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

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.

ADULT THORNY-HEADED WORM (ACANTHOCEPHALA) PARASITES OF NORTH AMERICAN HERPETOFAUNA: CHECKLIST OF SPECIES AND IDENTIFICATION KEY TO FAMILIES AND GENERA

An updated checklist of adult thorny-headed worms (Acanthocephala) that parasitize wild North American amphibians and reptiles is presented: A total of 21 species grouped in 4 genera, 4 families, 2 orders, and 2 classes are registered; these infect a total of 19 species of reptiles and 17 species of amphibians in the region. An illustrated identification key for the families and genera listed is proposed.

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.

Acanthocephalans of marine and freshwater fishes from Taiwan with description of a new species

During an ichthyoparasitological survey in 2017-2019, six species of acanthocephalans were found among Taiwan's freshwater (Cypriniformes: Xenocyprididae, Cyprinidae) and marine fishes (Scombriformes: Scombridae, Trichiuridae; Anabantiformes: Channidae; Carangaria/misc: Latidae): Micracanthorhynchina dakusuiensis (Harada, 1938), Rhadinorhynchus laterospinosus Amin, Heckmann et Ha, 2011, Pallisentis rexus Wongkham et Whitfield, 1999, Longicollum sp., Bolbosoma vasculosum (Rudolphi, 1819), and one new species, Micracanthorynchina brevelemniscus sp. n. All species are morphologically characterised and illustrated using light and scanning electron microscopy. The finding of R. laterospinosus, P. rexus and B. vasculosum is the first record for these species in Taiwan. Micracanthorhynchina brevelemniscus is similar to Micracanthorhynchina motomurai (Harada, 1935) and M. dakusuiensis in proboscis armature but differs from M. motomurai by larger eggs (53-59 × 15-16 µm vs 40 × 16 µm) and by the number of cement glands (6 vs 4) and from M. dakusuiensis by shorter body length (2.2-2.9 mm vs 4.0 mm in males and 2.9-4.1 mm vs 7.6 mm in females), by the location of the organs of the male reproductive system (from level of the posterior third of the proboscis receptacle in M. brevelemniscus vs in the posterior half of the trunk in M. dakusuiensis), and by length of lemnisci (lemnisci shorter than the proboscis receptacle vs lemnisci longer than the proboscis receptacle). Phylogenetic analyses of almost complete 18S rRNA gene revealed paraphyly of the family Rhadinorhynchidae suggested in previous studies. Micracanthorhynchina dakusuiensis and M. brevelemniscus formed a strongly supported cluster, which formed the earliest diverging branch to the rest of the rhadinorhynchids and transvenids.

Morphological and molecular characterization of a new species of the genus Echinorhynchus Zoega in Müller, 1776 (Acanthocephala: Echinorhynchidae) parasitizing the rock greenling Hexagrammos lagocephalus (Pallas) (Scorpaeniformes: Hexagrammidae) from eastern Hokkaido, Japan

A new species of marine-fish-parasitizing echinorhynchid palaeacanthocephalan, Echinorhynchus sasakiae sp. nov., is described based on material from the intestine of the rock greenling Hexagrammos lagocephalus (Pallas) obtained in two localities (Akkeshi and Nemuro) in Hokkaido, northern Japan. Echinorhynchus sasakiae sp. nov. can be distinguished from other congeners by having an oval-shaped proboscis covered with hooks arranged in 14-15 rows, each consisting of 7-10 hooks that are anteriorly short and curved, but posteriorly long and weakly curved. The phylogenetic position of Echinorhynchus sasakiae sp. nov. is inferred based on three gene markers (cytochrome c oxidase subunit I, 18S rRNA, and 28S rRNA) along with relevant sequences from ten congeners available in public databases. Echinorhynchus sasakiae sp. nov. represents the 54th member of the genus and the ninth marine congener known from Japan.

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.