Component community of larval trematodes in the mudsnail Hydrobia ventrosa: temporal variations in prevalence in relation to host life history

Temporal variations in the prevalence of larval trematodes in the short-lived prosobranch mudsnail Hydrobia ventrosa (Montagu) were investigated in relation to host life history and season for 4 successive years in temperate windflats of the southern Baltic Sea. The component community of trematode larvae in H. ventrosa comprises at least 10 species; families (and species) represented include Notocotylidae (1), Echinostomatidae (1 or 2), Heterophyidae (2), Monorchidae (1), Microphallidae (3 or 4), Psilostomatidae (1), and Hemiuridae (1). The notocotylid Paramonostomum alveatum was the most prevalent species, followed by the microphallids Maritrema subdolum and Microphallus sp. Trematode prevalence in H. ventrosa fluctuated seasonally. Prevalence usually peaked in summer between July and September-October and decreased in late winter-early spring. This seasonal change is chiefly explained by the life history patterns of the semelparous snail host. Hydrobia ventrosa has a maximum life span of about 2 yr and reproduces between June and November of its second calendar year. The first trematode infections appeared annually in May when the most abundant cohort of H. ventrosa, the second-calendar-year snails, mature. The prevalence continued to increase until August-September, throughout the reproductive period of the second-calendar-year snails, Prevalence decreased during winter, when most of the second-calendar-year snails died after reproduction. On the basis of longterm laboratory experiments, it has been shown that the late autumn-winter mortality was not the result of trematode infections. Seasonal patterns of prevalence were similar among the trematode species except for the monorchid Asymphylodora demeli, the only one using fish definitive hosts. Species-specific differences in the seasonal occurrence of prepatent infections and the predominance of certain larval stages in winter are interpreted as different strategies of the trematode species to survive the harsh winter conditions, or to survive the death of the first intermediate host in autumn-winter, or both.     

Evaluating the role of regional and local processes in structuring a larval trematode metacommunity of Helisoma trivolvis

Metacommunity theory has advanced our understanding of how local and regional processes affect the structure of ecological communities. While parasites have largely been omitted from metacommunity research, parasite communities can provide the large sample sizes and discrete boundaries often required for evaluating metacommunity patterns. Here, we used assemblages of flatworm parasites that infect freshwater snails (Helisoma trivolvis) to evaluate three questions: 1) what factors affect individual host infections within ponds? 2) Is the parasite metacommunity structured among ponds? And 3) what is the relative role of local versus regional processes in determining metacommunity structure and species richness among ponds? We examined 10 821 snails from 96 sites in five park complexes in the San Francisco Bay area, California, and found 953 infections from six parasite groups. At the within‐pond level, infection status of host snails correlated positively with individual snail size and pond infection prevalence for all six parasite groups. Using an ordination method to test for metacommunity structure, we found that the parasite metacommunity was organized in a non‐random pattern with species responding individually along an environmental gradient. Based on a model selection approach involving local and regional predictors, parasite species richness and metacommunity structure correlated with both local abiotic (pH and total dissolved nitrogen) and biotic (non‐host mollusk density, and H. trivolvis biomass) factors, with little support for regional predictors. Overall, this trematode metacommunity most closely followed the predictions from the species sorting or mass effects metacommunity paradigm, in which community diversity is filtered by local site characteristics.     

Range limits and parasite prevalence in a freshwater snail

Geographical range limits are thought to be set by species' physiological or ecological adaptation to abiotic factors, but the importance of biotic factors such as parasitism in determining range limits has not been well explored. In this study the prevalence of trematode parasitism in populations of a freshwater gastropod snail, Lymnaea stagnalis, increased sharply as this species approached its western UK range limit. The likelihood of trematode infection increased with snail size, but high prevalence at the range edge was not a result of interpopulation variation in snail size. Changes in population growth rates resulting from high rates of parasitism at the range edge could contribute to range limitation. The mechanism driving high rates of parasitism at the range edge is not clear, but changes in abiotic factors towards the range limit may influence snail life history and immune response to trematode infection, indirectly altering the prevalence of parasites in marginal host populations.     

Relationship between Snail Population Density and Infection Status of Snails and Fish with Zoonotic Trematodes in Vietnamese Carp Nurseries

Background

Fish-borne zoonotic trematodes (FZT) are a food safety and health concern in Vietnam. Humans and other final hosts acquire these parasites from eating raw or under-cooked fish with FZT metacercariae. Fish raised in ponds are exposed to cercariae shed by snail hosts that are common in fish farm ponds. Previous risk assessment on FZT transmission in the Red River Delta of Vietnam identified carp nursery ponds as major sites of transmission. In this study, we analyzed the association between snail population density and heterophyid trematode infection in snails with the rate of FZT transmission to juvenile fish raised in carp nurseries.

Methodology/Principal Findings

Snail population density and prevalence of trematode (Heterophyidae) infections were determined in 48 carp nurseries producing Rohu juveniles, (Labeo rohita) in the Red River Delta area. Fish samples were examined at 3, 6 and 9 weeks after the juvenile fish were introduced into the ponds. There was a significant positive correlation between prevalence of FZT metacercariae in juvenile fish and density of infected snails. Thus, the odds of infection in juvenile fish were 4.36 and 11.32 times higher for ponds with medium and high density of snails, respectively, compared to ponds where no infected snails were found. Further, the intensity of fish FZT infections increased with the density of infected snails. Interestingly, however, some ponds with no or few infected snails were collected also had high prevalence and intensity of FZT in juvenile fish. This may be due to immigration of cercariae into the pond from external water sources.

Conclusions/Significance

The total number and density of potential host snails and density of host snails infected with heterophyid trematodes in the aquaculture pond is a useful predictor for infections in juvenile fish, although infection levels in juvenile fish can occur despite low density or absence infected snails. This suggests that intervention programs to control FZT infection of fish should include not only intra-pond snail control, but also include water sources of allochthonous cercariae, i.e. canals supplying water to ponds as well as snail habitats outside the pond such as rice fields and surrounding ponds.     

Predation differentially structures immature mosquito populations in stormwater ponds

1. Understanding the factors underlying the abundance and distribution of species requires the consideration of a complex suite of interacting biotic and abiotic factors operating on multiple spatial and temporal scales. Larval mosquitoes inhabiting small human-constructed ponds represent a unique opportunity to investigate the relative importance of these structuring mechanisms while simultaneously generating applied knowledge on mosquito control. 2. A multi-year field survey of 32 stormwater ponds was conducted in central Illinois (Champaign County). From each pond, data were collected on pond structure type and hydroperiod, the presence/absence of cattails (Typha spp.), and measures of total nitrogen, phosphorus, and organic carbon, and chlorophyll a. The communities of crustacean zooplankton and aquatic insects were characterised, and these taxa were assigned into two main groups: predators and competitors of larval mosquitoes. Structural equation modelling was used to explore the direct and indirect effects of these biotic and abiotic factors on larval density for three species of culicine mosquitoes (Culex pipiens, Culex restuans, and Aedes vexans). 3. Hydroperiod had an indirect negative effect on C. pipiens density. However, this effect was mediated by predator density; more permanent ponds had more predators, which therefore reduced the density of C. pipiens larvae. Aedes vexans density was positively correlated with predator density. No predictor variables were found that explained variation in C. restuans density. 4. This study show that the relative importance of these biotic and abiotic factors varies among species of culicine mosquitoes inhabiting stormwater ponds.     

The effect of local environmental variables on the helminth parasite communities of the pointedbelly frog Leptodactylus podicipinus from ponds in the Pantanal wetlands

Understanding the patterns of species distribution and abundance has been at the core of ecology. In general, these patterns are determined by species dispersion as well as by abiotic and biotic environmental conditions. Similarly, host-parasite relations and the structure of parasite assemblages are also shaped by environmental conditions and landscape composition. Herein, we assessed the influence of environmental variables and parasite species dispersion on the structure of helminth parasites communities in the frog Leptodactylus podicipinus. We sampled 10 ponds and recorded area, depth, altitude, pH, dissolved oxygen, salinity, temperature, and extent of soil, water, and vegetation cover as well as the distances between the ponds. We collected 121 frogs and found 9 helminth taxa; 2 of them were core species (prevalence higher than 50%), which contributed to the relatively high similarity observed among the ponds. Most of the helminths showed some variation in the frequencies of occurrence among communities from different ponds. The change in species composition among ponds was explained by the environmental variables but not by the distance between the ponds. Moreover, the results indicated that local processes (variation in environmental conditions) were more important than the regional processes (species distribution) in determining the structure of parasite communities. The variation in helminth communities among ponds in response to moderate differences in pond environmental characteristics points to the potential of helminth species as indicators of environmental conditions.     

Complex interactions among a nematode parasite (Daubaylia potomaca), a commensalistic annelid (Chaetogaster limnaei limnaei), and trematode parasites in a snail host (Helisoma anceps)

Many biotic interactions can affect the prevalence and intensity of parasite infections in aquatic snails. Historically, these studies have centered on interactions between trematode parasites or between trematodes and other organisms. The present investigation focuses on the nematode parasite Daubaylia potomaca and its interactions with a commensal, Chaetogaster limnaei limnaei , and a variety of trematode species. It was found that the presence of C. l. limnaei indirectly increased the mean intensity of D. potomaca infections, apparently by acting as a restraint for various trematode parasites, particularly the rediae of Echinostoma sp. In turn, Echinostoma sp. rediae adversely affected the mean intensity of D. potomaca by their consumption of both juvenile and adult nematodes present in tissues of the snail. These organisms not only belong to 3 different phyla but occupy distinct trophic levels as well. The complex interactions among these 3 organisms in the snail host provide an excellent example of biotic interactions influencing the infection dynamics of parasites in aquatic snails.     

Relationships between nutrient enrichment,pleurocerid snail density and trematode infection rate in streams

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Spatial covariation between infection levels and intermediate host densities in two trematode species

Both theoretical arguments and empirical evidence suggest that parasite transmission depends on host density. In helminths with complex life cycles, however, it is not clear which host, if any, is the most important. Here, the relationships between the abundance of metacercariae in second intermediate hosts, and the local density of both the first and second intermediate hosts of two trematode species, are investigated. Samples of the snail Potamopyrgus antipodarum, the amphipod Paracalliope fluviatilis and the isopod Austridotea annectens were collected from ten stations in a New Zealand lake. In the trematode Coitocaecum parvum, neither the density of the snail first intermediate host nor that of the amphipod second intermediate host correlated with infection levels in amphipods. In contrast, in the trematode Microphallus, infection levels in isopod second intermediate hosts were positively associated with isopod density and negatively associated with the density of snail first intermediate hosts. These relationships are explained by a negative correlation between snail and isopod densities, mediated in part by their different use of macrophyte beds in the lake. Overall, the results suggest that, at least for Microphallus, local infection levels depend on local intermediate host densities.     

The role of spatial and temporal heterogeneity and competition in structuring trematode communities in the great pond snail, Lymnaea stagnalis (L.)

We assessed how spatial and temporal heterogeneity and competition structure larval trematode communities in the pulmonate snail Lymnaea stagnalis . To postulate a dominance hierarchy, mark-release-recapture was used to monitor replacements of trematode species within snails over time. In addition, we sampled the trematode community in snails in different ponds in 3 consecutive years. A total of 7,623 snails (10,382 capture events) was sampled in 7 fishponds in the Jind?ich?v Hradec and T?eboň areas in South Bohemia (Czech Republic) from August 2006 to October 2008. Overall, 39% of snails were infected by a community of 14 trematode species; 7% of snails were infected with more than 1 trematode species (constituting 16 double- and 4 triple-species combinations). Results of the null-model analyses suggested that spatial heterogeneity in recruitment among ponds isolated trematode species from each other, whereas seasonal pulses in recruitment increased species interactions in some ponds. Competitive exclusion among trematodes led to a rarity of multiple infections compared to null-model expectations. Competitive relationships among trematode species were hypothesized as a dominance hierarchy based on direct evidence of replacement and invasion and on indirect evidence. Seven top dominant species with putatively similar competitive abilities (6 rediae and 1 sporocyst species) reduced the prevalence of the other trematode species developing in sporocysts only.     

The component community structure of larval trematodes in the pulmonate snail Helisoma anceps

Factors that affected the component community structure of larval trematodes in the pulmonate snail Helisoma anceps in Charlie's Pond, North Carolina, were studied over a 15-mo period using a multiple mark-recapture protocol. Patent infections of 8 species were observed in 1,485 of 4,899 snails examined. Reproductive activity, population size, and survival rate of the snail population were estimated to evaluate the extent of resource availability for the parasites. Antagonistic interactions between trematode species that occurred at the infracommunity level had a neglible effect on the composition and structure of the component community. The patterns observed at this level were related to temporal heterogeneity in the abundance of infective stages (mostly miracidia), differential responses of trematode species to the diverse and constantly changing distribution of snail size and abundance, differential mortality of snails infected with certain trematode species, constant recruitment of 1 trematode species over time, and the existence of predictable disturbances such as the complete mortality of the host population and recruitment of a replacement population during a 6-8 wk period. The last factor operated as a reset mechanism for this snail-trematode system once each year. A model of patch dynamics, with snails as patch resources, best explains the organization and dynamics of this system.     

Parasite-induced alteration of diurnal rhythms in a freshwater snail

The trematode Microphallus sp. alters the behavior of its snail intermediate host, Potamopyrgus antipodarum, in ways that seem to increase transmission to its final host, e.g., waterfowl, and decrease the probability of being eaten by other predators, e.g., fish. The parasite seems to cause the snail to move from the top to the bottom of rocks at about 0900 hr. Waterfowl feed predominantly before 0900 hr, and fish feed predominantly after 0900 hr. In the present study, we tested the hypothesis that Microphallus sp.-infected snails exhibit a change in behavior at around 0900 hr by examining their response to light and vertical orientation before and after 0900 hr. Results demonstrated that uninfected snails generally move toward light, oriented downward, and move a greater distance in the light compared with the dark at all times of day. Microphallus sp.-infected snails behaved differently from uninfected snails in the early morning but similarly to uninfected snails in the late morning with regard to downward orientation and distance moved in response to light. Snails infected with parasites other than Microphallus sp. behaved similarly to uninfected snails during both time periods. These results suggest that Microphallus sp. manipulates the behavior of Potamopyrgus sp. by altering rates of movement in response to light and vertical orientation in a manner consistent with the hypothesized 0900-hr shift.     

Environmental factors influencing trematode prevalence in grey tree frog (Hyla versicolor) tadpoles in southern Ontario

The emergence or increased prevalence of various parasites may be linked to alterations in host-parasite interactions caused by environmental changes. We investigated prevalence of trematode infections in grey tree frog (Hyla versicolor) tadpoles from ponds in nonagricultural settings versus ponds adjacent to cornfields in southern Ontario. We found that agricultural activity was a significant factor in determining the percentage of tadpoles infected by 1 or more trematodes from 1 or more species (combined trematode infection). However, we found no associations between combined trematode infection and forest cover; pond size; road density; and measures of water quality, such as nitrate level and the presence of the herbicide atrazine. Although combined trematode prevalence was associated only with agricultural activity, prevalence of Alaria species showed a positive association with forest cover. This latter result probably reflects the importance of habitat suitability for the canid definitive hosts of this trematode species.     

Temporal variations in the infection of a population of Cerithidea cingulata by larval trematodes in Kuwait Bay

The prosobranch gastropod Cerithidea cingulata (Gastropoda: Potamididae) in Kuwait Bay was examined for larval trematode infections over a 17-month period. A total of 2537 snails were examined and 1265 (49.9%) found to be infected with one or more species of trematodes. The component community in the snail comprised 12 species representing the families Cyathocotylidae (2), Echinostomatidae (2), Haplosplanchnidae (1), Heterophyidae (2), Microphallidae (1), Philophthalmidae (2), Plagiorchiidae (1) and Schistosomatidae (1). Cyathocotylid II (41.6%) was by far the most prevalent species followed by the microphallid (3.9%), the two species comprised 90% of the total trematode fauna. The prevalence of infection increased with shell size and was significantly higher in male (47%) than female (33%) snails. Multiple infections were observed in only 15 (1.2%) of the infected snails; cyathocotylid I and cyathocotylid II combination occurred 14 times and heterophyid I and the microphallid occurred once. Trematode species were more diverse and prevalent in winter, and cercarial shedding peaked in summer. Behaviour of the definitive host and snail population dynamics were probably the major contributors to the detected temporal pattern in the infections.     

Environmental factors influencing community composition of gastropods and their trematode parasites in southern Ontario

Agricultural activity and landscape features have previously been associated with diversity and prevalence of trematode species in amphibian second intermediate hosts. In this study, the density, diversity, and size of snail first intermediate hosts, and the diversity and prevalence of their trematode species, were assessed in 2 types of ponds, i.e., those adjacent to cornfields and those from the same region in southwestern Ontario that were adjacent to nonagricultural settings. Species of trematodes included, but were not restricted to, those that are known parasites of larval and adult frogs. We also assessed landscape factors likely to influence use by definitive hosts. Presence of the herbicide atrazine in ponds was measured to check that ponds adjacent to agriculture had potential to be affected by agricultural runoff. Both snail size and the proportion of snails releasing cercariae were greater in nonagricultural ponds, contrasting with a previous finding of lower trematode infection in tadpoles from nonagricultural ponds. Percentage of forest cover was associated with prevalence of certain trematode species, but not with estimates of combined prevalence. Absence of relations of trematode prevalence to measures of road density also contrasted with previous studies. We interpret our results in light of how agricultural activity might influence trematode viability, snail growth, and use by wildlife definitive hosts, independently of landscape factors.     

Relating fish kills to upwellings and wind patterns in the Salton Sea

Awareness of pond conservation value is growing all over Europe. Ponds are recognized as important ecosystems supporting large numbers of species and several rare and threatened aquatic plants, macroinvertebrates and amphibians. Notwithstanding ponds, particularly temporary ones, are still neglected in Italy. There are some gaps in our understanding of the macrophyte ecology and the conservation value of Mediterranean small still waters. Therefore, this study investigated the macrophyte communities and physico-chemical characteristics of 8 permanent and 13 temporary ponds along the Tyrrhenian coast near Rome, with the aim to relate the distribution of aquatic plants to environmental variables, and to define the botanical conservation value of ponds. Throughout the study period (Spring 2002), Principal Component Analysis performed on abiotic variables clearly discriminated temporary ponds, smaller and more eutrophic, from permanent ponds, larger and with higher pH and oxygen concentration. A total of 73 macrophyte taxa were collected in the study ponds. Temporary waters hosted a smaller number of plant species than permanent ones. Besides hydroperiod length, the environmental factors related to plant richness were maximum depth, surface area, dissolved oxygen and nitrogen concentration in the water. Moreover, the Non-metric Multidimensional Scaling showed a high dissimilarity in the taxonomic composition of aquatic plants between temporary and permanent ponds. The former contained more annual fast-growing species (Callitriche sp. pl. and Ranunculus sp. pl.), while in the latter species with long life-cycles (i.e. Potamogeton sp. pl.) were more abundant. Our results highlighted that temporary and permanent ponds in central Italy have different macrophyte assemblages, with aquatic species (including some of conservation interest at regional scale) exclusively found in each pond type. This suggested that both type of ponds could give an irreplaceable contribution to the conservation of aquatic plant diversity of these freshwater ecosystems. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: R. Céréghino, J. Biggs, B. Oertli & S. Declerck The ecology of European ponds: defining the characteristics of a neglected freshwater habitat     

Environmental gradients and the structure of freshwater snail communities

A fundamental goal of ecology is to understand the factors that influence community structure and, consequently, generate heterogeneity in species richness across habitats. While niche‐assembly (e.g. species‐sorting) and dispersal‐assembly mechanisms are widely recognized as factors structuring communities, there remains substantial debate concerning the relative importance of each of these mechanisms. Using freshwater snails as a model system, we explore how abiotic and biotic factors interact with dispersal to structure local communities and generate regional patterns in species richness. Our data set consisted of 24 snail species from 43 ponds and lakes surveyed for seven years on the Univ. of Michigan's E. S. George Reserve and Pinckney State Recreation Area near Ann Arbor, Michigan. We found that heterogeneity in habitat conditions mediated species‐sorting mechanism to drive patterns in snail species richness across sites. In particular, physical environmental variables (i.e. habitat area, hydroperiod, and canopy cover), pH, and fish presence accounted for the majority of variation in the species richness across sites. We also found evidence of Gleasonian structure (i.e. significant species turnover with stochastic species loss) in the metacommunity. Turnover in snail species distributions was driven by the replacement of several pulmonate species with prosobranch species at the pond permanence transition. Turnover appeared to be driven by physiological constraints associated with differences in respiration mode between the snail orders and shell characteristics that deter molluscivorous fish. In contrast to these niche‐assembly mechanisms, there was no evidence that dispersal‐assembly mechanisms were structuring the communities. This suggests that niche‐assembly mechanisms are more important than dispersal‐assembly mechanisms for structuring local snail communities.     

Amphibian species richness across environmental gradients

Large‐scale field patterns are a fundamental source of inferences on processes responsible for variation in species richness among habitats. We examined species richness of larval amphibian communities in 37 ponds over seven years on the Univ. of Michigan's E. S. George Reserve. Ordination of the community incidence matrix indicated a strong major axis of variation in species associations that was correlated with pond hydroperiod, surface area and forest canopy cover. Communities were significantly nested with those species found in ponds with high canopy cover, small area and short hydroperiod being nested subsets of those found in ponds with contrasting characteristics. Presence of fish had strong negative effects on species richness; relaxation of this effect also was apparent when fish were extirpated from ponds by drought. We employed a model selection analysis to identify the most appropriate statistical model for predicting the long‐term average species richness of these ponds from local abiotic and biotic (predator and competitor density) factors. A model including only the abiotic factors was overwhelmingly superior for the anurans; hierarchical partitioning indicated that area and canopy cover alone accounted for over 70% of the independent effects of predictor variables. The global model including both abiotic and biotic factors was the best supported model for the caudates, and correspondingly hierarchical partitioning suggested that area, hydroperiod, invertebrate predators and caudate biomass all accounted for 9–16% of the independent effects. Overall, biotic factors accounted for much less of the variation in species richness than abiotic factors. The patterns in larger, open‐canopy ponds provided little evidence of competitive effects on species richness, though there were patterns consistent with competitive effects in small, closed‐canopy ponds. The unusual temporal and spatial extent of these data enabled us to critically evaluate ideas regarding patterns in larval amphibian communities, and the effects of area, disturbance (hydroperiod) and productivity (canopy cover) on species richness of these communities. These results have important implications to the conservation of amphibian species richness in freshwater wetlands, which are among the most threatened ecosystems worldwide.     

Spatial and temporal structure of the trematode component community in Valvata macrostoma (Gastropoda, Prosobranchia)

We conducted the first comprehensive study on the spatiotemporal structure of trematode communities in the large-mouthed valve snail, Valvata macrostoma. A total of 1103 snails were examined monthly between May and October 2007 from Lake Konnevesi, Central Finland, from a shallow (1-2 m deep) and an offshore site (5-6 m deep), located ca. 50-70 m apart. Snails were infected by 10 trematode species. The species composition and prevalence were strikingly different between the sites with high species diversity in the shallow site (all 10 species; total prevalence of sporocysts/rediae 12.1%, metacercariae 55.4%) compared to the deeper site (3 species; prevalence 15.0% and 1.9%, respectively). This difference persisted throughout our study and is probably related to the spatial distribution of bird definitive hosts, whereas the seasonal parasite dynamics are likely to be affected by changes in the age-structure of the snail population. The probability of sporocyst infections increased with snail size, but no such trend was observed in redial or metacercarial infections which decreased with host size. Our results show that generally well-described spatiotemporal differences in trematode infection of molluscs can emerge in very narrow spatial and temporal scales, which emphasizes the importance of these factors in community studies.     

Larval trematodes (Digenea) of the great pond snail, Lymnaea stagnalis (L.), (Gastropoda, Pulmonata) in Central Europe: a survey of species and key to their identification

A survey of cercariae and metacercariae (Trematoda, Digenea) from the great pond snail (Lymnaea stagnalis) in Central Europe (Austria, Czech Republic, South-East Germany, Poland and Slovak Republic) is presented, based on a study of 3,628 snails examined from 1998 to 2005. A total of 953 (26.3%) L. stagnalis were infected with 24 trematode species comprising 19 species of cercariae and 11 species of metacercariae (six species occurred both as cercarie and metacercarie) of eight families. The dominant cercariae were those of Opisthioglyphe ranae (159 hosts infected), Plagiorchis elegans (141) (both family Plagiorchiidae) and Echinoparyphium aconiatum (153) (Echinostomatidae); 14 double infections were found. The most frequent metacercariae were those of Neoglyphe locellus (71) (Omphalometridae), E. aconiatum (66), Echinostoma sp. (59) and Moliniella anceps (48) (Echinostomatidae). In the previous studies carried out in Central Europe, a very similar spectrum of nine trematode families of 22 cercariae determined to species level and 43 types of cercariae reported under generic or provisional names, which can be in many cases conspecific with the previous taxa, were found. A simple key to identification of cercariae and metacercariae, together with their illustrations, is provided.