fish specimens were examined for monogenean parasites. The parasitic species were isolated and morphologically and molecularly studied. The presence of one monogenean species of Haliotrema susanae (F: Ancyrocephalidae) infecting gills was observed in 50% of the investigated fish species. The ancyrocephalid species Haliotrema susanae is characterized by having all generic features within the genus Haliotrema. It could be distinguished from other species within this genus by the male copulatory organ including a copulatory tube with no accessory piece and a haptor made up of two pairs of anchors, two bars, and seven pairs of marginal hooks. As ectoparasitic taxa of the investigated sparid fish, the current study of Haliotrema species constitutes the first report of this genus. A molecular phylogenetic analysis based on the partial 28S rRNA gene region was analyzed to investigate the phylogenetic affinity of this parasite with the genus Haliotrema belonging to Ancyrocephalidae. This study considers the addition of a new genetic sequence for this parasite species.

Mitochondrial phylogenomics provides conclusive evidence that the family Ancyrocephalidae is deeply paraphyletic

BACKGROUND

Unresolved taxonomic classification and paraphyly pervade the flatworm class Monogenea: the class itself may be paraphyletic and split into Polyopisthocotylea and Monopisthocotylea; there are some indications that the monopisthocotylean order Dactylogyridea may also be paraphyletic; single-gene markers and some morphological traits indicate that the family Ancyrocephalidae is paraphyletic and intertwined with the family Dactylogyridae.

METHODS

To attempt to study the relationships of Ancyrocephalidae and Monopisthocotylea using a phylogenetic marker with high resolution, we sequenced mitochondrial genomes of two fish ectoparasites from the family Dactylogyridae: Dactylogyrus simplex and Dactylogyrus tuba. We conducted phylogenetic analyses using three datasets and three methods. Datasets were ITS1 (nuclear) and nucleotide and amino acid sequences of almost complete mitogenomes of almost all available Monopisthocotylea mitogenomes. Methods were maximum likelihood (IQ-TREE), Bayesian inference (MrBayes) and CAT-GTR (PhyloBayes).

RESULTS

Both mitogenomes exhibited the ancestral gene order for Neodermata, and both were compact, with few and small intergenic regions and many and large overlaps. Gene sequences were remarkably divergent for nominally congeneric species, with only trnI exhibiting an identity value > 80%. Both mitogenomes had exceptionally low A + T base content and AT skews. We found evidence of pervasive compositional heterogeneity in the dataset and indications that base composition biases cause phylogenetic artefacts. All six mitogenomic analyses produced unique topologies, but all nine analyses produced topologies that rendered Ancyrocephalidae deeply paraphyletic. Mitogenomic data consistently resolved the order Capsalidea as nested within the Dactylogyridea.

CONCLUSIONS

The analyses indicate that taxonomic revisions are needed for multiple Polyopisthocotylea lineages, from genera to orders. In combination with previous findings, these results offer conclusive evidence that Ancyrocephalidae is a paraphyletic taxon. The most parsimonious solution to resolve this is to create a catch-all Dactylogyridae sensu lato clade comprising the current Ancyrocephalidae, Ancylodiscoididae, Pseudodactylogyridae and Dactylogyridae families, but the revision needs to be confirmed by another marker with a sufficient resolution.

Revision of the systematics of the Polystomoidinae (Platyhelminthes, Monogenea, Polystomatidae) with redefinition of Polystomoides Ward, 1917 and Uteropolystomoides Tinsley, 2017

Polystomatids are platyhelminth parasites that infect mainly amphibians and freshwater turtles. For more than seven decades, chelonian polystomes were classified into three genera according to the number of hamuli, i.e. absent for Neopolystoma, one pair for Polystomoidella and two pairs for Polystomoides. Following re-examination of morphological characters, seven new genera were erected the past six years, namely Apaloneotrema, Aussietrema, Fornixtrema, Manotrema, Pleurodirotrema, Uropolystomoides and Uteropolystomoides. However, the polyphyly of Neopolystoma and Polystomoides on the one hand, and the nested position of Uteropolystomoides within a clade encompassing all Neopolystoma and Polystomoides spp. on the other, still raised questions about the validity of these genera. We therefore re-examined several types, paratypes and voucher specimens, and investigated the molecular phylogeny of polystomes sampled from the oral cavity of North American turtles to re-evaluate their systematic status. We show that all Polystomoides Ward, 1917, sensu Du Preez et al., 2022, Neopolystoma Price, 1939, sensu Du Preez et al., 2022 and Uteropolystomoides Tinsley, 2017 species, display vaginae that are peripheral and extend well beyond the intestine. We thus reassign all species of the clade to Polystomoides and propose nine new combinations; however, although Uteropolystomoides is nested within this clade, based on its unique morphological features, we propose to keep it as a valid taxon. Polystomoides as redefined herein groups all polystome species infecting either the oral cavity or the urinary bladder of cryptodires, with peripheral vaginae and with or without two pairs of small hamuli. Uteropolystomoides nelsoni (Du Preez & Van Rooyen 2015), originally described from Pseudemys nelsoni Carr is now regarded as Uteropolystomoides multifalx (Stunkard, 1924) n. comb. infecting three distinct Pseudemys species of North America.

From development to taxonomy: the case of Sciaenacotyle pancerii (Monogenea: Microcotylidae) in the Mediterranean meagre

The microcotylid Sciaenacotyle pancerii is a pathogenic monogenean infecting Argyrosomus regius, a candidate for species diversification in the Mediterranean aquaculture. Life-history stages of S. pancerii commonly co-occur in field infections, but to date, morphological data have only been provided for oncomiracidia and adults although identifying life-history stages can be useful in infection management. A total of 114 specimens of S. pancerii were analysed to characterize the developmental events and to assess morphological and morphometric variations before and after maturity. The post-larval development of S. pancerii is characterized by: expansion and bifurcation of the gut, loss of the larval haptor, protandrous development of the genitalia and vitellaria formation. The size variability of larval hooks, hamuli and germanium of S. pancerii is firstly reported and dimensional ranges of parasite body, haptor, testes, posteriormost clamps and eggs are widened. The size of most of the diagnostic features of S. pancerii significantly increases after parasite maturity and therefore, only those specimens with more than 116 clamps should be considered for minimising development-related variability in size. The high number of clamps, their fast development and the asymmetry in their size and arrangement suggest that S. pancerii may use a mixed attachment strategy between the closely related microcotylids and heteraxinids. This combination of features may be host related and linked to the gill structure of the sciaenid fish and the phylogenetic position of the genus Sciaenacotyle; distant from other microcotylids while close to heteraxinid species.

Complete Mitochondrial Genome of Two Ectoparasitic Capsalids (Platyhelminthes: Monogenea: Monopisthocotylea): Gene Content, Composition, and Rearrangement

The capsalid monogeneans are important pathogens that generally infect marine fishes and have a substantial impact on fish welfare in aquaculture systems worldwide. However, the current mitogenome information on capsalids has received little attention, limiting the understanding of their evolution and phylogenetic relationships with other monogeneans. This paper reports the complete mitochondrial genomes of Capsala katsuwoni and Capsala martinieri for the first time, which we obtained using a next-generation sequencing method. The mitogenomes of C. katsuwoni and C. martinieri are 13,265 and 13,984 bp in length, respectively. Both species contain the typical 12 protein-coding genes, 2 ribosomal RNA genes, 22 transfer RNA genes, and a control region. The genome compositions show a moderate A+T bias (66.5% and 63.9% for C. katsuwoni and C. martinieri, respectively) and exhibit a negative AT skew but a positive GC skew in both species. One gene block rearrangement was found in C. katsuwoni in comparison with other capsalid species. Instead of being basal to the Gyrodactylidea and Dactylogyridea or being clustered with Dactylogyridea, all species of Capsalidea are grouped into a monophyletic clade. Our results clarify the gene rearrangement process and evolutionary status of Capsalidae and lay a foundation for further phylogenetic studies of monogeneans.

Morphomolecular identification and considerations of the infestation site adaptations of Pricea multae (Thoracocotylidae: Priceinae) from Scomberomorus commerson, off Arabian Gulf, Saudi Arabia

Monogeneans Pricea multae naturally infested 42 of the 120 (35%) mackerel fish (Scomberomorus commerson) examined. For the first time, an infestation was discovered off the coast of Jubil in the Arabian Gulf of Saudi Arabia. Based on the structure clarified through light and electron microscopy of mounted specimens and molecular analysis of rDNA and measurements of this monogenean parasite was identified as P. multae. The tegumental surface of the parasite was characterized by tegumental ridges running transversally, generating folds in both the dorsal and ventral surfaces of the body at regular intervals. The study clarified the importance and function of the micro-structures, such as tegumental folds, perforations, sensory ganglia present on the parasite's surface, and the larger hamulus supported by a relatively unmodified internal spine. This monogenean parasite has adapted to its host infestation site uniquely.

Kannaphallus leptosomus n. sp. (Monogenea: Heteraxinidae: Cemocotylinae) parasitizing Scyris indica (Carangiformes: Carangidae) from Malaysia

A new monogenean species, Kannaphallus leptosomus n. sp., from the gills of the diamond trevally, Scyris indica Rüppell, caught off Terengganu, Peninsular Malaysia is described with molecular data. The new species differs from other species of the genus by the morphology of the largest clamp, the presence of a penis gun-associated needle, the unarmed genital atrium size, and the presence of two independent vaginal tubes. Previous records of Kannaphallus species were compiled, and four nominal species including one species incertae sedis (K. virilis Unnithan, 1957; K. lateriporis Mamaev, 1988; K. leptosomus n. sp.; and K. mochimae Fuentes Zambrano, 1998 incertae sedis) and two undescribed species recorded as invalid names were listed. Cemocotylelloides carangis Ramalingam, 1969 was considered a junior objective synonym of K. univaginalis Ramalingam, 1960; this species was treated as Cemocotylelloides univaginalis n. comb. In addition, Unnithan's materials including type specimens of K. virilis could not be found in specimen repositories in India, and it appears that the specimens were probably not deposited in any institution or have been subsequently lost. Based on the phylogenetic analysis of 28S rDNA sequences, Heteraxinidae was broadly divided into two clades, and Heteraxininae and Cemocotylinae were shown as polyphyletic groups, respectively.

Under the radar: co-introduced monogeneans (Polyopisthocotylea: Gastrocotylinea) of the invasive fish Scomberomorus commerson in the Mediterranean Sea

The Levant Basin is in many ways the world's most invaded marine ecosystem owing to the existence of the man-made Suez Canal. The invasion of free-living organisms through this pathway is increasingly documented and monitored in the past two decades, and their ecological impact recognized. Nonetheless, while tremendous scientific effort is invested in documenting introduced fishes, co-introduction events of these fishes and their parasites have drawn relatively little interest. In our research, we examined the presence of gill parasites (Monogenea) on the invasive narrow barred Spanish mackerel Scomberomorus commerson which has been known in the Mediterranean Sea for 80 years. The gills of S. commerson supported numerous, relatively large monogeneans (Monogenea: Gastrocotylinea), reaching prevalence levels of 100% with a mean intensity of ~ 80 worms per host. Using an integrated molecular and morphological approach, four gastrocotylinean species were identified: Gotocotyla acanthura, Cathucotyle cathuaui, Pricea multae, and Pseudothoracocotyla ovalis. Two species, C. cathuaui and P. ovalis, are reported here for the first time from the Mediterranean. Sequences of the 28S rRNA gene of G. acanthura from native hosts, Pomatomus saltatrix and Trachinotus ovatus, differed from individuals collected from S. commerson by 1.8%. We therefore suggest that the taxonomic status and distribution of G. acanthura should be revisited, and we recommend an integrated approach as essential to accurately detect co-introductions.

Redescription, complete mitochondrial genome and phylogenetic relationships of Hexostoma thynni (Delaroche, 1811) Rafinesque, 1815 (Monogenea, Hexostomatidae)

Specimens of Hexostoma thynni (Delaroche, 1811) Rafinesque, 1815 were collected from their type-host, the bluefin tuna Thunnus thynnus, caught off Algeria, i.e. close to the type-locality, off Mallorca, which is also in the Mediterranean. The species is briefly redescribed and compared to previous descriptions, under the same name or as its synonym Plagiopeltis duplicata Diesing, 1858, to ascertain identity of specimens. The three genera within the Hexostomatidae (Hexostoma Rafinesque, 1815, Neohexostoma Price, 1961 and Homostoma Unnithan, 1965) are briefly discussed, with comments on the fragility of characters used to distinguish them. Using next-generation sequencing, the complete mitogenome and the cluster of ribosomal genes (SSU, LSU, ITS1, ITS2, 5.8S) were obtained. The mitogenome is 14,649 bp long and codes for 12 protein-coding genes, 2 ribosomal RNA genes and 22 transfer RNA genes; its size is similar to other mitogenomes obtained from polyopisthocotylean monogeneans. A phylogeny based on concatenated mitogenome protein-coding genes from nine species of polyopisthocotylean monogeneans produced a tree in which the Hexostomatidae H. thynni was associated with other Mazocraeidea, such as Chauhaneidae and Diclidophoridae. This invalidates the hypothesis of Boeger & Kritsky (1993) of Hexostomatidae as sister-group to the Mazocraeidea and suggests the demise of the suborder Hexostomatinea Boeger & Kritsky, 1993. We insist on the usefulness of depositing parts of specimens used for molecular analyses, prepared on permanent slides, in a curated collection.

Five new and two known species of Heterobothrium (Monogenea: Diclidophoridae) infecting puffers of the genus Takifugu from Japanese waters

Seven species of puffers of the genus Takifugu caught in Japanese waters were examined for monogeneans on the gills. Five new species of Heterobothrium (H. gotoi n. sp. from T. porphyreus, H. tabetai n. sp. from T. vermicularis, H. aljufailiae n. sp. and H. iwatai n. sp. from T. snyderi, H. matsubarai n. sp. from T. stictonotus) and two known species (H. praeorchis Bychowsky, Mamaev & Nagibina, 1976 from T. pardalis, T. chrysops and T. flavipterus and H. bychowskyi Ogawa, 1991 from T. flavipterus) were found and described. Heterobothrium tetrodonis of Iwata (1991) was synonymized with H. bychowskyi. Currently, a total of 11 species of Heterobothrium, including the seven species in this study, were recorded from nine species of Japanese Takifugu spp. Ten species excluding H. praeorchis were found from a single host species, suggesting that they are highly host-specific and have co-evolved with the host Takifugu spp. Tagia Sproston, 1946 is synonymized with Heterobothrium. Earlier divergence of Heterobothrium of tetraodontid puffers in Diclidophoridae was suggested by the large subunit ribosomal DNA (rDNA) analyses, and interspecific relationships in this genus inferred from the internal transcribed spacer region of rDNA well corresponded to those inferred from their morphology and adhesive mode to the gills. Including the five new species and synonymization of Tagia with Heterobothrium, the genus Heterobothrium now comprises 19 species.

Dactylogyridae 2022: a meta-analysis of phylogenetic studies and generic diagnoses of parasitic flatworms using published genetic and morphological data

Dactylogyridae is one of the most studied families of parasitic flatworms with more than 1000 species and 166 genera described to date including ecto- and endoparasites. Dactylogyrid monogeneans were suggested as model organisms for host-parasite macroevolutionary and biogeographical studies due to the scientific and economic importance of some of their host lineages. Consequently, an array of phylogenetic research into different dactylogyrid lineages has been produced over the past years but the last family-wide study was published 16 years ago. Here, we provide a meta-analysis of the phylogenetic relationships of Dactylogyridae including representatives of all genera with available molecular data (n=67). First, we investigate the systematic informativeness of morphological characters widely used to diagnose dactylogyrid genera through a parsimony analysis of the characters, character mapping, and phylogenetic comparative methods. Second, we provide an overview of the current state of the systematics of the family and its subfamilies, and summarise potentially poly- and paraphyletic genera. Third, we elaborate on the implications of taxonomic, citation, and confirmation bias in past studies. Fourth, we discuss host range, biogeographical, and freshwater-marine patterns. We found two well-supported macroclades which we assigned to the subfamilies Dactylogyrinae and Ancyrocephalinae. These subfamilies further include 16 well-supported clades with only a few synapomorphies that could be deduced from generic diagnoses in the literature. Furthermore, few morphological characters considered systematically informative at the genus level display a strong phylogenetic signal. However, the parsimony analysis suggests that these characters provide little information on the relationships between genera. We conclude that a strong taxonomic bias and low coverage of DNA sequences and regions limit knowledge on morphological and biogeographical evolutionary patterns that can be inferred from these results. We propose addressing potential citation and confirmation biases through a 'level playing field' multiple sequence alignment as provided by this study.

A revision of Plectanocotyle (Monogenea, Plectanocotylidae), with molecular barcoding of three species and the description of a new species from the streaked gurnard Chelidonichthys lastoviza off Algeria

BACKGROUND

The family Plectanocotylidae includes parasites of the gills of marine fish; although nine genera and about 20 species have been described, almost no molecular information is available. Putting aside Plectanocotyle elliptica Diesing, 1850, supposedly a parasite of the white perch Morone americana, never found again since its original description, two species were valid within Plectanocotyle Diesing, 1850 before this work: Plectanocotyle gurnardi (Van Beneden & Hesse, 1863) Llewellyn, 1941 and Plectanocotyle major Boudaya, Neifar & Euzet, 2006.

METHODS

In this paper, we describe the third species of the genus Plectanocotyle and perform a comparative morphological and molecular analysis of the three species and of Triglicola obscura (Euzet & Suriano, 1974) Mamaev, 1976. Host fishes were also barcoded (COI) for confirmation of host identifications.

RESULTS

Plectanocotyle lastovizae n. sp. is described from the gills of the streaked gurnard Chelidonichthys lastoviza collected off Algeria. The species is compared with specimens of Plectanocotyle cf. gurnardi (from C. lastoviza) from the same locality and P. major and T. obscura (both from the longfin gurnard C. obscurus). Molecules from Plectanocotyle cf. gurnardi could not be compared with P. gurnardi from the type-host and type-locality and we kept the status of the Mediterranean specimens as pending. Algeria is a new geographic record for P. major and T. obscura. Plectanocotyle lastovizae n. sp. is distinguished from the other species found in the Mediterranean by the measurements of clamps, number of testes, and COI sequences, with notable divergence (7.8-11.8%) from the other two species of the genus.

DISCUSSION

We briefly present a list of currently known members of the family Plectanocotylidae, their biology and their hosts.

Occurrence and molecular identification of Monogenea from blue-spotted flathead Platycephalus caeruleopunctatus (Scorpaeniformes: Platycephalidae) in Australian waters

This study describes the occurrence and molecular identification of Monogenea from blue-spotted flathead Platycephalus caeruleopunctatus (McCulloch) (Scorpaeniformes: Platycephalidae) from waters off the NSW coast, Australia. Platycephalus spp. are favoured by consumers for delicate, white, mild flavoured flesh and therefore are commercially important species within Australia. Platycephalus spp. are also extensively targeted by Australian recreational fishers. There has been no previous study that has exclusively focused on Pl. caeruleopunctatus in Australia or globally. Although a single study by Dillon (1985), of monogeneans infecting Platycephalus spp. from Australian waters, identified Microcotyle bassensis Murray, 1931 in Pl. caeruleopunctatus. The present study combines both morphological and molecular methods to identify both host and parasites. A total of 116 fish, sourced from the waters off the coast of New South Wales, Australia, were examined. A total of 1498 Monogenea were recovered from the gills. The overall prevalence, mean intensity, and mean abundance were 72%, 18.05, and 12.91, respectively. Monogenea were initially classified morphologically as two different species M. bassensis (family: Microcotylidae) and Platycephalotrema bassense (Hughes, 1928) Kritsky & Nitta, 2019 (family: Ancyrocephalidae). Molecular identification of Monogenea was conducted through sequencing of their mitochondrial cytochrome c oxidase subunit 1 (cox1) and nuclear 28S genes. The specific identification of host Pl. caeruleopunctatus was confirmed through sequencing the cox1 gene. There was no comparable sequence for cox1 and 28S genes available in GenBank for the monogenean species found in the present study. Only a single sequence (obtained from the nuclear ITS2-rDNA) was deposited in GenBank for M. bassensis. However, the phylogenetic analyses of mitochondrial and nuclear sequences revealed that the identified Monogenea clustered according to their familial groups. Platycephalotrema bassense was identified for the first time in Pl. caeruleopunctatus in the present study. This study has provided the first evidence for the exploration of both cox1 and 28S sequences of all Monogenea. The findings of this study serve as a foundation for future monogenean research on other Platycephalus spp. from Australian waters.

Novel molecular data for monogenean parasites of sparid fishes in the Mediterranean and a molecular phylogeny of the Microcotylidae Taschenberg, 1879

During a study of the monogeneans of four sparid fishes (Diplodus vulgaris, Pagellus bogaraveo, Pagrus pagrus and Sparus aurata) from the Western Mediterranean off Algeria, a large collection of parasites was characterised molecularly (28S rRNA and cox1 genes). A total of 46 partial sequences (23 for each gene) were generated from 38 isolates of monogeneans which included four species (Atrispinum acarne, Microcotyle erythrini (sensu stricto), Sparicotyle chrysophrii and Prostatomicrocotylinae gen. sp.) of the family Microcotylidae, two putative species of the family Capsalidae (Encotyllabe spp.), and one species (Choricotyle chrysophryi) of the family Diclidophoridae. Our study provides (i) the first molecular data for the Capsalidae in the Mediterranean; (ii) the first record of a member of the Prostatomicrocotylinae in the Mediterranean and in a sparid fish (D. vulgaris); (iii) the first cox1 sequences for A. acarne; (iv) the second record of M. erythrini (s.s.) from P. pagrus; and (v) the second confirmed by molecular data record of S. chrysophrii in wild populations of S. aurata. The first phylogenetic hypotheses for the family Microcotylidae developed here, revealed the monophyly of the subfamily Prostatomicrocotylinae and the genus Microcotyle but the relationships among the subfamilies were still largely unresolved with the best represented subfamily Microcotylinae being polyphyletic. Our results highlight the importance of molecular methods in the assessment of monogenean diversity and the need for a thorough taxon-sampling approach to increase the accuracy of phylogenetic reconstruction of the relationships of the large and taxonomically complex polyopisthocotylean family Microcotylidae.

Capsalids (Platyhelminthes: Monogenea) from marine fishes off Okinawa in Japan with the proposal of two new genera

Molecular studies of the Capsalidae suggested that the genus Benedenia is polyphyletic, but a taxonomic organization of the genus that reflects molecular data has not yet been proposed. As a result of molecular analysis (28S rDNA, ITS1-5.8S-ITS2, and cox1 data) including specimens of Benedeniinae newly obtained from Okinawa-jima Island in Japan, two new genera and the revival of Tareenia independent to the genus Benedenia are proposed. Gracilobenedenia n. gen. is distinguished from the other genera of Benedeniinae based on morphological characteristics. This new genus comprises 6 species: G. lutjani n. comb. (type species), G. anticavaginata n. comb., G. rohdei n. comb., G. beverleyburtonae n. comb., G. kuremibai n. gen., n. sp., and G. hichi n. gen., n. sp. Armatobenedenia n. gen. is a monotypic genus for A. armata n. comb. The present molecular phylogenetic analysis showed the independence of Tareenia, and it can be morphologically separated from the other benedeniines. Four species including two new species obtained from Okinawa-jima Island are reported: G. kuremibai n. sp., G. hichi n. sp., G. lutjani n. comb., and Metabenedeniella parva. Furthermore, in the species identification and phylogenetic analysis of capsalids, the usefulness of not only the 28S rDNA but also ITS and the cox1 regions was suggested. These genes were evaluated the efficacy of those regions in DNA barcoding, and the ITS and cox1 regions shown to be useful for DNA barcoding in capsalids compared to the 28S rDNA sequence.

Heteromicrocotyla polyorchis Unnithan, 1961 (Monogenea: Heteromicrocotylidae), a gill parasite of the yellow-spotted trevally, Carangoides fulvoguttatus (Carangidae) from Saudi Arabia: Morphology and phylogeny

Little information for parasitic infections of Carangoides fulvoguttatus was recorded. The present study was intended to investigate the gill parasite Heteromicrocotyla polyorchis of this fish and to provide a full morphological description and clarify its taxonomic status through phylogenetic analysis of the 28S rRNA gene region. A total of sixty fish specimens have been collected from the studied area (the Red Sea in Jeddah Province, Saudi Arabia) and gills were isolated and examined for identification of parasites. Using light electron microscopy, the recovered monogenean parasite's morphology was exhaustively characterized and described. Microscope examinations found that this parasite species represent Heteromicrocotyla polyorchis, and it could be distinguished from congeners of the same genus by armed genital atrium and cirrus sac, follicular post-ovarian testes, unique shape and number of clamps on both haptor sides, and the dorsally curved tip of the male copulatory organ. Morphological features were combined with molecular analysis of the 28S rRNA gene region. The selected gene for the isolated Heteromicrocotyla species was analyzed using appropriate primers to assist in phylogeny with those in the GenBank database. The present monogenean species was characterized by unique genetic sequences that were analyzed and deposited in the GenBank for the first time under the accession number MW406473. Phylogenetic analyses reported that the maximum identity between the current Heteromicrocotyla species and taxa of Heteromicrocotylidae was between 91.42 and 92.09% and confirmed its taxonomic status in this family with a well-distinct clade. The present study supported the second report of H. polyorchis as carangid fish ectoparasites and investigates the first appearance in C. fulvoguttatus inhabiting Saudi Arabia.

Molecular and morphological phylogeny of host-specific Dactylogyrus parasites (Monogenea) sheds new light on the puzzling Middle Eastern origin of European and African lineages

Background

Freshwater fauna of the Middle East encompass elements shared with three continents—Africa, Asia, and Europe—and the Middle East is, therefore, considered a historical geographic crossroad between these three regions. Even though various dispersion scenarios have been proposed to explain the current distribution of cyprinids in the peri-Mediterranean, all of them congruently suggest an Asian origin for this group. Herein, we investigated the proposed scenarios using monogenean parasites of the genus Dactylogyrus, which is host-specific to cyprinoid fishes.

Methods

A total of 48 Dactylogyrus species parasitizing cyprinids belonging to seven genera were used for molecular phylogenetic reconstruction. Taxonomically important morphological features, i.e., sclerotized elements of the attachment organ, were further evaluated to resolve ambiguous relationships between individual phylogenetic lineages. For 37 species, sequences of partial genes coding 18S and 28S rRNA, and the ITS1 region were retrieved from GenBank. Ten Dactylogyrus species collected from Middle Eastern cyprinoids and D. falciformis were de novo sequenced for the aforementioned molecular markers.

Results

The phylogenetic reconstruction divided all investigated Dactylogyrus species into four phylogenetic clades. The first one encompassed species with the “varicorhini” type of haptoral ventral bar with a putative origin linked to the historical dispersion of cyprinids via the North African coastline. The second clade included the majority of the investigated species parasitizing various phylogenetically divergent cyprinid hosts. The morphological and molecular data suggest the ancestral diversification of the species of this clade into two groups: (1) the group possessing the haptoral ventral bar of the “cornu” type, and (2) the group possessing the “wunderi” type. Dactylogyrus diversification apparently occurred in the Middle East, which is indicated by the presence of species with all morphotypes in the region. The last two clades included species parasitizing cyprinids with an East Asian origin, and species possessing the “magnihamatus” type of ventral bar.

Conclusions

The molecular data suggest that some morphological characters of host-specific parasites may undergo convergent evolution in the divergent lineages, and therefore, to fully resolve the phylogenetic relationships among host-specific parasites, an integrative approach combining morphological and molecular data is still needed. In addition, our study indicates that parasite diversity in many regions is still under-explored, and thus we highlight the importance of studies of host-associated parasites, especially in the context of freshwater fish biogeography.

Graphical Abstract

REDESCRIPTION OF CATHARIOTREMA SELACHII (MACCALLUM, 1916) JOHNSTON AND TIEGS, 1922 (MONOGENOIDEA: MONOCOTYLIDAE), EMENDATION OF MONOTYPIC CATHARIOTREMA JOHNSTON AND TIEGS, 1922, AND PROPOSAL OF CATHARIOTREMATINAE N. SUBFAM. BASED ON MORPHOLOGICAL AND NUCLEOTIDE EVIDENCE

We herein redescribe the enigmatic Cathariotrema selachii (MacCallum, 1916) Johnston and Tiegs, 1922 based on the holotype, paratypes, and newly collected specimens infecting the olfactory organ of 5 shark species from the Gulf of Mexico (all new host records): scalloped hammerhead shark, Sphyrna lewini (Griffith and Smith, 1834) (Carcharhiniformes: Sphyrnidae); great hammerhead shark, Sphyrna mokarran (Rüppell, 1837); blacktip shark, Carcharhinus limbatus (Müller and Henle, 1839) (Carcharhiniformes: Carcharhinidae); spinner shark, Carcharhinus brevipinna (Müller and Henle, 1839); and Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson, 1836) (Carcharhinidae). These specimens were morphologically indistinguishable from each other and from MacCallum's holotype and paratypes. Those sequenced had identical first internal transcribed spacer (ITS1) and large subunit ribosomal DNA (28S) nucleotide sequences. As such, C. selachii infects sharks of 2 orders (Carcharhiniformes, Lamniformes) and 3 families (Carcharhinidae, Sphyrnidae, Lamnidae) in the Northwestern Atlantic Ocean (type locality) and Gulf of Mexico (new records herein). This report is the first of new specimens of C. selachii in the Atlantic Ocean Basin in 95 yr and corrects long-standing error cascades and ambiguities concerning the morphology and systematic placement of C. selachii. Considering morphology and nucleotide-based phylogenetic evidence (28S, Bayesian analysis), we herein emend monotypic CathariotremaJohnston and Tiegs, 1922 and propose Cathariotrematinae Bullard n. subfam. for it and 4 other genera (all formerly assigned to Merizocotylinae Johnston and Tiegs, 1922). These genera comprise species infecting only the nose of sharks (monotypic Cathariotrema, SqualotremaKearn and Green, 1983 and SeptitremaKheddam, Chisholm, and Tazerouti, 2020 plus 3 species of TriloculotremaKearn, 1993) and nose of a chimaera (monotypic HolocephalocotyleDerouiche, Neifar, Gey, Justine, and Tazerouti, 2019). Cathariotrematinae differs from Merizocotylinae by having a 3-part attachment organ and by lacking open loculi that symmetrically encircle a cluster of >2 loculi in the center of the haptor. Monophyletic Cathariotrematinae (with sequences representing species of Cathariotrema, Triloculotrema, and Holocephalocotyle only) was sister to monophyletic Merizocotylinae, which together were sister to monophyletic Calicotylinae Monticelli, 1903. These subfamilies comprise a monophyletic group of monocotylids that have a double vagina and infect extrabranchial, enclosed niches (urogenital system, body cavity, olfactory chamber/nose) on their shark, ray, and chimaera hosts (all other monocotylids have a single vagina and infect the gill or body surfaces of rays only). Monocotylinae Taschenberg, 1879 and Decacotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 were recovered as monophyletic. Heterocotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 remained paraphyletic. We accept ParacalicotyleSzidat, 1970.

Redescription of Paradiplozoon opsariichthydis (Jiang, Wu et Wang 1984) Jiang, Wu et Wang, 1989 (Monogenea, Diplozoidae)

Paradiplozoon opsariichthydis (Jiang, Wu et Wang, 1984) Jiang, Wu et Wang, 1989 (Platyhelminthes, Monogenea, Diplozoidae) is blood-feeding parasite from the gills of Asian cyprinid fish Opsariichthys bidens Günther, 1873. In this study, we present a morphological redescription of P. opsariichthydis neotype main morphological features e.g. size of body and clamps due to the fact that the type material is missing. We decided to supplement morphological descriptions by the relevant molecular data (internal transcribed spacer - ITS2) related to P. opsariichthydis adult worm isolates and other representatives of genus Paradiplozoon to cross verify our findings. In addition to that, this study also brings an attention to the host identification. Thus, parasite data were complemented by the determinant cytochrome oxidase b (cytb) sequences of its hosts. All novel sequences are deposited in GenBank. This combination of the morphological and molecular data related to both the parasite and its host seems to be the optimal approach to the general process of (re)description of highly host-specific parasitic organisms, which can then lead to a meaningful phylogenetic analysis.

Triple barcoding for a hyperparasite, its parasitic host, and the host itself: a study of Cyclocotyla bellones (Monogenea) on Ceratothoa parallela (Isopoda) on Boops boops (Teleostei)

Cyclocotyla bellones Otto, 1823 (Diclidophoridae) is a monogenean characterised by an exceptional way of life. It is a hyperparasite that attaches itself to the dorsal face of isopods, themselves parasites in the buccal cavity of fishes. In this study, Cy. bellones was found on Ceratothoa parallela (Otto, 1828), a cymothoid isopod parasite of the sparid fish Boops boops off Algeria in the Mediterranean Sea. We provide, for the first time, molecular barcoding information of a hyperparasitic monogenean, the parasitic crustacean host, and the fish host, with COI sequences.

A new species of Neoheterobothrium Price, 1943 (Monogenea, Diclidophoridae) from Syacium papillosum (Linnaeus) (Pleuronectiformes, Paralichthyidae) in the Yucatan Shelf, with notes on the validity of the subfamilies in the Diclidophoridae

Neoheterobothrium papillosum n. sp. (Monogenea: Diclidophoridae) is described based on specimens collected from the gills of the dusky flounder Syacium papillosum (Linnaeus) (Paralichthyidae) in the Yucatan Shelf. The new species can be differentiated from other congeneric species by the following characteristics: (1) number of hooks in the genital atrium (8 hooks), (2) number of testes (20-34), (3) pharynx size, (4) peduncle length, and (5) egg size. Neoheterobothrium papillosum n. sp. resembles Neoheterobothrium syacii; however, detailed morphological analysis allowed for their separation into two different species. Sequences of the nuclear ribosomal DNA partial 28S and ITS1 were obtained and compared with available sequences of other species and genera of the family Diclidophoridae from GenBank. A phylogenetic analysis was conducted, including 33 sequences, 18 of which represented 17 species and 11 genera of the family Diclidophoridae. The phylogenetic tree showed that Diclidophoridae is a monophyletic family and species of Diclidophora were grouped as the sister group of Neoheterobothrium papillosum n. sp. Our phylogenetic analyses were consistent with Mamaev's hypothesis, who divided Diclidophoridae into Diclidophorinae and Choricotylinae and concluded that Neoheterobothrium was a genus belonging to Diclidophorinae.

A first for Southern Africa: description of a new Heterobothrium (Monogenea: Diclidophoridae) parasitizing the evileye pufferfish Amblyrhynchotes honckenii (Tetraodontiformes: Tetraodontidae)

The monogenean genus Heterobothrium (Monogenea: Diclidophoridae) currently consists of 12 accepted species described globally from various pufferfishes (Tetraodontidae). This includes the economically important Heterobothrium okamotoi Ogawa 1991 that causes severe disease in the cultured tiger puffer Takifugu rubripes in Japan. During parasitological surveys targeting near shore marine fishes of South Africa, a new Heterobothrium was discovered on the gills of five evileye pufferfish Amblyrhynchotes honckenii with a prevalence of 100% and mean intensity of 23 (4-72). Specimens were morphologically studied using both light and scanning electron microscopy and molecularly characterized by sequencing the partial ribosomal gene 28S. Heterobothrium victorwepeneri n. sp. differs from its 12 congeners by a combination of morphological characters, such as fourth clamp pair (anteriormost, 180° inverted) as the smallest with some of the sclerites differing in shape from the other pairs, 8 to 9 genital hooks, number of testes 40-50, and absent isthmus. The 28S tree depicted two main branches, one clustering together species of mazocraeidean families while the other clustered together only species of the Diclidophoridae. Heterobothrium victorwepeneri n. sp. is the first species of its genus to be recorded and described from South Africa and from the tetraodontid A. honckenii. This study also provides for the first time 28S sequence for a species of this highly host-specific genus.

Neohexostoma gymnosardae n. sp. (Monogenea, Hexostomatidae), a gill parasite of Gymnosarda unicolor (Valenciennes) (Teleostei, Scombridae) in the South China Sea

Parasite biodiversity of fish in coral reefs of the South China Sea is still incompletely explored. We describe here a new species of Neohexostoma (Monogenea: Hexostomatidae) from the gill filaments of the dogtooth tuna Gymnosarda unicolor (Scombridae), collected off Yongshu Reef, South China Sea. Neohexostoma gymnosardae n. sp. is distinguished from its congeners by the following features: (i) haptor clearly marked from body proper by a strongly constricted peduncle, divided in its posterior margin into two symmetrical lobes, (ii) vagina armed with scattered small blunt spines, (iii) eggs tied by their long polar filaments, (vi) esophagus with several lateral diverticula, (v) intestinal ceca unfused and extending into the haptor. We present an analysis of the relationships of this monogenean based on partial 28S rDNA sequences. An identification key for species of Neohexostoma is provided. This is the first member of the genus Neohexostoma known to parasitize a species of Gymnosarda.

Glyphidohaptor safiensis n. sp. (Monogenea: Ancyrocephalidae) from the white-spotted rabbitfish Siganus canaliculatus (Park) (Perciformes: Siganidae) off Oman, with notes on its phylogenetic position within the Ancyrocephalidae Bychowsky & Nagibina, 1968 (sensu lato)

A new ancyrocephalid monogenean is described from the gills of wild White-spottedrabbitfish Siganus canaliculatus (Park) based on morphological and molecular analyses. Glyphidohaptor safiensis n. sp. can be distinguished from other members of the genus by the shape of the accessory piece of the male copulatory organ (MCO). Unlike its congeners, the rod-shaped accessory piece of G. safiensis n. sp. is distally broad and flattened. The MCO of G. safiensis n. sp. is curved, enclosed in a heavy sheath with a terminal flap. Partial large subunit (LSU), partial small subunit (SSU) and the partial SSU, entire internal transcribed spacer region 1 (ITS1) and partial 5.8S rDNA of the new species and two species of Tetrancistrum Goto & Kikuchi, 1917 from the same host and locality were sequenced and subjected to phylogenetic analysis. The LSU rDNA analysis grouped G. safiensis n. sp. with Tetrancistrum sp. from the gills of Siganus fuscescens Houttuyn from Australia, indicating a possible misidentification of the latter. Sequences of the SSU rDNA of the new species were most similar to those for Pseudohaliotrema sphincteroporus Yamaguti, 1953, demonstrating the close relatedness of the genera Pseudohaliotrema Yamaguti, 1953 and Glyphidohaptor Kritsky, Galli & Yang, 2007 within the Ancyrocephalidae. The comparison of the partial SSU (424 bp) and entire ITS1 and partial 5.8S rDNA (246 bp) sequences obtained for G. safiensis n. sp. with the only available sequence of another member of Glyphidohaptor Kritsky, Galli & Yang, 2007, G. pletocirra Paperna, 1972 (HE601931-HE601933) yielded on average 1.08% dissimilarity (a difference of 7 bases), with a p-distance of 0.010 ± 0.004%. This is the first record of a species of Glyphidohaptor from S. canaliculatus and from the Persian Gulf, the Gulf of Oman and the Arabian Sea.

Re-description and molecular characterisation of Choricotyle australiensis Roubal, Armitage & Rohde, 1983 (Monogenea: Diclidophoridae) infecting Chrysophrys auratus (Forster) (Perciformes: Sparidae)

Choricotyle australiensis Roubal, Armitage & Rohde, 1983, a diclidophorid monogenean species, is redescribed and genetically characterised using the partial nuclear 28S ribosomal RNA gene (28S rRNA) and a fragment of mitochondrial cytochrome c oxidase subunit 1 (cox1) gene sequences for specimens collected from Chrysophrys auratus (Forster) off Australia and New Zealand. Previous studies have either provided morphological or genetic results, whereas this study combines morphological and advanced molecular methods. A total of 70 Ch. auratus were examined with 22 individuals of C. australiensis recovered from the gills (overall prevalence of 23%). This study has provided the first evidence for the exploration of mitochondrial cox1 region for C. australiensis. Comparison of the newly generated sequences with other available data supported the distinction of C. australiensis among diclidophorid Furhmann, 1928 species thus confirming its taxonomic status.

Review on the molecular study of the Diplozoidae: analyses of currently available genetic data, what it tells us, and where to go from here

The use of molecular tools in the study of parasite taxonomy and systematics have become a substantial and crucial component of parasitology. Having genetic characterisation at the disposal of researchers has produced mostly useful, and arguably more objective conclusions. However, there are several groups for which limited genetic information is available and, coupled with the lack of standardised protocols, renders molecular study of these groups challenging. The Diplozoidae are fascinating and unique monogeneans parasitizing mainly freshwater cyprinid fishes in Europe, Asia and Africa. This group was studied from a molecular aspect since the turn of the century and as such, limitations and variability concerning the use of these techniques have not been clearly defined. In this review, all literature and molecular information, primarily from online databases such as GenBank, were compiled and scrupulously analysed for the Diplozoidae. This was done to review the information, detect possible pitfalls, and provide a "checkpoint" for future molecular studies of the family. Hindrances detected are the availability of sequence data for only a limited number of species, frequently limited to a single sequence per species, and the heavy reliance on one non-coding ribosomal marker (ITS2 rDNA) which is difficult to align objectively and displays massive divergences between taxa. Challenging species identification and limited understanding of diplozoid species diversity and plasticity are also likely restricting factors, all of which hamper the accurate taxonomic and phylogenetic study of this group. Thus, a more integrated taxonomic approach through the inclusion of additional markers, application of more rigorous morphological assessment, more structured barcoding techniques, alongside thorough capturing of species descriptions including genetypes, genophore vouchers and reference collections in open sources are encouraged. The pitfalls highlighted are not singular to the Diplozoidae, and the study of other groups may benefit from the points raised here as well.

Ultrastructural patterns of the excretory ducts of basal neodermatan groups (Platyhelminthes) and new protonephridial characters of basal cestodes

BACKGROUND

The flatworms (Lophotrochozoa: Platyhelminthes) are one of the major phyla of invertebrates but their interrelationships are still not well understood including unravelling the most closely related taxon of the Neodermata, which includes exclusively obligate parasites of all main groups of vertebrates with some 60,000 estimated species. Recent phylogenomic studies indicate that the freshwater 'microturbellarian' Bothrioplana semperi may be the closest ancestor to the Neodermata, but this hypothesis receives little morphological support. Therefore, additional morphological and ultrastructural characters that might help understand interrelations within the Neodermata are needed.

METHODS

Ultrastructure of the excretory ducts of representatives of the most basal parasitic flatworms (Neodermata), namely monocotylid (Monopisthocotylea) and chimaericolid (Polyopisthocotylea) monogeneans, aspidogastreans (Trematoda), as well as gyrocotylidean and amphilinidean tapeworms (Cestoda), were studied using transmission electron microscopy (TEM).

RESULTS

The present study revealed the same pattern of the cytoarchitecture of excretory ducts in all studied species of the basal neodermatans. This pattern is characterised by the presence of septate junctions between the adjacent epithelial cells and lateral ciliary flames along different levels of the excretory ducts. Additionally, a new character was observed in the protonephridial terminal cell of Gyrocotyle urna, namely a septate junction between terminal and adjacent duct cells at the level of the distal extremity of the flame tuft. In Amphilina foliacea, a new type of protonephridial cell with multiple flame bulbs and unique character of its weir, which consists of a single row of the ribs, is described. A remarkable difference has been observed between the structure of the luminal surface of the excretory ducts of the studied basal neodermatan groups and B. semperi.

CONCLUSIONS

The present study does not provide ultrastructural support for a close relationship between the Neodermata and B. semperi.

Morphological and molecular studies of Eudiplozoon nipponicum (Goto, 1891) and Eudiplozoon kamegaii sp. n. (Monogenea; Diplozoidae)

Eudiplozoon nipponicum (Goto, 1891) Khotenovsky, 1985 (Monogenea: Diplozoidae), is known to parasitise Cyprinus carpio Linnaeus and species of Carassius. In this study, we conducted a taxonomic re-examination of E. nipponicum using genetic analysis and morphological comparisons from different host species from a single water system. rDNA nucleotide sequences of the internal transcription spacer 2 (ITS-2) region (645 bp) showed interspecific-level genetic differences among diplozoids from species of Carassius and C. carpio (p-distance: 3.1-4.0%) but no difference among those from different species of Carassius (0-0.4%) or between those from C. carpio collected in Asia and Europe (0-1.1%). Large variation was observed among 346 bp cytochrome c oxidase subunit I (COI) sequences (0.3-16.0 %); the topology of the phylogenetic tree showed no relationship to host genera or geographical regions of origin. Morphological observation showed that average clamp size of diplozoids from C. carpio was larger than those from Carassius spp. The number of folds on the hindbody was 10-25 for diplozoids from C. carpio and 12-19 for those from Carassius spp. Thus, our ITS-2 sequence and morphological comparison results indicate that diplozoids from C. carpio and species of Carassius belong to different species. The scientific name E. nipponicum should be applied to the species infected to the type host, Carassius sp. of Nakabo (2013) (Japanese name ginbuna). The diplozoid infecting C. carpio (Eurasian type) should be established as a new species: Eudiplozoon kamegaii sp. n. A neotype of E. nipponicum is designated in this report because the original E. nipponicum specimens are thought to have been lost.

Disentangling the evolutionary history of peri-Mediterranean cyprinids using host-specific gill monogeneans

The diversification of Mediterranean fish appears to be far more complex than could be explained by a single dispersion model. Cyprinids represent one of the most species-rich groups of freshwater fishes living in this region. The current distribution of several highly divergent cyprinid taxa is most likely the result of multiple dispersion events. Cyprinid fish serve as hosts for the highly diversified and host-specific monogenean parasites of the genus Dactylogyrus. On the assumption that the distribution of Dactylogyrus spp. reflects the biogeography and evolutionary history of their hosts, we used these parasites as an additional tool to shed new light on the evolutionary history of peri-Mediterranean cyprinids of the subfamily Barbinae. The degree of congruence between host and parasite phylogenies was investigated using 29 Dactylogyrus spp. and 34 Barbinae hosts belonging to the genera Aulopyge, Barbus and Luciobarbus. We showed that the morphological adaptation of Dactylogyrus (i.e. of the ventral bar, representing the most variable morphological character of the attachment organ) is linked with parasite phylogeny. By applying distance-based and event-based cophylogenetic approaches, we revealed a significant global coevolutionary signal. A total of 62% of individual host-parasite links contributed significantly to the coevolutionary structure evidenced between hosts of Barbus spp. and Iberian Luciobarbus spp., and their host-specific Dactylogyrus spp. The host switching of parasites was revealed as the most important coevolutionary event in the Dactylogyrus-Barbinae system in the peri-Mediterranean region. Cophylogenetic analyses and the mapping of the morphological character of the parasite attachment organ onto the phylogeny of Dactylogyrus indicate that endemic southern European Dactylogyrus spp. parasitizing cyprinids of Barbinae have multiple origins. We suggest that continental bridges connecting southern Europe and North Africa played a crucial role in the dispersion of cyprinids, affecting the distribution of their host-specific gill parasites.

Paracaesicola nanshaensis n. gen., n. sp. (Monogenea, Microcotylidae) a gill parasite of Paracaesio sordida (Teleostei, Lutjanidae) from the South China Sea

Paracaesicola n. gen., is erected herein to accommodate a new microcotylid species, Paracaesicola nanshaensis n. sp., collected from the Yongshu Reef, South China Sea. This species is the first monogenean to be recorded from the gills of Paracaesio sordida. The new species is characterized by the following features: (i) haptor short, with clamps arranged in two equal bilateral rows; (ii) testes numerous, arranged in two roughly alternating longitudinal rows, extending into the haptor; (iii) genital atrium armed with 16 robust spines, which are vertically arranged on top of the sausage shaped muscular male copulatory organ; and (iv) single vagina, bottle-shaped, with a distinctly bulbous vaginal atrium. The terminals of the reproductive system discriminate Paracaesicola n. gen. from all other genera in the Microcotylidae. Molecular phylogenetic analyses, based on partial 28S rDNA, places Paracaesicola nanshaensis n. sp. within the microcotylid clade, but its sequence differs from all known available microcotylid sequences.

Considerations on the taxonomy and morphology of Microcotyle spp.: redescription of M. erythrini van Beneden & Hesse, 1863 (sensu stricto) (Monogenea: Microcotylidae) and the description of a new species from Dentex dentex (L.) (Teleostei: Sparidae)

Background

Microcotyle erythrini van Beneden & Hesse, 1863 (Platyhelminthes: Monogenea) and other closely related species of the genus are often considered as cryptic. Records in hosts other than the type-host with no species confirmation by molecular analyses have contributed to this situation.

Methods

Gill parasites of five sparid fishes, Boops boops (L.), Pagellus erythrinus (L.), P. acarne (Risso), Dentex dentex (L.) and Pagrus pagrus (L.), from the Western Mediterranean off Spain were collected. Specimens of Microcotyle spp. were characterised both molecularly and morphologically. Partial fragments (domains D1-D3) of the 28S rRNA gene and the cytochrome c oxidase subunit 1 (cox1) gene were amplified and used for molecular identification and phylogenetic reconstruction. Principal components analysis was used to look for patterns of morphological separation.

Results

Molecular analyses confirmed the identity of three species: M. erythrini ex P. erythrinus and Pa. pagrus; M. isyebi Bouguerche, Gey, Justine & Tazerouti, 2019 ex B. boops; and a species new to science described herein, M. whittingtoni n. sp. ex D. dentex. The specific morphological traits and confirmed hosts (P. erythrinus and Pa. pagrus) are delimited here in order to avoid misidentifications of M. erythrini (sensu stricto). Microcotyle erythrini (s.s.) is mostly differentiated by the shape of its haptor, which is also longer than in the other congeners. New morphological and molecular data are provided for M. isyebi from the Spanish Mediterranean enlarging the data on its geographical range. Microcotyle whittingtoni n. sp. is described from D. dentex and distinguished from the remaining currently recognised species of the genus by the number and robustness of the clamps.

Conclusions

New diagnostic morphological traits useful to differentiate Microcotyle spp. are suggested: (i) haptor dimensions including lobes; (ii) the thickness of the clamps; (iii) the size and shape of spines of the genital atrium; (iv) the extension of the posterior extremities of vitelline fields; and (v) the shape of egg filaments. The use of new morphological approaches may allow considering these species of Microcotyle as being pseudocryptic. The use of representative undamaged specimens that have been genetically confirmed as conspecific is considered crucial to avoid abnormally wide morphological ranges that prevent species differentiation.

Calicotyle hydrolagi n. sp. (Monogenea: Monocotylidae) infecting the deep-sea Eastern Pacific black ghost shark Hydrolagus melanophasma from the Atacama Trench, with comments on host specificity of Calicotyle spp

We describe Calicotyle hydrolagi n. sp. (Monogenea: Monocotylidae) infecting the cloaca of deep-water Eastern Pacific black ghost sharks, Hydrolagus melanophasma captured as bycatch at a local fishery for Patagonian toothfish Dissostichus eleginoides, (Nototheniidae) in the Atacama Trench using morphological and nucleotide (LSU rRNA and SSU rRNA) data. This new species is differentiated from its congeners by a number of characters, including the absence of a cecal diverticula, the size and shape of the male copulatory organ and the shape of the vagina, as well as by differences in molecular data (SSU rRNA and LSU rRNA). The suitability of some sclerotized structures such as the male copulatory organ (MCO) as a taxonomic character is discussed; specifically, we found that the relationship between MCO and total length exhibit different trends in members of Calicotyle isolated from sharks, skates and chimaeras. Additional efforts to obtain sample of Calicotyle species and further molecular studies based on ribosomal and mitochondrial genes are necessary to clarify the degree of host specificity in this genus. Additionally, this is the first report of a member of Calicotyle to be reported in the Southeastern Pacific Ocean.

Two new species of Mazocraes Hermann (Monogenea: Mazocraeidae) from clupeoid fishes off Visakhapatnam, Bay of Bengal

Two new species of Mazocraes Hermann (Monogenea: Mazocraeidae) are described infecting clupeoid fishes of Visakhapatnam coast, Bay of Bengal: Mazocraes bengalensis n. sp. from Opisthopterus tardoore Cuvier and M. stolephorusi n. sp. from Stolephorus indicus van Hasselt and S. commersoni Lacepede. L. bengalensis n.sp. is distinguished from the most closely related species (M. gussevi, M. australis, M. alosae, M. mamaevi) by the combination of following characters: Body size, extent of caeca, number and arrangement of testes, size and structure of the clamps and the armature of genital complex. M. stolephorusi n. sp. differs from all the other species of Mazocraes in the pedunculate nature and the sizes of the haptoral clamps and the structure of the genital complex. A detailed analysis of the species of the genus Mazocraes is presented. The partial 28SrDNa sequences of M. bengalensis was generated and deposited in the GenBank.

Neither Diplectanum nor specific: a dramatic twist to the taxonomic framework of Diplectanum (Monogenea: Diplectanidae)

The taxonomy of the genus Diplectanum has been exclusively based on morphological features, with 28 nominal species parasitic on perciform fishes recognised. We used molecular data, to our knowledge for the first time, to evaluate the taxonomic framework of Diplectanum, infer the relationships amongst species attributed to this genus, re-assess the degree of host specificity and explore the population genetic structure of Diplectanum spp. parasitising Mediterranean sciaenids, which are potential target fish species for aquaculture diversification in the region. A minimum of 10 specimens of Diplectanum spp. were sequenced per host species (Argyrosomus regius, Sciaena umbra, Umbrina canariensis and Umbrina cirrosa) and locality (Burriana, Sant Carles de la Ràpita and Santa Pola (Spain)) together with five individuals of the type species Diplectanum aequans. Sequences of partial 28S rDNA and internal transcribed spacer region of Diplectanum spp. were analysed together with those from other Diplectanidae spp. in GenBank using Bayesian inference and maximum likelihood phylogenetic methods. Population genetic analyses were performed using cytochrome c oxidase subunit I gene sequences for a diplectanid species with a wide distribution across host species and localities. Results showed that Diplectanum was not monophyletic, nor were the specimens infecting sciaenids. Instead they formed two separate clades, 26.1-28.6% divergent for the internal transcribed spacer and 13.2-16.9% for the 28S region from D. aequans. Altogether, our results suggest that these specimens represent two distinct new genera from Diplectanum and five putative species with low host specificity. It is likely that morphological variability has led to the description of more species than were detected by molecular methods. In contrast to other monogeneans, Diplectaninae gen. spp. are chiefly generalists. Nonetheless, intraspecific genetic divergence in the internal transcribed spacer region of Diplectaninae gen. spp., and population genetic analyses of one presumed generalist species, Diplectaninae gen. sp. 1.2, showed significant variation between subpopulations living on different hosts. The intraspecific genetic structure by host also suggests different cross-infection potential amongst sciaenid species.

Morphological and molecular analyses of Pseudomazocraes sulamericana n. sp., Pseudomazocraes selene Hargis, 1957, Cemocotyle carangis (MacCallum, 1913) and Zeuxapta seriolae (Meserve, 1938) (Monogenea: Mazocraeidea) from carangid fishes in the south-western Atlantic Ocean

An integrative taxonomy approach was followed to analyse morphological and molecular characters of the monogenean species Pseudomazocraes selene, Cemocotyle carangis and Zeuxapta seriolae; specimens were collected from the gills of the carangid fishes Selene vomer, Caranx latus and Seriola lalandi caught off the coasts of the states of Rio de Janeiro and Santa Catarina, Brazil. The research revealed the presence of Pseudomazocraes sulamericana n. sp., which can be differentiated from other congeners by the shape of clamps mid-sclerite possessing a ventral piece bifurcated at the end, with large and right-angled edges of almost the same length, and by the shape of larval hooks and rounded terminal lappet. New genetic sequences include partial 28S and 18S rDNA genes for all species, ITS1 and 5.8S rDNA for Zeuxapta seriolae and Cemocotyle carangis, and ITS2 and mtDNA cox1 for C. carangis. The phylogenetic concatenated analysis based on partial 28S rDNA and 18S rDNA sequences confirmed the position of C. carangis and Z. seriolae within the Heteraxinidae. The previous phylogenetic position of Chauhaneidae was discussed based on morphological studies and it is now confirmed by molecular data that Chauhaneidae is the sister group of Allodiscocotylidae and Protomicrocotylidae.

Mitochondrial genomes of two diplectanids (Platyhelminthes: Monogenea) expose paraphyly of the order Dactylogyridea and extensive tRNA gene rearrangements

BACKGROUND

Recent mitochondrial phylogenomics studies have reported a sister-group relationship of the orders Capsalidea and Dactylogyridea, which is inconsistent with previous morphology- and molecular-based phylogenies. As Dactylogyridea mitochondrial genomes (mitogenomes) are currently represented by only one family, to improve the phylogenetic resolution, we sequenced and characterized two dactylogyridean parasites, Lamellodiscus spari and Lepidotrema longipenis, belonging to a non-represented family Diplectanidae.

RESULTS

The L. longipenis mitogenome (15,433 bp) contains the standard 36 flatworm mitochondrial genes (atp8 is absent), whereas we failed to detect trnS1, trnC and trnG in L. spari (14,614 bp). Both mitogenomes exhibit unique gene orders (among the Monogenea), with a number of tRNA rearrangements. Both long non-coding regions contain a number of different (partially overlapping) repeat sequences. Intriguingly, these include putative tRNA pseudogenes in a tandem array (17 trnV pseudogenes in L. longipenis, 13 trnY pseudogenes in L. spari). Combined nucleotide diversity, non-synonymous/synonymous substitutions ratio and average sequence identity analyses consistently showed that nad2, nad5 and nad4 were the most variable PCGs, whereas cox1, cox2 and cytb were the most conserved. Phylogenomic analysis showed that the newly sequenced species of the family Diplectanidae formed a sister-group with the Dactylogyridae + Capsalidae clade. Thus Dactylogyridea (represented by the Diplectanidae and Dactylogyridae) was rendered paraphyletic (with high statistical support) by the nested Capsalidea (represented by the Capsalidae) clade.

CONCLUSIONS

Our results show that nad2, nad5 and nad4 (fast-evolving) would be better candidates than cox1 (slow-evolving) for species identification and population genetics studies in the Diplectanidae. The unique gene order pattern further suggests discontinuous evolution of mitogenomic gene order arrangement in the Class Monogenea. This first report of paraphyly of the Dactylogyridea highlights the need to generate more molecular data for monogenean parasites, in order to be able to clarify their relationships using large datasets, as single-gene markers appear to provide a phylogenetic resolution which is too low for the task.

Three new Diplozoidae mitogenomes expose unusual compositional biases within the Monogenea class: implications for phylogenetic studies

BACKGROUND

As the topologies produced by previous molecular and morphological studies were contradictory and unstable (polytomy), evolutionary relationships within the Diplozoidae family and the Monogenea class (controversial relationships among the Discocotylinea, Microcotylinea and Gastrocotylinea suborders) remain unresolved. Complete mitogenomes carry a relatively large amount of information, sufficient to provide a much higher phylogenetic resolution than traditionally used morphological traits and/or single molecular markers. However, their implementation is hampered by the scarcity of available monogenean mitogenomes. Therefore, we sequenced and characterized mitogenomes belonging to three Diplozoidae family species, and conducted comparative genomic and phylogenomic analyses for the entire Monogenea class.

RESULTS

Taxonomic identification was inconclusive, so two of the species were identified merely to the genus level. The complete mitogenomes of Sindiplozoon sp. and Eudiplozoon sp. are 14,334 bp and 15,239 bp in size, respectively. Paradiplozoon opsariichthydis (15,385 bp) is incomplete: an approximately 2000 bp-long gap within a non-coding region could not be sequenced. Each genome contains the standard 36 genes (atp8 is missing). G + T content and the degree of GC- and AT-skews of these three mitogenome (and their individual elements) were higher than in other monogeneans. nad2, atp6 and nad6 were the most variable PCGs, whereas cox1, nad1 and cytb were the most conserved. Mitochondrial phylogenomics analysis, conducted using concatenated amino acid sequences of all PCGs, indicates that evolutionary relationships of the three genera are: (Eudiplozoon, (Paradiplozoon, Sindiplozoon)); and of the three suborders: (Discocotylinea, (Microcotylinea, Gastrocotylinea)). These intergeneric relationships were also supported by the skewness and principal component analyses.

CONCLUSIONS

Our results show that nad2, atp6 and nad6 (fast-evolving) would be better candidates than cox1 (slow-evolving) for species identification and population genetics studies in Diplozoidae. Nucleotide bias and codon and amino acid usage patterns of the three diplozoid mitogenomes are more similar to cestodes and trematodes than to other monogenean flatworms. This unusual mutational bias was reflected in disproportionately long branches in the phylogram. Our study offsets the scarcity of molecular data for the subclass Polyopisthocotylea to some extent, and might provide important new insights into the evolutionary history of the three genera and three suborders.

Xenoligophoroides cobitis (Ergens, 1963) n. g., n. comb. (Monogenea: Ancyrocephalidae), a parasite of Gobius cobitis Pallas (Perciformes: Gobiidae) from the Mediterranean and Black seas

Based on an integrative taxonomic approach, combining morphological characters and partial sequences of the nuclear 28S rRNA gene, a new genus and combination for the species Xenoligophoroides cobitis (Ergens, 1963) is proposed, to accommodate ancyrocephalid monogeneans, parasites on the gills of Gobius cobitis Pallas (Gobiidae) from the western Mediterranean Sea and the northern Black Sea. A morphological comparison of newly collected material with the descriptions of Ancyrocephalus cobitis Ergens, 1963 and Haliotrema cupensis Sasal, Pages & Euzet, 1998, recently synonymised and named as Haliotrema cobitis (Ergens, 1963), confirms their similarity and belonging to the same species. However, characters of this species, as the vas deferens not looping the caecal branch, the bilobed base of the male copulatory organ and the marginal hooks with an upright thumb, do not correspond to the diagnosis of Haliotrema Johnston & Tiegs, 1922. Morphologically, this species is close to members of Ligophorus Euzet & Suriano, 1977 and Kriboetrema Sarabeev, Rubtsova, Yang & Balbuena, 2013, but differs from the former in the accessory piece articulated with MCO and two prostatic reservoirs, and from the latter in the uncoiled MCO with bilobed base and the dextral vaginal pore. Moreover, all species of Ligophorus and Kriboetrema are parasites of grey mullets. A 28S rDNA-based phylogenetic analysis of sequences derived from specimens of X. cobitis from the Mediterranean and Black seas, along with sequences from several closely related genera of the Ancyrocephalidae, suggested the occurrence of a new taxonomic unit, which corresponded to the X. cobitis specimens. This finding supports the establishment of the new genus for the ancyrocephalid parasites on the gills of G. cobitis from the western Mediterranean Sea and the northern Black Sea.

The first next-generation sequencing approach to the mitochondrial phylogeny of African monogenean parasites (Platyhelminthes: Gyrodactylidae and Dactylogyridae)

BACKGROUND

Monogenean flatworms are the main ectoparasites of fishes. Representatives of the species-rich families Gyrodactylidae and Dactylogyridae, especially those infecting cichlid fishes and clariid catfishes, are important parasites in African aquaculture, even more so due to the massive anthropogenic translocation of their hosts worldwide. Several questions on their evolution, such as the phylogenetic position of Macrogyrodactylus and the highly speciose Gyrodactylus, remain unresolved with available molecular markers. Also, diagnostics and population-level research would benefit from the development of higher-resolution genetic markers. We aim to offer genetic resources for work on African monogeneans by providing mitogenomic data of four species (two belonging to Gyrodactylidae, two to Dactylogyridae), and analysing their gene sequences and gene order from a phylogenetic perspective.

RESULTS

Using Illumina technology, the first four mitochondrial genomes of African monogeneans were assembled and annotated for the cichlid parasites Gyrodactylus nyanzae, Cichlidogyrus halli, Cichlidogyrus mbirizei (near-complete mitogenome) and the catfish parasite Macrogyrodactylus karibae (near-complete mitogenome). Complete nuclear ribosomal operons were also retrieved, as molecular vouchers. The start codon TTG is new for Gyrodactylus and for Dactylogyridae, as is the incomplete stop codon TA for Dactylogyridae. Especially the nad2 gene is promising for primer development. Gene order was identical for protein-coding genes and differed between the African representatives of these families only in a tRNA gene transposition. A mitochondrial phylogeny based on an alignment of nearly 12,500 bp including 12 protein-coding and two ribosomal RNA genes confirms that the Neotropical oviparous Aglaiogyrodactylus forficulatus takes a sister group position with respect to the other gyrodactylids, instead of the supposedly 'primitive' African Macrogyrodactylus. Inclusion of the African Gyrodactylus nyanzae confirms the paraphyly of Gyrodactylus. The position of the African dactylogyrid Cichlidogyrus is unresolved, although gene order suggests it is closely related to marine ancyrocephalines.

CONCLUSIONS

The amount of mitogenomic data available for gyrodactylids and dactylogyrids is increased by roughly one-third. Our study underscores the potential of mitochondrial genes and gene order in flatworm phylogenetics, and of next-generation sequencing for marker development for these non-model helminths for which few primers are available.

Spermiogenesis and spermatozoon ultrastructure in basal polyopisthocotylean monogeneans, Hexabothriidae and Chimaericolidae, and their significance for the phylogeny of the Monogenea

Sperm ultrastructure provides morphological characters useful for understanding phylogeny; no study was available for two basal branches of the Polyopisthocotylea, the Chimaericolidea and Diclybothriidea. We describe here spermiogenesis and sperm in Chimaericola leptogaster (Chimaericolidae) and Rajonchocotyle emarginata (Hexabothriidae), and sperm in Callorhynchocotyle callorhynchi (Hexabothriidae). Spermiogenesis in C. leptogaster and R. emarginata shows the usual pattern of most Polyopisthocotylea with typical zones of differentiation and proximo-distal fusion of the flagella. In all three species, the structure of the spermatozoon is biflagellate, with two incorporated trepaxonematan 9 + "1" axonemes and a posterior nucleus. However, unexpected structures were also seen. An alleged synapomorphy of the Polyopisthocotylea is the presence of a continuous row of longitudinal microtubules in the nuclear region. The sperm of C. leptogaster has a posterior part with a single axoneme, and the part with the nucleus is devoid of the continuous row of microtubules. The spermatozoon of R. emarginata has an anterior region with membrane ornamentation, and posterior lateral microtubules are absent. The spermatozoon of C. callorhynchi has transverse sections with only dorsal and ventral microtubules, and its posterior part shows flat sections containing a single axoneme and the nucleus. These findings have important implications for phylogeny and for the definition of synapomorphies in the Neodermata. We point out a series of discrepancies between actual data and interpretation of character states in the matrix of a phylogeny of the Monogenea. Our main conclusion is that the synapomorphy "lateral microtubules in the principal region of the spermatozoon" does not define the Polyopisthocotylea but is restricted to the Mazocraeidea.

Redescription and New Host Record of Diplostamenides Sciaenae (Monogenea, Microcotylidae) and Its Phylogenetic Status Using Molecular Markers

A new host and new locality is recorded for Diplostamenides sciaenae (Goto, 1894) Lebedev, Parukhin et Roitman, 1970 from Johnius belangerii at Versova dock landing centre, Mumbai, India. The morphometric comparison of D. sciaenae with previously published data, provided redescription complements results of molecular analysis. The partial 28S and 18S rRNA gene sequences of D. sciaenae were amplified, sequenced through PCR and deposited to GenBank database. The BLASTn searches revealed the significant closeness of D. sciaenae to other microcotylid parasites in large and small ribosomal subunits. Th e phylogenetic tree analyses with neighbor joining and minimum evolution methods also expressed belonging of D. sciaenae to Microcotylidae.