Interrelationships and evolution of the tapeworms (Platyhelminthes: Cestoda)

Morphological and molecular identification of metacestodes infecting teleost fishes of Moreton Bay, Australia

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

Dasyrhynchus giganteus plerocercoids encysting in the musculature of Indian halibut (Psettodes erumei): seasonal prevalence, morpho-molecular characterization, and histopathological alterations

This study investigated the prevalence, morphology, molecular identification, and histopathological effects of larval tapeworms (plerocercoids) infecting the skeletal muscles of the Indian halibut (Psettodes erumei) collected from the coastal waters of the Arabian Gulf. Numerous oval or round blastocysts, measuring 13-26 mm, were found embedded within the muscular tissues of the Indian halibut, rendering the fish unsuitable for human consumption. Morphological and molecular analyses identified the plerocercoids as Dasyrhynchus giganteus (family Dasyrhynchidae), with an overall prevalence of 15.4%. The seasonal prevalence was the highest in summer (14.6%), followed by spring (10.6%), winter (4.4%), and autumn (3.5%). Infection rates increased with fish size. Histopathological examination revealed fibrous connective tissue capsules surrounding the larvae, causing muscular atrophy and degenerative changes, with few inflammatory eosinophilic cells. Molecular and phylogenetic analysis of the 28S rDNA gene sequences confirmed the specimens as D. giganteus, clustered closely with other sequences of D. giganteus with 100% bootstrap values. This study provided valuable insights into the parasitic infection dynamics, seasonal variation, molecular identification, and histopathological effects, highlighting the importance of monitoring fish for food safety and public health implications.

Phylogenetic relationships and systematics of tapeworms of the family Davaineidae (Cestoda, Cyclophyllidea), with emphasis on species in rodents

The present study aims at clarifying the poorly known phylogenetic relationships and systematics of cestodes of the family Davaineidae Braun, 1900 (Cyclophyllidea), primarily the genus Raillietina Fuhrmann, 1920 and of the subfamily Inermicapsiferinae (Anoplocephalidae) from mammals (mostly rodents, 31 new isolates) and birds (eight new isolates). Phylogenetic analyses are based on sequences of the large subunit ribosomal RNA gene (28S) and mitochondrial NADH dehydrogenase subunit 1 gene (nad1). The main phylogenetic pattern emerging from the present analysis is the presence of three independent lineages within the main clade of the subfamily Davaineinae, one of which is almost entirely confined to species from rodents and the other two show a mixture of species from birds and mammals. It is suggested that the major diversification of the main clade took place in birds, possibly in galliforms. The subsequent diversification included repeated host shifts from birds to mammals and to other birds, and from rodents to other mammals, showing that colonisation of new host lineages has been the main driver in the diversification of davaineine cestodes. It is also shown that all isolates of Inermicapsifer Janicki, 1910, mainly from rodents, form a monophyletic group positioned among Raillietina spp. in the "rodent lineage", indicating that the genus Inermicapsifer is a member of the family Davaineidae. This means that the subfamily Inermicapsiferinae and the family Inermicapsiferidae should be treated as synonyms of the Davaineidae, specifically the subfamily Davaineinae. Three additional genera generally included in the Inermicapsiferinae, i.e. Metacapsifer Spasskii, 1951, Pericapsifer Spasskii, 1951 and Thysanotaenia Beddard, 1911, are also assigned here to the Davaineidae (subfamily Davaineinae). Raillietina spp. were present in all three main lineages and appeared as multiple independent sublineages from bird and mammalian hosts, verifying the non-monophyly of the genus Raillietina and suggesting a presence of multiple new species and genera.

Calliobothrium Narsisae n. sp. (Tetraphyllidea: Calliobothriidae) from the Triakid Shark Mustelus mosis Hemprich and Ehrenberg from the Persian Gulf, with a Note on Its Specific Proglottisation Process and a Key to the Species of the Genus

PURPOSE

The members of the tetraphyllidean genus Calliobothrium exhibit a high degree of host specificity in the shark genus Mustelus. In the Indian Ocean, where M. mosis occurs dominantly, there is no information on Calliobothrium. The purpose of this study was the evaluation of the Calliobothrium species in M. mosis in the Persian Gulf, northwestern Indian Ocean.

METHODS

Nine specimens of Mustelus mosis were caught from the Persian Gulf. The tapeworms isolated were stained, measured, and the line drawings were made.

RESULTS

Calliobothrium narsisae n. sp. is described and differs from C. creeveyae in the intact, rather than the three-lobed, posterior bothridial margins, from C. tylotocephalum in possessing three, rather than one, suckers per bothridial muscular pad, from C. nodosum in possessing the elongated, rather than robust and thorn-like, hooks, from C. shirozame in a maximum number of four, rather than three, dorsal and four, rather than three, ventral laciniations along the strobila, and from its other congeners in possessing three, rather than two, dorsal and three, rather than two, ventral laciniations in the anteriormost immature proglottids. A key to the species of the genus is presented and the proglottisation process, by the germinative zone placed in the terminal part of the worm at least in some stages of growth to maturity, is discussed.

CONCLUSION

The description of C. narsisae n. sp., which brings the total number of valid species of Calliobothrium to 10, also indicates that the germinative zone is not always at the anterior to strobila and in this new species it is placed in the terminal part of the worm at least in some stages of growth to maturity.

Muscular remodeling and anteroposterior patterning during tapeworm segmentation

BACKGROUND

Tapeworms are parasitic flatworms that independently evolved a segmented body plan, historically confounding comparisons with other animals. Anteroposterior (AP) patterning in free-living flatworms and in tapeworm larvae is associated with canonical Wnt signaling and positional control genes (PCGs) are expressed by their musculature in regionalized domains along the AP axis. Here, we extend investigations of PCG expression to the adult of the mouse bile-duct tapeworm Hymenolepis microstoma, focusing on the growth zone of the neck region and the initial establishment of segmental patterning.

RESULTS

We show that the adult musculature includes new, segmental elements that first appear in the neck and that the spatial patterns of Wnt factors are consistent with expression by muscle cells. Wnt factor expression is highly regionalized and becomes AP-polarized in segments, marking them with axes in agreement with the polarity of the main body axis, while the transition between the neck and strobila is specifically demarcated by the expression domain of a Wnt11 paralog.

CONCLUSION

We suggest that segmentation could originate in the muscular system and participate in patterning the AP axis through regional and polarized expression of PCGs, akin to the gene regulatory networks employed by free-living flatworms and other animals.

Phylogeny of the cestode family Escherbothriidae (Cestoda: Rhinebothriidea) reveals unexpected patterns of association with skate hosts

The rhinebothriidean tapeworm family Escherbothriidae has recently been expanded to include the genus Ivanovcestus , species of which parasitise arhynchobatid skates. Similarities in morphology and host associations between Ivanovcestus and Semiorbiseptum - a genus yet to be assigned to one of the families in the order Rhinebothriidea - led us to explore the possibility that Semiorbiseptum might also belong in the Escherbothriidae. Morphological similarities with Scalithrium ivanovae , Scalithrium kirchneri and Rhinebothrium scobinae , all of which also parasitise arhynchobatid skates, raised questions regarding the generic placements of these species. In addition, new collections from the skate Sympterygia brevicaudata revealed two new species that morphologically resemble species of Ivanovcestus . A combination of morphological and molecular data were used to assess the generic placement of the newly discovered species and refine our understanding of the membership of the family Escherbothriidae. Sequence data for the D1-D3 region of the 28S rDNA gene were generated de novo for 14 specimens of 7 rhinebothriidean species and combined with comparable published data to represent all 6 families in the Rhinebothriidea in the analysis. The phylogenetic tree resulting from maximum likelihood analysis strongly supports the inclusion of the genus Semiorbiseptum in the family Escherbothriidae. Our work also suggests that the skate-hosted species previously assigned to Scalithrium and Rhinebothrium are also members of Semiorbiseptum and that Ivanovcestus is a junior synonym of Semiorbiseptum . Six species are transferred to Semiorbiseptum , bringing the total number of species in the genus to ten. The diagnosis of Semiorbiseptum is amended to accommodate the additional species. A second species in the previously monotypic type genus of the family, Escherbothrium , is described. The diagnosis of the Escherbothriidae is amended to include the new and transferred species. This study underscores the importance of integrating morphological and molecular data in bringing resolution to cestode systematics. We believe our findings provide a robust foundation for future research into the evolutionary history and host associations of cestodes within the order Rhinebothriidea and beyond. These also highlight the importance of expanding our understanding of skate-hosted cestodes. ZooBank: urn:lsid:zoobank.org:pub:8052AFCA-5FBD-4430-95F4-0E5E368DEA3D.

Phylogenetic Relationships of Avian Cestodes from Brine Shrimp and Congruence with Larval Morphology

Determining molecular markers for parasites provides a useful tool for their identification, particularly for larval stages with few distinguishable diagnostic characters. Avian cestodes play a key role in the food webs and biodiversity of hypersaline wetlands, yet they remain understudied. Using naturally infected Artemia, we identified cestode larvae (cysticercoids), assessed their genetic diversity, and explored phylogenetic relationships in relation to larval morphology and waterbird final hosts. We obtained partial 18S rDNA sequences for 60 cysticercoids of the family Hymenolepidae infecting Artemia spp. from seven localities and three countries (Spain, the USA, and Chile). We present the first DNA sequences for six taxa: Confluaria podicipina, Fimbriarioides sp., Flamingolepis liguloides, Flamingolepis sp. 1, Flamingolepis sp. 2, and Hymenolepis californicus. Intraspecific sequence variation (0.00-0.19% diversity) was lower than intergroup genetic distance (0.7-14.75%). Phylogenetic analysis revealed three main clades: 1-Flamingolepis, 2-Fimbriarioides, 3-Confluaria and Hymenolepis, all of which separated from hymenolepidids from mammals and terrestrial birds. This clear separation among taxa is congruent with previous morphological identification, validating the 18S gene as a useful marker to discriminate at generic/species level. Working with intermediate hosts allows the expansion of knowledge of taxonomic and genetic diversity of cestodes in wildlife, as well as elucidation of their life cycles.

microRNA silencing in a whole worm cestode model provides insight into miR-71 function

Parasites belonging to the class Cestoda include zoonotic species such as Echinococcus spp. and Taenia spp. that cause morbidity and mortality in endemic areas, mainly affecting pastoral and rural communities in low income countries but also upper middle income countries. Cestodes show remarkable developmental plasticity, implying tight regulation of gene expression throughout their complex life cycles. Despite the recent availability of genomic data for cestodes, little progress was made on postgenomic functional studies. MicroRNAs (miRNAs) are key components of gene regulatory systems that guide diverse developmental processes in multicellular organisms. miR-71 is a highly expressed miRNA in cestodes, which is absent in vertebrates and targets essential parasite genes, representing a potential key player in understanding the role of miRNAs in cestodes biology. Here we used transfection with antisense oligonucleotides to perform whole worm miRNA knockdown in tetrathyridia of Mesocestoides vogae (syn. Mesocestoides corti), a laboratory model of cestodes. We believe this is the first report of miRNA knockdown at the organism level in these parasites. Our results showed that M. vogae miR-71 is involved in the control of strobilation in vitro and in the establishment of murine infection. In addition, we identified miR-71 targets in M. vogae, several of them being de-repressed upon miR-71 knockdown. This study provides new knowledge on gene expression regulation in cestodes and suggests that miRNAs could be evaluated as new selective therapeutic targets for treating Neglected Tropical Diseases prioritised by the World Health Organization.

First Insights into Population Structure and Genetic Diversity Versus Host Specificity in Trypanorhynch Tapeworms Using Multiplexed Shotgun Genotyping

Theory predicts relaxed host specificity and high host vagility should contribute to reduced genetic structure in parasites while strict host specificity and low host vagility should increase genetic structure. Though these predictions are intuitive, they have never been explicitly tested in a population genomic framework. Trypanorhynch tapeworms, which parasitize sharks and rays (elasmobranchs) as definitive hosts, are the only order of elasmobranch tapeworms that exhibit considerable variability in their definitive host specificity. This allows for unique combinations of host use and geographic range, making trypanorhynchs ideal candidates for studying how these traits influence population-level structure and genetic diversity. Multiplexed shotgun genotyping (MSG) data sets were generated to characterize component population structure and infrapopulation diversity for a representative of each trypanorhynch suborder: the ray-hosted Rhinoptericola megacantha (Trypanobatoida) and the shark-hosted Callitetrarhynchus gracilis (Trypanoselachoida). Adults of R. megacantha are more host-specific and less broadly distributed than adults of C. gracilis, allowing correlation between these factors and genetic structure. Replicate tapeworm specimens were sequenced from the same host individual, from multiple conspecific hosts within and across geographic regions, and from multiple definitive host species. For R. megacantha, population structure coincided with geography rather than host species. For C. gracilis, limited population structure was found, suggesting a potential link between degree of host specificity and structure. Conspecific trypanorhynchs from the same host individual were found to be as, or more, genetically divergent from one another as from conspecifics from different host individuals. For both species, high levels of homozygosity and positive FIS values were documented.

Wood mouse (Apodemus sylvaticus L.) as intermediate host for Mesocestoides canislagopodis (Rudolphi, 1810) (Krabbe 1865) in Iceland

Mesocestoides canislagopodis is a common parasite of the arctic fox (Vulpes lagopus) in Iceland. In the past, household dogs (Canis familiaris) and cats (Felis catus) were also reported in Iceland to be infected. Recently, scolices of a non-maturing Mesocestoides sp. were detected in the intestines of the gyrfalcon (Falco rusticolus), and tetrathyridia were isolated in the body cavity of rock ptarmigan (Lagopus muta) and subsequently described. All stages were confirmed, using both morphological and molecular methods, to belong to the same species, M. canislagopodis. In the present study, post-mortem examination of wood mice (Apodemus sylvaticus), sampled in autumn 2014 on a farm in Northeast Iceland, revealed the presence of tetrathyridia in the peritoneal cavity and in the liver. Most tetrathyridia in the peritoneal cavity were free, but some were encapsulated in a thin connective tissue stroma and loosely attached to the inner organs. They appear as whitish, heart-shaped, flattened, unsegmented bodies with a slightly pointed posterior end. In the liver, tetrathyridia were seen as pale-tanned nodules embedded in the parenchyma. Comparative molecular analysis, both at the generic level (D1 domain LSU ribosomal DNA), and at the specific level (cytochrome c oxidase subunit I (cox1) and 12S mitochondrial DNA), revealed that the tetrathyridia belonged to M. canislagopodis. A. sylvaticus represents a new second intermediate host record in Iceland, and the first description of a rodent as intermediate host for this species, thus participating in the life cycle of the parasite.

Novelty and phylogenetic affinities of a new family of tapeworms (Cestoda: Rhinebothriidea) from endangered sawfish and guitarfish

The parasites of hosts of conservation concern are often poorly known. This is the case with the iconic group of elasmobranchs known as the sawfish of the genus Pristis, all four species of which are considered as Endangered or Critically Endangered by the International Union for Conservation of Nature (IUCN, Switzerland). Examination of cestodes from three species of sawfish (Pristis pristis, Pristis clavata, and Pristis zijsron) in Australia and one of their close relatives, the also critically endangered widenose guitarfish, Glaucostegus obtusus, in India collected over the past 25 years yielded four new species of tapeworms which are described herein. All four belong to the previously monotypic Mixobothrium; the diagnosis of the genus is revised to accommodate the new species. Among the new taxa is a species that had been included in previous molecular phylogenies but whose identity and affinities within the order Rhinebothriidea and thus also its familial placement were unclear. This species exhibits the morphological features of Mixobothrium and thus its identity is, at long last, revealed. Sequence data generated for the 28S rDNA gene for three of the new species, as well as an additional new but yet undescribed species from Pristis pectinata from Florida (USA), confirms the uniqueness of this group among the rhinebothriideans. The new family Mixobothriidae is established to house these taxa. The members of this family differ from all but one of the five other families of rhinebothriideans in lacking apical suckers on their bothridia. They are also distinctive in that their bothridia are divided into three distinct regions. The anterior and posterior regions have similar locular configurations to one another and differ from the locular configuration of the middle region. As a consequence, the bothridia are symmetrical along both their vertical and horizontal axes. We predict that a focus on species of guitarfish in the genus Glaucostegus will be the most productive approach for discovering additional diversity in this family of cestodes.

Parasites and prey of the nursehound shark Scyliorhinus stellaris (Linnaeus, 1758): Insights into hidden trophic web interactions in the Mediterranean Sea

The metazoan parasite community and the stomach contents of the nursehound shark Scyliorhinus stellaris from the Gulf of Naples (central Mediterranean Sea) were studied. The nursehound shark harboured a poor parasite community composed of a species of gill monogenean (Hexabothrium appendiculatum) and three intestinal cestode taxa (Acanthobothrium coronatum and two unidentified species of the genera Yamaguticestus and Scyphophyllidium), all represented by adult stages. Hosts were mostly parasitized by individuals of A. coronatum, which was the most abundant species and contributed to almost 80% of the total number of parasites found. Conversely, other trophically transmitted parasites (i.e., Yamaguticestus sp. and Scyphophyllidium sp.) showed low prevalence and abundance. The parasite infracommunity was poor, showing low values of species richness, total mean abundance, and diversity indices. Overall, 52 prey items belonging to 13 taxa were identified in the stomach contents. Cephalopods were the most important prey items (represented by nine taxa) and the most diverse and abundant group. In the multivariate space provided by a principal component of mixed data (PCAmix), nursehound sharks distributed along two main axes, related to individual traits (first axis) and stomach contents (including empty ones, second axis). A logistic regression based on the first two axes of the PCAmix showed a significant influence of host individual traits and, to a lesser extent, of stomach contents, regarding the probability of being infected by A. coronatum. Alongside specific traits already associated with parasites transmission, our results highlight the importance of cephalopods in transferring cestode infections through trophic web interactions in the top-predator nursehound shark.

Morphological and molecular characterization of the parasite Dipylidium caninum infecting an infant in Colombia: a case report

BACKGROUND

Dipylidium caninum is the causal agent of dipylidiasis affecting mainly cats and dogs worldwide. Human cases of dipylidiasis are rare, and the diagnosis is prevalently based on morphological features of the parasite. Here we report the diagnosis of dipylidiasis through morphological and molecular characterization of D. caninum infecting an 11-month-old boy in Cajicá, Colombia.

METHODS

Fresh faecal samples were obtained from the infant, and morphological identification of the parasite was performed through faecal smears. DNA was extracted from proglottids and used in PCR analyses for amplification of a 653-bp fragment of the nuclear ribosomal RNA (rRNA) encoding the 28S rRNA gene. A phylogeny study to better characterize the obtained DNA sequence was inferred using the maximum likelihood method and the Tamura-Nei model.

RESULTS

After morphological and molecular analyses, D. caninum was identified as the etiological agent causing the infection in the infant. Results of phylogenetical analyses showed that the obtained sequence clusters within the feline genotype clade. After the diagnosis of the parasite, effective treatment with praziquantel was administered to the infant.

CONCLUSIONS

This is the third human case of dipylidiasis reported in Colombia, and the first study in South America to provide a molecular identification of D. caninum.

Fish tapeworms (Cestoda) in the molecular era: achievements, gaps and prospects

The tapeworms of fishes (Chondrichthyes and Actinopterygii) account one-third (1670 from around 5000) of the total tapeworm (Platyhelminthes: Cestoda) species diversity. In total 1186 species from 9 orders occur as adults in elasmobranchs (sharks, rays and chimaeras), and 484 species from 8 orders mature in ray-finned fishes (referred to here as teleosts). Teleost tapeworms are dominated by freshwater species (78%), but only 3% of elasmobranch tapeworms are known from freshwater rays of South America and Asia (Borneo). In the last 2 decades, vast progress has been made in understanding species diversity, host associations and interrelationships among fish tapeworms. In total, 172 new species have been described since 2017 (149 from elasmobranchs and 23 from teleosts; invalidly described taxa are not included, especially those from the Oriental region). Molecular data, however, largely limited to a few molecular markers (mainly 28S rDNA, but also 18S and cox1), are available for about 40% of fish tapeworm species. They allowed us to significantly improve our understanding of their interrelationships, including proposals of a new, more natural classification at the higher-taxonomy level (orders and families) as well as at the lower-taxonomy level (genera). In this review, we summarize the main advances and provide perspectives for future research.

Rodentolepis microstoma isolated from different species of Sigmodontinae rodents (Rodentia: Cricetidae) in the Cuenca del Plata, Argentina: Morphological aspects and molecular characterization

The purpose of this paper was to study specimens of the genus Rodentolepis isolated from eight species of Sigmodontinae rodents (Rodentia: Cricetidae) from six provinces in the Cuenca del Plata, Argentina, based on morphological, morphometric and molecular characteristics (ITS1 rDNA and cox1 mtDNA). The genetic distances among studied specimens and other Hymenolepididae from rodents available in the GenBank were analyzed and phylogenetic inferences were provided. A total of 955 specimens of Sigmodontinae rodents were examined from seven localities of six provinces in the Cuenca del Plata region in Argentina. Tapeworms were removed from the rodents’ small intestines. Conventional studies were used for the morphological and molecular analysis. Specimens of R. microstoma were identified. An amended diagnosis and detailed morphological description of this species is provided. The molecular analyses showed that the specimens studied form the same clade as that of R. microstoma previously studied from other hosts and regions. The genetic polymorphisms of R. microstoma observed corresponded to different groups of species hosts and regions. Moreover, eight species of sigmodontine rodents and 33 localities from the Cuenca del Plata region in Argentina constitute new host and geographical records. This study shows the importance of using integrative taxonomic approaches that combine morphological and molecular characters to understand biological diversity. Moreover, the discovery of R. microstoma in humans suggests the importance of further studies on this zoonotic cestode. This study provides important data on the taxonomy and distribution of R. microstoma to advance knowledge of the transmission dynamics of this parasite.

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Rodentolepis microstoma is recorded parasitizing Sigmodontinae rodents in Argentina.

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Morphological variations are observed in R. microstoma between host species and areas.

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Amended diagnosis of Rodentolepis microstoma is provided.

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Phylogenetic inferences of Hymenolepididae from rodents are proposed.

A young parasite in an old fish host: A new genus for proteocephalid tapeworms (Cestoda) of bowfin (Amia calva) (Holostei: Amiiformes), and a revised list of its cestodes

A new genus, Laruella n. gen., is proposed for the proteocephalid cestode L. perplexa (La Rue, 1911) n. comb. (syn. Proteocephalus perplexus La Rue, 1911), a parasite of a ‘living fossil’, the bowfin (Amia calva), in North America. The new genus is differentiated from other proteocephalid genera by having a massive four-lobed scolex without an apical organ and bearing suckers possessing tear-shaped sphincters on their inner rim, vitelline follicles forming L-shaped lateral fields, with the vitellarium turned inwards (medially) ventrally alongside the posterior margin of the ovary, a ring-like vaginal sphincter situated at a considerable distance from the genital atrium, and ellipsoid eggs resembling those of bothriocephalid and diphyllobothriid tapeworms, except for the absence of an operculum. Phylogenetic relationships of the new genus are not resolved, but it belongs to the so-called Neotropical clade of the Proteocephalidae, which is composed mainly of Neotropical tapeworms of siluriforms and other teleosts, but also Nearctic and Palaearctic species of Ophiotaenia La Rue, 1911 from snakes and amphibians. A morphologically similar species, Proteocephalus ambloplitis (Leidy, 1887) from bass (Micropterus spp.) in North America, is provisionally retained in Proteocephalus Weinland, 1858 because its relationships to L. perplexa are not yet clear. The former species differs from L. perplexa by the presence of a large apical organ, large, elongate vaginal sphincter situated near the genital atrium, vitelline follicles limited to lateral longitudinal fields, strongly coiled vas deferens within the cirrus sac, and a convoluted vaginal canal anterior to the ovarian isthmus. Laruella perplexa reportedly has a s broad spectrum of hosts but most are likely postcyclic or accidental hosts. A list of cestode parasites reported from bowfin is provided; it includes eight species and three taxa not identified to the species level. However, only three adult cestodes, L. perplexa and two species of Haplobothrium Cooper, 1914, are typical tapeworm parasites of bowfin, but previous molecular studies indicate possible existence of a putative new species in bowfin.

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A new genus, Laruella n. gen. (Cestoda), is proposed for Proteocephalus perplexus, a parasite of a ‘living fossil’ Amia calva.

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Laruella perplexa new comb. is redescribed and a list of cestode parasites of bowfin is provided.

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Only three adult cestodes, L. perplexa and two species of Haplobothrium, are considered as typical parasites of owfin.

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Molecular studies indicate possible existence of (a) putative new species of fish tapeworm(s) in bowfin.

Hymenolepidid cestodes: Diversity, morphological and molecular characterization of a new species, and phylogeny of parasitic species of rodents from North and South America

Rodents are hosts of a wide diversity of cestodes. Fifteen genera included in the family Hymenolepididae parasitize rodents, and only four of these genera have been recorded from the Neotropical region. The purpose of this paper is to update species of Hymenolepididae from rodents, describe a new species of Hymenolepis based on morphological and molecular characterization (ITS1 rDNA and cox1 mtDNA), comparing the features among the species from North and South American rodents, and provide phylogenetic inferences of Hymenolepididae from rodents based on sequences available in the GenBank. Rodents were collected in the Parque Provincial Ernesto Tornquist, Buenos Aires, Argentina. Hymenolepis ivanovae n. sp. differs from other Hymenolepis species registered from North and South American rodents by body size, scolex, suckers, cirrus sac, cirrus, testes, and eggs, among others. Comparative morphometric data for Hymenolepis species from North and South American rodents is provided. Molecular analyses place H. ivanovae n. sp. within the genus Hymenolepis with strong support, and show it close to species of zoonotic importance. The new species is the first species of Hymenolepis described from Sigmodontinae rodents.

A new genus of caryophyllidean tapeworms (Cestoda) from Mystus catfishes (Bagridae) in India: cleaning up taxonomic chaos

A new genus, Mystocestus, is proposed to accommodate a new species, Mystocestus anindoi n. g., n. sp. from Mystus vittatus (Bloch) (type host) in West Bengal and Mystus cavasius (Hamilton) (Siluriformes: Bagridae) in Maharashtra, India. The new genus is most similar to Lucknowia Gupta, 1961 in the shape of the body, which is elongate, slightly tapering towards the anterior end, and scolex, which is digitiform, but differs in the shape of the ovary, which is H-shaped (vs. inverted A-shaped in Lucknowia), the absence of a seminal receptacle (present in Lucknowia) and exclusively cortical vitelline follicles (vs. some follicles in the medulla in the latter genus). Molecular data support the erection of the new genus and place it close to Bovienia Fuhrmann, 1931, species of which can be easily distinguished by exclusively lateral vitelline follicles (lateral and median in the new genus), the presence of a seminal receptacle (absent in Mystocestus) and scolex shape (digitiform, with blunt or slightly concave anterior edge in the new genus vs. small, unspecialized or spatulate in Bovienia). The convoluted taxonomy of tapeworms placed in Mystoides Mathur, 1992 is critically reviewed to clean up taxonomic chaos in Indo-Malayan caryophyllideans. Mystoides was erected in an unpublished PhD thesis and thus its generic name becomes unavailable and also, its type species is conspecific with Lucknowia fossilisi Gupta, 1961 from the stinging catfish, Heteropneustes fossilis (Bloch). Other species of this genus are also conspecific with L. fossilisi. In addition, specific names of most of these taxa are unavailable because they were described in unpublished theses or conference abstracts. Based on recent revisions of Indo-Malayan caryophyllideans, the following nine genera with 15 species are considered valid (numbers of species of individual genera are provided in parentheses): Bovienia (3), Djombangia (1), Lucknowia (2), Lytocestus (2), Mystocestus (1), Pseudocaryophyllaeus (2) (all family Lytocestidae); Adenoscolex (1), Lobulovarium (2), Paracaryophyllaeus (1) (all family Caryophyllaeidae).

A synergistic, global approach to revising the trypanorhynch tapeworm family Rhinoptericolidae (Trypanobatoida)

Since 2010, the trypanorhynch tapeworm family Rhinoptericolidae Carvajal & Campbell, 1975 has housed just two distinctive, monotypic genera (Rhinoptericola Carvajal & Campbell, 1975 and Nataliella Palm, 2010). However, global collections of tapeworms from sharks and rays over the last more than three decades brought to light the need for major revision of the family by suggesting a much greater species-level diversity for the nominal genus Rhinoptericola. Through synonymy and the description of new species, the number of species in the genus is increased from one to eight. A phylogenetic analysis of the D1-D3 gene region of 28S rRNA (28S), including seven of the now nine species of rhinoptericolids, and a broad sampling of the other Trypanobatoida is the first to recover a monophyletic Rhinoptericolidae. In addition to systematic revision, this study allowed for the first evaluation of the degree of intraspecific vs interspecific variation in 28S for adult trypanorhynchs across the various hosts and geographic localities from which they have been reported, suggesting a relatively consistent boundary for Rhinoptericola. It is further suggested that detailed scanning electron microscopy (SEM) images of both the basal and metabasal armatures greatly aid in the interpretation of hook arrangement and shape. A schematic to streamline determination of the tentacular surface presented in scanning electron micrographs and line drawings of trypanorhynchs is presented for species with both two and four bothria. In combination, these methodological refinements can now be used as a model to resolve issues of classification and non-monophyly within both major lineages of the Trypanorhyncha. As a result of the taxonomic work, Rhinoptericola megacantha Carvajal & Campbell, 1975 (previously only known from the American cownose ray from the Chesapeake Bay and the Ticon cownose ray from the Gulf of Mexico, Venezuela, and Brazil) is now known from an additional species of cownose ray and a species of stingray, and is revealed to have a transatlantic distribution. Data from SEM suggest a simpler interpretation of hook arrangement in the metabasal armature for Rhinoptercola and-in combination with 28S sequence data-support Shirleyrhynchus Beveridge & Campbell, 1988 (a former rhinoptericolid) as its junior synonym. The three species formerly assigned to Shirleyrhynchus are thus transferred to Rhinoptericola. Data from light microscopy on whole-mounted specimens and histological sections, SEM, and 28S showed the eutetrarhynchid Prochristianella jensenae Schaeffner & Beveridge, 2012b to be morphologically consistent with species of Rhinoptericola and it is thus transferred to the genus. The type series of P. jensenae was determined to be mixed, representing two distinct species which are here redescribed and described as new, respectively. Two additional novel species of Rhinoptericola are described from cownose rays from off Mozambique and the Gulf of California.

Phylogenetic position of Acanthobothrium cleofanus (Cestoda: Onchoproteocephalidea) using molecular evidence

Despite the large number of species described to date for the onchoprotepcephalid genus Acanthobothrium (207), only 16 named species have a genetic sequence. With this background, specimens of adult cestodes of the stingray Hypanus longus were collected off San Blas, Nayarit, and onchoproteocephalid larvae in the carangid fish Trachinotus rhodopus from Puerto Ángel, Oaxaca, both located on the Pacific coast of Mexico. The objective of this work is to investigate the phylogenetic position of these adults and larvae using nuclear ribosomal markers (18S rDNA and 28S rDNA). Morphologically, adult specimens were identified as Acanthobothrium cleofanus; larvae were identified only to family level. The phylogenetic position of both taxa was investigated based on the information of two nuclear molecular markers analyzed under Parsimony (PA) and Bayesian Inference (BI) methods. The newly generated sequences of A. cleofanus from Nayarit are identical to the sequences of several samples of Acanthobothrium sp. collected in the Mexican Pacific, which sequence are available in GenBank; DNA sequences obtained from onchoproteocephalid larva clearly place this taxon within Acanthobothrium but representing an independent lineage. In the resulting phylogenetic trees, Uncibilocularis okei was found nested within Acanthobothrium with an unstable position depending on the optimality criteria, indicating the need for more molecular analyzes with a greater number of species of both genera prior to define its phylogenetic relationships.

A molecular and ecological study of Grillotia (Cestoda: Trypanorhyncha) larval infection in small to mid-sized benthonic sharks in the Gulf of Naples, Mediterranean Sea

AIM

Trypanorhyncha cestodes comprise a wide range of heteroxenous parasites infecting elasmobranchs as definitive hosts. Limited data exist on the larval infection of these cestodes and the role of intermediate and paratenic hosts in the life cycle of these parasites. We investigated the factors that determine the occurrence and the level of infection of Grillotia plerocerci in the skeletal muscles of various benthonic sharks and analyzed the parasites through an integrative taxonomic approach.

LOCATION

Mediterranean Sea.

METHODS

Sharks obtained as bycatch of commercial trawling activities (i.e., Etmopterus spinax, Galeus melastomus, and Scyliorhinus canicula) were used in this study. Data from a limited number of Dalatias licha and Scyliorhinus stellaris were also included. Grillotia plerocerci were molecularly characterized using the partial 28S large subunit rDNA. Boosted regression trees were used to model the relationship between the abundance of infection with both morphological and physiological predictors in each host.

RESULTS

Plerocerci of Grillotia were detected in all shark species except S. stellaris. Host species significantly differed in terms of parasite abundance, with the highest and lowest prevalence and abundance of infection detected in G. melastomus and E. spinax, respectively. The relative influence of the traits involved in explaining the parasite abundance was related to the host size in G. melastomus, while both morphology- and physiology-related traits explained the patterns observed in E. spinax and S. canicula. The 28S rDNA sequences shared an identity of ∼99.40% with a Grillotia species previously found in the Mediterranean Sea. At intraspecific level, two different genotypes were found. A first type was retrieved only from D. licha, whereas a second type was found in G. melastomus, E. spinax, and S. canicula.

MAIN CONCLUSIONS

Present results suggest that the two genotypes could be involved in different consumer-resource systems and confirm most of the examined shark species as transport hosts of Grillotia species for unknown larger top predators.

Morphological updates, host-specificity, molecular data and phylogenetic analysis of Acanthobothrium coronatum (Cestoda: Onchoproteocephalidea), a neglected parasite of the nursehound Scyliorhinus stellaris

Acanthobothrium is the most speciose genus of onchoproteocephalidean cestodes, whose adults parasitize the intestine of elasmobranch fishes. Acanthobothrium coronatum, the type species of the genus described from Mediterranean elasmobranchs, remains a little known parasite, with the most recent reports dating back to the fifties. We hereby investigate host-specificity and redescribe A. coronatum from the same locality of its original description by using light and scanning electron microscopy approaches. Moreover, molecular and phylogenetic data inferred from the analysis of the 28S rDNA gene are reported for the first time. Out of the nine elasmobranch species examined from Gulf of Naples, we only detected A. coronatum in the intestine of Scyliorhinus stellaris, with infection patterns that supports evident host-specificity for this shark species. The genetic characterization of 28S rDNA showed 99.8-100% similarity with larvae previously found in Octopus vulgaris from the same area investigated here. Conspecificity between the present material and the larvae found in the octopus was also confirmed by the tree topology. The host-parasite phylogeny is discussed, even if additional molecular data are needed to clarify potential host-parasite patterns. Notwithstanding this limitation, this is the first molecular study revealing conspecificity between an adult Acanthobothrium species from a shark and the larvae found in an intermediate/paratenic host, shedding light on the transmission pathway of A. coronatum in S. stellaris. Finally, the taxonomic, molecular, and phylogenetic data presented here allow a better characterization of a neglected parasite.

A systematic review of tapeworms (Plathelminthes, Cestoda) of domestic ducks (Anas platyrhynchos dom.)

Tapeworms of domestic ducks (Anas platyrhynchos dom.) causing helminthiasis and serious damage to the hosts, cause economic damage in the poultry industry. Helminthological research devoted to the study of the parasite fauna, including tapeworms of domestic ducks, has been carried out in many countries. But there is no review information on the study of the helminth fauna of domestic ducks. We take our own materials and literature data and summarise the information on cestode parasites of Anas platyrhynchos dom., which have been recorded in the world until 2020. Each species is provided with the following data: scientific name, authority and year, intermediate and auxiliary hosts, habitat in the host body, collecting localities and geographic distribution, prevalence and intensity of infection and literature sources. Based on our own research and analysis of literature data, it was revealed that hitherto there are 419 species of helminths (Trematoda – 213, Cestoda – 89, Nematoda – 79, Acanthocephala – 11) recorded parasitising domestic ducks. The tapeworms found in Azerbaijan belong to four families (Dilepididae – 3, Hymenolepididae – 68, Davaineidae – 13, Diphyllobothriidae – 5). In Azerbaijan, 11 out of 89 species of helminths have been found in domestic ducks. Six of them were also noted in the course of our helminthological studies. The cestoda Diorchis inflata was recorded the first time in domestic ducks in Azerbaijan. Most species of cestodes were found in the north-eastern regions of Azerbaijan (Shabran – 11 species, Khachmaz – 6 species) and the southern region (Astara – 4 species). All of these areas are located on the shores of the Caspian Sea and are located on the annual migration route of wild birds involved in the spread of cestodes, which are considered biohelminths. Six species (Drepanidotaenia lanceolata, Hymenolepis apodemi, Hymenolepis diminuta, Ligula interrupta, Ligula intestinalis, Schistocephalus solidus) of cestodes parasitize both birds and mammals (D. lanceolata, H. diminuta in humans).

Phylogeny of hymenolepidids (Cestoda: Cyclophyllidea) from mammals: sequences of 18S rRNA and COI genes confirm major clades revealed by the 28S rRNA analyses

The aim of the study is to test a hypothesis for the phylogenetic relationships among mammalian hymenolepidid tapeworms, based on partial (D1-D3) nuclear 28S ribosomal RNA (rRNA) genes, by estimating new molecular phylogenies for the group based on partial mitochondrial cytochrome c oxidase I (COI) and nuclear 18S rRNA genes, as well as a combined analysis using all three genes. New sequences of COI and 18S rRNA genes were obtained for Coronacanthus integrus, C. magnihamatus, C. omissus, C. vassilevi, Ditestolepis diaphana, Lineolepis scutigera, Spasskylepis ovaluteri, Staphylocystis tiara, S. furcata, S. uncinata, Vaucherilepis trichophorus and Neoskrjabinolepis sp. The phylogenetic analyses confirmed the major clades identified by Haukisalmi et al. (Zoologica Scripta 39: 631-641, 2010): Ditestolepis clade, Hymenolepis clade, Rodentolepis clade and Arostrilepis clade. While the Ditestolepis clade is associated with soricids, the structure of the other three clades suggests multiple evolutionary events of host switching between shrews and rodents. Two of the present analyses (18S rRNA and COI genes) show that the basal relationships of the four mammalian clades are branching at the same polytomy with several hymenolepidids from birds (both terrestrial and aquatic). This may indicate a rapid radiation of the group, with multiple events of colonizations of mammalian hosts by avian parasites.

Hidden diversity of the most basal tapeworms (Cestoda, Gyrocotylidea), the enigmatic parasites of holocephalans (Chimaeriformes)

Gyrocotylideans are evolutionary ancient parasitic flatworms, and like their hosts—a relict group of holocephalan fishes (Chimaeriformes)—they are considered to be “living fossils” of a vanished past. However, the species diversity, host associations and biogeography of these most basal tapeworms are poorly known. Herein, we provide evidence of a conspicuous contrast between the genetic and morphological data based on an examination of newly collected and properly processed Gyrocotyle specimens (hologenophores) isolated from holocephalans off Taiwan and Argentina. Our molecular data, inferred from three genes (COI, 28S rRNA, 18S rRNA), showed unexpected genetic interrelationships among isolates of the genus Gyrocotyle, because each of the four genotypes from Taiwan clustered with isolates of distinct gyrocotylideans from the North Atlantic. Three genotypes of Gyrocotyle from Taiwan were morphologically almost indistinguishable from each other but represented distinct genetic lineages; a single specimen of Gyrocotyle sp. genotype 4 exhibited a clear genetic and morphological distinctness, though its formal description as a new species would be premature. Additionally, specimens of Gyrocotyle rugosa Diesing, 1850, from the type host Callorhinchus callorynchus from Argentina, provided the first genetic data on the type species of the genus and enabled us to characterise it, which is necessary for future taxonomic studies. The finding of some specimens of Gyrocotyle sp. genotype 3 in Chimaera phantasma, and another one in C. cf. argiloba, together with the putative conspecificity of an unidentified gyrocotylidean from Callorhinchus milii off Australia and G. rugosa from C. callorynchus off Argentina, represent evidence that one gyrocotylidean species may parasitise more than one holocephalan host species. Existing taxonomic problems and conflicts between morphological and molecular data on species of Gyrocotyle can only be resolved if hologenophores from type hosts and localities of nominal taxa are properly characterised genetically and morphologically.

Emerging global novelty in phyllobothriidean tapeworms (Cestoda: Phyllobothriidea) from sharks and skates (Elasmobranchii)

New genera are erected for three clades of tapeworms originally discovered using molecular sequence data. The morphological features of each are characterized after examination of specimens with light and scanning electron microscopy. Rockacestus gen. nov. parasitizes skates. Ruhnkebothrium gen. nov. parasitizes hammerhead sharks. Yamaguticestus gen. nov. parasitizes small squaliform sharks and catsharks. The novelty of these genera is supported by a taxonomically comprehensive molecular phylogenetic analysis of the D1–D3 region of the 28S rDNA gene, which, with the addition of newly generated sequence data, is the first to include representation of 15 of the 18 genera of phyllobothriideans plus the three new genera. Five new species are described from elasmobranchs in the western Atlantic Ocean, the Gulf of California, Chile, the Falkland Islands and South Africa to help circumscribe the new genera. Two of the genera provide appropriate generic homes for ten species of phyllobothriideans from catsharks and skates with uncertain generic affinities and thus resolve longstanding taxonomic issues. Given that these genera parasitize some of the most poorly sampled groups of elasmobranchs (i.e. hammerhead sharks, squaliform sharks, catsharks and skates), based on the strict degree of host specificity observed, we predict that further work on other members of these groups will yield as many as 200 additional species in these three genera of tapeworms globally. This brings the total number of genera in the Phyllobothriidea to 21.

A new species of Grillotia Guiart, 1927 (Cestoda: Trypanorhyncha) from the spotted skate, Raja straeleni Poll, in South Africa

A new species of Grillotia Guiart, 1927 was recovered from the spotted skate (Raja straeleni Poll) from the south coast of the Western Cape, South Africa. Grillotia sasciae n. sp. is described based on morphological and molecular data. This species most closely resembles species in the subgenus Grillotia (viz., Grillotia borealis Keeney and Campbell, 2001, Grillotia brayi Beveridge and Campbell, 2007, Grillotia dollfusi Carvajal, 1971, Grillotia erinaceus Dollfus, 1969, Grillotia musculara Hart, 1936 and Grillotia patagonica Menoret and Ivanov, 2012) in having four hooks per principal row and intercalary hook rows in the metabasal region of the tentacular armature, a band of hooks on the external tentacular surface, numerous proglottids, and the presence of an uterine pore, a hermaphroditic sac, and internal and external seminal vesicles. The molecular phylogenetic analysis of the partial 28S rDNA gene, confirms the morphological data as it also groups Grillotia sasciae n. sp. within the G. erinaceus species complex. Grillotia sasciae n. sp. is distinctive among all other valid species in the complex by having two enlarged, uncinate hooks in the basal armature, of a different shape and size from the remaining hooks 1(1') in the metabasal armature. In addition, the retractor muscle of Grillotia sasciae n. sp. attaches at the posterior region of the tentacular bulb rather than the middle portion, continuing posteriorly as seen in most congeners (viz., G. erinaceus, G. borealis, G. brayi, G. musculara and G. pantagonica). The new species is the seventh species within the subgenus Grillotia and the first record of a species of Grillotia from southern African waters.

Three New Species of Rhinebothrium (Cestoda: Rhinebothriidea) from the Leopard Whipray, Himantura Leoparda, in Australia

Examination of 4 specimens of the leopard whipray Himantura leoparda, a dasyatid stingray from northern Australia, led to the discovery of 3 new species of Rhinebothrium. Rhinebothrium leopardensis n. sp., Rhinebothrium nandoi n. sp., and Rhinebothrium ruhnkei n. sp. are described, increasing the diversity of the genus to 51 species globally. All 3 new species differ from their congeners in terms of testis number, proglottid number, loculus number, and size. With respect to one another, R. leopardensis n. sp. has bothridia that are weakly constricted at their centers and has a greater number of proglottids than the other 2 species (93-108 vs. 11-15, and 48-78, respectively). Rhinebothrium nandoi n. sp. is the smallest of the 3 species found in H. leoparda (3.6-5 vs. 10-15 mm and 10.1-15.8 mm in total length [TL], respectively) and bears bothridia that are constricted at their centers. Rhinebothrium ruhnkei n. sp. bears bothridia that are conspicuously constricted at their centers and has more testes than R. leopardensis and fewer than R. nandoi (7-10 vs. fewer than 7 and 21-33, respectively). Before this study, 56% (27 of 48) of Rhinebothrium species had been described from the freshwater river systems of South America and the marine waters surrounding South and North America. In contrast, despite the remarkably diverse nature of its batoid fauna, only 19 species were known from the Indo-Pacific region. Our work increases this number to 22, emphasizing the highly underestimated nature of Rhinebothrium diversity in this region of the globe. The discovery of these 3 new species was not unexpected, given the relatively poor status of our current knowledge of the cestode faunas of dasyatid stingrays in the Indo-Pacific region, and given the fact that it is common for a single batoid species to host 2 or more species of Rhinebothrium. Our results suggest that additional work on the cestode faunas of the batoids, especially dasyatids, from the Indo-Pacific region is likely to be highly productive in terms of contributing to the knowledge of Rhinebothrium diversity.

A NEW SPECIES OF ACANTHOBOTHRIUM (CESTODA: ONCHOPROTEOCEPHALIDEA) FROM THE SMALLEYE PYGMY SHARK, SQUALIOLUS ALIAE (CHONDRICHTHYES: SQUALIFORMES: DALATIIDAE), FROM TAIWAN

The cestode fauna of Squaliolus aliae was examined for the first time following the collection of elasmobranch specimens from Taiwan in 2005, 2013, and 2017. This small shark was found to host 2 tapeworm species. These consist of Acanthobothrium katherineae n. sp., which is new to science and is described herein, and a second species, in the genus Scyphophyllidium, which also appears to be new, but which is represented by insufficient material for formal description. Acanthobothrium katherineae is a category 5 species. It can be distinguished from 5 of the 19 other category 5 species in that it is apolytic, retaining proglottids on its strobila until they are gravid. This new species differs from the remaining 14 category 5 species in its combination of the following features: It is a smaller worm, has fewer than 100 proglottids, has a relatively short cephalic peduncle, and differs in bothridial size and loculus ratio. Sequence data for the D1-D3 region of the 28S rDNA gene were generated for one specimen of A. katherineae. This sequence, along with comparable sequence data for adults of 14 described and 2 undescribed species as well as specimens of 6 undescribed larval members of the genus, was included in a maximum likelihood phylogenetic analysis. The resulting tree places the shark-hosted A. katherineae within a clade of stingray-hosted species, with Acanthobothrium romanowi as its sister taxon. Acanthobothrium katherineae is 1 of only 19 Acanthobothrium species known to parasitize sharks. The tree resulting from this study, which is preliminary given the relatively poor taxon sampling of the diversity in the genus, included 3 of the shark-parasitizing Acanthobothrium species and suggests that all 3 represent host-switching events. This is the first report of an Acanthobothrium species from the family Dalatiidae and the first report of a Scyphophyllidium species from the order Squaliformes. These findings suggest that other members of the Squaliformes, many of which have not previously been examined for parasites, may host additional novel cestode taxa.

Detection of Raillietina saudiae from the domestic pigeon in Saudi Arabia through 18S and 28S rDNA genes

Raillietina saudiae is a well-studied avian gastrointestinal parasite belonging to the family Davaineidae and is the most prevalent cyclophyllid tapeworm infecting pigeon in Saudi Arabia. The present study considered as a complementary analysis of Al-Quraishy et al. (2019; Parasitol Int 71, 59-72) with molecular studies for two ribosomal DNA genes employed for precise recognition of this Raillietina species. The annotated partial 18S and 28S rDNA gene regions were found to be 888 and 900 bp long that utilized further to elucidate their genetic relationships at species level using maximum likelihood method. The query sequence of R. saudiae is well aligned and placed within the Davaineidae family, with the same clade of all species of Raillietina that well separated from other cyclophyllidean cestodes especially taeniid and hymenolepid species. Sequence data recorded the monophyly of Raillietina species. The current phylogeny supports the usage of the partial 18S and 28S rDNA genes as reliable markers for phylogenetic reconstructions.

Dynamics of protein synthesis in the initial steps of strobilation in the model cestode parasite Mesocestoides corti (syn. vogae)

Mesocestoides corti (syn. vogae) is a useful model for developmental studies of platyhelminth parasites of the Cestoda class, such as Taenia spp. or Echinococcus spp. It has been used in studies to characterize cestode strobilation, i.e. the development of larvae into adult worms. So far, little is known about the initial molecular events involved in cestode strobilation and, therefore, we carried out a study to characterize newly synthesized (NS) proteins upon strobilation induction. An approach based on bioorthogonal noncanonical amino acid tagging and mass spectrometry was used to label, isolate, identify, and quantify NS proteins in the initial steps of M. corti strobilation. Overall, 121 NS proteins were detected exclusively after induction of strobilation, including proteins related to development pathways, such as insulin and notch signaling. Metabolic changes that take place in the transition from the larval stage to adult worm were noted in special NS protein subsets related to developmental processes, such as focal adhesion, cell leading edge, and maintenance of location. The data shed light on mechanisms underlying early steps of cestode strobilation and enabled identification of possible developmental markers. We also consider the use of developmental responsive proteins as potential drug targets for developing novel anthelmintics. BIOLOGICAL SIGNIFICANCE: Larval cestodiases are life-threatening parasitic diseases that affect both man and domestic animals worldwide. Cestode parasites present complex life cycles, in which they undergo major morphological and physiological changes in the transition from one life-stage to the next. One of these transitions occurs during cestode strobilation, when the mostly undifferentiated and non-segmented larval or pre-adult form develops into a fully segmented and sexually differentiated (strobilated) adult worm. Although the proteomes of bona fide larvae and strobialted adults have been previously characterized for a few cestode species, little is still known about the dynamic of protein synthesis during the early steps of cestode strobilation. Now, the assessment of newly synthesized (NS) proteins within the first 48 h of strobilation the model cestode M. corti allowed to shed light on molecular mechanisms that are triggered by strobilation induction. The functional analyses of this repertoire of over a hundred NS proteins pointed out to changes in metabolism and activation of classical developmental signaling pathways in early strobilation. Many of the identified NS proteins may become valuable cestode developmental markers and their involvement in vital processes make them also good candidate targets for novel anthelmintic drugs.

Intrigue surrounding the life-cycles of species of Clistobothrium (Cestoda: Phyllobothriidea) parasitising large pelagic sharks

This study aimed to locate the adults, and thus also the definitive hosts, of three species of marine mammal-parasitising larval cestodes that have molecular affinities with Clistobothrium. New collections led to the discovery of adults of two new species of Clistobothrium, one from the longfin mako shark and one from the salmon shark. New material of Clistobothrium tumidum was collected from the great white shark and new material of a previously reported undescribed species of Clistobothrium was collected from the porbeagle shark. Larvae of Clistobothrium were opportunistically collected from sockeye salmon and four species of small squaliform sharks. Sequence data for the D1-D3 region of the 28S rDNA gene were generated for all but one of these taxa. The tree resulting from maximum likelihood analysis of those data, in combination with comparable data from GenBank, indicates that squaliform sharks can serve as intermediate hosts for the species from the porbeagle shark. The larvae from salmon exhibit a unique molecular signature and, based on diet data, may be conspecific with adults from the salmon shark. Informed by sequence data for new material of Monorygma and existing data for Phyllobothrium, the larvae provisionally identified as Monorygma grimaldii and Phyllobothrium delphini were formally transferred to Clistobothrium. Especially puzzling was that the molecular signatures of none of the eight species of Clistobothrium match those of the three marine mammal-parasitising larval forms. We are at a loss as to where else to look for the three corresponding adult forms. The great white shark remains the most likely candidate given it consumes marine mammals with some regularity, but seems unlikely to host five species of Clistobothrium. Alternatively, we are left wondering if the large marine mammal predator Carcharocles megalodon may not be extinct after all.

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.

Spermiogenesis produces the spermatozoa with 9 + '1' and 9 + 0 axonemal pattern in progenetic cestode Diplocotyle olrikii Krabbe, 1874 (Spathebothriidea: Acrobothriidae)

Spermiogenesis in the progenetic spathebothriidean cestode Diplocotyle olrikii has been examined using transmission electron microscopy (TEM) for the first time. Along with the typical features of spermatozoon cytodifferentiation (e.g., the electron-dense material in the apical region of the differentiation zone in the early stage of spermiogenesis, the intercentriolar body which is composed of three electron-dense plates and two electron-lucent zones, the orthogonal development of the two flagella, a flagellar rotation, proximo-distal fusion, the presence of two pairs of electron-dense attachment zones), new for the Eucestoda is detection of the formation of two types of free flagella during spermiogenesis in progenetic D. olrikii, exhibiting either standard 9 + '1' trepaxonematan pattern, or atypical 9 + 0 structure. Various combinations of these two types of flagella resulted in the production of three types of male gametes during spermiogenesis in this spathebothriidean cestode. The first type is represented with the two axonemes of the 9 + '1' structure; the second type exhibits two different axonemes, i.e., one with 9 + '1' and the other of 9 + 0 pattern; and the third type has two axonemes with atypical 9 + 0 structure. The occurrence of three sperm types in progenetic D. olrikii is associated with typical spermiogenesis and has never been described previously in the Platyhelminthes. We suppose that heteromorphism of male gametes in D. olrikii might be linked to progenesis, i.e., the programmed sexual maturation detected during the larval/developmental stage of an organism.

Free-ranging avifauna as a source of generalist parasites for captive birds in zoological settings: An overview of parasite records and potential for cross-transmission

Captive birds in zoological settings often harbor parasites, but little information is available about the potential for free-ranging avifauna to act as a source of infection. This review summarizes the gastrointestinal parasites found in zoo birds globally and in seven common free-ranging avian species [mallard (Anas platyrhynchos), Eurasian blackbird (Turdus merula), common starling (Sturnus vulgaris), Eurasian jackdaw (Corvus monedula), house sparrow (Passer domesticus), European robin (Erithacus rubecula), and rock dove (Columba livia)] to identify the overlap and discuss the potential for cross-species transmission. Over 70 references were assessed, and papers spanned over 90 years from 1925 to 2019. A total of 60 studies from 1987 to 2019 met the eligibility criteria. All examined free-ranging avifauna harbored parasite species that were also reported in zoo birds, except for the European jackdaw. Parasites reported in captive and free-ranging birds include nematodes (Capillaria caudinflata, Dispharynx nasuta, Ornithostrongylus quadriradiatus, Strongyloides avium, Syngamus trachea, and Tetrameres fissispina), cestodes (Dicranotaenia coronula, Diorchis stefanskii, Fimbriaria fasciolaris, and Raillietina cesticillus, Sobolevicanthus gracilis), trematode (Echinostoma revolutum), and protozoa (Cryptosporidium baileyi). Although no study effectively proved cross-transmission either experimentally or by genetic analysis, these parasites demonstrate low host specificity and a high potential for parasite sharing. There is potential for parasite sharing whenever determinants such as host specificity, life cycle, and husbandry are favorable. More research should be carried out to describe parasites in both captive and free-ranging birds in zoological settings and the likelihood of cross-infection. Such information would contribute to evidence-based control measures, enhancing effective husbandry and preventive medicine protocols.

Morphological abnormalities in fish parasites: a potential tool for biomonitoring natural contaminants?

A comparative study on the strobilar morphology of the tapeworm Proteocephalus percae (Müller, 1780) (Cestoda), a parasite of the perch Perca fluviatilis (L.), showed a high percentage of abnormally developed parasite individuals. The evaluation of biological samples showed seven types of morphological abnormalities, mostly related to reproductive organs of the model tapeworm species. The most commonly identified deformity was an incomplete segmentation of the strobila. A malformed ovary, which is a structural anomaly linked with proglottization and maturation of the strobila, was also shown to be rather frequent. Offish hosts (P. percae) were collected from two localities with different levels of heavy metal pollution, the highly contaminated water reservoir Ružín and a control locality, the water reservoir Palcmanská Maša, which belongs to the European network of protected areas in Slovakia. Tapeworm abnormalities occurred more frequently in individuals from the contaminated environment (29.9%) compared with individuals from the control site (4.9%). The concentrations of heavy metals found in the parasites and their fish hosts from the heavily polluted reservoir support our assumption that the occurrence of abnormalities could be linked with the destructive effect of toxic substances. The present study also demonstrates that the enumeration of body deformities exceeding the common level of phenotypic variability of particular parasitic species could potentially be used as an indicator of environmental problems.

Molecular Characterization of Clistobothrium sp. Viable Plerocercoids in Fresh Longfin Inshore Squid (Doryteuthis pealeii) and Implications for Cephalopod Inspection

Cephalopods, an appreciated seafood product, are common hosts of marine cestodes. The aim of this work is to report visible alive plerocercoids in longfin inshore squid (Doryteuthis pealeii), a cephalopod species commercialized as fresh and whole in Italy. Seventy D. pealeii from the Northwest Atlantic (FAO area 21) were collected and visually inspected. In total, 18 plerocercoid larvae were found in the viscera of 10 host specimens (P: 14.3% 95% CI 7.1–24.7; MI: 1.8, MA: 0.26; range 1–4) and molecularly analyzed targeting the variable D2 region of the large subunit (LSU) rRNA gene and the cytochrome c oxidase subunit I (COI) gene. The molecular characterization allowed to identify all the plerocercoids as Clistobothrium sp., a cestode of the Phyllobothriidae family with Lamnidae sharks as definitive hosts, and cephalopods as second intermediate hosts. These findings represent the first molecular record of Clistobothrium sp. in D. pealeii, thus contributing to elucidate its poorly known life cycle. Even if not affecting consumer’s health, these visible parasites may represent a reason for disgust for consumers. Therefore, the results suggest that Food Business Operators should also check for the presence of these visible parasites during inspection and underline the importance of a correct consumers’ education.

Cestode strobilation: prediction of developmental genes and pathways

BACKGROUND

Cestoda is a class of endoparasitic worms in the flatworm phylum (Platyhelminthes). During the course of their evolution cestodes have evolved some interesting aspects, such as their increased reproductive capacity. In this sense, they have serial repetition of their reproductive organs in the adult stage, which is often associated with external segmentation in a developmental process called strobilation. However, the molecular basis of strobilation is poorly understood. To assess this issue, an evolutionary comparative study among strobilated and non-strobilated flatworm species was conducted to identify genes and proteins related to the strobilation process.

RESULTS

We compared the genomic content of 10 parasitic platyhelminth species; five from cestode species, representing strobilated parasitic platyhelminths, and five from trematode species, representing non-strobilated parasitic platyhelminths. This dataset was used to identify 1813 genes with orthologues that are present in all cestode (strobilated) species, but absent from at least one trematode (non-strobilated) species. Development-related genes, along with genes of unknown function (UF), were then selected based on their transcriptional profiles, resulting in a total of 34 genes that were differentially expressed between the larval (pre-strobilation) and adult (strobilated) stages in at least one cestode species. These 34 genes were then assumed to be strobilation related; they included 12 encoding proteins of known function, with 6 related to the Wnt, TGF-β/BMP, or G-protein coupled receptor signaling pathways; and 22 encoding UF proteins. In order to assign function to at least some of the UF genes/proteins, a global gene co-expression analysis was performed for the cestode species Echinococcus multilocularis. This resulted in eight UF genes/proteins being predicted as related to developmental, reproductive, vesicle transport, or signaling processes.

CONCLUSIONS

Overall, the described in silico data provided evidence of the involvement of 34 genes/proteins and at least 3 developmental pathways in the cestode strobilation process. These results highlight on the molecular mechanisms and evolution of the cestode strobilation process, and point to several interesting proteins as potential developmental markers and/or targets for the development of novel antihelminthic drugs.

Transcriptomic Analysis of the Early Strobilar Development of Echinococcus granulosus

Echinococcus granulosus has a complex life cycle involving two mammalian hosts. The transition from one host to another is accompanied by changes in gene expression, and the transcriptional events that underlie this transition have not yet been fully characterized. In this study, RNA-seq was used to compare the transcription profiles of samples from E. granulosus protoscoleces induced in vitro to strobilar development at three time points. We identified 818 differentially expressed genes, which were divided into eight expression clusters formed over the entire 24 h period. An enrichment of gene transcripts with molecular functions of signal transduction, enzymes, and protein modifications was observed upon induction and developmental progression. This transcriptomic study provides insights for understanding the complex life cycle of E. granulosus and contributes for searching for the key genes correlating with the strobilar development, which can be used to identify potential candidates for the development of anthelmintic drugs.

Molecular circumscription of new species of Gyrocotyle Diesing, 1850 (Cestoda) from deep-sea chimaeriform holocephalans in the North Atlantic

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

Characterization and phylogenomics of the complete mitochondrial genome of the polyzoic cestode Gangesia oligonchis (Platyhelminthes: Onchoproteocephalidea)

The order Onchoproteocephalidea (Eucestoda) was recently erected to accommodate the hook-bearing tetraphyllideans and the proteocephalideans, which are characterized by internal proglottization and a tetra-acetabulate scolex. The recognized subfamilies in the Proteocephalidae appeared to be non-monophyletic based on 28S recombinant DNA (rDNA) sequence data. Other molecular markers with higher phylogenetic resolution, such as large mitochondrial DNA fragments and multiple genes, are obviously needed. Thus the mitochondrial genome of Gangesia oligonchis, belonging to the putative earliest diverging group of the Proteocephalidae, was sequenced. The circular mitogenome of G. oligonchis was 13,958 bp in size, and contained the standard 36 genes: 22 transfer RNA genes, two rRNA genes and 12 protein-coding genes, as well as two major non-coding regions. A short NCR and a large NCR (lNCR) region were 216 bp and 419 bp in size, respectively. Highly repetitive regions in the lNCR region were detected with that of 11 repeat units. The mitogenome of G. oligonchis shared 71.1% nucleotide identity with Testudotaenia sp. WL-2016. Phylogenetic analyses of the complete mitochondrial genomes with Bayesian inference and maximum likelihood methods indicated that G. oligonchis formed a sister clade with Testudotaenia sp. WL-2016 with maximum support. The ordinal topology is (Caryophyllidea, (Diphyllobothriidea, (Bothriocephalidea, (Onchoproteocephalidea, Cyclophyllidea)))). The mitogenomic gene arrangement of G. oligonchis was identical to that of Testudotaenia sp. WL-2016. Both mitogenomic and nuclear sequence data for many more taxa are required to effectively explore the inter-relationships among the Onchoproteocephalidea.

Morphological and molecular insights of a new species of trypanorhynchid cestode parasite, Nybelinia exostigmi, in the Narrowstripe cardinal fish Apogon exostigma

Forty specimens of the Narrowstripe cardinal fish Apogon exostigma were examined for gastrointestinal helminthes, and 62.5% were infected with a new trypanorhynchid larval cestode parasite. The morphology of its larval stage was studied based on light and scanning electron microscopy. The data revealed plerocercoid larvae characterized by a pyriform body lined with prominent microtriches; the acraspedote scolex had four overlapping bothridia; four tentacles protruded through the pars bothridialis; the armature of the tentacles was homeocanthous, homeomorphous, and consisted of falcate compact rose-thorn-shaped tentacular hooks; four oval-shaped bulbs in pars bulbosa; and short appendix at terminal end of the body. Molecular analysis of the 18S rRNA sequences verified the taxonomy of this parasite and supported its morphology. We discovered that there was a close identity (up to 87%) with alternative species obtained for comparison from GenBank. The data also showed that there were high blast scores and low divergence values between this parasite and other Tentaculariidae species. The phyletic analysis showed that parasite sequences in conjunction with existing data places this trypanorhynchid species among the Tentaculariidae. This species is deeply embedded within genus Nybelinia with close relationships to Nybelinia queenslandensis as a putative sister taxon.

Massive infection of a song thrush by Mesocestoides sp. (Cestoda) tetrathyridia that genetically match acephalic metacestodes causing lethal peritoneal larval cestodiasis in domesticated mammals

Background

Peritoneal larval cestodiasis induced by Mesocestoides Vaillant, 1863 (Cyclophyllidea: Mesocestoididae) is a common cause of severe infections in domestic dogs and cats, reported also from other mammals and less frequently from birds. However, there is a limited knowledge on the taxonomy of causative agents of this disease.

Results

In the present study, we investigated a massive, likely lethal, infection of a song thrush Turdus philomelos (Passeriformes: Turdidae) by Mesocestoides sp. tetrathyridia. We performed combined morphological and phylogenetic analysis of the tetrathyridia and compared them with the materials obtained previously from other birds and mammals. The metrical data fitted within the wide range reported by previous authors but confirmed the limited value of morphological data for species identification of tetrathyridia of Mesocestoides spp. The molecular analyses suggested that the isolates represented an unidentified Mesocestoides sp. that was previously repeatedly isolated and sequenced in larval and adult forms from domestic dogs and cats in Europe, the Middle East and North Africa. In contrast to the present study, which found encysted tetrathyridia, four of the five previous studies that identified the same species described infections by acephalic metacestodes only.

Conclusions

The tetrathyridia of the examined Mesocestoides sp. are described in the present study for the first time. However, the possible match with the species that were previously reported to infect birds remains uncertain. The phylogenetic analyses also suggested the rejection of two cases that were previously identified as Mesocestoides corti as they were likely caused by the same species as in the presently reported infection case. The newly provided DNA sequences should allow the assignment to species in the future, when adults of the genus Mesocestoides are more thoroughly sequenced.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3480-1) contains supplementary material, which is available to authorized users.