The dominant helminths infecting spiny mice (Acomys dimidiatus) in the montane wadis of the Sinai Peninsula of Egypt are spirurid nematodes, notably Protospirura muricola and Mastophorus muris. Both are relatively large robust stomach worms that accumulate in hosts resulting in high worm burdens. To ascertain whether the presence of spirurid worms or their burdens alters the host's likelihood of infection with other helminth species, we analysed a database containing quantitative data on helminth parasites of these mice (n = 431). This comprised of worm burdens recorded during 4 surveys, conducted at 4-year intervals, in 4 wadis, during late summer of each year. The presence of spirurid worms did not significantly alter species richness with other helminth species nor the likelihood of mice carrying other nematode species. However, there was a significant association, particularly of P. muricola, with the presence of intestinal stages of cestodes, and with the acanthocephalan Moniliformis acomysi. After controlling for intrinsic and extrinsic factors, mice harbouring spirurid worms had greater worm burdens of other helminths compared with mice without spirurids. Moreover, spirurid worm burdens showed a significant positive covariation with similarly adjusted species richness of other helminths, non-spirurid helminths, non-spirurid nematodes, oxyuroid nematodes and intestinal stage cestode worm burdens. We interpret these results as an indication that the key driver for co-occurrence of spirurids with other helminths is likely to be transmission via common arthropod hosts (for cestodes and acanthocephalans), but also that mice carrying the heavier spirurid worm burdens become more susceptible to directly transmitted nematodes such as the Oxyuroidea.

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.

A new species of Moniliformis, M. tupaia n. sp. is described using integrated morphological methods (light and scanning electron microscopy) and molecular techniques (sequencing and analysing the nuclear 18S, ITS, 28S regions and mitochondrial cox1 and cox2 genes), based on specimens collected from the intestine of the northern tree shrew Tupaia belangeri chinensis Anderson (Scandentia: Tupaiidae) in China. Phylogenetic analyses show that M. tupaia n. sp. is a sister to M. moniliformis in the genus Moniliformis, and also challenge the systematic status of Nephridiacanthus major. Moniliformis tupaia n. sp. represents the third Moniliformis species reported from China.

Acanthocephalans constitute a small taxonomic group related to rotifers and specialized in a parasitic lifestyle. Anurans act as paratenic and definitive hosts and infections always occur trophically. Our objective is to describe and summarize the richness of acanthocephalans in Neotropical anurans. We conducted a literature review in the main research databases, compiling data published until August 2021. We identified 66 articles with records of acanthocephalan-anuran association, 53.03% were carried out in Brazil. We detected 108 species of anurans from 11 families parasitized by acanthocephalans. With the exception of Bufonidae, Hylidae and Leptodactylidae, which are relatively well-studied families, interaction with acanthocephalans remains largely unexplored for most anuran species. We found six families of acanthocephalans: Centrorhynchidae, Echinorhynchidae, Oligacanthorhynchidae, Cavisomidae, Neoechinorhynchidae and Plagiorhynchidae. Centrorhynchidae and Echinorhynchidae presented the largest number of taxa associated with anurans. The largest number of records corresponded to acanthocephalans in the larval stage (cystacanths), for which anurans act as paratenic hosts. We observed a lack of specific taxonomic resolution in the identifications of most reports, because a large part of the records in the larval stage make morphological identification difficult. Brazil, Mexico, Paraguay, Argentina, Ecuador and Peru are the countries with the most records, while Costa Rica, Venezuela, Colombia, Chile and Uruguay exhibited the lowest publication numbers, resulting in gaps in the distribution of acanthocephalans. We expanded the known number of anuran species parasitized by acanthocephalans, compared to the last published review. Overall, we aim to contribute to the understanding of diversity within this intriguing but understudied group.

Of the total 47 species in the subgenus Acanthosentis, 43 have been reported from the freshwater fishes of Asia. Amin et al. (2017) provided a key to the 23 species of the genus Acanthogyrus reported from the Indian subcontinent. The present study reports two new species: Acanthogyrus bispinosa n. sp. and A. garciai n. sp. from Cirrhinus mrigala Hamilton and Labeo calbasu Hamilton, respectively, and two previously described species: A. golvani Gupta and Jain, 1980 and A. hereterospinus Khan and Bilqees, 1990 from L. rohita Hamilton and L. catla Hamilton, respectively. A. bispinosa n. sp. comprises 3 circles of 6 proboscis hooks each. Trunk spines in A. bispinosa n. sp are divided into two groups: anterior and posterior separated by unarmed region, which has not been previously reported in the subgenus. Anterior spines are present in 7–8 and 7–10 circles in females and males, respectively, whereas posterior spines are in 23–28 and 31–38 circles in males and females, respectively. A. garciai n. sp. comprises 3 circles of 6–8 hooks each and a single set of trunk spines is present in A. garciai n. sp., comprising 35–42 and 25–45 circles in males and females, respectively. All four species were also characterised based on the 18S, 28S, and ITS1-5.8S-ITS2 rRNA molecular markers. The Bayesian inference tree generated based on these markers showed distinct identities of all the species, with a significant molecular divergence, ranging from 3.2 to 53.6%.

The phylum Acanthocephala is an important group of parasites with more than 1,300 species parasitizing intestine of all major vertebrate groups. However, our present knowledge of the mitochondrial genomes of Acanthocephala remains very limited. In the present study, we sequenced and annotated the complete mitochondrial genome of Acanthogyrus (Acanthosentis) bilaspurensis (Gyracanthocephala: Quadrigyridae) for the first time based on the specimens recovered from the intestine of common carp Cyprinus carpio Linnaeus (Cyprinidae) in Pakistan. The mitochondrial genome of A. bilaspurensis is 13,360 bp in size and contains 36 genes, representing the smallest mitogenome of acanthocephalans reported so far. The mitogenome of A. bilaspurensis also has the lowest level of overall A+T contents (59.3%) in the mitogenomes of Eoacanthocephala, and the non-coding region 3 (NCR3) lies between trnS2 and trnI, which is different from all of the other acanthocephalan species. Phylogenetic analyses based on concatenating the amino acid sequences of 12 protein-coding genes using maximum likelihood (ML) and Bayesian inference (BI) methods revealed that the family Pseudoacanthocephalidae is a sister to the Arhythmacanthidae rather than the Cavisomatidae, and the families Rhadinorhynchidae and Cavisomatidae showed sister relationships.

Acanthocephalans of the order Polymorphida mainly parasitic in birds and mammals, are of veterinary, medical and economic importance. However, the evolutionary relationships of its 3 families (Centrorhynchidae, Polymorphidae and Plagiorhynchidae) remain under debate. Additionally, some species of Polymorphida (i.e. Bolbosoma spp. and Corynosoma spp.) are recognized as zoonotic parasites, associated with human acanthocephaliasis, but the mitochondrial genomes for representatives of Bolbosoma and Corynosoma have not been reported so far. In the present study, the complete mitochondrial genomes B. nipponicum and C. villosum (Acanthocephala: Polymorphidae) are reported for the first time, which are 14 296 and 14 241 bp in length, respectively, and both contain 36 genes [including 12 PCGs, 22 tRNA genes and 2 rRNA genes] and 2 non-coding regions (NCR1 and NCR2). The gene arrangement of some tRNAs in the mitogenomes of B. nipponicum and C. villosum differs from that found in all other acanthocephalans, except Polymorphus minutus. Phylogenetic results based on concatenated amino acid (AA) sequences of the 12 protein-coding genes (PCGs) strongly supported that the family Polymorphidae is a sister to the Centrorhynchidae rather than the Plagiorhynchidae, and also confirmed the sister relationship of the genera Bolbosoma and Corynosoma in the Polymorphidae based on the mitogenomic data for the first time. Our present findings further clarified the phylogenetic relationships of the 3 families Plagiorhynchidae, Centrorhynchidae and Polymorphidae, enriched the mitogenome data of the phylum Acanthocephala (especially the order Polymorphida), and provided the resource of genetic data for diagnosing these 2 pathogenic parasites of human acanthocephaliasis.

In the present study, we sought to determine whether i) a waterfowl signal induces avoidance behaviour of the amphipod Hyalella patagonica, ii) infection by the acanthocephalan Pseudocorynosoma enrietti affects the behaviour of the amphipod, and iii) the parasite interferes with the amphipod response to waterfowl. We evaluated amphipod behaviour experimentally by measuring activity levels, phototaxis, geotaxis, and clinging behaviour. The main findings of this study indicate that uninfected amphipods show avoidance behaviour by reducing their activity in the presence of a predator signal. Secondly, infected amphipods show altered behaviour, such as swimming in bright areas near the water surface, which makes them more visible to predators in nature. Lastly, the presence of predatory cues causes infected amphipods to drop to the bottom, which increases their visibility to predators. The present research allows us to perceive the intricate interplay among predators, parasites, and their intermediate hosts and advance our understanding of these complex ecological dynamics.

Previous descriptions of Corynosoma bullosum (Linstow, 1892) show that specimens vary greatly in the proportions of different body structures, measurements of females and males, number of rows of hooks, and egg measurements, among other features. We redescribe this species from specimens found in southern elephant seal faeces from King George Island. We also provide a molecular characterization, in addition to 5.8S and internal transcribed spacer (ITS) existing sequences. We examined 41 elephant seals, and 30 adult acanthocephalans were found in 15 of them. The specimens were identified as belonging to the genus Corynosoma due to each having a tubular body with an inflated anterior part forming a thorny disk and the posterior part bearing somatic spines on the ventral surface, and genital spines surrounding the genital pore. Individual morphology corresponded to C. bullosum: large size, marked sexual dimorphism, and proboscis with 16–18 rows of spines with 11–15 spines per row. The molecular profile of three specimens of C. bullosum was analysed using 18S rDNA. We inferred phylogenetic relationships of the family Polymorphidae using maximum likelihood and Bayesian inference. We provide an updated morphological redescription for C. bullosum including electron microscopy photographs and molecular data. The 18S gene sequences showed low genetic variation and supported that C. bullosum is a sister to Corynosoma australe.

Fully developed, sexually mature small male and female acanthocephalans, Microsentis wardae Martin & Multani, 1966 (Neoechinorhynchidae) reaching only 2.25 mm and 2.42 mm, respectively, were collected from the rectum of longjaw mudsuckers, Gillichthys mirabilis Cooper, in the salty marches of Anaheim Bay and San Diego Bay, California. Our specimens were half the size of those reported in the original description from the same host in Scammon's Lagoon over 700 km to the south. The ratio of proboscis and receptacle size to trunk size was markedly higher in our specimens compared to the larger specimens measured in the original description. The anatomy of all structures in our specimens from Anaheim Bay was comparable to that of the larger Scammon's Lagoon specimens that have apparently realized more growth in the Scammon's Lagoon. We have observed more structures that are not reported in the original description, especially evident from our scanning electron microscopy images, which are not possible to observe in the original line drawings. In our specimens, the micropores were unusually widely spaced and the energy dispersive X-ray analysis showed longitudinal hook sections with high levels of sulphur and phosphorus and moderate levels of calcium, but the whole hooks showed highest levels of sodium and magnesium – the biochemical hook signature of this species. Sequences of the small subunit (18S) of the nuclear ribosomal DNA were generated and compared with acanthocephalan sequences available from GenBank. As M. wardae comprises a monotypic genus, therefore, phylogenetic analyses inferred from the 18S gene showed its relationship with other species of closely related genera of Eoacanthocephala. This is the first report of molecular data of M. wardae.

The egg is one of the fundamental parts of the life cycle of Neoechinorhynchus buttnerae, and this stage involves the acanthor larva. It is also the infection phase for the intermediate host. Under normal conditions, the larva inside the egg can survive for months in the environment; however, information regarding this phase of life of the parasite is scarce. In addition, there is no quantitative information about the structural composition of the parasite's body from a histological point of view. Such information is essential in order to support decisions aimed at controlling infestations by these parasites in fish farming. This study aimed to present a detailed description of the stages of embryonic development of N. buttnerae eggs, as well as a stereological evaluation of the body of adult females of the parasite. Three phases of development characterized the eggs: cell division (with four stages), formation of the internal nuclear mass (with four stages) and formation of the acanthor larva (with five stages). The ovary comprised 26.61% of the volume of the animal and most of it contained eggs (21.28%), ovarian balls (3.88%) and empty spaces (1.45%). These results are of great importance and will support future studies that seek to interrupt the life cycle of this parasite.

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.

A total of 61 specimens representing five species of shag – Auckland Island shag Leucocarbo colensoi, little pied shag Microcarbo melanoleucos brevirostris, black shag Phalacrocorax carbo novaehollandiae, Otago shag Leucocarbo chalconotus and spotted shag Phalacrocorax punctatus – from the coast around Otago, South Island, New Zealand, were examined for helminths. A total of 18 helminth species was found: six nematodes (Anisakis pegreffi, Contracaecum rudolphii E, Baruscapillaria sp., Cosmocephalus jaenschi, Ingliseria cirrohamata, Desmidocercella australis), four trematodes (Apatemon sp. ‘jamiesoni’, Cardiocephaloides ovicorpus, Apophallus sp., Microphallidae gen. sp.), four cestodes (Microsomacanthus cormoranti, Microsomacanthus sp., Paradilepis urceina, Tetrabothrius sp.) and four acanthocephalans (Andracantha leucocarboi, A. sigma, Corynosoma hannae, Profilicollis novaezelandensis). Descriptions are provided for females of C. jaenschi and D. australis, which were previously undescribed. The data include 20 new host records and seven new locality records. New 18S ribosomal DNA and internal transcribed spacer (ITS1 and ITS2) DNA sequences have been provided where specimen conditions permitted. These data add considerably to our sparse knowledge of helminths in New Zealand shags, and provide a baseline for observations of change in the future.

Pallisentis (Pallisentis) nandai Sarkar, 1953 is a freshwater fish parasite restricted to the Indian subcontinent in the Ganga River and its tributaries. It was described from the leaffish, Nandus nandus (Hamilton) from the Ganga River delta at Calcutta. We recovered variant specimens from the same host species from the Ganga near its headwaters at Bijnor about 1500 km away. Our specimens were clearly identifiable as P. nandai but varied considerably from those in the original description, especially in the size of proboscis hooks, receptacle and lemnisci. The original description was incomplete (missing line drawings of female trunk and reproductive system, male trunk, complete proboscis, hooks and hook roots) and inaccurate (proboscis, hooks, receptacle wall), and some measurements were lumped together for both sexes. We provide a complete description and include new morphological information including the first description of para-receptacle structure in the genus Pallisentis Van Cleave, 1928, scanning electron microscopy and microscope images, molecular analysis, and energy dispersive X-ray analysis (EDXA) of hooks and spines of our specimens for the first time. Additional details of proboscis hook roots, trunk spines, micropores and micropore distribution are described. The unique metal composition of hooks (EDXA) demonstrated a considerably high but variable level of sulphur and negligible level of calcium in collar and trunk spines and hook tips, but a higher level of sulphur and calcium at the hook basal arch than at the hook tip and edge. A comparison with the EDXA pattern of another species of Pallisentis, P. İndica Mital & Lal, 1976, were considerably different. The phylogenetic position of P. nandai within Eoacanthocephala was generated to assess the molecular characterization based on 18S and ITS1-5.8S-ITS2 ribosomal DNA sequences. Maximum likelihood and Bayesian inference analyses placed P. nandai in a clade with other Pallisentis species under the family Quadrigyridae. This is the first report based on molecular evidence for P. nandai.

Centrorhynchus globocaudatus (Zeder, 1800) Lühe, 1911 (Centrorhynchidae) was reported in birds of prey. Our population from Falco tinnunculus Linnaeus (Falconidae) and Buteo buteo Linnaeus (Accipitridae) in northern Italy was morphologically distinct from others described elsewhere. The worms are elongate and cylindrical. Proboscis long, apically truncated and bare, with wider base and variably faint constriction at point of attachment of receptacle. Large anterior hooks well rooted; posterior spiniform hooks with reduced roots; transitional hooks with scutiform roots in-between. Four tubular cement glands extend into prominent ducts overlapping a large Saefftigen's pouch. Bursa large, with sensory plates. Vagina with laterally slit orifice in sub-ventral pit of globular terminal extension. Thick-shelled eggs ovoid without polar prolongation of fertilization membrane. In our specimens, proboscis hooks, receptacle, male reproductive system, and lemnisci especially in males varied in size from those from Ukraine, India, Egypt, Kyrgystan, Russia, Georgia, Armenia and Asian Soviet Republics. Our description of the Italian specimens includes new morphological information supported by scanning electron microscopy and microscope images, molecular analysis and energy dispersive X-ray analysis (EDXA) of hooks. Additional new details of proboscis hook roots, micropores and micropore distribution are described. Metal composition of hooks (EDXA) demonstrated high levels of calcium and phosphorous, and high levels of sulphur in core and cortical layers of eggs. The molecular profile based on sequences of 18S and cytochrome c oxidase 1 genes is also provided, as well as phylogenetic reconstructions including all available sequences of the family Centrorhynchidae, although further sequences are needed in order to clarify their phylogenetic relationships.

Wild and domestic populations of waterfowl garner economic benefits, as they are hunted for human consumption or as a recreational activity. Waterfowl migrate to their wintering grounds in Mexican wetlands where habitat conditions are more favourable. In this study, we present a list of helminth species sampled from the gastrointestinal tract of 59 wild birds belonging to the family Anatidae in three localities of Mexico, and a checklist of the helminth parasite fauna of the members of the family in the whole country, built from literature records. After helminthological examination, 25 taxa were identified: eight trematodes; four cestodes; 12 nematodes; and one acanthocephalan. Obtained records dated from 1943 to 2019. Our literature search yielded 563 records corresponding to 95 parasite taxa: 38 trematodes, 24 cestodes, 23 nematodes and ten acanthocephalans. In Mexico, 17 anatid species have been studied for helminths. Records correspond to 55 locations from 20 Mexican states. An insight gained from the collated literature and recent records was that trematodes represent the most diverse parasite group in anatids in Mexico. We briefly discuss that the information about helminths parasitizing waterfowl will be useful for understanding the effect of habitat loss and pollution of wetlands where migratory birds spend the breeding season, for addressing ecological programs aimed to guarantee the health and conservation of North American migratory birds or the effect of bird migration in the composition of the helminth parasite communities, and for freshwater biologists interested in the understanding of freshwater ecosystem health.

Pseudocorynosoma constrictum (Van Cleave, 1918) is a polymorphid acanthocephalan that attaches to the digestive tract of waterfowl to complete its life cycle, causing severe histological damage to its definitive avian hosts. In the present study, we present a histopathological analysis of the lesions that P. constrictum induced in the layers of the ileum of the blue-winged teal Anas discors. The results revealed that worms insert the attachment structures into the inner gut muscular layer, which causes substantial swelling, haemorrhaging and necrosis in the tissue near the parasite's proboscis. We also observed that the number of parasites attached to the tissue can obstruct the intestinal lumen; in the most serious case, we observed more than 30 parasites penetrating completely the walls of the bird intestine.

Our present genetic data of Acanthocephala, especially the mitochondrial (mt) genomes, remains very limited. In the present study, the nearly complete mt genome sequences of Sphaerirostris lanceoides (Petrochenko, 1949) was sequenced and determined for the first time based on specimens collected from the Indian pond heron Ardeola grayii (Sykes) (Ciconiiformes: Ardeidae) in Pakistan. The mt genome of S. lanceoides is 13 478 bp in size and contains 36 genes, including 12 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs) and two ribosomal RNA genes (rRNAs). Moreover, in order to clarify the phylogenetic relationship of the genera Centrorhynchus and Sphaerirostris, and to test the systematic position of S. lanceoides in the Centrorhynchidae, the phylogenetic analyses were performed using Bayesian inference and maximum likelihood methods, based on concatenated nucleotide sequences of 12 PCGs, rRNAs and tRNAs. The phylogenetic results further confirmed the monophyly of the order Polymorphida and the paraphyly of the order Echinorhynchida in the class Palaeacanthocephala. Our results also challenged the validity of the genus Sphaerirostris (Polymorphida: Centrorhynchidae) and showed a sister relationship between S. lanceoides and S. picae (Rudolphi, 1819).

Helminthological studies may contribute with valuable information on host biology and conservation. Herein, we provide new data on helminths infecting the lizard Norops fuscoauratus, testing one of the factors considered most important in parasitic ecology: host size. We analysed 25 specimens of N. fuscoauratus from three highland marshes in the Brazilian semi-arid. Eight taxa of helminths belonging to Nematoda, Trematoda and Acanthocephala were found. Physaloptera sp. showed the higher prevalence (40%), with a mean intensity of infection of 3.3 ± 1.46 (1–16) and mean abundance 1.32 ± 0.65 (0–16). Norops fuscoauratus represents four new host records for the helminths Cyrtosomum sp., Pharyngodon travassosi, Strongyloides sp. and Centrorhynchus sp. There is no relationship of host body size (P = 0.79) and mass (P = 0.50) with parasite richness. In addition, the present study contributes to the knowledge of the parasitic fauna of N. fuscoauratus and the Neotropical region.

A new species of Moniliformis Travassos, 1915 (Acanthocephala: Moniliformidae) is described from the hairy-tailed bolo mouse, Necromys lasiurus Lund, 1840 (Cricetidae: Sigmondontinae), captured in the Brazilian Cerrado, in Uberlândia, state of Minas Gerais, Brazil. The specimens were studied by light and scanning electron microscopy. Molecular phylogenies were inferred from partial nuclear large subunit ribosomal RNA gene sequences and partial mitochondrial cytochrome c oxidase subunit I gene. The new species is distinguished from other moniliformid species by the number of rows and number of hooks per row, size of the proboscis, size of the eggs, host species and geographical distribution. Molecular phylogenies and genetic distances analyses demonstrated that Moniliformis necromysi sp. n. forms a well-supported monophyletic group with sequences of other species of Moniliformis and is distinguished from them, which agrees with the morphological characteristics, allocating the new species to this genus and to the family Moniliformidae Van Cleave, 1924. This is the first moniliformid acanthocephalan described from a wild rodent in Brazil.