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The structure of the parasitic infracommunity of Pellona flavipinnis, a carnivorous fish species of economic and ecological importance in the Amazon region, was characterized. Fifty-five P. flavipinnis specimens were collected in Catalão lake, euthanized, and necropsied for metazoan parasite examination. Of these, 41 P. flavipinnis specimens were parasitized. A total of 249 metazoans from five taxonomic groups were identified: Myxozoa (Myxobolus sp.) in the gills and operculum; Digenea, (Austrodiplostomum compactum) in the eyes; Acanthocephala (Neoechinorhynchus (Neoechinorhynchus) pellonis) in the intestine; Nematoda (Anisakis sp.) in the liver, stomach, and intestine and Branchiura (Argulus angelae) on the tegument. Pellona flavipinnis is reported here as a new host for all five parasite species. Anisakis sp. showed the highest prevalence value, followed by N. (N.) pellonis. The parasitic community was dominated by Anisakis sp., which exhibited the greatest importance index. Pellona flavipinnis parasitic fauna comprised one secondary species and four satellite species. No significant relationship was found between parasite abundance or richness and host body size.

Digenea Carus, 1863 represent a highly diverse group of parasitic platyhelminths that infect all major vertebrate groups as definitive hosts. Morphology is the cornerstone of digenean systematics, but molecular markers have been instrumental in searching for a stable classification system of the subclass and in establishing more accurate species limits. The first comprehensive molecular phylogenetic tree of Digenea published in 2003 used two nuclear rRNA genes (ssrDNA = 18S rDNA and lsrDNA = 28S rDNA) and was based on 163 taxa representing 77 nominal families, resulting in a widely accepted phylogenetic classification. The genetic library for the 28S rRNA gene has increased steadily over the last 15 years because this marker possesses a strong phylogenetic signal to resolve sister-group relationships among species and to infer phylogenetic relationships at higher levels of the taxonomic hierarchy. Here, we have updated the database of 18S and 28S rRNA genes until December 2017, we have added newly generated 28S rDNA sequences and we have reassessed phylogenetic relationships to test the current higher-level classification of digeneans (at the subordinal and subfamilial levels). The new dataset consisted of 1077 digenean taxa allocated to 106 nominal families for 28S and 419 taxa in 98 families for 18S. Overall, the results were consistent with previous higher-level classification schemes, and most superfamilies and suborders were recovered as monophyletic assemblages. With the advancement of next-generation sequencing (NGS) technologies, new phylogenetic hypotheses from complete mitochondrial genomes have been proposed, although their power to resolve deep levels of trees remains controversial. Since data from NGS methods are replacing other widely used markers for phylogenetic analyses, it is timely to reassess the phylogenetic relationships of digeneans with conventional nuclear rRNA genes, and to use the new analysis to test the performance of genomic information gathered from NGS, e.g. mitogenomes, to infer higher-level relationships of this group of parasitic platyhelminths.

Contributing to the knowledge of digenetic trematodes in northern Australia, this study uses both morphological and molecular analysis to augment the taxonomic descriptions of existing digenean trematodes from the black-spotted croaker, Protonibea diacanthus (Lacepède, 1802) (Teleostei: Sciaenidae) from waters off northern Australia. Using a combination of morphological and molecular techniques, Orientodiploproctodaeum diacanthi Bhutta and Khan, 1970 (Digenea: Cryptogonimidae) and Pleorchis sciaenae Yamaguti, 1938 (Digenea: Acanthocolpidae) are compared with closely related specimens representing new geographical records of these species, and contributing the first phylogenetic analysis of both digenean species. Both O. diacanthi and P. sciaenae were genetically distinct from other reported specimens of the respective families Cryptogonimidae and Acanthocolpidae, based on phylogenetic results and the supporting morphological descriptions from past publications. Despite the conclusive findings in this study, the species presented in the phylogenetic analyses lack sequences across a range of genes, leading to difficulties in deciphering the phylogenetic and evolutionary relationships of many species and highlighting the need for future research to improve species-level identification of parasites in Australian waters.

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.

In the present study, we aim to provide an inventory of digenetic trematodes (Platyhelminthes, Trematoda, Digenea) from Georgia including records from the freshwater, marine and terrestrial realms. The checklist is based on a critical review of data from 109 papers, 11 monographs and four Ph.D. theses published between 1935 and 2019 and our new records. The checklist includes information on synonymy, the host species, site of infection, geographical distribution and bibliographical references. The present data will serve as a baseline for further studies on trematodes from Georgia focused on integrative taxonomy, life-cycle elucidation, parasite ecology and epidemiology. We compiled data on the digenean trematode fauna of Georgia, which is represented by 186 species (of these 173 identified to species level) belonging to 108 genera, 47 families and 17 superfamilies. This is the first checklist of the digeneans of Georgia. The majority of digenean species were recorded as adults (160 species), only a small fraction being found as cercariae (33 species) or metacercariae (24 species), in their first or second intermediate hosts, respectively. Predominantly, records of trematodes (62 species) from birds were found, followed by those parasitising fish (50 species, i.e. 32 species as adults and 18 as metacercariae), mammals (33 species) and amphibians (25 species, i.e. 23 species as adults and 2 as metacercariae), with the least number of species reported from reptiles (12 species, i.e. 9 species as adults and 3 as metacercariae). Adult digeneans recorded together with another life-cycle stage (metacercariae and/or cercariae) comprised 28 species, i.e. for 15% of the total trematode species number, a part of their life-cycle is known.

Hypostomus commersoni is a freshwater fish, native to the Paraná River basin, which plays an important role in trophic networks of this system. This study aimed at analyzing the structure of the endohelminth community of H. commersoni from two shallow lagoons in the municipality of Santa Fe, Argentina. In the 51 hosts analyzed, 2103 helminths were found. Hosts from Belgrano Park lagoon were infested with Genarchella genarchella, Saccocoelioides nanii, Raphidascaris (Sprentascaris) sp., and Gorytocephalus elongorchi. Hosts from the Western Urban Nature Reserve lagoon were infested with Thometrema magnifica, Procamallanus (Procamallanus) annipetterae, Raphidascaris (Sprentascaris) sp., Gorytocephalus elongorchi, and Proteocephalidae spp. In both host populations, the prevalence of some parasites was high, and species richness and diversity of component communities were low. The distribution pattern of helminth was aggregated in all cases. No correlation was found between the length of the host and the richness and abundance of endoparasites. The total number of parasites and the specific richness per host in both lagoons did not differ significantly. The findings on G. genarchella, P. (P.) annipetterae, G. elongorchi, and Proteocephalidae spp. were the first records in his host

Background Genetic markers like the nuclear ribosomal RNA (rRNA) genes, internal transcribed spacer regions, mitochondrial protein-coding genes, and genomes have been utilized for molecular identification of parasitic trematodes. However, challenges such as the design of broadly applicable primers for the vast number of species within Digenea and the genetic markers’ ability to provide sufficient species-level resolution limited their utility. This study presented novel and broadly applicable primers using the mitochondrial 12S and 16S rRNA genes for Digenea and aimed to show their suitability as alternative genetic markers for molecular identification of orders Plagiorchiida, Echinostomida, and Strigeida. Results Our results revealed that the mitochondrial 12S and 16S rRNA genes are suitable for trematode molecular identification, with sufficient resolution to discriminate closely related species and achieve accurate species identification through phylogenetic placements. Moreover, the robustness of our newly designed primers to amplify medically important parasitic trematodes encompassing three orders was demonstrated through successful amplification. The convenience and applicability of the newly designed primers and adequate genetic variation of the mitochondrial rRNA genes can be useful as complementary markers for trematode molecular-based studies. Conclusions We demonstrated that the mitochondrial rRNA genes could be alternative genetic markers robust for trematode molecular identification and potentially helpful for DNA barcoding where our primers can be widely applied across the major Digenea orders. Furthermore, the potential of the mitochondrial rRNA genes for molecular systematics can be explored, enhancing their appeal for trematode molecular-based studies. The novelty of utilizing the mitochondrial rRNA genes and the designed primers in this study can potentially open avenues for species identification, discovery, and systematics in the future.

Parasite studies can provide insights into important aspects of host ecology, which can be particularly important for species of conservation concern. This research focused on the parasite diversity of two sea turtle species —the loggerhead Caretta caretta and the leatherback Dermochelys coriacea — in the temperate South West Atlantic, a region and species relatively understudied. Over a 15-year period (2008–2023), 30 sea turtles were sampled from the northern coast of Argentina. Through morphological and molecular tools, we identified five parasite species (the digeneans Pyelosomum renicapite and Pleurogonius longiusculus , the nematodes Kathlania leptura and Sulcascaris sulcata and the leech Ozobranchus margoi ) in loggerheads and two digeneans ( P. renicapite and Orchidasma amphiorchis ) in leatherbacks. All the species constitute the first report of the parasite in Argentina, and O. amphiorchis represents a new host-parasite association for leatherbacks. Comparative biogeographic analysis using the Regional Management Unit (RMU) framework suggested that parasites could reveal connectivity between RMUs, although there are several information gaps. An increasing number of parasite studies can help understand sea turtle feeding ecology, ontogenetic shifts and health status and thus enhance conservation strategies for sea turtles globally.

Geographical distribution plays a major role in our understanding of marine biodiversity. Some marine fish trematodes have been shown to have highly restricted geographical distributions, while some are known to occur over very wide ranges; however, very few of these wide distributions have been demonstrated genetically. Here, we analyse species of the genus Schikhobalotrema (Haplosplanchnidae) parasitizing beloniforms from the tropical west Pacific, the eastern Pacific and the Gulf of Mexico (GoM). We test the boundaries of these trematodes by integrating molecular and morphological data, host association, habitat of the hosts and geographical distribution, following a recently proposed and standardized delineation method for the recognition of marine trematode species. Based on the new collections, Schikhobalotrema huffmani is here synonymized with the type-species of the genus, Schikhobalotrema acutum; Sch. acutum is now considered to be widely distributed, from the GoM to the western Pacific. Additionally, we describe a new species, Schikhobalotrema minutum n. sp., from Strongylura notata and Strongylura marina (Belonidae) from La Carbonera coastal lagoon, northern Yucatán, GoM. We briefly discuss the role of host association and historical biogeography of the hosts as drivers of species diversification of Schikhobalotrema infecting beloniforms.