Idiopyrgus souleyetianus (Gastropoda: Tomichiidae) as an intermediate host of the liver fluke Amphimerus sp. (Trematoda: Opisthorchiidae) in Brazil.

Despite the importance of fish-borne trematodes of the family Opisthorchiidae as causative agents of human liver fluke disease, studies on these parasites outside Asia are relativally scarce. In South America, human focus of amphimerosis is known in Ecuador since the mid-20th century, and Amphimerus spp. have also been reported in wild and domestic mammals. Nevertheless, the knowledge on the snails that act as the first intermediate host of these potentially zoonotic parasites are scarce. Herein, a new cercaria of the pleurolophocercous morphotype found in the freshwater snail Idiopyrgus souleyetianus from Brazil was subjected to morphological and molecular studies. Multigene phylogenetic analyses based on 28S, 5.8S-ITS-2 and Cox-1 sequences enabled the identification of Amphimerus sp., a species distinct from that reported in humans from Ecuador. This cercariae was morphologically compared with other opisthorchiid cercariae known. The possible occurrence of human amphimerosis in Brazil is discussed.

Polymorphic parasitic larvae cooperate to build swimming colonies luring hosts.

Parasites have evolved a variety of astonishing strategies to survive within their hosts, yet the most challenging event in their personal chronicles is the passage from one host to another. It becomes even more complex when a parasite needs to pass through the external environment. Therefore, the free-living stages of parasites present a wide range of adaptations for transmission. Parasitic flatworms from the group Digenea (flukes) have free-living larvae, cercariae, which are remarkably diverse in structure and behavior.1,2 One of the cercariae transmission strategies is to attain a prey-like appearance for the host.3 This can be done through the formation of a swimming aggregate of several cercariae adjoined together by their tails.4 Through the use of live observations and light, electron, and confocal microscopy, we described such a supposedly prey-mimetic colony comprising cercariae of two distinct morphotypes. They are functionally specialized: larger morphotype (sailors) enable motility, and smaller morphotype (passengers) presumably facilitate infection. The analysis of local read alignments between the two samples reveals that both cercaria types have identical 18S, 28S, and 5.8S rRNA genes. Further phylogenetic analysis of these ribosomal sequences indicates that our specimen belongs to the digenean family Acanthocolpidae, likely genus Pleorchis. This discovery provides a unique example and a novel insight into how morphologically and functionally heterogeneous individuals of the same species cooperate to build colonial organisms for the purpose of infection. This strategy bears resemblance to the cooperating castes of the same species found among insects.5.

A putative new genus of avian schistosome transmitted by Biomphalaria straminea (Gastropoda: Planorbidae) in Brazil, with a discussion on the potential involvement in human cercarial dermatitis.

Human cercarial dermatitis (HCD) caused by avian schistosomes is an emerging health issue in different parts of the world. Nevertheless, parasite diversity, life cycle, and involvement in HCD remain poorly known or neglected in South America. Herein, we reported data obtained during a long-term malacological survey carried out in Pampulha Reservoir, an urban eutrophic waterbody from Brazil between 2009 and 2012. An ocellate brevifurcate cercaria emerged from 55 of 16,235 (0.34%) specimens of Biomphalaria straminea. Samples of the cercariae were subjected to morphological, experimental, and molecular study (analysis of partial sequences of nuclear 28S and mitochondrial cox1 genes). The molecular analysis revealed that the larva corresponds to an avian schistosome; however, it does not correspond to any named genus. A close related isolate was previously reported in Biomphalaria sudanica from Kenya (molecular divergences of 0.54% and 9.62% for 28S and cox1, respectively). The morphology of this cercaria was compared with other avian schistosome larvae from Biomphalaria spp. Attempts to infect experimentally ducks (Cairina moschata) and mice revealed cutaneous manifestations after exposure to cercariae, but adult parasites were not obtained in these hosts. Phylogenetic analysis suggests this parasite is a putative new genus and species of avian schistosome. The potential involvement of the larvae herein described in cases of HCD in Brazil cannot be ruled out. Surprisingly, HCD was not reported in the country so far, which can be related to difficulties in its diagnosis in areas of overlap with human schistosomes.

Echinostoma chankensis nom. nov., other Echinostoma spp. and Isthmiophora hortensis in East Asia: morphology, molecular data and phylogeny within Echinostomatidae.

Life cycles, and morphological and molecular data were obtained for Echinostoma chankensis nom. nov., Echinostoma cinetorchis, Echinostoma miyagawai and Isthmiophora hortensis from East Asia. It was established that, based on both life cycle and morphology data, one of the trematodes is identical to the worms designated as Euparyphium amurensis. Genetic data showed that this trematode belongs to Echinostoma. The complex data on biological, morphological and genetic characterizations establish that the distribution of the morphologically similar species, I. hortensis and Isthmiophora melis, in the Old World are limited by the East Asian and European regions, respectively. Data on mature worms of East Asian E. miyagawai revealed morphological and genetic identity with E. miyagawai from Europe. However, E. miyagawai from Europe differs from E. miyagawai from the type locality (East Asia) in terms of reaching maturity and the morphology of cercariae. These data indicate that the European worm, designated E. miyagawai, does not belong to this species. An analysis of the phylogenetic relationships of Echinostomatidae was conducted based on the 28S, ITS2 and nad1 markers. Analysis using the nad1 gene for the known representatives of Echinostomatidae is carried out for the first time, showing that nuclear markers are ineffective separate from mitochondrial ones.

A new species of Gorgoderina (Digenea: Gorgoderidae) from Rana berlandieri in Los Tuxtlas tropical rainforest, Mexico, with the elucidation of its life cycle.

Species in the genus Gorgoderina Looss, 1902 are parasites of the urinary bladder of amphibians and include around 50 species described globally. Molecular data on species of the genus are scarce, as is the information of their life-cycle patterns. During a survey on the genetic characterization of the frog trematodes in the tropical rain forest of Los Tuxtlas, in the Gulf of Mexico slope of Mexico, specimens of two morphotypes of Gorgoderina were sampled from the Rio Grande leopard frog, Rana berlandieri. One of them represented an undescribed species which is described herein as Gorgoderina rosamondae n. sp., whereas the other one was morphologically very similar to an apparently widely distributed North American species, G. attenuata, which has been previously reported in the same geographical area. Specimens of both morphotypes were sequenced for two nuclear and one mitochondrial genes. Phylogenetic trees corroborated the distinction of the new species, and data on the internal transcribed spacer 2 revealed genetic differences between G. attenuata sequenced from frogs in USA and specimens of Gorgoderina sp. from Los Tuxtlas, indicating the possibility that they also represent an undescribed species. COI sequences showed high genetic divergence values between the new species and Gorgoderina sp. from Los Tuxtlas (8.63-9.99%). Additionally, COI sequences of the larval forms (sporocyst, cercariae and metacercariae) sampled in the same locality from their first and second intermediate hosts (Pisidium sp. and Agriogomphus tumens, respectively) showed conspecificity, and the 3 host life-cycle of the new species was elucidated.

Parvatrema duboisi (Digenea: Gymnophallidae) Life Cycle Stages in Manila Clams, Ruditapes philippinarum, from Aphae-do (Island), Shinan-gun, Korea.

Life cycle stages, including daughter sporocysts, cercariae, and metacercariae, of Parvatrema duboisi (Dollfus, 1923) Bartoli, 1974 (Digenea: Gymnophallidae) have been found in the Manila clam Ruditapes philippinarum from Aphaedo (Island), Shinan-gun, Jeollanam-do, Korea. The daughter sporocysts were elongated sac-like and 307-570 (av. 395) µm long and 101-213 (av. 157) µm wide. Most of the daughter sporocysts contained 15-20 furcocercous cercariae each. The cercariae measured 112-146 (av. 134) µm in total length and 35-46 (av. 40) µm in width, with 69-92 (av. 85) µm long body and 39-54 (av. 49) µm long tail. The metacercariae were 210-250 (av. 231) µm in length and 170-195 (av. 185) µm in width, and characterized by having a large oral sucker, genital pore some distance anterior to the ventral sucker, no ventral pit, and 1 compact or slightly lobed vitellarium, strongly suggesting P. duboisi. The metacercariae were experimentally infected to ICR mice, and adults were recovered at day 7 post-infection. The adult flukes were morphologically similar to the metacercariae except in the presence of up to 20 eggs in the uterus. The daughter sporocysts and metacercariae were molecularly (ITS1-5.8S rDNA-ITS2) analyzed to confirm the species, and the results showed 99.8-99.9% identity with P. duboisi reported from Kyushu, Japan and Gochang, Korea. These results confirmed the presence of various life cycle stages of P. duboisi in the Manila clam, R. philippinarum, playing the role of the first as well as the second intermediate host, on Aphae-do (Island), Shinan-gun, Korea.

Evidence of a Putative Novel Species of Avian Schistosome Infecting Planorbella trivolvis.

Freshwater gastropods of the genera Lymnaea Lamarck, 1799, Physa Draparnaud, 1801, Gyraulus Charpentier, 1837, Radix Montfort, 1810, and Stagnicola Jeffreys, 1830 are considered suitable intermediate hosts for avian schistosomes. A large trematode biodiversity survey performed across 3 yr on 6 lakes in Alberta confirmed 3 already-reported snail hosts for 7 North American avian schistosomes; however, the cytochrome c oxidase subunit 1 (COI) nucleotide sequence from 1 cercarial sample (from a single specimen of Planorbella trivolvis) was distinct from all other COI schistosome sequences. As part of a simultaneous, comparable study of P. trivolvis by us in Michigan, we collected another cercarial type from 6 lakes that was 99% similar (COI) to the aforementioned cercarial type. Phylogenetic analyses of the COI and 28S rDNA genes recovered the former cercaria in a clade of avian schistosomes. In Michigan, the feces of a Canada goose (Branta canadensis Linnaeus, 1758) had a miracidium with an identical COI nucleotide sequence. Preliminary swimmer's itch and cercarial emergence studies were performed to determine if the cercariae could cause swimmer's itch and to study the emergence pattern as compared with species of Trichobilharzia Skrjabin and Zakharow, 1920.

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.

Morphological and molecular characterization of larval digenean trematodes (Parvatrema: Gymnophallidae) and their pathological effects on the clam Leukoma thaca (=Protothaca thaca) (Bivalvia:Veneridae) (Molina, 1782) from northern Chile.

Trematodes are one of the largest taxa of mollusk parasites. The clam Leukoma thaca is an economically exploited bivalve found along the south-eastern Pacific coast of Peru and Chile. This bivalve is parasitized by various unidentified larval stages of digeneans in the mantle, gonads and digestive gland. The aims of this study were to determine and describe the different larval stages of the digeneans based on morphological characteristics, to identify them at the species level by performing molecular analyses, and to evaluate pathologies associated with the parasites of this clam. Individuals of L. thaca were collected in San Jorge Bay (23°S), Chile, between November 2018 and February 2019. Morphological description was carried out using in vivo and fixed specimens, and analyses including histological and scanning electron microscopy were performed. Individuals were also isolated for molecular analysis using nuclear ribosomal internal transcribed spacer 1 (ITS1), including partial subunit 18S rDNA (18S) and small subunit 5.8S gene (5.8S). Morphological characteristics indicated that the metacercaria larval stage belongs to the family Gymnophallidae, genus Parvatrema, which was supported by molecular analysis. Molecular results revealed that metacercaria, sporocysts and cercaria stages found in this clam belong to the same species of Parvatrema (genetic distance 0%), evidencing that this species uses L. thaca as the first and second intermediate host. Pathologies examined in the host were similar in nature to those reported in other gymnophallids in bivalves, but high prevalence of cercariae (20%) in gonads suggested an important castrator effect on the host.

The Life Cycle of Heterophyes yacyretana n. sp. (Digenea, Heterophyidae), Parasitic in the Endemic Snail Aylacostoma chloroticum (Caenogastropoda, Thiaridae) in Argentina.

Here we describe a new heterophyid species, Heterophyes yacyretana n. sp., and resolve its life cycle experimentally. We found the prosobranch snail Aylacostoma chloroticum in Candelaria, Province of Misiones, Argentina (a sector of the High Paraná River affected by the Yacyretá Dam), naturally infected with opisthorchioid cercariae. These cercariae lacked pigmented eyespots as well as body pigment and possessed 7 pairs of penetration glands arranged in 2 lateral bands, together with 18 pairs of flame cells and a V-shaped excretory vesicle. We exposed specimens of 21 fish species to emerging cercariae and obtained metacercariae from the muscles of the caudal peduncle of 3 species of siluriform fish, and adults from chicks infected with experimentally obtained metacercariae from the albino variety of the bronce corydoras, Corydoras aeneus. The new species differs from other species in the genus by the number of sclerites on the genital sac, the distribution of the vitelline follicles, and the combination of the size relationship of the suckers and the genital sac with respect to the posterior extent of intestinal ceca. Heterophyes yacyretana is the first species of the genus reported from the Americas.

Molecular and Morphological Elucidation of the Life Cycle of the Frog Trematode Langeronia macrocirra (Digenea: Pleurogenidae) in Los Tuxtlas, Veracruz, Mexico.

The genus LangeroniaCaballero and Bravo-Hollis, 1949, currently contains 6 species of amphibian trematodes distributed in North and Middle America. The type species of the genus, Langeronia macrocirraCaballero and Bravo-Hollis, 1949, occurs in Mexico and is relatively commonly found as a parasite of leopard frogs. However, information regarding its life cycle is lacking. In this paper, we study the life cycle of L. macrocirra in Laguna Escondida, Los Tuxtlas, Veracruz. Definitive hosts (Rana spp.) as well as potential intermediate hosts (gastropods, bivalves, crustaceans, tadpoles, hemipterans, and odonate naiads) were sampled in the locality and studied to search for the presence of adults and larval stages of the trematode. Specimens were morphologically characterized, and some individuals were sequenced for 1 ribosomal gene (28S rRNA) and 1 mitochondrial gene (COI). DNA sequences of the adults obtained from leopard frogs were matched with those of the larval forms in their intermediate hosts (metacercariae, cercariae, and sporocysts) to demonstrate conspecificity. Further, we conducted a detailed study of the tegument of the body surface with scanning electron microscopy to characterize each of the developmental stages of the life cycle of L. macrocirra.

Cryptic speciation of the zoogonid digenean Diphterostomum flavum n. sp. demonstrated by morphological and molecular data.

Diphterostomum brusinae (Zoogonidae) is a digenean species that has been recorded worldwide parasitizing marine fishes. Several species have been synonymized with D. brusinae because they lack conspicuous morphological differences. However, due to the breadth of its geographic distribution and the variety of hosts involved in the life cycles, it is likely to be an assemblage of cryptic species. Diphterostomum flavum n. sp. is described here as a morphologically cryptic relative of D. brusinae, in the fish Pinguipes brasilianus (Pinguipedidae) off the Patagonian coast, Southwestern Atlantic Ocean, and its life cycle is elucidated through morphology and molecular analysis. This species uses the gastropod Buccinanops deformis (Nassariidae) as first and second intermediate host with metacercariae encysting within sporocysts. They also, however, use the polychaete Kinbergonuphis dorsalis (Onuphidae) as second intermediate host. No morphological differences were found between adults of D. flavum n. sp. and D. brusinae; however, the number of penetration glands of the cercariae, a diagnostic feature, differed (9 vs. 3 pairs), as well as the ITS2 sequences for the two species. This work provides morphological and molecular evidence of cryptic diversification among species described as D. brusinae, in which the only clear differences are in larval morphology and host spectrum. The strict specificity to the snail acting as the first intermediate host and the variety of fishes with different feeding habits acting as definitive hosts support the likely existence of multiple cryptic species around the world.

TITLE: Spéciation cryptique du Digène Zoogonidae Diphterostomum flavum n. sp. démontrée par des données morphologiques et moléculaires. ABSTRACT: Diphterostomum brusinae (Zoogonidae) est une espèce de digène, parasite des poissons marins, qui a été signalée dans le monde entier. Plusieurs espèces ont été synonymisées avec D. brusinae parce qu'elles ne montrent pas de différences morphologiques visibles. Cependant, en raison de l'étendue de sa répartition géographique et de la variété d'hôtes impliqués dans les cycles de vie, il est probable qu'il s'agisse d'un assemblage d'espèces cryptiques. Diphterostomum flavum n. sp. est décrit ici comme une espèce morphologiquement cryptique de D. brusinae, chez le poisson Pinguipes brasilianus (Pinguipedidae) au large de la côte de la Patagonie, dans le sud-ouest de l'océan Atlantique, et son cycle de vie est élucidé par la morphologie et l'analyse moléculaire. Cette espèce utilise le gastéropode Buccinanops deformis (Nassariidae) comme premier et deuxième hôte intermédiaire avec des métacercaires s'enkystant dans les sporocystes. Cependant, elle utilise également le polychète Kinbergonuphis dorsalis (Onuphidae) comme deuxième hôte intermédiaire. Aucune différence morphologique n'a été trouvée entre les adultes de D. flavum n. sp. et D. brusinae, mais le nombre de glandes de pénétration des cercaires, une caractéristique diagnostique, diffère (9 paires contre 3), ainsi que les séquences ITS2 pour les deux espèces. Ce travail fournit des preuves morphologiques et moléculaires de la diversification cryptique parmi les espèces décrites comme D. brusinae, dans lesquelles les seules différences claires sont dans la morphologie des larves et le spectre de l'hôte. La spécificité stricte au mollusque servant de premier hôte intermédiaire et la variété de poissons avec différentes habitudes alimentaires servant d'hôtes définitifs soutiennent l'existence probable de plusieurs espèces cryptiques dans le monde.

Fine structure of the nervous system of Cercaria parvicaudata Stunkard & Shaw, 1931 (Digenea, Renicolidae).

The biology of free-living and parasitic Platyhelminthes is diverse. Taking into account the widespread prevalence of parasitic flatworms, Digenea is the least studied group regarding the fine structure of nervous system especially of the cercarial life stage. Here, we present a description of the fine structure of central nervous system (CNS) and two types of uniciliate sensory papillae of xiphidiocercaria Cercaria parvicaudata (Microphalloidea, Renicolidae). The present study documents that C. parvicaudata has a complex nervous system that includes a well-developed ganglion with a cortex of perikarya and glia-like sheaths, myelin-like structures within one of the dorsal nerve cords and four types of polarized synapses between neurites. Different types of neurons in the CNS could not be distinguished on ultrastructural level due to high similarity in their fine structure. Shared polarized synapses with high electron density of presynaptic components are numerous in the neuropile and nerve cords of this larva. Within the larval body, we detected specialized "support" processes that relate to different tissues. Some "support" processes are also closely related to the nervous system of C. parvicaudata, where they are considered as glia-like structures. In this case, the fine structure of glia-like "support" cells of C. parvicaudata differs from those described as glia-like cells in adult flatworms. We suggest a wide prevalence of glia-like cells among cercariae, as well as the fact that glia-like structures in digenean nervous systems can develop from various nonneuronal tissues.

Pronocephaloid cercariae (Platyhelminthes: Trematoda) from gastropods of the Queensland coast, Australia.

The superfamily Pronocephaloidea Looss, 1899 comprises digeneans occurring in the gut and respiratory organs of fishes, turtles, marine iguanas, birds and mammals. Although many life cycles are known for species of the Notocotylidae Lühe, 1909 maturing in birds and mammals, relatively few are known for the remaining pronocephaloid lineages. We report the cercariae of five pronocephaloid species from marine gastropods of the Queensland coast, Australia. From Lizard Island, northern Great Barrier Reef, we report three cercariae, two from Rhinoclavis vertagus (Cerithiidae) and one from Nassarius coronatus (Nassariidae). From Moreton Bay, southern Queensland, an additional two cercariae are reported from two genotypes of the gastropod worm shell Thylacodes sp. (Vermetidae). Phylogenetic analysis using 28S rRNA gene sequences shows all five species are nested within the Pronocephaloidea, but not matching or particularly close to any previously sequenced taxon. In combination, phylogenetic and ecological evidence suggests that most of these species will prove to be pronocephalids parasitic in marine turtles. The Vermetidae is a new host family for the Pronocephaloidea.

Heads or tails? Differential translational regulation in cercarial heads and tails of schistosome worms.

Schistosomes are obligate helminths responsible for over 218 million cases of human schistosomiasis in 78 countries around the world. Infection occurs when free-swimming cercariae penetrate human skin and initiate developmental progression into parasitic obligate worms that consume red blood cells. Transcriptomic studies of infectious cercariae reveal abundant mRNAs associated with energy metabolism and host invasion. However, the cercaria is mostly transcriptionally quiescent, suggesting that most mRNAs are primed prior to cercarial escape from the snail host. The use of transcriptomics to understand protein expression presumes that transcription and translation are functionally coupled and the cercarial stage has categorically been treated as a single unit for -omic analysis. Per contra, the relationship between transcription and translation in infectious cercariae has not been described. To understand the correlation between transcription and translation in cercariae, we separately measured nascent translation levels in cercarial heads, cercarial tails and in the developing schistosomula, the next stage of its life cycle. The loss of the cercarial tail is essential for the transformation from a cercaria to a schistosomulum. We observed that translation was initially limited and the translation rate accelerated during the first 72-hours after tail loss. When we tested nascent translation in cercarial heads, cercarial tails, whole cercariae, and 4-hour schistosomula, we found that translation is significantly upregulated in the cercarial tail when compared to the cercarial head and that translation was undetectable in heads using immunofluorescent image quantification (p = .0005). These data represent a major shift in how we understand the cercarial stage. The cercarial head is mostly transcriptionally and translationally quiescent while being sufficient for progression into a schistosomulum. In addition, transcription and translation are not linked in Schistosoma mansoni cercaria. Thus, our current conceptual approach of treating the cercaria as a single functional unit for -omic studies may be insufficient to understand cercarial development.

Molecular, morphological and experimental-infection studies of cercariae of five species in the superfamily Diplostomoidea (Trematoda: Digenea) infecting Biomphalaria straminea (Mollusca: Planorbidae) in Brazil.

Trematodes belonging to the superfamily Diplostomoidea have complex life cycles involving birds, mammals and reptiles as definitive hosts, and gastropods and different groups of invertebrates and vertebrates as intermediate hosts. Molecular studies of these parasites are numerous, but data from larval stages in molluscs remain scarce, particularly in South America. The present study focused mainly on five morphotypes of longifurcate cercariae found in Biomphalaria straminea (Dunker, 1848) from Belo Horizonte, Minas Gerais, Brazil, collected between 2009 and 2017. In each morphotype, nuclear internal transcribed spacer (ITS1-5.8S ITS-2) rDNA and mitochondrial cytochrome c oxidase 1 (COI) genes were sequenced. Laboratory-reared fish, Poecilia reticulata Peters, 1859 or snails, Biomphalaria glabrata (Say, 1818) were exposed to cercariae to obtain metacercariae. The morphology of cercariae, experimentally obtained metacercariae, and phylogenetic analyses led to the identification of three species of Diplostomidae [Austrodiplostomum compactum (Lutz, 1928), Crassiphialinae gen. sp. and Hysteromorpha sp.] and two species of Strigeidae (Cotylurus sp., Apharyngostrigea sp.). Previously published sequences allowed species-level identification for only A. compactum, although provisional identifications were possible in two cases. First, the COI from cercariae of Apharyngostrigea sp. in Brazil matched those of metacercariae from naturally infected Cnesterodon decemmaculatus (Jenyns, 1842) in Argentina; although a positive identification is not possible, the material presents morphological similarities with larval stages previously described for A. simplex. Secondly, Cotylurus sp. resembles C. lutzi. Our analysis of previously published COI sequences suggests that Cotylurus cornutus (Rudolphi, 1808) has a Holarctic distribution. Both the morphology of experimentally obtained metacercariae and COI sequences indicate that Hysteromorpha sp. in Brazil is distinct from congeners in North America [Hysteromorpha corti (Hughes, 1929)] and Europe [Hysteromorpha triloba (Rudolphi, 1819)].

New data on the nervous system of Cercaria parvicaudata Stunkard & Shaw, 1931 (Trematoda: Renicolidae): revisiting old hypotheses.

Data on the interposition of the immunoreactive nerve cords in Cercaria parvicaudata Stunkard & Shaw, 1931 (Trematoda: Renicolidae) and its chaetotaxy were obtained. The nervous system of C. parvicaudata was described using immunostaining of 5-hydroxytryptamine and FMRFamide immunoreactive nerve elements. The morphology and distribution of sensory receptors were analysed using scanning electron microscopy and the silver nitrate impregnation technique. Our integrated approach to the study of the nervous system revealed a clear colocalization of surface papillae with nerve cords and commissures in C. parvicaudata. The structure of the nervous system in C. parvicaudata differs partly from the classical model that defines the entire nomenclature of chaetotaxy.

Histological description of Cercaria etgesii Shchenkov, 2017 daughter sporocysts (Trematoda: Pleurogenidae): compartmentalization of the brood cavity and germinal mass morphology.

Morphology of the daughter sporocysts of Cercaria etgesii Shchenkov, 2017 (Pleurogenidae) has been described according to conventional histological techniques and subsequent 3D reconstruction with Bitplanelmaris® software. Novel data were obtained concerning the spatial organization of the brood cavity of Pleurogenidae daughter sporocysts. It was shown that the laminated structures of the endocyst are lining the brood cavity and carry out its compartmentalisation by formation of the chambers around developing and disintegrating embryos of cercariae. First description of the germinal mass of the Pleurogenidae daughter sporocysts is given. No mitoses in germinal mass were evident although apparent production of the cercariae embryos by the sporocysts take place. The analogous principle of daughter sporocysts morphofunctional organisation was noted for the studied representatives of closely related taxa of trematodes: Pleurogenidae (C. etgesii) and Microphallidae (Microphallus 'pygmaeus' group).

Molecular and morphological characterization of the cercariae of Lecithodendrium linstowi (Dollfus, 1931), a trematode of bats, and incrimination of the first intermediate snail host, Radix balthica.

Lecithodendrium linstowi is one of the most prevalent and abundant trematodes of bats, but the larval stages and intermediate hosts have not been identified. We present the first molecular and morphological characterization of the cercariae of L. linstowi based on a phylogenetic analysis of partial fragments of LSU and ITS2 rDNA. The first intermediate host was incriminated as Radix balthica by DNA barcoding using cox1 and ITS2 sequences, although the snail morphologically resembled Radix peregra, emphasizing the requirement for molecular identification of lymnaeids as important intermediate hosts of medical and veterinary impact. The application of molecular data in this study has enabled linkage of life cycle stages and accurate incrimination of the first intermediate host.