Gyraulus Parvus Research Articles

Gyraulus laevis and G. parvus (Mollusca: Gastropoda), two distinct species

Lorencová et al. (2021) found by barcoding of Gyraulus laevis from Europe and G. parvus from Northern America that the tested gene fragments are similar and so the authors believed that both taxa are conspecific. However, they ignored anatomical and morphological differences which have to be considered because genetic data are not a priori higher weighted than morphology. Summarized we can say that Gyraulus parvus and G. laevis are distinct species, because, (1) they differ in the vas deferens, (2) the penultimate whorl in G. parvus tends to be elevated (visible in the adults only), and (3) G. laevis occurs in shallow water of lakes and ponds, while G. parvus prefers (in Europe) artificial water bodies.

Prey-mimetism in cercariae of Apatemon (Digenea, Strigeidae) in freshwater in northern latitudes.

Cercariae, the free-living larval stages of trematodes, have adopted an amazing variety of transmission strategies. One of them is prey-mimetism, i.e. cercariae mimicking prey to attract motile hosts to be eaten. In a period between 2002 and 2019, we examined small planorbid snails, Bathyomphalus contortus, Gyraulus parvus and Planorbis planorbis from lakes in Finland and Iceland and from the Curonian Lagoon in Lithuania. Cercariae with conspicuously enlarged tails and unusual swimming behaviour, likely mimicking invertebrate prey, were detected and studied by the use of morphological and molecular (cox1, ITS1-5.8S-ITS2 and 28S rDNA) methods. Cercariae of two species belonging to the genus Apatemon (Strigeidae) were recognised. We consider Apatemon sp. 5 ex P. planorbis from the Curonian Lagoon identical to Cercaria globocaudata U. Szidat, 1940. Cercariae ex G. parvus from Iceland and ex B. contortus from Finland were conspecific, and we named them Apatemon sp. 6; these cercariae could not be associated with any known species. For the first time, we verified that cercariae of the Bulbocauda group belong to the genus Apatemon. We provide a mini-review on records of furcocercariae of the family Strigeidae with enlarged tails reported in freshwaters of the northern hemisphere and reveal that it is not only Apatemon but also Australapatemon and most likely Strigea which belong to the Bulbocauda group, rendering it a purely ecological assemblage. Understanding which invertebrate swimming behaviour these cercariae are mimicking will enhance our knowledge of the processes behind trematode transmission and will help to assess evolutionary pathways of host-finding strategies in trematodes.

Gastropod Assemblages Associated with Habitat Heterogeneity and Hydrological Shifts in Two Shallow Waterbodies

We aimed to determine the effects of water level and habitat heterogeneity on gastropod fauna in the littoral zone, and the differentiation of functional feeding guilds (FFG) of gastropods. Two periods were analyzed: 2012 (low water level, LWL) and 2013 (high water level, HWL) in the littoral zone of two shallow waterbodies (Sutla backwater, NW Croatia). Waterbody S1, covered with Ceratophyllum demersum, was sampled in the macrophyte stands, and the littoral benthal area, while waterbody S2, without macrophytes, was sampled only in the littoral benthal area. It was observed discovered that among the macrophyte stands in S1, gastropods were significantly more abundant during LWL. The same trend was observed in the littoral benthal area of S2. In contrast, gastropod abundance was higher in the littoral benthal area of S1 during HWL. Comparing gastropods in the two waterbodies, the abundance in S1 was ten times higher than in S2. The most abundant species was Gyraulus parvus, which accounted for 51–92% of the gastropods observed among the macrophytes of S1 and 86% in the adjacent benthic zone. Among the FFG groups, grazers (particularly those feeding on gymnamoebae and rotifers) had the largest proportion, followed by shredders feeding on small pieces of macrophytes. In our research, we indicate the important role of microhabitat diversity and submerged macrophytes as a rich food source for gastropods and safe shelter from predators.

DNA Barcoding and Distribution of Gastropods and Malacostracans in the Lower Danube Region

This survey reports the spatial distribution of gastropods belonging to Caenogastropoda, Architaenioglossa, Littorinimorpha, Cycloneritida and Hygrophila orders, and malacostracans from Amphipoda and Mysida orders in the lower sector of the Danube River, Romania, using DNA barcoding based on the cytochrome C oxidase I (COI) gene sequence. Sampling was performed for eight locations of Danube Delta branches and Bechet area during three consecutive years (2019–2021). Molecular identification of sixteen gastropods and twelve crustacean individuals was confirmed to the species level, providing the first molecular identification of gastropods from the Lower Danube sector. Phylogenetic analysis showed that species of gastropods and crustaceans clustered in monophyletic groups. Among gastropods, Microcolpia daudebartii acicularis, Viviparus viviparus, Bithynia tentaculata, Physa fontinalis, Ampullaceana lagotis and Planorbarius corneus were identified in Chilia and Sulina branches; and the Bechet area was populated by Holandriana holandrii, Theodoxus transversalis and Gyraulus parvus. The amphipods and mysids were present along the three main Danube branches. The calculated density of these species revealed an abundant community of crustacean Chelicorophium robustum on Sulina branch, and Dikerogammarus haemobaphes and D. villosus in extended areas of the Danube Delta. The presence of these invertebrates along Danube River was reported in relation to the sediment type and water depth.

Invasion at the population level: a story of the freshwater snails Gyraulus parvus and G. laevis

Invasion at the population level: a story of the freshwater snails Gyraulus parvus and G. laevis

The Orava dam reservoir – an important site of aquatic molluscs in north-western Slovakia

Mollusc assemblages of the Orava reservoir, the biggest dam reservoir in Slovakia, were studied in 2020. The reservoir, built in 1941–1953, is situated in north-western Slovakia. Sixteen aquatic mollusc species (13 gastropods, 3 bivalves) were recorded. Valvata piscinalis (O. F. Müller), Radix auricularia (Linnaeus) and Gyraulus parvus (Say) were the most frequent; they were recorded in more than ten sites each. Rich mollusc assemblages, composed mainly of gastropods, were found in sites with rich littoral vegetation of macrophytes. The bivalve diversity and abundance were very small, especially compared to the other studied dam reservoirs. The current results were compared with the previous surveys. The occurrence of Radix lagotis (Schrank) is its first reliable record in Slovakia. Viviparus acerosus (Bourguignat), Aplexa hypnorum (Linnaeus), Anodonta cygnea (Linnaeus), non-native Potamopyrgus antipodarum (Gray) and Physa acuta (Draparnaud) were recorded in this area for the first time and their sites are outside their known range in Slovakia.

Biology, immature stages, and systematics of snail-killing flies of the genus Colobaea (Diptera: Sciomyzidae), with overviews of aspects of the tribe Sciomyzini.

All reared larvae of flies of the genus Colobaea Zetterstedt, 1837 (Diptera: Sciomyzidae), which comprises 15 valid species, kill and consume freshwater nonoperculate pulmonate snails. New data are presented on the geographic distribution, biology, morphology of immature stages, and classification of Colobaea. Life cycle information is provided from field data and laboratory rearings for four of the 11 Palearctic species-C. bifasciella (Fallén), C. deemingi Knutson Bratt n.sp., C. pectoralis (Zetterstedt), and C. punctata (Lundbeck)-and for one of the three Nearctic species, C. americana Steyskal. Colobaea bifasciella is shown to be one of the most highly specialized parasitoid Sciomyzini, laying eggs on shells of Galba truncatula (O.F. Müller) and Stagnicola palustris (O.F. Müller) in temporary, intermittent, or vernal semiterrestrial situations. Each larva feeds in only one host snail, which is not killed until shortly before the larva completes development. Puparia are strongly modified to fit tightly within the shell of the host. The other reared species are shown to be less specialized than C. bifasciella, with eggs being laid upon vegetation, the larvae behaving as parasitoids-predators-saprophages of exposed aquatic snails, and the puparia of all four species being adapted to a lesser degree than C. bifasciella to fitting within the shell of the host snail. In nature, C. americana attacks Gyraulus parvus (Say) and Physa Draparnaud sp.; C. pectoralis attacks Anisus vortex (L.) and Bathyomphalus contortus (L.); and C. punctata attacks Gyraulus albus O.F. Müller, Lymnaea "peregra," Planorbarius corneus (L.), and Planorbis planorbis (L.). In the laboratory, these species also attacked and consumed other freshwater nonoperculate snails; C. deemingi was reared on Gyraulus intermixtus (Mousson) and Radix gedrosiana (Say), and an adult fly of the Palearctic C. distincta (Meigen) emerged from a puparium found in the shell of Anisus spirorbis (L.) collected in nature. Described and figured are eggs, larvae of all three instars, and puparia of the five laboratory-reared species. To provide perspective on features of Colobaea, diagnostic features are summarized of the immature stages of the Sciomyzini and the suprageneric categories of Sciomyzidae. The biogeography of the tribe Sciomyzini is presented, along with details of known geographical distribution. The classification and phylogenetic position of Colobaea are discussed. Included are a checklist of all known taxa of Colobaea, maps of geographic distribution, and a key to adults of the 15 valid species.

Vodní měkkýši Zoologické zahrady hl. m. Prahy [Aquatic molluscs of Prague Zoo

The Prague zoological garden is one of the most famous zoos in Europe. It covers an area of 58 ha on the right bank of the Vltava River (a tributary of the Elbe River). Aquatic molluscs of this zoo were studied mostly in 2019. Altogether 17 species were found at various outdoor habitats such as an old oxbow of the Vltava River, artificial pools, wetlands and small watercourses. Poor communities consisting of 1–4 species were found in most sites while 5–6 species were recorded at only four sites. Bithynia tentaculata, Gyraulus albus, and the non-native Physa acuta and Gyraulus parvus belonged among the most often recorded species. More diverse communities and numerous populations of aquatic molluscs were found mainly at sites overgrown with vegetation. On the contrary, it was difficult to find molluscs in habitats poor in vegetation with predatory pressure (e. g. water birds) and eutrophication.

Vodní měkkýši Sázavy a vybraných přítoků se zaměřením na ohrožené a nepůvodní druhy [Aquatic molluscs of the Sázava River and its selected tributaries with a focus on threatened and non-native species

This paper presents the results of a malacological survey of the Sázava River and its tributaries conducted over the last 20 years. The Sázava River (Czech Republic, Central and Eastern Bohemia) is one of the major tributaries of the Vltava River. Altogether 45 species of aquatic molluscs were found at 221 sites located at the Sázava River and its tributaries. More than 60% of recorded species of the Sázava River and its tributaries are common and widespread. The population of critically endangered Margaritifera margaritifera in the Jankovský potok is near extinction. Other threatened bivalves Pseudanodonta complanata, Unio crassus and Sphaerium rivicola were recorded in the Sázava River. Populations of U. crassus were also found in several tributaries (Blanice, Hejlovka, Martinický potok) while in the Sázavka Brook and the Želivka River only a few individuals were found. Gyraulus acronicus, a rare gastropod in the Czech Republic, was recorded in the Blanice River and several dam reservoirs. Four non-native species (Potamopyrgus antipodarum, Physa acuta, Gyraulus parvus, Dreissena polymorpha) were found in the monitored streams and reservoirs but usually in a relatively small number of localities. Most of these were located in the lower section of the Sázava River, Švihov dam reservoir and some tributaries.

Distribution and Conservation Status of the freshwater gastropods of Nebraska

This survey of freshwater gastropods within Nebraska includes 159 sample sites and encompasses the four primary level III ecoregions of the State. I identified sixteen species in five families. Six of the seven species with the highest incidence, Physa gyrina, Planorbella trivolvis, Stagnicola elodes, Gyraulus parvus, Stagnicola caperata, and Galba humilis were collected in each of Nebraska’s four major level III ecoregions. The exception, Physa acuta, was not collected in the Western High Plains ecoregion. Seven indigenous species, Valvata tricarinata, Helisoma anceps, Campeloma decisum, Galba bulimoides, Physa jennessi, Ferrissia rivularis, and Planorbula armigera, display incidence rarity, being collected at five or fewer samples sites. The non-indigenous Chinese mystery snail, Bellamya chinensis, was collected at five sites all within southeastern Nebraska. The Nebraska Sand Hills had the highest species richness, with 12 species. The wetland complex with the highest species richness of 8 was the lakes region of the Nebraska Sand Hills. Reservoirs and permanent/semi-permanent water bodies were the most species rich among water body types and hydrologic conditions with 13 and 14 species respectively. I assign a tentative conservation status to each species of indigenous freshwater snail observed following a modified quartile analysis.

Do freshwater gastropods avoid the benthic cyanobacterium Lyngbya wollei?

We experimentally assessed the mechanisms underlying the reduction in gastropod abundance in areas dominated by the filamentous, toxin-producing cyanobacterium Lyngbya wollei, which has replaced the large beds of Vallisneria americana in some areas of the St. Lawrence River. We hypothesized that the reduction in gastropod abundance was due to adult avoidance of cyanobacterial mats in favour of filamentous chlorophytes or vascular macrophytes. Of the 4 gastropod taxa offered a choice between L. wollei and filamentous chlorophytes, 3 (Pleurocera acuta, Amnicola limosa, and Gyraulus parvus) were either indifferent or even attracted to the cyanobacterium, and only Viviparus sp. preferred the chlorophytes. Lyngbya wollei exhibited higher nitrogen (N) contents (5–6%) and a lower carbon to nitrogen (C:N) ratio (6.1–7.6) than filamentous chlorophytes (3–5% N, C:N ratio 8.2–11.6). When offered a choice between L. wollei and the ribbon-leaved V. americana supporting either natural or partially removed epiphyte cover, P. acuta and A. limosa preferred the macrophyte with its natural epiphyte cover. Epiphytes on V. americana were twice as abundant and had a lower C:N ratio than natural epiphytes on L. wollei. Additional experiments exposing juvenile Bithynia tentaculata and Physa gyrina to different filamentous substrata showed similar growth but lower survival when gastropods were reared with L. wollei rather than with chlorophytes. Overall, our results showed that direct avoidance of L. wollei by adult gastropods did not explain their decline in areas dominated by cyanobacterial mats. Instead, gastropod decline likely resulted from habitat degradation coincident with reduced macrophyte abundance combined with decreased survival of juveniles exposed to L. wollei.

Vodní měkkýši nově vzniklého jezera Most v severních Čechách [Freshwater molluscs of the Most, a newly created lake in Northern Bohemia (Czech Republic)

This paper summarizes the knowledge of freshwater mollusc fauna of the Most Lake. It was created in 2008–2013 by flooding of the majority of the former coal quarry of Ležáky (Northern Bohemia). This water reservoir originated in the area of 311 ha and with the maximum depth of 75 m it is the largest water body of the area. The research was conducted in summer 2013, when the water level was about 0.5 m bellow the final expected level. In total, only six species of freshwater molluscs (five gastropods, one bivalve) were found at 11 sites. Two autochtonous molluscs (Radix auricularia and Gyraulus crista) and four allochtonous species (Physella acuta, Gyraulus parvus, Menetus dilatatus and Dreissena polymorpha) were found. The occurrence of all species except D. polymorpha was scattered, while the latter occurred in numerous populations sometimes with more than 80 specimens per 10 cm². Most of the molluscs were found on stones of the lake banks or at areas of shallow water. The results obtained during this research have recorded mollusc assemblages at the first successional stages of this artificial lake, thus enabling future comparison.

Anserobilharzia gen. n. (Digenea, Schistosomatidae) and redescription of A. brantae (Farr & Blankemeyer, 1956) comb. n. (syn. Trichobilharzia brantae), a parasite of geese (Anseriformes).

A new genus, Anserobilharzia, is proposed to accommodate Anserobilharzia brantae n. comb. (syn. Trichobilharzia bran- tae Farr & Blankemeyer, 1956), a species of avian schistosome thus far found exclusively in anserini geese (Anser, Branta, Chen) from Europe and North America, and Gyraulus snails. Recent collections and subsequent molecular analyses showed that A. brantae was distinct from Allobilharzia and Trichobilharzia and grouped basal to Trichobilharzia. Using nuclear 28S, ITS and mitochondrial cox1 as genetic yardsticks, samples of A. brantae from North America and Europe were each other's closest relative and distinct from Allobilharzia and Trichobilharzia. Anserobilharzia brantae was also distinct when compared morphologically with other species of closely related avian schistosomes. The following descrip- tion is based on males, females, eggs, and cercariae. The new genus is characterized by a) ovoid egg (72-145µm x 44- 89 µm) with spine, b) male with > 500 testes and caecal reunion anteriad to seminal vesicle, c) cercariae with 5+1 flame cells, and d) intermediate hosts are planorbid snails. The only confirmed species of snail host is Gyraulus parvus in North America. Based on presented data, we propose a new genus and new combination for A. brantae justified by morpholog- ical, host use, and molecular characteristics.

Herbiciding invasive reed: indirect effects on habitat conditions and snail–algal assemblages one year post-application

Invasive common reed (Phragmites australis) can rapidly form expansive, near-monotypic stands, and thereby lower plant diversity and change marsh habitat structure. Consequently, North American wetland managers often use herbicides, such as glyphosate-based AquaNeat® and imazypr-based Habitat®, to control its establishment and spread. However, herbiciding might indirectly affect benthic community structure by directly altering habitat structure, and habitat alterations may vary with herbicide and concentration. These effects may be particularly pronounced ≥1 year post-herbiciding when dead above-ground biomass collapses and submerges. To evaluate how herbicide-caused alterations in habitat affect key trophic linkages, we compared snail and epiphytic algal assemblages, and habitat conditions, among 20- × 20-m replicated plots of reed treated with either AquaNeat® (30 % solution), Habitat® (5 % solution), or left herbicide-free (i.e., controls) in an eutrophic Lake Erie coastal marsh 1-y post-herbiciding. Both herbicides equally reduced reed above-ground growth by >90 % relative to controls. Fossaria spp. and Gyraulus parvus snails were more abundant in herbicide-treated plots than in controls, but Shannon-Wiener diversity was similar (H′ ≈ 1.0) across treatments. All snails collected were pulmonates, suggesting habitat drying might be driving assemblage structure. Snails were denser in plots with metaphyton (mostly Spirogyra) than without, and metaphyton was more abundant in herbicide-treated plots with higher incident light levels and warmer water temperatures than in controls. Snail biomass was positively related to amount of benthic macro-organic matter but not epiphytic algal biomass, which was similar among treatments. Diatoms dominated algal communities in all treatments. In June, Navicula spp. was dominant in controls, whereas Nitzschia palea and Aulacoseira italic, and Nitzschia spp., were dominant in AquaNeat® and Habitat® treatments, respectively. However, algal and diatom assemblages were similar in treatments by early-July when marsh water levels significantly decreased and nitrate levels were <1 μg/L. Marsh hydrologic patterns may mediate herbiciding’s indirect effects on trophic structure.

New Intermediate Host Records for the Avian Schistosomes Dendritobilharzia pulverulenta, Gigantobilharzia huronensis, and Trichobilharzia querquedulae From North America

Here we provide the first North American report of a naturally infected snail, Gyraulus parvus, harboring the larval stages of the cosmopolitan, arterial schistosome, Dendritobilharzia pulverulenta. The relatively small cercariae of this species are shed in the early morning, are sticky, and adhere to the water's surface film. We also provide a report of the snail host, Physa gyrina, of the widespread North American passerine schistosome, Gigantobilharzia huronensis. Finally, we provide unambiguous documentation that Physa gyrina is a natural snail host for Trichobilharzia querquedulae, a schistosome primarily of dabbling ducks.

Influence of water hardness and sulfate on the acute toxicity of chloride to sensitive freshwater invertebrates

Total dissolved solids (TDS) represent the sum of all common ions (e.g., Na, K, Ca, Mg, chloride, sulfate, and bicarbonate) in freshwater. Currently, no federal water quality criteria exist for the protection of aquatic life for TDS, but because the constituents that constitute TDS are variable, the development of aquatic life criteria for specific ions is more practical than development of aquatic life criteria for TDS. Chloride is one such ion for which aquatic life criteria exist; however, the current aquatic life criteria dataset for chloride is more than 20 years old. Therefore, additional toxicity tests were conducted in the current study to confirm the acute toxicity of chloride to several potentially sensitive invertebrates: water flea (Ceriodaphnia dubia), fingernail clams (Sphaerium simile and Musculium transversum), snail (Gyraulus parvus), and worm (Tubifex tubifex), and determine the extent to which hardness and sulfate modify chloride toxicity. The results indicated a significant ameliorating effect of water hardness (calcium and magnesium) on chloride toxicity for all species tested except the snail; for example, the 48-h chloride median lethal concentration (LC50) for C. dubia at 50 mg/L hardness (977 mg Cl(-) /L) was half that at 800 mg/L hardness (1,836 mg Cl(-) /L). Conversely, sulfate over the range of 25 to 600 mg/L exerted a negligible effect on chloride toxicity to C. dubia. Rank order of LC50 values for chloride at a given water hardness was in the order (lowest to highest): S. simile < C. dubia < M. transversum < G. parvus < T. tubifex. Results of the current study support the contention that the specific conductivity or TDS concentration of a water body alone is not a sufficient predictor of acute toxicity and that knowledge of the specific ion composition is critical.

Molecular Systematics of the Avian Schistosome Genus Trichobilharzia (Trematoda: Schistosomatidae) in North America

Trichobilharzia is a genus of threadlike schistosomes with a cosmopolitan distribution in birds. Species of Trichobilharzia achieve notoriety as major etiological agents of cercarial dermatitis, or swimmer's itch. There are 40 species described in the literature, for which the majority lacks molecular sequence information. To better understand the phylogenetic relationships, diversity, species boundaries, host use, and geographic distribution of this genus better, we surveyed 378 birds and over 10,000 snails from North America. The phylogenetic analysis was based on nuclear 18S, 28S rDNA, internal transcribed spacer region and mitochondrial cytochrome oxidase I sequence data. Specimens were recovered that could be related to 6 of the 14 described species of Trichobilharzia from North America (Trichobilharzia physellae, Trichobilharzia querquedulae, Trichobilharzia szidati, Trichobilharzia stagnicolae, Trichobilharzia franki, and Trichobilharzia brantae). An additional 5 lineages were found that could not be related directly to previously described species. Trichobilharzia brantae, transmitted by Gyraulus parvus, grouped outside the clade containing the recognized species of Trichobilharzia. A subgroup of the Trichobilharzia clade designated Clade Q was comprised of closely related species whose adults and eggs are similar, yet the European species use lymnaeids whereas the North American species use physids as snail hosts. This molecular phylogeny provides a useful framework (1) to facilitate identification of worms, including those involved in dermatitis outbreaks; (2) to test hypotheses about the evolution, diversification, host-parasite interactions and character evolution of Trichobilharzia; and (3) to guide future taxonomic revision of Trichobilharzia.

Schistosomes in the southwest United States and their potential for causing cercarial dermatitis or ‘swimmer's itch’

Cercarial dermatitis or swimmer's itch results when cercariae of schistosomes penetrate human skin and initiate inflammatory responses. The parasites typically die in the skin but in some cases may persist and infect other organs. Cercarial dermatitis is caused by a complex and poorly known assemblage of schistosome species, and can occur in any location where people come in contact with water bodies harbouring schistosome-infected snails. In North America, most cases are reported from the upper Midwest. In south-western USA, this phenomenon has not been well studied, and it is not known which schistosome species are present, or if cercarial dermatitis occurs with any regularity. As part of our ongoing studies of schistosome diversity, using morphological traits and sequence data to differentiate species, we have thus far identified eight schistosome genetic lineages from snails from New Mexico and Colorado. We have investigated two cercarial dermatitis outbreaks, one occurring in Stubblefield Lake in northern New Mexico, and one in Prospect Lake in the heart of Colorado Springs, Colorado. The New Mexico outbreak involved either one or two different avian schistosome species, both transmitted by physid snails. The Colorado outbreak was due to Trichobilharzia brantae, a species transmitted by geese and the snail Gyraulus parvus. These outbreaks are in contrast to those in northern states where schistosomes infecting snails of the family Lymnaeidae are more often responsible for outbreaks. Our survey suggests that dermatitis-causing schistosomes are not rare in the southwest, and that there are plenty of opportunities for dermatitis outbreaks to occur in this region.

Příspěvek k poznání vodních měkkýšů Vsetínské Bečvy a okolí (Česká republika) [Contribution to the knowledge of aquatic molluscs of the Vsetínská Bečva River and its surroundings (Czech Republic)

This paper brings a review of a malacological survey of the Vsetínská Bečva River, its tributaries, canals and other different aquatic habitats in surroundings (Eastern Moravia, Czech Republic). Vsetínská Bečva is a 58 km long river which rises in 870 m a.s.l. and joins Rožnovská Bečva River in Valašské Meziříčí at 288 m asl. Research was focused on endangered bivalve Unio crassus. Aquatic molluscs at 63 sites were studied in 2007. Altogether 19 species of aquatic molluscs (12 gastropods, 7 bivalves) were found. Three non-native species Potamopyrgus antipodarum, Physella acuta, and Gyraulus parvus, which are rare in Moravia, were found. Occurrence of vulnerable but in this region relatively common prosobranch Bythinella austriaca was confirmed in springs and rivulets. Research based on bivalves provided more interesting results. Existence of two large populations of Unio crassus were documented in two canals (mill races) in Hovězí and Vsetín. Populations of Unio crassus were estimated at 1500–2500 individuals in Hovězí and 1000–4000 individuals in Vsetín. Occurrence of young individuals of Unio crassus were confirmed in both cases. Rare bivalves Pisidium amnicum and P. moitessierianum were found at one site in Canal in Vsetín and also non-native Dreissena polymorpha was found at one site – the gravel pit near Nový Hrozenkov.

Příspěvek k poznání vodních měkkýšů CHKO Blaník (Česká republika) [A contribution to the knowledge of aquatic molluscs of the Blaník PLA (Czech Republic)

This paper brings a review of a malacological survey of the Blaník Protected Landscape Area (Central Bohemia, Czech Republic). Aquatic molluscs at 35 different sites (wetlands, springs, brooks, small river, pools, ponds) were studied from 1996 to 2006. Altogether, 28 species of aquatic molluscs (14 gastropods, 14 bivalves) represented 36% of the total Czech aquatic mollusc fauna were found. The scattered population of endangered bivalve Unio crassus was confirmed in the Blanice River. A population of Gyraulus acronicus, a rare boreal element of the Czech malacofauna, was documented from one site. There an occurrence of only one non-native mollusc was confirmed at the area under study. Gyraulus parvus was identified from Býkovický Rybník pond.