Manipulative neuroparasites: uncovering the intricacies of neurological host control.

Manipulative neuroparasites are a fascinating group of organisms that possess the ability to hijack the nervous systems of their hosts, manipulating their behavior in order to enhance their own survival and reproductive success. This review provides an overview of the different strategies employed by manipulative neuroparasites, ranging from viruses to parasitic worms and fungi. By examining specific examples, such as Toxoplasma gondii, Leucochloridium paradoxum, and Ophiocordyceps unilateralis, we highlight the complex mechanisms employed by these parasites to manipulate their hosts' behavior. We explore the mechanisms through which these parasites alter the neural processes and behavior of their hosts, including the modulation of neurotransmitters, hormonal pathways, and neural circuits. This review focuses less on the diseases that neuroparasites induce and more on the process of their neurological manipulation. We also investigate the fundamental mechanisms of host manipulation in the developing field of neuroparasitology, which blends neuroscience and parasitology. Finally, understanding the complex interaction between manipulative neuroparasites and their hosts may help us to better understand the fundamentals of behavior, neurology, and host-parasite relationships.

Effects of first intermediate host density, host size and salinity on trematode infections in mussels of the south-western Baltic Sea.

Trematode prevalence and abundance in hosts are known to be affected by biotic drivers as well as by abiotic drivers. In this study, we used the unique salinity gradient found in the south-western Baltic Sea to: (i) investigate patterns of trematode infections in the first intermediate host, the periwinkle Littorina littorea and in the downstream host, the mussel Mytilus edulis, along a regional salinity gradient (from 13 to 22) and (ii) evaluate the effects of first intermediate host (periwinkle) density, host size and salinity on trematode infections in mussels. Two species dominated the trematode community, Renicola roscovita and Himasthla elongata. Salinity, mussel size and density of infected periwinkles were significantly correlated with R. roscovita, and salinity and density correlated with H. elongata abundance. These results suggest that salinity, first intermediate host density and host size play an important role in determining infection levels in mussels, with salinity being the main major driver. Under expected global change scenarios, the predicted freshening of the Baltic Sea might lead to reduced trematode transmission, which may be further enhanced by a potential decrease in periwinkle density and mussel size.

Exploring Neotropical anuran parasites: a morphological, life cycle and phylogenetic study of Catadiscus marinholutzi (Trematoda: Diplodiscidae).

Amphistome species belonging to the genus Catadiscus are poorly studied intestinal trematodes found primarily in Neotropical anurans. Herein, developmental stages of an amphistome species found during herpetological and malacological surveys in a temporary marsh pond from Brazil were subjected to morphological (light and scanning electron microscopy) and molecular analyses. Adult parasites recovered from anurans were identified as Catadiscus marinholutzi. Amphistome cercariae found in the planorbid snails Drepanotrema depressissimum and Drepanotrema lucidum from the same waterbody were used for experimental and molecular studies. Immature parasites, morphologically compatible with members of Catadiscus, were experimentally obtained in laboratory-reared tadpoles. Sequencing of a partial region of 28S rDNA gene of both adult and cercariae revealed 100% similarity between these developmental stages, confirming their conspecificity. Phylogenetic analyses were attempted for the first time to reveal the position of a species of Catadiscus in the superfamily Paramphistomoidea. Catadiscus marinholutzi falls in a virtual polytomy together with other paramphistomoids, which leaves its phylogenetic relationships within the group unclear. Moreover, the high genetic divergence to Diplodiscus spp. (10.06­10.84%) cast doubts on the placement of Catadiscus within Diplodiscidae. Hence the species composition of the Diplodiscidae should be re-evaluated in further studies using a broader spectrum of related taxa.

Cercarial trematodes in freshwater snails from Bangkok, Thailand: prevalence, morphological and molecular studies and human parasite perspective.

We investigated the prevalence, morphological characters and molecular classifications of trematode cercariae in freshwater snails randomly collected from 59 sampling localities in Bangkok from May 2018 to March 2019. We used a crushing technique to observe the cercarial stage inside each snail body and amplified the internal transcribed spacer 2 regions of cercarial DNA using polymerase chain reaction methodology. The associated phylogenetic tree was reconstructed using Bayesian inference analyses. A total of 517 of 15 621 examined snails were infected with trematode cercariae, and the infected snails were classified into 11 species of seven families with a 3.31% overall prevalence of the infection. The Bithynia siamensis siamensis snail displayed the highest prevalence of infection (16.16%), whereas the Physella acuta snail exhibited the lowest prevalence (0.08%) of infection. Eight morphological types of cercariae were observed. The highest prevalence of infection was observed in mutabile cercaria (1.86%). Based on molecular investigations, the phylogram revealed eight cercaria types assigned to at least nine digenean trematode families, of which five belong to groups of human intestinal flukes. Although, with the exception of schistosome cercaria, trematode cercariae are not known to directly damage humans, understanding the general biology of trematode cercariae (including diversity, distribution, infection rates and host range) is important and necessary for the prevention and control of parasitic transmission that impacts aquatic cultivations, livestock farming and human health.

Identification of the avian tracheal trematode Typhlocoelum cucumerinum (Trematoda: Cyclocoelidae) in a host-parasite-environment system: diagnosis, life cycle and molecular phylogeny.

Typhlocoelum cucumerinum is a tracheal parasite of birds widely distributed across the globe. Nevertheless, aspects of the biology of this cyclocoelid are still poorly understood. Herein, we report the finding of T. cucumerinum in definitive and intermediate hosts from an urban waterbody of Brazil. The parasite was initially detected during the necropsy of domestic Muscovy ducks (Cairina moschata) found dead in the locality. Coproparasitological tests in live animals revealed that 12/47 (25.53%) Muscovy ducks and 2/8 (25%) mallards (Anas platyrhynchos platyrhynchos) were infected with T. cucumerinum. Moreover, rediae and metacercariae morphologically similar to T. cucumerinum were found in 3/248 (1.33%) Biomphalaria straminea collected in the same waterbody frequented by the birds. The conspecificity between the adult and the larval stages was confirmed molecularly (100% similarity in Cox-1). Moreover, the phylogenetic position of T. cucumerinum was determined for the first time based on partial fragments of the 28S, Cox-1 and Nad-1 genes. The species grouped with other members of the subfamily Typhlocoelinae with sequences available, but the data obtained do not support the distinctiveness of the genera Typhlocoelum and Tracheophilus. Further studies involving a broader range of species can result in taxonomic rearrangements in Typhlocoelinae.

Diversity and phylogeny of Paradiplozoon species (Monogenea: Diplozoidae) parasitising endemic cyprinoids in the peri-Mediterranean area, with a description of three new Paradiplozoon species.

The Diplozoidae are monogenean parasites of mainly cyprinoid fishes with a unique life cycle, whereby two larvae undergo anastomosis and fuse into a single cross-shaped specimen. Paradiplozoon is the most species rich and widespread genus of the family, with a distribution range covering Eurasia and Africa; however, some areas remain underexplored and their diplozoid fauna is uncertain. In the present study, the Paradiplozoon diversity was investigated in the peri-Mediterranean region, which has the highest levels of cyprinoid diversity and endemism in Europe. A total of 36 endemic cyprinoid species were sampled from sites in north-west Africa and the southern European peninsulas and investigated for the presence of diplozoid parasites. Of five Paradiplozoon species collected, three were identified as new to science: Paradiplozoon moroccoensis n. sp. from the Moroccan endemic Luciobarbus lepineyi; Paradiplozoon ibericus n. sp. from Iberian endemic cyprinids and leuciscids and Paradiplozoon helleni n. sp. from the Greek endemic Scardinius acarnicus and Tropidophoxinellus hellenicus (descriptions provided herein). In addition, new host records for P. homoion and P. megan are presented, with the former being most prevalent in the investigated region. Phylogenetic analysis supported paraphyly of the genus Paradiplozoon, and suggests the need for a careful taxonomic re-evaluation of this genus. Furthermore, the results showed that endemic Paradiplozoon of the peri-Mediterranean do not form a monophyletic group, suggesting multiple origins of this parasite groups in different peri-Mediterranean regions.

Ultrastructural observations on the oncomiracidium epidermis and adult tegument of Discocotyle sagittata, a monogenean gill parasite of salmonids.

During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral "metamorphoses" to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium's outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.

The life cycle of Magnivitellinum saltaensis n. sp. (Digenea: Alloglossidiidae) in Salta Province, Argentina.

We describe the alloglossiid trematode Magnivitellinum saltaensis n. sp., a parasite of the characiform fish Psalidodon endy, and its life cycle from Salta, northwest of Argentina. This is the first life cycle described for a species belonging to the genus Magnivitellinum. Cercariae emerged naturally from Biomphalaria tenagophila snails and infected experimentally exposed larvae of Diptera and Ephemeroptera as second intermediate hosts. These larvae in turn were exposed to commercially raised fish, and adults were recovered from characiform albino fish Gymnocorymbus ternetzi. Molecular analysis of natural and experimental adults showed the same genetic sequence for the partial region of 28S rDNA, thus confirming conspecificity. Comparison of these sequences with those published for M. simplex from Mexico showed 1.45% divergence, indicating that the specimens found in Salta belong to a different species, the third described of Magnivitellinum, in agreement with morphological data, geographical location, and host species composition. The new species is distinguished by its small body, vitelline follicles extending from the mid-level of the ventral sucker, Y-shaped excretory vesicle, and presence of papillae around the mouth.

The contributions of a trematode parasite infectious stage to carbon cycling in a model freshwater system.

Parasites remainunderstudied members of most ecosystems, especially free-living infectious stages, such as the aquatic cercariae of trematodes (flatworms). Recent studies are shedding more light on their roles, particularly as prey for a diverse array of aquatic predators, but the possible fates of cercariae remain unclear. While this is critical to elucidate because cercariae represent a large potential source of energy and nutrients, determining the fate of cercariae-derived organic matter involves many logistical challenges. Previous studies utilized elemental and stable isotope analysis when examining host-parasite interactions, but none has used such approaches to track the movement of cercariae biomass within food webs. Here we report that Plagiorchis sp. cercariae were effectively labelled with 13C by introducing this compound in the food of their snail host. We then added 13C-labelled cercariae as a potential food source to experimental mesocosms containing a simplified model freshwater food web represented by diving beetles (Dytiscidae sp.), dragonfly larvae (Leucorrhinia intacta), oligochaete worms (Lumbriculus variegatus), and a zooplankton community dominated by Daphnia pulex. The oligochaetes had the highest ratio of 13C to 12C, suggesting benthic detritivores are substantial, but previously unrecognized, consumers of cercariae biomass. In an experiment where L. variegatus were fed mass equivalents of dead D. pulex or cercariae, growth was greater with the latter diet, supporting the importance of cercariae as food source for benthic organisms. Given the substantial cercariae biomass possible in natural settings, understanding their contributions to energy flow and nutrient cycling is important, along with developing methods to do so.

Elucidation of Himasthla leptosoma (Creplin, 1829) Dietz, 1909 (Digenea, Himasthlidae) life cycle with insights into species composition of the north Atlantic Himasthla associated with periwinkles Littorina spp.

Trematodes of the genus Himasthla are usual parasites of coastal birds in nearshore ecosystems of northern European seas and the Atlantic coast of North America. Their first intermediate hosts are marine and brackish-water gastropods, while second intermediate hosts are various invertebrates. We analysed sequences of partial 28S rRNA and nad1 genes and the morphology of intramolluscan stages, particularly cercariae of Himasthla spp. parasitizing intertidal molluscs Littorina spp. in the White Sea, the Barents Sea and coasts of North Norway and Iceland. We showed that only three Himasthla spp. are associated with periwinkles in these regions. Intramolluscan stages of H. elongata were found in Littorina littorea, of H. littorinae, in both L. saxatilis and L. obtusata, and of Cercaria littorinae obtusatae, predominantly, in L. obtusata. Other Himasthla spp. previously reported from Littorina spp. in North Atlantic are either synonymous with one of these species or described erroneously. Based on a comparison of newly generated 28S rDNA sequences with GenBank data, rediae and cercariae of C. littorinae obtusatae were identified as belonging to H. leptosoma. Some previously unknown morphological features of young and mature rediae and cercariae of the three Himasthla spp. are described. We provide a key to the rediae and highlight characters important for identification of cercariae. Genetic diversity within the studied species was only partially determined by their specificity to the molluscan host. The nad1 network constructed for H. leptosoma lacked geographical structure, which is explained by a high gene flow owing to highly vagile definitive hosts, shorebirds.

Alaria alata mesocercariae prevalence and predilection sites in amphibians in Latvia.

Alaria alata is known as a trematode with a complex life cycle. The trematode Alaria alata infects amphibians as second intermediate hosts. In the present study, we examined 390 amphibians-European water frogs Pelophylax esculentus complex (n = 335), common frogs Rana temporaria (n = 19), moor frogs Rana arvalis (n = 3), and common toads Bufo bufo (n = 30) collected from randomly selected wetland habitats in Latvia. Out of all examined specimens, 80 were tadpoles and 310 were adult amphibians. Mesocercariae of A. alata was detected in 108 specimens from all examined amphibian species, except the common toad, reaching the overall prevalence of 27.7%. Tadpoles were found to be more frequently infected with A. alata, when compared with adults, 58.8% and 22.4%, respectively. The results showed that mesocercariae accumulate in visceral membranes, different internal organs, and muscles in the head area. This is a comprehensive study to identify A. alata mesocercariae predilection sites in amphibians.

Insights on foodborne zoonotic trematodes in freshwater snails in North and Central Vietnam.

Foodborne zoonotic trematode (FZT) infections are common neglected tropical diseases in Southeast Asia. Their complicated life cycles involve freshwater snails as intermediate hosts. A cross-sectional study was conducted in Yen Bai and Thanh Hoa provinces in North and Central Vietnam, to investigate the diversity of cercariae of potential FZT and to construct the phylogenetic relationship of trematode cercariae based on the Internal Transcribed Spacer 2 (ITS2) region. Among 17 snail species collected from various habitats, 13 were infected by 10 cercarial groups among which parapleurolophocercous, pleurolophocercous, and echinostome cercariae were of zoonotic importance. The monophyletic tree separated cercarial sequences into different groups following the description of the cercariae families in which Haplorchidae, Opisthorchiidae, Echinochasmidae, and Echinostomatidae are important families of FZT. The overall prevalence was different among snail species and habitats and showed a seasonal trend. Parapleurolophocercous and echinostome cercariae emerged as the most common cercariae in snails in Yen Bai, while monostome, echinostome, and megalura cercariae were most common in Thanh Hoa. Using a molecular approach, we identified Parafossarulus striatulus as the first intermediate snail host of Clonorchis sinensis in Thac Ba Lake. Melanoides tuberculata and Bithynia fuchsiana were we identified preferred intermediate snail hosts of a diverse range of trematode species including intestinal flukes (i.e., Haplorchis pumilio and Echinochasmus japonicus) in Yen Bai and Thanh Hoa, respectively.

An efficient photograph-based quantitative method for assessing castrating trematode parasites in bivalve molluscs.

Parasitic castration of bivalves by trematodes is common, and may significantly reduce the reproductive capacity of ecologically important species. Understanding the intensity of infection is desirable, as it can indicate the time that has passed since infection, and influence the host's physiological and reproductive response. In addition, it is useful to know the developmental stage of the trematode, to understand trematode population trends and reproductive success. However, most existing methods (e.g. visually estimating the degree of infection) to assess intensity are approximate only and not reproducible. Here, we present a method to accurately quantify the percentage of bivalve gonad filled with digenean trematode tissue, based on small squashes of gonad tissue rapidly photographed under light microscopy. A maximum of 15 photographs is required to determine the percentage of the whole gonad occupied by trematodes with a minimum of 90% confidence, with smaller mussels requiring fewer. In addition, the stage of trematode infection can be assessed because full sporocysts, spent sporocysts and free cercariae are clearly distinguishable. Although variation exists in the distribution of trematodes in gonad tissue, and thus in the estimate of percentage of the gonad filled with trematodes, this method represents a marked improvement on current coarse assessments of infection which typically focus on binary presence/absence measures. This technique can be used to facilitate a more sophisticated understanding of host-parasite interactions in bivalves, and can inform the conservation and reproductive biology of environmentally crucial species.

How costly are metacercarial infections in a bivalve host? Effects of two trematode species on biochemical performance of cockles.

Bivalve stocks have been decreasing in the last decades largely due to emergent diseases and consequent mass mortality episodes. Cerastoderma edule (the edible cockle) is one of the most exploited bivalves in Europe and is among the most common hosts for trematodes, the most prevalent macroparasites in coastal waters but yet poorly studied. Therefore, in the present study, this bivalve species was used as host model to determine if trematode infection exerts a negative effect on bivalve energy metabolism and balance and if the tissues targeted by different trematodes influence the metabolic cost, with physiological and biochemical consequences. Cockles were experimentally infected with two trematode species, Himasthla elongata and Renicola roscovitus, that infect the foot and palps, respectively. Trematode infection exerted a negative effect on the metabolism of C. edule, the second intermediate host, by reduction of oxygen consumption. A different host biochemical response was found depending on trematode species, especially in regard to the level of oxygen consumption decrease and the preferential accumulation of lipids and glycogen. This study represents a step towards the understanding of host-trematode relationships that can be used to better predict potential conservation threats to bivalve populations and to maximize the success of stock and disease management.

Molecular characterization of Urosporidium tapetis sp. nov., a haplosporidian hyperparasite infecting metacercariae of Parvatrema duboisi (Dollfus 1923), a trematode parasite of Manila clam Ruditapes philippinarum on the west coast of Korea.

Recently, a putative new hyperparasitic haplosporidian in the genus Urosporidium was identified from metacercariae of the trematode Parvatrema duboisi infecting Manila clam Ruditapes philippinarum on the west coast of Korea. In this study, we applied small subunit ribosomal DNA (SSU rDNA) sequences as a marker to substantiate the phylogenetic relationship of the unidentified Urosporidium within the Order Haplosporida. In our phylogenetic analysis, the 1890 bp of SSU rDNA sequences obtained were closely related to a haplosporidian parasite forming a sister clade to Urosporidium group, although the gene sequences were only 89.22-89.70% similar to Urosporidium spp. Such molecular phylogenetic distance within the genus suggested that the unidentified Urosporidium is a new member of the genus. Accordingly, we report the unidentified haplosporidian hyperparasite as Urosporidium tapetis sp. nov.

Temperature does not influence functional response of amphipods consuming different trematode prey.

Direct consumption on free-living cercariae stages of trematodes by non-host organisms interferes with trematode transmission and leads to reduced infections in the next suitable hosts. Consumer functional responses provide a useful tool to examine relationships between consumption rates and ecologically relevant prey densities, whilst also accounting for abiotic factors that likely influence consumption rates. We investigated how temperature influences the consumer functional response of the amphipod Gammarus lacustris towards the cercariae of three freshwater trematodes (Diplostomum, Apatemon and Trichobilharzia). Amphipods displayed different functional responses towards the parasites, with Type II responses for Diplostomum and Type I responses for Apatemon prey. Temperature did not alter the consumption rate of the amphipod predator. Trichobilharzia was likely consumed at similar proportions as Diplostomum; however, this could not be fully evaluated due to low replication. Whilst Type II responses of invertebrate predators are common to various invertebrate prey types, this is the first time a non-filter feeding predator has been shown to exhibit Type I response towards cercarial prey. The prey-specific consumption patterns of amphipods were related to cercarial distribution in the water column rather than to the size of cercariae or temperature influence. The substantial energy flow into food webs by non-host consumer organisms highlights the importance of understanding the mechanisms that modulate functional responses and direct predation in the context of parasitic organisms.

Phylogenetic position of Diplostomum spp. from New World herons based on complete mitogenomes, rDNA operons, and DNA barcodes, including a new species with partially elucidated life cycle.

Diplostomum ardeae Dubois, 1969 has seldom been reported since its description from the great blue heron (Ardea herodias L., 1758) in the USA. Sequences obtained in this study from the barcode region of cytochrome c oxidase 1 (CO1) in diplostomids from black-crowned night heron (Nycticorax nycticorax (L., 1758)) in Puerto Rico matched data from D. ardeae from A. herodias in the type region. We also obtained DNA barcodes from morphologically similar diplostomids from a rufescent tiger heron (Tigrisoma lineatum (Boddaert, 1783)) and from metacercariae from eye lenses of Trachelyopterus galeatus (Linnaeus, 1766) from the Paraná River basin in Argentina and Brazil, respectively. Barcodes matched (97-100% identity) in these South American adult and larval specimens as well as in recently published sequences from metacercariae from 11 other siluriform fishes from the same region. Barcodes from the South American species, which we describe as Diplostomum lunaschiae n. sp., differed from those of D. ardeae by 7.2-9.8%, and the new species differs from D. ardeae in its size, pharynx:oral sucker length ratio, egg:body length ratio, and distribution of vitellaria. As in prior phylogenetic analysis of CO1 sequences, both D. ardeae and D. lunaschiae n. sp. were not associated with Diplostomum. In more character-rich analyses of nuclear rDNA and of mitochondrial genomes, D. ardeae was an early divergent member of clades of species of Diplostomum. Consequently, we continue to consider D. ardeae and D. lunaschiae n. sp. members of Diplostomum, in contrast to recent suggestions that these species may belong to a different genus.

Reproductive compensation in female Palaemonetes argentinus (Decapoda: Natantia) due to Microphallus szidati (Trematoda) infection.

Parasites may affect host demographic characteristics because they can directly or indirectly cause the death of their hosts and/or influence their reproduction. Parasitism is therefore recognized as a factor that influences the composition and structure of populations and communities. One of these behaviours is the compensatory response: the host can compensate for the parasite losses effect, modifying the reproductive effort to enhance fitness. Ovigerus female Palaemonetes argentinus was collected and sorted into two groups according to the degree of development of their embryos: newly spawned embryos and embryos ready to hatch. The number of embryos and their dry weight for each female were determined. All parts of the female body were checked for parasites. The females of P. argentinus were parasitized by Microphalus szidati. We found that parasitized females produce more embryos but had more egg loss during development and the percentage of embryonic loss was higher in the parasitized females than in non-parasitized. Parasitized females produced lighter eggs than those from uninfected females. This supports the compensatory reproduction hypothesis suggested for this species. Parasitism can change life history traits in a way that fecundity can be compensated; this co-evolution between host and parasites will be population or context dependent. Parasites are a functional part of any ecosystem and as our results show, deleting parasites in life history traits and reproduction studies in free living organisms could lead to an incomplete picture of the true processes that happen in nature.

Studies on the life cycle of Pleurogenoides wayanadensis Shinad & Prasadan, 2018 (Digenea: Pleurogenidae) from the Western Ghats, India.

The life cycle of Pleurogenoides wayanadensis Shinad & Prasadan, 2018, infecting the frogs Hoplobatrachus tigerinus and Euphlyctis cyanophlyctis, is elucidated in this study. All the life cycle stages from egg to egg-producing adults were elucidated under natural conditions and successfully established in the laboratory. The life cycle took about 58 to 65 days for completion. Miracidia were released by teasing the eggs with fine needles. Sporocysts were found in the freshwater snail, Bithynia (Digoniostoma) pulchella, collected from paddy fields at Payode, Western Ghats, Wayanad region, in the months of October and November 2019. Cercariae were of the virgulate xiphidiocercous type. Metacercariae were recovered from the eyes of the damselfly naiads of the species Ischnura sp. and Copera sp., and the thorax and abdomen of the dragonfly naiads, Orthetrum sp. The metacercariae showed progenetic development. The growth and development of the metacercariae in the naiads that were exposed to cercariae, and development of the trematode in frogs that were force-fed with encysted metacercariae, have been studied at regular intervals. The prepatent period is 14-19 days. The present life cycle study of a Pleurogenoides spp. forms the seventh report from the world, fourth report from India and the third from Kerala.

DNA sequencing demonstrates the importance of jellyfish in life cycles of lepocreadiid trematodes.

Sequence data were combined with morphological analyses to identify two lepocreadiid trematode species from jellyfishes and fishes. Three species of jellyfish were captured within Port Phillip Bay, Australia, and three species of fish that feed on jellyfish were obtained from Moreton Bay (Queensland) and Port Phillip Bay and Portland (Victoria). The digeneans were distributed throughout most parts of the jellyfish. Opechona cf. kahawai Bray & Cribb, 2003 parasitized the scyphozoan jellyfish Aequorea eurodina and the scombrid fish Scomber australasicus. Cephalolepidapedon warehou Bray & Cribb, 2003 parasitized the scyphozoans Pseudorhiza haeckeli and Cyanea annaskala, and the centrolophid fishes Seriolella brama and Seriolella punctata. Intensities ranged from four to 96 in the jellyfish, and one to 30 in the fish. For both trematode species, internal transcribed spacer 2 of ribosomal DNA sequences from mature adults in the fishes matched those from metacercariae from the jellyfish. This is the first record of larval stages of C. warehou and O. cf. kahawai, and the first use of DNA sequencing to identify digenean trematode metacercariae from jellyfish. Three new host records are reported for C. warehou and two for O. cf. kahawai.