Molecular characterisation of acanthocephalans from Australian marine teleosts: proposal of a new family, synonymy of another and transfer of taxa between orders

Morphology and molecular phylogeny of Rhadinorhynchus nudus (Harada, 1938) (Acanthocephala: Rhadinorhynchidae) from Euthynnus affinis (Scombridae) in the Persian Gulf off Iran

Acanthocephalans collected from the stomach of the mackerel tuna (Euthynnus affinis Cantor) in the Persian Gulf off Iran were identified as Neorhadinorhynchus nudus Harada, 1938 based on morphological characters and molecular sequence data from mitochondrial (cytochrome c oxidase subunit I, COI) and nuclear ribosomal DNA (small and large subunit ribosomal DNA, 18S and 28S rDNA). Phylogenetic analyses of the order Echinorhynchida Southwell & Macfie, 1925 were performed based on the concatenated (18S+28S+COI) sequence data using maximum likelihood (ML) and Bayesian inference (BI) analyses. The results showed that N. nudus grouped together with species of Rhadinorhynchus Lühe, 1911, supporting the proposal that Neorhadinorhynchus Yamaguti, 1939 is a synonym of Rhadinorhynchus. Rhadinorhynchus mariserpentis Steinauer et al., 2019 was also treated as a junior synonym of Rhadinorhynchus nudus. Haplotype network analysis revealed no correlation between haplotype distribution and geographical origin of R. nudus.

Rhadinorhynchus villalobosi sp. n. (Acanthocephala: Rhadinorhynchidae) from the gafftopsail pompano Trachinotus rhodopus (Carangiformes: Carangidae) from the Pacific coast in Mexico

A new species of Acanthocephala is described based on specimens found parasitising the intestine of the gafftopsail pompano Trachinotus rhodopus Gill in the State of Oaxaca, off the Pacific coast of Mexico. Rhadinorhynchus villalobosi sp. n. differs from the other 25 species of the genus known from the Pacific Ocean by a combination of morphological traits, such as the fewer number of rows of hooks along the proboscis, the distribution of spines of the trunk forming two fields, the position of genital pore, subterminal in both sexes, a shorter neck and cement glands, among others. The phylogenetic analyses based on sequences of the nuclear 18S and 28S rRNA genes, as well as the mitochondrial cox1, all agree that R. villalobosi sp. n. is part of the genus, and closely related to Rhadinorhynchus trachinoti Grano-Maldonado, Sereno-Uribe, Hernández-Payán, Pérez-Ponce de León et García-Varela, 2025, a recently described Mexican species, despite the marked morphological differences between the two and being distributed in different areas.

Integrative taxonomy of the genus Pseudoacanthocephalus (Acanthocephala: Echinorhynchida) in China, with the description of two new species and the characterization of the mitochondrial genomes of Pseudoacanthocephalus sichuanensis sp. n. and Pseudoacanthocephalus nguyenthileae

BACKGROUND

Acanthocephalans (thorny headed worms) of the genus Pseudoacanthocephalus mainly parasitize amphibians and reptiles across the globe. Some species of the genus Pseudoacanthocephalus also can accidentally infect human and cause human acanthocephaliasis. Current knowledge of the species composition of the genus Pseudoacanthocephalus from amphibians and reptiles in China is incomplete. An insufficiency of genetic data on species of the genus Pseudoacanthocephalus, including the complete mitochondrial genomes, has limited the use of molecular-based methods to better define the taxonomy and phylogeny of the genus Pseudoacanthocephalus. A more rigorous molecular phylogeny with broader representatives of the genus Pseudoacanthocephalus is required to further clarify the systematic status of the family Pseudoacanthocephalidae.

METHODS

Many specimens of the genus Pseudoacanthocephalus collected from toads and frogs in China were identified to species level using integrated morphological methods (light and scanning electron microscopy) and molecular approaches (sequencing different nuclear and mitochondrial genetic markers). The Assemble Species by Automatic Partitioning (ASAP) and Bayesian inference (BI) methods were applied for species delimitation. The complete mitochondrial genomes of two Pseudoacanthocephalus species were also sequenced and annotated to enrich the body of mitogenomic data on acanthocephalans. Additionally, phylogenetic analyses based on the amino acid sequences of 12 protein-coding genes (PCGs) of mitochondrial genomes of acanthocephalans using maximum likelihood (ML) and BI were performed to further investigate the phylogenetic position of the family Pseudoacanthocephalidae in the order Echinorhynchida.

RESULTS

Three Pseudoacanthocephalus species, including P. sichuanensis sp. n., P. previatesticulus sp. n. and P. nguyenthileae were described. The results of ASAP and BI analyses based on the cytochrome c oxidase subunit 1 and subunit 2 (cox1, cox2) and 12S ribosomal RNA (12S) sequences supported the separation of P. sichuanensis and P. previatesticulus from the congeneric species. The results of BI inference using the internal transcribed spacer (ITS), cox1, cox2 and 12S sequence data indicated that P. sichuanensis and P. nguyenthileae have a closer relationship than P. previatesticulus and P. bufonis in Pseudoacanthocephalus. The complete mitogenomes of P. sichuanensis and P. nguyenthileae have 15,812 and 13,701 bp, respectively, with both including 36 genes and two non-coding regions. Phylogenetic results based on mitogenomic data demonstrated that the two families Pseudoacanthocephalidae and Arhythmacanthidae have a sister relationship in the order Echinorhynchida.

CONCLUSIONS

Two new species of the genus Pseudoacanthocephalus, namely P. sichuanensis sp. n. and P. previatesticulus sp. n., were identified based on integrated evidence. This is the first report of P. nguyenthileae in China. A revised key for the species of the genus Pseudoacanthocephalus was provided. Molecular analyses revealed that the mitochondrial cox1, cox2 and 12S genes as genetic markers seem to be more suitable for species delimitation of Pseudoacanthocephalus than the nuclear ITS region. BI results suggested a close affinity between P. sichuanensis and P. nguyenthileae. The mitochondrial genomic data of P. sichuanensis and P. nguyenthileae are provided for the first time. Mitogenomic phylogenetic results further confirmed the validity of the family Pseudoacanthocephalidae.

Linking adults and cystacanths of a new species of Rhadinorhynchus Lühe, 1911 (Acanthocephala: Rhadinorhynchidae) from the Pacific coast of Mexico by using morphological and molecular data

During parasitological surveys of marine fishes and zooplankton in localities of the Northwestern Pacific coast of Mexico, 28 Gafftopsail pompano (Trachinotus rhodopus Gill) and 50 mysid crustaceans (Metamysidopsis frankfiersi Hendrickx & Hernández-Payán) we identified to be infected with adults and cystacanths, respectively of an acanthocephalan morphologically corresponding to the genus Rhadinorhynchus Lühe, 1911. DNA sequences of the small (SSU) and large (LSU) subunits of ribosomal DNA, and cytochrome c oxidase subunit 1 (cox 1) from mitochondrial DNA were obtained. Phylogenetic analyses revealed that the newly sequenced individuals in a clade with Rhadinorhynchus sp. from carangids in other localities of the Pacific coast of Mexico; together, all these individuals formed an independent lineage that is recognized herein as a new species, Rhadinorhynchus trachinoti n. sp. The new species is morphologically distinguished from the other 38 congeners by having a long and cylindrical proboscis armed with 12 longitudinal rows bearing 16-18 hooks each. The ecological information gathered from the parasites, together with genetic evidence, confirms that the Gafftopsail pompano is the definitive host of R. trachinoti n. sp., while mysid crustaceans serve as the intermediate host. Current records also indicate that R. trachinoti n. sp. is distributed along the Pacific coast of Mexico, from Mazatlán, Sinaloa in the north to Puerto Angel, Oaxaca in the south. This distribution aligns with the Mexican Coastal Current, which extends from the Gulf of Tehuantepec in Oaxaca to the entrance of the Gulf of California and southern Baja California.

Systematics of Pseudocavisoma (Acanthocephala: Echinorhynchida): assessment of familial affiliation, establishment of a new species, and complementary redescription of the type species based on syntypes

The familial affiliation of the so-far-monotypic palaeacanthocephalan genus Pseudocavisoma Golvan & Houin, 1964 has solely been based on morphological characteristics, lacking nucleotide sequence data. In this paper, we assess the phylogenetic position of the genus with a dataset consisting of partial sequences of the mitochondrial cytochrome c oxidase subunit I, and the nuclear 18S and 28S rRNA genes for 37 species of palaeacanthocephalans available in public databases along with the ones determined from the new species Pseudocavisoma setoense sp. nov., herein established with specimens collected from the intestine of the pearl-spot chromis Chromis notata (Temminck & Schlegel, 1843) obtained in the Seto Inland Sea, Japan. Our results suggested that Pseudocavisoma should be placed in Micracanthorhynchinidae Yamaguti, 1963, rather than in Cavisomatidae Meyer, 1932 as had been considered by previous authors. Because Micracanthorhynchinidae has been regarded synonymous with Rhadinorhynchidae Lühe, 1912 since 1985, we re-validate the former taxon while providing an amended diagnosis for it. Pseudocavisoma setoense sp. nov. can be distinguished from the sole congener Pseudocavisoma chromitidis (Cable & Quick, 1954) by the distributional pattern and the size of spines on the trunk. We provide a partial morphological redescription of the latter species based on syntypes of Cavisoma chromitidis Cable & Quick, 1954. We also provide an amended diagnosis for Pseudocavisoma to accommodate P. setoense sp. nov.

Molecular Systematics and Type-material-based Redescription of Metarhadinorhynchus lateolabracis, With Taxonomic Revisions of Metarhadinorhynchus, Indorhynchus, and Neotegorhynchus (Acanthocephala: Palaeacanthocephala)

PURPOSE

Molecular phylogenetics has been improving the acanthocephalan systematics, yet numerous taxa remain unexplored. The palaeacanthocephalan Metarhadinorhynchus Yamaguti, 1959 and its type species M. lateolabracis Yamaguti, 1959 are such to-be-explored taxa. We aim to refine (i) the systematic placement, (ii) the morphological circumscription, and (iii) the taxonomic components of the genus. We also aim to examine the taxonomic status of the species that have been assigned to the genus.

METHODS

Morphological observations on newly collected specimens as well as the type material of Metarhadinorhynchus lateolabracis were conducted. Also, molecular phylogenetic analyses with maximum-likelihood method and Bayesian inference were performed based on freshly collected specimens. Nominal species that have at least once been assigned in Metarhadinorhynchus, as well as a related form, Gorgorhynchus lateolabri Yin and Wu, 1984, are taxonomically re-evaluated based on literature information.

RESULTS

Our re-examination of the type material of M. lateolabracis revealed that the number of cement glands is six, instead of eight as described and illustrated in the original description. In the resulting phylogenetic tree, M. lateolabracis was nested in Isthmosacanthidae. Gorgorhynchoides Cable and Linderoth, 1963 was found to be a junior synonym of Metarhadinorhynchus. Taxonomic re-evaluations of six nominal species that have once belonged in Metarhadinorhynchus led to modifications of generic diagnoses for Indorhynchus Golvan, 1969 and Neotegorhynchus Lisitsyna, Xi, Orosová, Barčák, and Oros, 2022.

CONCLUSIONS

Metarhadinorhynchus has been assigned to Leptorhynchoididae (Echinorhynchida), but our study now locates it in Isthmosacanthidae (Polymorphida). We propose 13 new combinations of specific names in Metarhadinorhynchus and three in Indorhynchus. Metarhadinorhynchus lateolabri (Yin and Wu, 1984) comb. nov. may be synonymous with M. orientalis (Wang, 1966) comb. nov.

The white grunt, Haemulon plumierii (Lacepède, 1801) as paratenic and definitive host of two acanthocephalan species, with the description of a new species of Dollfusentis (Palaeacanthocephala: Leptohynchoididae) from the Yucatán Peninsula, Mexico

Acanthocephalans are a group of obligate endoparasites that alternate between vertebrates and invertebrates to complete their life cycles. Occasionally, the same individual host acts as a definitive or paratenic host for different acanthocephalan species. In this study, acanthocephalans were sampled in marine fish in three localities of the Yucatán Peninsula; adults and cystacanths were recovered from the intestine and body cavity, respectively, of Haemulon plumierii from off the coast of Sisal, Yucatán. Ribosomal DNA sequences (small and large subunits) were used to test the phylogenetic position of the species of the genus Dollfusentis, whereas the mtDNA gene cox 1 was used for assessing species delimitation. The cox 1 analysis revealed an independent genetic lineage, which is recognized herein as a new species, Dollfusentis mayae n. sp. The new species is morphologically distinguished from the other six congeners by having a cylindrical proboscis armed with 22-25 longitudinal rows bearing 12 hooks each. The cystacanths were morphologically identified as Gorgorhynchus medius by having a cylindrical trunk covered with tiny irregular spines on the anterior region, and a cylindrical proboscis armed with 17-18 longitudinal rows of 21 hooks each; small and large subunit phylogenetic analyses yielded G. medius within the family Isthomosacanthidae, suggesting that Gorgorhynchus should be transferred to this family from Rhadinorhynchidae where it is currently allocated.

First molecular description of Neorhadinorhynchus nudus (Acanthocephala: Cavisomidae) from fish in the pacific coast of Vietnam, with notes on biogeography

Neorhadinorhynchus nudus (Harada, 1938) Yamaguti, 1939 (Cavisomidae) was morphologically described from the frigate tuna Auxis thazard (Lacépède) (Scombridae) in Nha Trang, Pacific south Vietnam. Females of N. nudus were fully described for the first time in the Pacific. Its original inadequate description as Rhadinorhynchus nudus (Harada, 1938) was corrected in material from Fiji Island, the Red Sea and Pacific Vietnam and errors in the text and line drawings of Harada were repeated in subsequent major publications where it underwent considerable nomenclature changes. New descriptive and biogeographical notes are included. We also provided here the molecular characterization of the nuclear gene (18S) and the mitochondrial cytochrome c oxidase subunit 1 (cox1) sequence data of N. nudus. Furthermore, to elucidate the phylogenetic relationship of N. nudus within the family Cavisomidae and with other isolates were performed incorporating nuclear (18S) and mitochondrial (cox1) sequence data using maximum likelihood (ML) and Bayesian inference (BI). The phylogenetic results showed that N. nudus has a relationship with other isolates of the same species and the median-joining network showed the pattern of haplotypes that reflected the structure of the populations.

Morphometric, histopathological and molecular findings of Macracanthorhynchus hirudinaceus infection in wild boar (Sus scrofa) from continental Italy

Although Macracanthorhynchus hirudinaceus is a neglected acanthocephalan of suids occasionally responsible for severe infections in humans, the spread of wild boar (Sus scrofa) populations in Europe could promote the circulation. Herein, we report the first morphometric, histological and molecular characterization of a severe M. hirudinaceus infection in a boar from continental Italy. The boar's intestine displayed granulomatous enteritis due to 24 helminths (14 females, 10 males), identified as adults of M. hirudinaceus by a combined morphometric/molecular approach. The phylogenetic analysis of the cox1 gene revealed a close relationship of the M. hirudinaceus sequence type found herein with those from Hungary and insular Italy. The high haplotype diversity and low nucleotide diversity of M. hirudinaceus specimens would suggest its rapid demographic expansion in the Mediterranean basin. More research is needed to assess the presence of M. hirudinaceus in susceptible beetle species and the role of boars in the epidemiology of infection.

Integrative taxonomy of Serrasentis gibsoni n. sp. (Acanthocephala: Isthmosacanthidae) from flatfishes in the Gulf of Mexico

The Isthmosacanthidae acanthocephalan species of the genus Serrasentis are parasites of marine teleosts and an elasmobranch. In this study, Serrasentis gibsoni n. sp. is described from the intestines of four flatfish species (Paralichthyidae), namely Ancyclopsetta quadrocellata, Cyclopsetta chittendeni, Syacium gunteri, and S. papillosum from 10 oceanic sites in the Gulf of Mexico (GoM). Twenty sequences of the 'barcoding' region of cytochrome C oxidase subunit I gene were obtained from 20 adults of Serrasentis gibsoni n. sp. Additionally, five sequences of the barcoding region were obtained from five adults of rhadinorhynchid Gorgorhynchus lepidus from C. chittendeni, S. papillosum and one species of Haemulidae, Haemulom aurolineatum, from five oceanic sites from the GoM. Two phylogenetic approaches were followed: Bayesian inference and maximum likelihood. In both phylogenetic reconstructions, the sequences of Serrasentis gibsoni n. sp. were recovered as a monophyletic group within the genus Serrasentis and placed as a sister group to G. lepidus. However, due to the lack of molecular data for species of the Isthmosacanthidae and Rhadinorhynchidea, these phylogenetic inferences must be taken with caution. Serrasentis gibsoni n. sp. is the first species of Serrasentis described from Paralichthyidae flatfish species from marine waters of the Americas and from the GoM. Based on the barcoding data set analyzed, Serrasentis gibsoni n. sp. appears to have high intraspecific genetic variation; thus, it is necessary to continue exploring the genetic diversity of this species to infer its intraspecific evolutionary patterns.

Chromosome analysis and the occurrence of B chromosomes in fish parasite Acanthocephalus anguillae (Palaeacanthocephala: Echinorhynchida)

The cytogenetics of Acanthocephala is a neglected area in the study of this group of endoparasites. Chromosome number and/or karyotypes are known for only 12 of the 1,270 described species, and molecular cytogenetic data are limited to rDNA mapping in two species. The standard karyological technique and mapping of 18S rRNA and H3 histone genes on the chromosomes of Acanthocephalus anguillae individuals from three populations, one of which originated from the unfavorable environmental conditions of the Zemplínska Šírava reservoir in eastern Slovakia, were applied for the first time. All specimens had 2n = 7/8 (male/female); n = 1m + 1m-sm + 1a + 1a (X). Fluorescence in situ hybridization (FISH) revealed three loci of 18S rDNA on two autosomes and dispersion of H3 histone genes on all autosomes and the X chromosome. In addition to the standard A chromosome set, 34% of specimens from Zemplínska Šírava possessed a small acrocentric B chromosome, which was always found to be univalent, with no pairing observed between the B chromosome and the A complement. The B chromosome had a small amount of heterochromatin in the centromeric and telomeric regions of the chromosomal arms and showed two clusters of H3 genes. It is well known that an environment permanently polluted with chemicals leads to an increased incidence of chromosomal rearrangements. As a possible scenario for the B chromosome origin, we propose chromosomal breaks due to the mutagenic effect of pollutants in the aquatic environment. The results are discussed in comparison with previous chromosome data from Echinorhynchida species.

Redescription of Illiosentis cetratus Van Cleave, 1945 (Acanthocephala: Illiosentidae) from Menticirrhus undulatus (Girard) in California, with notes on Illiosentis furcatus from Peru

Illiosentis Van Cleave et Lincicome, 1939 initially included two species: Illiosentis furcatus Van Cleave et Lincicome, 1939 found in the West Atlantic from Cape Cod in Massachusetts, USA to northern Argentina and Illiosentis cetratus Van Cleave, 1945 with restricted distribution in the Pacific coast of southern California. We are reporting I. furcatus from Peru for the first time and describe a population of I. cetratus from the California corbina, Menticirrhus undulatus (Girard), from southern California. The proboscis hook formula was 14 longitudinal rows for I. furcatus of 18-23 hooks each compared to 16 rows of 19-24 hooks each reported by Van Cleave (1945). We complete the inadequate description of I. cetratus with new information on sexual differentiation in the length of the trunk, dorsal vs. ventral hooks, hook roots, trunk spines, two types of anterior recurved rooted hooks vs. posterior rootless straight hooks, measurements of dorsal and ventral hooks and spines, shape of hook roots, terminal position of the female gonopore, and of position of the cephalic ganglion at the anterior margin of the trunk. We also include new details of the reproductive system in both sexes including Saefftigen's pouch and cement gland ducts. We present new SEM and light microscope images. The Energy Dispersive X-ray analysis (EDXA) shows a high level of sulfur in anterior, middle and posterior hooks in various hook sites, as well as spectra of hook tips with a higher relative concentration of sulfur compared to other hook sites. For the placement of I. cetratus, phylogenetic analysis of sequences of three molecular markers, 18S, 28S rRNA and mitochondrial cox 1 genes, was performed with other related available sequences. The resulting analysis illustrated that I. cetratus was nested within a separate clade along with species of two genera, Dentitruncus truttae Sinzar, 1955 and Neotegorhynchus cyprini Lisitsyna, Xi, Orosová, Barčák et Oros, 2022 represented our species of Illiosentis separate from species of Tegorhynchus Van Cleave, 1921 (as also according to the morphology) with which the Illiosentis species were previously synonymised.

Systematic position of the genus Metacanthocephalus Yamaguti, 1959 (Palaeacanthocephala: Echinorhynchida) inferred from molecular evidence, with a redescription of Metacanthocephalus ovicephalus (Zhukov, 1960)

The familial affiliation of the echinorhynchid palaeacanthocephalan genus Metacanthocephalus has been uncertain, with the three families Echinorhynchidae, Leptorhynchoididae, and Rhadinorhynchidae having been suggested as its parent taxon. In this study, adult individuals of Metacanthocephalus ovicephalus from the intestine of the cresthead flounder Pseudopleuronectes schrenki (new host) and the dark flounder Pseudopleuronectes obscurus in Hokkaido, Japan, were examined. Using three gene markers (mitochondrial cytochrome c oxidase subunit I; nuclear 18S and 28S rRNA genes) determined from two specimens of M. ovicephalus, a molecular phylogenetic analysis was performed along with relevant sequences available in public databases representing 26 species in eight families of the order Echinorhynchida, along with five species from Polymorphida and two from Eoacanthocephala. The resulting phylogram showed that M. ovicephalus was nested within a clade along with nine species in eight genera (Brentisentis yangtzensis, Dentitruncus truttae, Dollfusentis bravoae, Koronacantha mexicana, K. pectinaria, Leptorhynchoides thecatus, Neotegorhynchus cyprini, Pseudoleptorhynchoides lamothei, and Tegorhynchus [= Illiosentis] sp.). In this paper, we propose i) a set of morphological characters to circumscribe members represented by this clade as a Linnaean higher taxon, ii) to place this taxon at the rank of family, iii) to refer to it as Leptorhynchoididae, and iv) to regard Illiosentidae as a junior synonym of Leptorhynchoididae. Our morphological examination revealed a single vaginal sphincter in M. ovicephalus, a character that was not mentioned in any of the previous literature. By this character, along with geographical distribution and host fish, six congeners currently recognized in Metacanthocephalus can be divided into two groups.

The mitochondrial genome of Heterosentis pseudobagri (Wang & Zhang, 1987) Pichelin & Cribb, 1999 reveals novel aspects of tRNA genes evolution in Acanthocephala

BACKGROUND

Acanthocephala is a clade of obligate endoparasites whose mitochondrial genomes (mitogenomes) and evolution remain relatively poorly understood. Previous studies reported that atp8 is lacking from acanthocephalan mitogenomes, and that tRNA genes often have nonstandard structures. Heterosentis pseudobagri (Arhythmacanthidae) is an acanthocephalan fish endoparasite for which no molecular data are currently available, and biological information is unavailable in the English language. Furthermore, there are currently no mitogenomes available for Arhythmacanthidae.

METHODS

We sequenced its mitogenome and transcriptome, and conducted comparative mitogenomic analyses with almost all available acanthocephalan mitogenomes.

RESULTS

The mitogenome had all genes encoded on the same strand and unique gene order in the dataset. Among the 12 protein-coding genes, several genes were highly divergent and annotated with difficulty. Moreover, several tRNA genes could not be identified automatically, so we had to identify them manually via a detailed comparison with orthologues. As common in acanthocephalans, some tRNAs lacked either the TWC arm or the DHU arm, but in several cases, we annotated tRNA genes only on the basis of the conserved narrow central segment comprising the anticodon, while the flanking 5' and 3' ends did not exhibit any resemblance to orthologues and they could not be folded into a tRNA secondary structure. We corroborated that these are not sequencing artefacts by assembling the mitogenome from transcriptomic data. Although this phenomenon was not observed in previous studies, our comparative analyses revealed the existence of highly divergent tRNAs in multiple acanthocephalan lineages.

CONCLUSIONS

These findings indicate either that multiple tRNA genes are non-functional or that (some) tRNA genes in (some) acanthocephalans might undergo extensive posttranscriptional tRNA processing which restores them to more conventional structures. It is necessary to sequence mitogenomes from yet unrepresented lineages and further explore the unusual patterns of tRNA evolution in Acanthocephala.

Mitochondrial phylogenomics of Acanthocephala: nucleotide alignments produce long-branch attraction artefacts

BACKGROUND

Classification of the Acanthocephala, a clade of obligate endoparasites, remains unresolved because of insufficiently strong resolution of morphological characters and scarcity of molecular data with a sufficient resolution. Mitochondrial genomes may be a suitable candidate, but they are available for a small number of species and their suitability for the task has not been tested thoroughly.

METHODS

Herein, we sequenced the first mitogenome for the large family Rhadinorhynchidae: Micracanthorhynchina dakusuiensis. These are also the first molecular data generated for this entire genus. We conducted a series of phylogenetic analyses using concatenated nucleotides (NUC) and amino acids (AAs) of all 12 protein-coding genes, three different algorithms, and the entire available acanthocephalan mitogenomic dataset.

RESULTS

We found evidence for strong compositional heterogeneity in the dataset, and Micracanthorhynchina dakusuiensis exhibited a disproportionately long branch in all analyses. This caused a long-branch attraction artefact (LBA) of M. dakusuiensis resolved at the base of the Echinorhynchida clade when the NUC dataset was used in combination with standard phylogenetic algorithms, maximum likelihood (ML) and Bayesian inference (BI). Both the use of the AA dataset (BI-AAs and ML-AAs) and the CAT-GTR model designed for suppression of LBA (CAT-GTR-AAs and CAT-GTR-NUC) at least partially attenuated this LBA artefact. The results support Illiosentidae as the basal radiation of Echinorhynchida and Rhadinorhynchidae forming a clade with Echinorhynchidae and Pomporhynchidae. The questions of the monophyly of Rhadinorhynchidae and its sister lineage remain unresolved. The order Echinorhynchida was paraphyletic in all of our analyses.

CONCLUSIONS

Future studies should take care to attenuate compositional heterogeneity-driven LBA artefacts when applying mitogenomic data to resolve the phylogeny of Acanthocephala.

An Evaluation of the Genera Longicollum and Paralongicollum (Pomphorhynchidae: Acanthocephala) in Australia

PURPOSE

To confirm the identity of Longicollum edmondsi Golvan, 1969, Pomphorhynchidae Yamaguti, 1939, from Australia.

METHODS

All the relevant specimens registered in Australian museums were examined. Those held as permanent slide preparations were examined directly and those stored in 70% ethanol were examined as temporary wet mounts, after clearing in lactophenol, using an Olympus BH-2 microscope with differential interference optics. Measurements were made with an eyepiece micrometer and figures drawn using a drawing tube.

RESULTS

All the material registered as either Longicollum edmondsi or Paralongicollum sp. was determined to be Paralongicollum edmondsi (Golvan, 1969) comb. nov. based, amongst other characters, on the morphology of the neck.

DISCUSSION

The significance of known host species of P. edmondsi and their geographical distribution around the Australian coast was analysed. The geographical distribution of the genus Paralongicollum, Amin, Bauer & Siderov, 1991, across the Indo Pacific was compared to that of the acanthocephalan genus Sclerocollum Schmidt & Paperna, 1978.

Molecular characterisation and updated description of Neoechinorhynchus aldrichettae Edmonds, 1971 (Acanthocephala: Neoechinorhynchidae), based on material from Aldrichetta forsteri (Valenciennes) collected in Tasmania, Australia

We report on Neoechinorhynchus aldrichettae Edmonds, 1971 (Acanthocephala: Neoechinorhynchidae), obtained from yellow-eye mullet Aldrichetta forsteri (Valenciennes) (Mugiliformes: Mugilidae) from the Huon River, Tasmania, Australia. We provide new 18S and 28S rDNA gene sequence data for N. aldrichettae, assess its phylogenetic position relative to other species of Neoechinorhynchus and provide an updated morphological account of this species including detail of features omitted in the type-description, specifically of the apical organ, a collar at the base of the neck and a para-receptacle structure associated with the proboscis receptacle. We determine that eggs in this species are ovoid, without polar prolongations of fertilisation membrane, which permits assignment of N. aldrichettae to the subgenus Neoechinorhynchus. Our phylogenetic analyses place N. (N.) aldrichettae in a clade with other species of Neoechinorhynchus which parasitise mullets in marine and estuarine waters. We find that, in terms of monophyletic clades, the current subgeneric classification system for Neoechinorhynchus is not reflected in our phylogenetic analyses.

First molecular description of Macracanthorhynchus hirudinaceus in wild boars from Italy with pathomorphological and epidemiological insights

Macracanthorhynchus hirudinaceus is a zoonotic parasite affecting suids worldwide which are the definitive hosts for this helminth species. Macracanthorhynchus hirudinaceus is of significant economic and management concern due to its pathogenicity, causing intestinal obstruction and perforation in the definitive hosts. Current study is the preliminary investigation from Sardinia, Italy, reporting the pathomorphological findings and molecular characterization of M. hirudinaceus in the wild boars (Sus scrofa meridionalis). A total of 59 wild boars were examined showing acanthocephalan infection in 8 (13.6%) animals. In total, 49 parasites were collected with a mean intensity of 6.1. Comparatively higher infection levels were observed for males (16.7%) and young boars (14.3%); however, these epidemiological differences were statistically non-significant. Histopathological examination revealed the presence of a variable number of nodules (∼5 mm) in the intestine of M. hirudinaceus infested animals surrounded by a hyperemic-hemorrhagic halo. Several parasites were recovered from the intestinal lumen attached by the means of characteristic hooks showing necrosis in muscle layers. A moderate number of plump reactive fibroblasts and lesser numbers of fibrocytes were embedded with and at the borders of the inflammatory nodules in a moderate amount of homogeneous intensely eosinophilic fibrillary material rupturing the cell membrane. For molecular characterization, six isolated worms were amplified for the partial mitochondrial cox1 gene showing distinct interindividual variations. This first pathological and molecular description from southern Europe provided new knowledge about the diffusion of M. hirudinaceus in wild boars, furthering the research into the origin and transmission status of M. hirudinaceus in endemic localities.

The molecular profile of Acanthogyrus (Acanthosentis) kashmirensis from the Indian subcontinent

PURPOSE

The purpose of the present study was to provide molecular support for the validity of the morphological description of Acanthosentis kashmirensis Amin, Heckmann, Zargar, 2017 which was originally poorly described as Neoechinorhynchus kashmirensis Fotedar and Dar, 1977 from the Indian subcontinent, and to characterise its molecular identity and phylogenetic relationships.

METHODS

Total DNA was extracted, and the partial region of the small subunit (SSU) 18S rDNA and ITS-rDNA genes were amplified and sequenced. Genetic diversity was calculated and phylogenetic analysis of the nucleotide sequence data was performed.

RESULTS

In this study, the molecular profile of this acanthocephalan was generated for the first time. Based on the partial 18S rDNA, interspecific variation between A. kashmirensis with different species of Acanthosentis and were 3.6-10.3% and 22.4-38.2% based on 18S rDNA and ITS-rDNA genes, respectively. We described the phylogenetic relationships of A. kashmirensis compared with other species of the genus and also with members of the family Quadrigyridae.

CONCLUSIONS

The ITS-rDNA sequences of members of the family Quadrigyridae are more variable than 18S rDNA that can be useful for achieving a proper assessment of biodiversity. Sequence data generation from additional species of Acanthosentis will be needed to reconstruct the phylogenetic relationships of this group of acanthocephalans.

Characterization of Filisoma argusum n. sp. (Acanthocephala: Cavisomatidae Meyer, 1932) infecting the spotted scat, Scatophagus argus (Linnaeus, 1766) from the Indian coast

The present paper describes Filisoma argusum n. sp. (Cavisomatidae), an acanthocephalan parasite infecting the intestine of the spotted scat, Scatophagus argus (Linnaeus, 1766), in the south-west coast of India. The prevalence is 18% (mean intensity: 1.61 and abundance: 1-4 worms/host). Filisoma argusum n. sp. is morphologically characterized by a creamy-white, cylindrical, elongate, aspinose, and robust trunk; a collar-like neck; and a cylindrical proboscis with 18-20 longitudinal rows of hooks, with 19-22 hooks/row. Proboscis receptacle long, double-walled. Lemnisci digitiform, equal, longer than proboscis receptacle. Females 79.14 ± 33.69 × 0.593 ± 0.19 mm; males 32.62 ± 2.98 × 0.46 ± 0.071 mm. Males with four cement glands; bulbous muscular copulatory bursa with six digitiform rays. SEM studies revealed smooth hooks, sensory pits, and epidermal micropores. Histopathological changes at the site of parasite attachment included inflammation, hemorrhage, sloughing of epithelium, and detachment of mucosal layer of the intestine. In molecular and phylogenetic analyses, the parasite occupied an independent position within the Cavisomatidae clade with high bootstrap values for both ITS1-5.8S and ITS2, and mt-CO1 regions. Considering the morphologic and morphometric differences with previously described species of Filisoma along with its phylogenetic positioning, the present acanthocephalan is treated as a new species and the name Filisoma argusum n. sp. is proposed.

Gorgorhynchoides pseudocarangis n. sp. (Acanthocephala: Isthmosacanthidae) from Pseudocaranx dentex (Carangidae) in southeast Queensland, Australia, with comments on the Isthmosacanthidae

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

New perspectives on Aspersentis Megarhynchus (Acanthocephala: Heteracanthocephalidae) from Notothenia Coriiceps Richardson (Nototheniidae) in the West Antarctic, with emended generic diagnosis

A number of variable descriptive accounts of Aspersentis megarhynchus (von Linstow, 1892) Golvan, 1960 have been reported from specimens collected from many species of fish in various locations off Antarctic islands. We have described a new population from Notothenia coriiceps Richardson (Nototheniidae) off Galindez Island, West Antarctica, and features not previously reported, resolved the taxonomic controversies and nomenclature, and emended and updated the generic diagnosis taking into account the newly observed structures. These are depicted in microscopic images and include the outer spiral wall of the proboscis receptacle, the thicker dorsal wall of the receptacle compared to the ventral wall, parts of the female reproductive system, the separate cement gland ducts, the dorsal position of the male gonopore and more detail of proboscis hooks and trunk spines. It is surprising that the newly observed features were missed from the many descriptions of A. megarhynchus created since the original description. The variability in A. megarhynchus is noted with a comparison of the morphometrics of our specimens vs. those in six other descriptions. We also analysed the metal composition of hooks and spines using energy-dispersive X-ray analysis and concluded a molecular characterization of the species based on 18S DNA gene, with related phylogenetic analyses.

First steps to understand the systematics of Echinorhynchidae Cobbold, 1876 (Acanthocephala), inferred through nuclear gene sequences

Acanthocephalans of the order Echinorhynchida are one of the most diverse groups in their phylum, with approximately 470 species classified into 11 families that largely consist of parasites of freshwater, brackish and marine fishes and, sporadically, reptiles and amphibians distributed worldwide. Previous phylogenies inferred with molecular data have supported the paraphyly or polyphyly of some families, suggesting that most of them have been diagnosed based on unique combinations of characters, rather than shared derivative features. We expand the taxonomic sampling of several genera such as Acanthocephalus, Echinorhynchus and Pseudoacanthocephalus of Echinorhynchidae from diverse biogeographical zones in the Americas, Europe and Asia with the aim of testing the monophyly of the family by using two molecular markers. Sequences from small (SSU) and large (LSU) subunits of ribosomal DNA were obtained for six species representing the genera Acanthocephalus and Echinorhynchus from the Neotropical, Nearctic, Palearctic and Oriental regions. These sequences were aligned with other sequences available in the GenBank dataset from Echinorhynchidae. Phylogenetic trees inferred with the combined (SSU + LSU) and the individual data sets consistently placed the genera Acanthocephalus, Pseudoacanthocephalus and Echinorhynchus into three independent lineages. Two families, Paracanthocephalidae Golvan, 1960, and Pseudoacanthocephalidae Petrochenko, 1956, were resurrected to accommodate the genera Acanthocephalus and Pseudoacanthocephalus, respectively. The species of the genus Acanthocephalus from the Nearctic, Palearctic and Oriental biogeographic regions formed a clade that was well supported. However, Acanthocephalus amini from the Neotropical region was nested inside Arhythmacanthidae. Therefore, the genus Calakmulrhynchus was created to accommodate A. amini and resolve the paraphyly of Acanthocephalus. Finally, the diagnoses of the families Echinorhynchidae and Arhythmacanthidae were amended. The molecular phylogenies should be used as a taxonomic framework to find shared derived characters (synapomorphies) and build a more robust classification scheme that reflects the evolutionary history of the acanthocephalans.

Profilicollis chasmagnathi (Acanthocephala) parasitizing freshwater fishes: paratenicity and an exception to the phylogenetic conservatism of the genus?

Polymorphid acanthocephalans are parasites of marine mammals, waterfowl and ichthyophagous birds. Among these, the genus Profilicollis is known to use exclusively decapods as intermediate hosts. Here, we report the first record of living cystacanths of Profilicollis parasitizing the body cavity of a fish host, Oligosarcus jenynsii, inhabiting the freshwater section of an estuarial system, Mar Chiquita coastal lagoon, in south-east Buenos Aires Province, Argentina. In this environment, cystacanths of Profilicollis chasmagnathi have been previously recorded infecting decapod crabs and as transient accidental infections in the gut of some carcinophagous fishes. In the present study, larvae from the crab Neohelice granulata, from the intestine of the estuarine fish Odontesthes argentinensis and from the body cavity of O. jenynsii were morphologically and genetically compared, confirming their identity as P. chasmagnathi, a species characteristic of estuaries and marine coasts along Argentina, Uruguay and Chile. These findings can be interpreted as a possible case of incipient paratenicity for Profilicollis, and a colonization event of freshwater habitats, probably promoted by the highly variable conditions, typical of ecotonal environments. In addition, cystacanths of the genus Polymorphus were also found in O. jenynsii, representing the first record of this genus in Oligosarcus from Argentina.