How host ecology influences the parasite communities of three Australian flathead fishes, Platycephalus spp. (Scorpaeniformes: Platycephalidae).

This study investigated the role of host traits, habitat, and sampling season on the prevalence and intensity of parasites in three species of platycephalid fishes. Three host species sampled were dusky flathead (Platycephalus fuscus, n = 3), blue-spotted flathead (Platycephalus caeruleopunctatus, n = 38), and tiger flathead (Platycephalus richardsoni, n = 59). A total of 14 metazoan parasite species were collected over 15 months, between July 2020 and September 2021. The parasites found included a chondracanthid copepod, adult hemiuroidean trematodes, cestode plerocercoids, larval and adult acanthocephalans, larval and adult nematodes, and an unknown species of helminth. General linear models were used to assess the relationship between host traits and sampling season with parasite infection intensity. The infection intensity of an unidentified plerocercoid species in P. caeruleopunctatus was found to be significantly associated with both sampling season and the interaction of host mass with sex. In P. richardsoni the infection intensity of the acanthocephalan, Corynosoma sp. was found to correlate with sampling season. The highest richness of parasite taxa was recorded from P. richardsoni, which may be due to the wide depth range of P. richardsoni, coupled with its generalist diet.

Use of stable isotope ratio analysis to investigate the biology and clinical significance of seal parasites.

Stranded seals are often infected with a broad range of parasites, although whether they are the cause of significant morbidity or an incidental finding is usually unclear. In this study we used stable isotope ratio analysis, a method frequently used to investigate food webs, to explore the extent to which common seal parasites feed directly on host tissue and fluids or absorb host-derived metabolites, which in turn may give an indication of their potential impact on the host's health. The trophic discrimination factor Δ15N for the nasal mite, Halarachne halichoeri, was mostly positive, ranging between −0.015 and 3.2‰ (n = 6), while for the Acanthocephalan worm, Corynosoma strumosum and the anisakid nematode, Pseudoterranova decipiens, Δ15N ranged between −4.2 and −2.0‰ (n = 7), and between −6.7 and −0.8‰ (n = 5) respectively. In the case of the lungworm, Otostrongylus circumlitus, Δ15N measured between −5.6 and 0‰ for worms collected in the stomach (n = 5), between −1.1 and 0.2‰ for worms collected from the heart (n = 3), between −0.7 and 1.9‰ for worms situated in the lungs (n = 4). Based on Δ15N, parasites could be clearly divided into those that were on a higher trophic level than their host suggesting a predator­prey-like relationship, and those that were not. It is hypothesized that Δ15N may be indicative of the clinical significance of parasite­host associations.

Organization of the Nuclei in the Tegument of Some Palaeacanthocephala and Archiacanthocephala.

The giant tegument nuclei of the acanthocephalans of the classes Archiacanthocephala and Palaeacanthocephala are fragmented at the final stage of cystacanthus formation in the intermediate host, but remain connected with each other during later life. It can be assumed that the fragments of each giant tegument nucleus are united with each other to form an independent network that ensures the vital activity of the tegument, the volume of which increases many times during the period of intensive growth of the parasite in the definitive host.

Characterization of the complete mitochondrial genomes of the zoonotic parasites Bolbosoma nipponicum and Corynosoma villosum (Acanthocephala: Polymorphida) and the molecular phylogeny of the order Polymorphida.

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.

The elevation of a unique population of Corynosoma strumosum (Acanthocephala: Polymorphidae) from the Caspian seal, Pusa caspica, in the Caspian Sea to Corynosoma neostrumosum n. sp.

An isolated population of 700 specimens initially described as Corynosoma strumosum (Rudolphi, 1802) Lühe, 1904 and currently reassigned to Corynosoma neostrumosum n. sp. was collected from one young male Caspian seal, Pusa caspica (Gmelin) in the southern land-locked Caspian Sea in April 2009. Collected worms were morphologically unique compared with those reported by other observers in open waters, especially in shape and distribution of proboscis hooks and trunk spines, dorso-ventral differences in proboscis hooks and their organization, the baldness of anterior proboscis, consistently smaller size of trunk and testes, larger eggs, the rough egg topography, epidermal micropores, and variations in the female gonopore. Molecular data from the internal transcribed spacer region of rDNA and the mitochondrial cox1 gene was also provided to supplement the morphological study of the new species.

The prevalence of Corynosoma parasite worms in the great cormorants and the Baltic herring in the northern Baltic Sea, Finland.

During 2014-2019, the prevalence of Corynosoma spp., a parasite species in great cormorants (Phalacrocorax carbo spp.) and in Baltic herring (Clupea harengus membras), was studied in the Archipelago and the Bothnian Seas of the northern Baltic Sea. These results suggest that cormorants may act as a definitive host for these acanthocephalan parasites. Adults were more infected with the parasites than juveniles, which could be due to their larger size. A lower prevalence of Corynosoma spp. in juveniles may be because smaller cormorants eat smaller fish that have less parasites. We found that the most abundant corynosoma species in both the Baltic herring and cormorants were Corynosoma semerme, whereas only a few individuals of C. strumosum and only one C. magdaleni were found. The prevalence of corynosoma in herring increased from 2014 to 2018, and individuals in the Bothnian Sea were infected less frequently than herring in the Archipelago Sea. Results also showed that infected herring individuals were generally larger than non-infected individuals, which could be explained by their size and their feeding habits. Currently, the changing environment of the Baltic Sea may cause an effect on the herring making them more susceptible to infections. Our results, therefore, emphasize the importance of the regular monitoring of infections and the parasite-host relationships in the Baltic Sea.

Revision of Corynosoma australe Johnston, 1937 (Acanthocephala: Polymorphidae) from a North American population using novel SEM images, Energy Dispersive X-ray Analysis, and molecular analysis.

We describe a population of the acanthocephalan Corynosoma australe Johnston, 1937 (Polymorphidae) from a California sea lion Zalophus californianus (Lesson, 1828) in California using novel scanning electron microscopy (SEM) images, Energy Dispersive x-ray analysis (EDXA), and molecular analysis for the first time. The taxonomic history of C. australe is replete with accounts using only line drawings some of which proved erroneous. The distribution of ventral spines on the female trunk has been the primary distinction between C. australe and Corynosoma obtuscens Lincicome, 1943, its junior synonym; being continuous in the latter but discontinuous posteriorly in the former species. The distribution of ventral spines is invariably discontinuous in males. Our redescription and SEM images help to resolve this issue further validating the synonymy. Morphological variability has been documented between our California population and others from various host species in California, South Australia, South Shetlands, and the Argentinian coast. Our SEM images document features not previously detectable in line drawings, erroneously reported or missed in previous accounts. The EDXA spectra show high levels of calcium and phosphorous and low levels of sulfur characteristic of C. australe. EDXA for other species of Corynosoma Lühe, 1904 provide support for the diagnostic distinction of C. australe. EDXA spectra were shown to be species specific and have diagnostic value in the taxonomy of the Acanthocephala. Our molecular analysis used amplification of 18S of ribosomal DNA and cytochrome c oxidase 1 (Cox1) gene. Phylogenetic analyses for Cox1 gene revealed a close relationship between Corynosoma hannae Zdzitowiecki, 1984 and C. australe. The phylogenetic trees confirmed that the isolates belonged to C. australe. The haplotype network inferred by Cox1 with C. australe sequences revealed that haplotypes clearly separated from each other and formed clusters related to samples from the Northern Hemisphere (the USA and Mexico), and the second from the Southern Hemisphere (Argentina, Brazil and Peru).

New perspectives on morphological and genetic variability of Corynosoma bullosum [Linstow, 1892] parasitizing southern elephant seals from the Antarctic Peninsula.

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.

Using DNA barcoding to link cystacanths and adults of the acanthocephalan Corynosoma australe of the Southeastern Pacific Ocean (off Peru coast).

The objective of this study is to use DNA barcoding to link cystacanths and adults belonging to the acanthocephalans Corynosoma australe found in the Southeastern Pacific Ocean off the coast central from Peru. We sampled three species of commercial fish (Paralichthys adspersus (Steindachner), Paralabrax humeralis (Valenciennes), and Cheilodactylus variegatus (Valenciennes)) and two South American sea lions, Otaria byronia, stranded on the beaches of the city of Huacho and Barranca, Lima province. A total of 509 acanthocephalan larvae were found in the body cavity of 95 fish (prevalence 54.28%, total mean intensity 8.64). A total of 127 adult worms were found in the large intestine from two South American sea lions (P= 100%, MI= 63.5). A total of 203 larvae from P. humeralis were isolates (P=65.71%; MI= 8.83; MA=5.8), 235 (P=54.29%; MI= 12.37; MA= 6.71) from C. variegatus, and 71 (P=42.86%; MI= 4.73; MA= 2.03) from P. adspersus. All adult and larval specimens were morphologically identified as C. australe. They were generated cytochrome c oxidase subunit 1 (cox1) gene sequences of specimens and were compared with available data from GenBank. Molecular phylogenetic analysis supported our morphological identification, where the Peruvian isolates formed a clade with other isolates of C. australe from other countries of the American continent. Of the sequences obtained, two haplotypes were detected and were not identical with previous reports. Based on both DNA barcoding and morphological analyses, our finding represents the first molecular data of C. australe from Peru and the report of Cheilodactylus variegatus as a new paratenic host on the central coast, extending the knowledge and distribution range of this acanthocephalan in Southeastern Pacific Ocean.

Genetic diversity and phylogeography of Corynosoma australe Johnston, 1937 (Acanthocephala: Polymorphidae), an endoparasite of otariids from the Americas in the northern and southern hemispheres.

Adult specimens of Corynosoma australe Johnston, 1937 were recorded from the intestines of California sea lions, Zalophus californianus (Lesson), from Baja California Peninsula, Mexico, whereas larval forms were collected from two fish species on the Argentinian coast. Adult specimens of C. australe were morphologically characterized by having a cylindrical proboscis with 18-20 rows of 12-14 hooks per row and a cylindrical trunk expanded anteriorly into a disk with tiny, triangular spines spreading almost to three quarters of the hind-trunk in males and to the posterior body end in females. The aim of this study was to explore the genetic diversity and systematic position of C. australe distributed in the Americas. Newly generated sequences of the mitochondrial cytochrome c oxidase subunit 1 (cox 1) gene were compared with sequences available from GenBank. Phylogenetic analyses performed with the cox 1 dataset using maximum likelihood and Bayesian inference showed that the 11 new sequences of C. australe recovered from the California sea lion in northern Mexico plus the six sequences from Argentinian seashores formed a clade with other sequences of specimens previously identified as C. australe. The intraspecific genetic divergence among the isolates was very low, ranging from 1 to 1.7%, and in combination with the phylogenetic trees confirmed that the isolates belonged to the same species. The cox 1 haplotype network inferred with 27 sequences revealed 18 haplotypes divided into two clusters clearly separated from each other by 5 substitutions. The first cluster corresponded to specimens from the Northern Hemisphere (United States of America and Mexico), and the second corresponded to specimens from the Southern Hemisphere (Argentina and Brazil). The current evidence suggests that C. australe has an amphitemperate distribution and is associated mainly with otariids with secondary and independent colonization events to other mammals and the Magellanic penguin in the Southern Hemisphere.

Habitat selection and populations of Corynosoma (Acanthocephala) in the intestines of sea otters (Enhydra lutris) and seals.

Acanthocephalans are common intestinal parasites of marine mammals, the most widespread of which is the genus Corynosoma. In this study, parasite infrapopulations of two closely related species of Corynosoma were examined: Corynosoma enhydri from sea otters (Enhydra lutris) in Alaska (n = 12) and California (n = 19), and Corynosoma strumosum from seals in Germany (n = 22). Prevalence of C. enhydri was 100% in Californian otters, with a mean abundance of 30, and 83% in Alaskan otters, with a mean abundance of 232. In seals, C. strumosum had a prevalence of 65%, with a mean abundance of 33. Female C. enhydri dominated both Californian (82%) and Alaskan (79%) infections, while, in seals, female C. strumosum made up 68% of the parasite population. Reproduction rates for C. enhydri, with 16% (California) and 18% (Alaska) of females mated, were low compared to C. strumosum in seals, of which 40% of females were mated. Habitat selection also differed significantly between the two species. Corynosoma enhydri was found most frequently in the second and third fifths of the small intestine, while C. strumosum was found most frequently in the fourth. The differences in habitat selection and prevalence analysed in this study may be related to a trade-off between growth and reproduction between the two species.

Host records and geographical distribution of Corynosoma magdaleni, C. semerme and C. strumosum (Acanthocephala: Polymorphidae).

A literature survey was conducted to investigate the host and geographical distribution patterns of three Corynosoma species (Acanthocephala: Polymorphidae), viz. C. magdaleni, C. semerme and C. strumosum. All three species appear to be restricted to the Northern Hemisphere. Occurrence records of C. magdaleni are limited to the Northern Atlantic coasts, while C. semerme has a circumpolar distribution. The geographical range of Corynosoma strumosum encompasses the distributions of the other two species, but also extends into warmer southern regions. Some Corynosoma populations are living with their definitive hosts in very isolated locations, such as in the brackish Baltic Sea or different freshwater lakes (e.g. Lake Saimaa). All three species have a heteroxenous life cycle, comprising a peracaridan intermediate host, a fish paratenic host and a mammalian definitive host. Occasionally, an acanthocephalan may enter an accidental host, from which it is unable to complete its life cycle. The host records reported here are categorised by type, i.e. intermediate, paratenic, definitive or accidental. While most of the definitive hosts are shared amongst the three Corynosoma species, C. strumosum showed the broadest range of paratenic hosts, which reflects its more extensive geographical distribution. One aim of this study and extensive literature summary is to guide future sampling efforts and therewith contribute to throw more light on the on-going species and morphotype discussion for this interesting parasite species.

Pathological findings in North Sea and Baltic grey seal and harbour seal intestines associated with acanthocephalan infections.

Grey seals Halichoerus grypus and harbour seals Phoca vitulina are common seal species in the North and Baltic seas and final hosts of Corynosoma acanthocephalans. C. strumosum and C. magdaleni infect the small intestines of both seal species. In contrast to harbour seals, Baltic grey seals in the past have regularly displayed severe C. semerme infections in the caecum and colon, with associated tunica muscularis hypertrophy, inflammation and ulcerations as part of the Baltic seal disease complex (BSDC). Pathogenesis and correlation of acanthocephalan infections with these lesions are still unknown. This study describes the intestinal pathology and parasitic distribution in each seal species. Grey seal (n = 83) and harbour seal (n = 1156) intestines of all age groups and sexes, collected in Poland, Germany and Estonia from 1998 to 2017, were investigated. Most harbour seals came from the North Sea, whereas grey seals were predominantly derived from the Baltic Sea. Both species featured mild to moderate small intestinal infections. Grey seals showed colonic infections not found in harbour seals and featured a chronic erosive to ulcerative, eosinophilic or lympho-plasmacytic colitis with tunica muscularis hypertrophy, indicating still prevailing clinical signs of the BSDC. Harbour seals displayed granulomatous, eosinophilic, lympho-plasmacytic or catarrhal enteritis. The prevalence of acanthocephalan infections in harbour seals increased from 2012 onwards. Furthermore, significant associations between acanthocephalan infection and the presence of intestinal inflammation were found for both seal species. This study suggests that the level of acanthocephalan infection and associated lesions are suitable seal population health indicators, with the colon being a specific target organ for Baltic grey seal health monitoring.

Morphological and molecular identification of Corynosoma caspicum, and its histopathological effect on the intestinal tissue of a Caspian seal (Pusa caspica).

BACKGROUND: Corynosoma is a parasite from the Acanthocephala phylum with worldwide distribution. Corynosoma parasites are found in pinnipeds as their definitive host. AIMS: This study aimed to investigate the morphological and molecular characteristics of Corynosoma, and its histopathological effect on the intestinal tissue of Pusa caspica. METHODS: A severe Corynosoma infection was observed in the small intestine of a juvenile male Caspian seal (P. caspica). The morphological descriptions were done using light microscopy, and scanning electron microscopy (SEM). The molecular diagnosis was performed using partial sequences of internal transcribed spacer 1 (ITS1) and 5.8S ribosomal RNA (rRNA) gene. RESULTS: According to the results, the Corynosoma specimens were identified as Corynosoma caspicum. The histopathological inspection of intestinal tissue revealed lesions in epithelial cells, mucosa, submucosa and muscle layers, destruction of intestinal glands, and infiltration of inflammatory cells. CONCLUSION: Presence of such a severe infection in one of the individual Caspian seals can suggest the possibility of morbidity among other seals in the landlocked Caspian Sea. Thus, further research on their parasite infections is required for understating the status of the Caspian seal population and conserving this endangered species.

Distribution patterns of two species of Corynosoma (Acanthocephala: Polymorphidae) in fishes from Southwestern Atlantic.

Corynosoma australe and C. cetaceum are the most frequently reported acanthocephalans in fish from the Argentine Sea, particularly in central and northern areas. Their definitive hosts are otariids and odontocete cetaceans, respectively. The low specificity of these larvae, in combination with high infective capability and long survival periods in fish, make them potentially good biological markers for stocks and other biological features of their fish hosts. In order to determine the distribution patterns of these species and their determining factors, a large dataset composed by newly collected fish samples, published and unpublished data from previous studies by the authors in the region were analysed in relation to host and environmental variables. The complete dataset comprised a total of 5084 fish, belonging to 29 species distributed in 21 families and 9 orders. Host size and trophic habits arose as the main determinants of abundance for both species of Corynosoma, showing higher abundances on larger fish and on higher trophic levels, as it is usual for trophically transmitted parasites. Biogeographic province and depth (indirectly representing the temperature of water) were the main drivers of the spatial distribution, displaying a latitudinal pattern associated to the temperature clines created by the interaction of Malvinas and Brazil currents, determining a decrease in abundance southwards and towards the deeper areas. No patterns were found regarding the distribution of definitive hosts. The knowledge of these distribution patterns of Corynosoma spp. in fish at regional scale, as well as of their causes, provides useful information to design management and conservation policies thus contributing to maintain the full and sustainable productivity of fisheries.

Infection status of commercial fish with cystacanth larvae of the genus Corynosoma (Acanthocephala: Polymorphidae) in Hokkaido, Japan.

Acanthocephalans of the genus Corynosoma are known as intestinal parasites, mainly of pinnipeds. Human corynosomiasis has been reported as an infrequent foodborne disease in Hokkaido, the northernmost island of Japan. Potential sources of the human infection are marine fish, because they are paratenic hosts of these parasites. In this study, the prevalence and intensity of larval Corynosoma in commercial fish from 17 fishing ports of Hokkaido were examined from April 2016 to January 2019. Out of a total of 1217 fish examined, 122 (10.0%) were infected with cystacanth larvae. The infected fish assemblage was composed of 7 families and 13 species from all the coastal seas of Hokkaido (the Pacific Ocean, Okhotsk Sea, and Japan Sea), showing that commercial fish can be source of human infection when eaten raw. Flatfish of the family Pleuronectidae showed the highest intensity of cystacanths, ranging from 1 to 56. A DNA barcoding system was developed in this study, based on the standard mitochondrial cox1 sequences of morphologically identified adults of Corynosoma spp. from pinnipeds in Hokkaido. By using the DNA barcoding, most of the fish-derived cystacanths were identified as either C. strumosum or C. villosum, and furthermore, a clinical isolate from human as C. villosum. Both of the species were commonly detected from various fish of Hokkaido, irrespective of the coastal seas. Flatfish frequently harbored C. villosum. Considering the wide range of commercial fish in Hokkaido and the advanced transportation system of fresh fish, there is a possibility that human corynosomiasis will occur everywhere in Japan.

Transmission of Corynosoma australe (Acanthocephala: Polymorphidae) from fishes to South American sea lions Otaria flavescens in Patagonia, Argentina.

Acanthocephalans display a two-host life cycle that involves arthropods as intermediate hosts and vertebrates as definitive hosts. Some species also use paratenic hosts to bridge the trophic gap between both obligatory hosts. However, the relative role of these paratenic hosts in the transmission to definitive hosts has seldom been assessed quantitatively. We report on infection patterns of cystacanths of Corynosoma australe Johnston, 1937 in 20 common teleost species and the Argentine shortfin squid Illex argentinus (Castellanos) from the Patagonian shelf of Argentina. We also explore the role of different fish species in the transmission of C. australe to the most important definitive host in the area, i.e. the South American sea lion Otaria flavescens Shaw. Cystacanths of C. australe were found in all host species except Heliconus lahillei Norman, Merluccius hubbsi Marini and I. argentinus. In eight fish species, the prevalence of C. australe was > 50% and mean intensity > 4, i.e. Acanthistius patachonicus (Jenyns), Nemadactylus bergi (Norman), Paralichthys isosceles Jordan, Percophis brasiliensis Quoy & Gaimard, Prionotus nudigula Ginsburg, Scomber colias Gmelin, Raneya brasiliensis (Kaup) and Xystreurys rasile (Jordan). Two surveys on the trophic ecology of South American sea lions in the study area consistently found a generalist diet dominated by M. hubbsi, and data on the frequency of occurrence and number of other fish and cephalopod species in stomach contents strongly suggest that only R. brasiliensis may play a prominent role in the transmission of C. australe. This result raises interesting questions on the costs of paratenicity.

Morphology, performance and attachment function in Corynosoma spp. (Acanthocephala).

BACKGROUND: Functional inference on the attachment of acanthocephalans has generally been drawn directly from morphology. However, performance of structures is often non-intuitive and context-dependent, thus performance analysis should be included whenever possible to improve functional interpretation. In acanthocephalans, performance analysis of attachment is available only for Acanthocephalus ranae, a species that solely relies on the proboscis to attach. Here we compare body morphology and muscle arrangement in 13 species of Corynosoma, which use their spiny body as a fundamental holdfast. A basic performance analysis using live cystacanths of two representative species is also provided. METHODS: Adults of 13 Corynosoma spp. were obtained from 11 marine mammal species. Specimens were cut and carefully cleaned to examine muscle arrangement through light and scanning electron microscopy. Live cystacanths of C. australe and C. cetaceum were selected for performance analysis. Video records of evagination-invagination cycles of the proboscis were obtained and analysed with a video editor. RESULTS: The basic arrangement of proboscis retractors, trunk circular and longitudinal muscles, neck retractors and receptacle retractors, was conserved in all Corynosoma species. Interspecific variability was found in the relative development of disk muscles: minimum in C. enhydri, maximum in C. cetaceum; the distal insertion of the ventral neck retractor: ventro-lateral in C. cetaceum, C. hamannni and C. pseudohamanni and ventral in the other species; and the distal insertion of the receptacle retractors: more proximal in species with a longer hindtrunk. Performance analysis indicated striking similarities to that described for A. ranae except that (i) the foretrunk bends ventrally during the evagination-invagination cycles of the proboscis; (ii) disk muscles can flatten the tip of the foretrunk regardless of these cycles; and (iii) the receptacle bends ventrally and is driven to the hindtrunk by coordinated action of receptacle retractors. CONCLUSIONS: Species of Corynosoma are able to use up to six holfast mechanisms. Attachment relies on a similar performance to that described for A. ranae. However, structural ventral bending of an inflated, spiny foretrunk, with a parallel re-arrangement of foretrunk muscles, have generated unexpected novel functions that make attachment extremely effective in species of Corynosoma. Interspecific variability in trunk shape and muscle arrangement grossly correlates with the rheological conditions each species experiences in their microhabitats within the gut of marine mammals.

Preliminary report of occurrence of Corynosoma spp. (Acanthocephala: Polymorphidae) in Southern Caspian sprat (Clupeonella grimmi).

In recent years, there has been a steady decline in the populations of clupeid fish in the Caspian Sea which has been attributed to factors such as overfishing and introduced invasive species of jellyfish. Very little is known about the diseases and possible health impacts of infectious agents such as parasites on the population of these important fish in the Caspian Sea. The aim of this study was to determine if infection with parasites can have adverse impacts on fish health and population. Sixty fish were collected, measured for weight and length, aged, and then examined for presence of Acanthocephala. Ages were recorded, as well as length and weight data for each age category and the number of acanthocephalan parasites. The internal organs, including the liver, ovary, and testis, were subjected to histopathological examination. Ninety percent of fish were found to be infected with acanthocephalan parasites, identified as Corynosoma strumosum. Fish data including the number of parasites, age, length, and weight showed that there was no significant difference in length and weight between different age groups, e.g., between 2 and 6 years old, suggesting that those fish may not grow fully as they age. There were several granuloma of different sizes in the liver and gonads, indicating the occurrence of a chronic inflammation. It is known that large numbers of granuloma may disturb the normal function of the liver and gonads and if associated with long term infection this may cause sterility, affecting the population numbers. Further research, with targeted aims, is needed to understand the impact of infection with acanthocephala on this fish and to determine the causative agents of the histopathological changes observed in the present study.

Ecotoxicoparasitology of the gastrointestinal tracts of pinnipeds: the effect of parasites on the potential bioavailability of total mercury (THg).

Acanthocephalans, cestodes, and some species of nematodes acquire nutrients from the lumen contents in the gastrointestinal (GI) tract of their definitive host. These parasites are exposed to toxicants, such as mercury (Hg), through passive or active feeding mechanisms; therefore, the focus of this study was to determine if there is an effect of parasites on the dietary availability of total mercury (THg) within piscivorous pinniped hosts. THg concentrations ([THg]) in selected host tissues, parasites, and GI lumen contents from 22 California sea lions (Zalophus californianus), 15 ringed seals (Phoca hispida), and 4 spotted seals (Phoca largha) were determined. Among all pinnipeds, [THg] in acanthocephalans of the large intestine were significantly higher than concentrations in other samples (host lumen contents, other parasites and host intestinal wall), irrespective of location within the host GI tract. δ15N values of parasites depended both on parasite group and location within the GI tract. δ15N values were consistently higher in parasites inhabiting the large intestine, compared to elsewhere in the GI tract, for both sea lions and seals. δ13C values in parasites did not differ significantly from host GI tissues. Based on both [THg] and stable isotope values, parasites are likely affecting the Hg bioavailability within the GI lumen contents and host tissues, and toxicant-parasite interactions appear to depend on both parasitic taxon as well as their location within the host intestine.