Prosobranch Snail Research Articles

Ecological and molecular studies on emerging schistosomiasis mansoni in Dhofar Governorate, Sultanate of Oman.

The recent detection of some cases of autochtonous schistosomiasis mansoni in Dhofar, Oman, prompted a search for the transmission sites. The five field surveys we conducted from November 2000 to February 2002 provided ecological data on schistosomiasis in Dhofar. Twenty-eight water bodies situated within 8-160 km from Salalah, the largest city of Dhofar and at altitudes of up to 900 m, were surveyed for freshwater snails. Biomphalaria arabica was found in 15 of them. Three sites (Tibraq, Siginitti and Arazat) had Schistosoma infected snails, the first snails shedding cercariae of this parasite ever collected in Oman. The parasite from Dhofar was analysed by Random Amplified Polymorphic DNA comparisons using 11 primers and 167 polymorphic fragments and had 87-88% similarity with Schistosoma mansoni from Guadeloupe, but only 37-38% similarity with S. rodhaini from Burundi. Thus, it is a strain of S. mansoni. During the November 2000 survey, the prosobranch snail Melanoides tuberculata was associated with B. arabica in 10 of the 13 B. arabica sites. Cercariae from other species of Digenea emerged from five of the B. arabica sites, including the three named above. This paper presents the first finding of S. mansoni in the Dhofar Governorate and represents an initial study of the biology of S. mansoni transmission. This parasite and its cycle need further biological and molecular characterization, and the clarification of its epidemiological status in Dhofar Governorate is an urgent task.

Trematode fauna of prosobranch snails of the genus Semisulcospira in Lake Biwa and the connected drainage system

The parasite fauna of prosobranch snails of the genus Semisulcospira was surveyed in Lake Biwa and the adjacent water system. One aspidogastrean and 28 digenetic trematode taxa were detected in 19 209 snails consisting of 10 morphological species. There was no trematode species peculiar to members of the subgenus Biwamelania that is endemic to the Lake Biwa water system. However, one species, Notocotylus magniovatus, was found only in the non-endemic subgenus Semisulcospira. Of 23 digenean taxa detected in more than one host, 13 were distributed in both the lake and the tributaries. Seven of these had host taxa, more than 1% of which were infected with the parasite in both the lake and the tributaries, four had such hosts only in the tributaries, and two had no such hosts. Three species detected only in Lake Biwa were previously reported from other rivers in Japan. In the seven species detected only in the tributaries, two species had life cycles that could be maintained only in rivers. These results indicate that the core areas for the distribution of parasites of Semisulcospira are tributaries, and the lake is a sink for these species. These results contradict the expectation that the parasite fauna should be richer in the lake than in tributaries because the lake is a stable habitat over a geological time scale and has more divergent freshwater animals than the adjacent water system.

Distributional Revisions and New and Amended Occurrence Records for Prosobranch Snails in Kansas

Gill-breathing operculate snails (Gastropoda: Prosobranchia) were reported historically from streams and wetlands throughout eastern Kansas. The past century has witnessed declines in the geographic range of most native taxa and the probable extirpation of at least two species, Campeloma crassulum and Amnicola limosus. Recent investigations have documented populations of five remaining prosobranch species. These include Probythinella emarginata, previously known in Kansas solely from the Pleistocene fossil record, and Pleurocera acuta, last reported in the state in 1956. Cincinnatia integra remains the most widely distributed prosobranch snail, occurring in scattered colonies throughout much of eastern Kansas. Pomatiopsis lapidaria, Elimia potosiensis, P. emarginata, and P. acuta are each relegated to a single known marsh or stream drainage. Earlier reports of Campeloma decisum in Kansas now are attributed to the conchologically similar species, C. crassulum. Changes observed in the prosobranch fauna during the past century have paralleled historical declines in habitat availability and surface water quality. The reversal of these environmental trends should serve as the initial focus of snail recovery efforts in Kansas.

Aspects of the feeding ecology of Sargochromis codringtonii in Lake Kariba, Zimbabwe

Abstract Sargochromis codringtonii has always been considered a good candidate for the biological control of snails. However, there is lack of data on the feeding ecology of this species. The diet of S. codringtonii was examined by an analysis of stomach contents. The food of adult S. codringtonii in Lake Kariba is dominated by prosobranch snails. Pulmonate snails form a small insignificant component of the diet of S. codringtonii , and the reasons for this are discussed. Electivity indices were used to investigate prey selection. S. codringtonii does not show a particular preference for any snail species. It feeds on any snail species that is readily available. A morphometrical analysis of the feeding structures of S. codringtonii showed that the fish is well adapted to handling a molluscivorous diet. The daily food consumption of S. codringtonii was estimated over different seasons using the Elliot & Persson (1978 ) model [ J. Anim. Ecol.47.977–991]. Estimates of food consumption indicate that the fish consumed 14.0% of their dry body weight per day in summer and this falls to 4.5% in winter. The low consumption of pulmonates means that S. codringtonii cannot be a successful biological control agent against the vectors of schistosomiasis.

Lowered nutritional quality supplements nudibranch chemical defense.

Reduced palatability through lowered nutritional content is a common defense for modular or gelatinous organisms, but commonly thought unavailable for active, mobile animals. However, nudibranchs - a group of brightly colored, shell-less snails - may supplement their chemical defenses via increased water and ash content. Among 33 gastropod species, nudibranchs differed from prosobranch snails by containing approximately half the digestible organic material per unit wet weight, indicating their caloric value per unit volume will likewise be less than that of shelled snails. Nudibranchs also allocated proportionally less organic material to exterior body regions than to the viscera. Because exterior regions are more easily regenerated and often contain nematocysts or high concentrations of chemical defense, the areas of slug bodies most vulnerable to attack are the best defended, the least valuable to potential predators, and the least costly for nudibranchs to replace. To test how these differences in organic content affect palatability to predators, I offered to Cancer productus, a common molluscivorous crab, pellets differing in organic content (12% or 22% of wet weight) and secondary chemistry (presence or absence of Archidoris montereyensis extract). In no-choice bioassays, chemical extracts reduced feeding by approximately 50%, while lowered organic content reduced feeding by approximately 19%. The effects of organic content did not significantly interact with those caused by chemical extracts, suggesting that, in some contexts, reduced nutritional quality offers a somewhat independent form of antipredator deterrence. Although the nutritional context of defenses is often considered in studies of plants and other organisms suffering partial predation, this study shows that such a multi-factor approach should be more commonly extended to mobile animals.

In vitro culture of the avian echinostome Himasthla elongata: from redia to marita

Axenic primary cultures of Himasthla elongata rediae harvested from hepatopancreas of naturally infected marine prosobranch snail Littorina littorea were maintained in Leibovitz’s L-15 medium (osmolarity of approximately 780 mOsm, pH 7.8, temperature 14 °C under normal atmospheric conditions). Cultured rediae were active, motile and demonstrated high synthetic activity in metabolic labelling experiment. Long-term cultivation experiment showed 50% survival level of the rediae for up to 70 days and significant differences between mortality in redia groups derived from different host individuals. Half of the rediae in the most robust group survived for up to 163 days, when the experiment was terminated. Development and emergence of in vivo preformed cercariae and daughter rediae was observed. Cercariae in the culture also encysted, transformed into metacercariae and some of them in one to two weeks after the transformation spontaneously excysted into juvenile maritae. The employed culture system is characterized by a very low level of proteolytic activity. This system is suggested as a method permitting to obtain rediae secretory–excretory products free of host-derived contaminants. Index Descriptors and Abbreviations: Himasthla elongata, Trematoda, redia, cercaria, metacercaria, marita, L. littorea, Gastropoda, in vitro, axenic primary cultures; SEP, secretory–excretory products; SSW, sterile seawater; SDS, sodium dodecyl sulfate; PAGE, polyacrylamide gel electrophoresis; PADK, protease activity detection kit; BSA, bovine serum albumin.

Östrogenartige wirkungen von bisphenol a auf vorderkiemenschnecken (Mollusca: Gastropoda: Prosobranchia)

Im Rahmen eines vom Umweltbundesamt geforderten Forschungsprojektes zur Entwicklung eines biologischen Tests mit der Suswasserschnecke Marisa cornuarietis fur geschlechtshormonahnlich wirkende Substanzen wurden unter anderem die Effekte des als Xenoostrogen verdachtigten Bisphenols A (BPA) untersucht. Zusatzlich zu den Laborversuchsreihen mit der Apfelschnecke M. cornuarietis wurden Versuche mit der Zwergdeckelschnecke Potamopyrgus antipodarum als Suswasserspezies sowie zwei marinen Arten, der Netzreusenschnecke Nassarius reticulatus und der Nordischen Purpurschnecke Nucella lapillus, durchgefuhrt. Wahrend N. reticulatus als sediment-bewohnende Art uber Kunstsedimente exponiert wurde, erfolgte fur die drei anderen Spezies die Exposition aquatisch. Die Tests mit der Apfelschnecke deckten einen nominalen Konzentrationsbereich von 1 bis 100 μg BPA/l in einem 5-monatigen Versuch mit adulten Tieren und einem kompletten Lebenszyklustest uber 12 Monate sowie einen Bereich von nominal 0,05–1 μg BPA/l (analytisch ermittelt: 0,0079–0,404 μg/l) in einem 6-monatigen Experiment mit adulten Exemplaren ab. In den drei Versuchsreihen loste die Testsubstanz ein komplexes Syndrom physiologischer und morphologischer Veranderungen bei M. cornuarietis aus, das als Ausbildung von ‘Superweibchen’ bezeichnet wird. Betroffene Exemplare sind durch zusatzliche weibliche Geschlechtsorgane, eine Vergroserung der akzessorischen Geschlechtsdrusen im Genitaltrakt, Missbildungen des pallialen Eileiterabschnitts mit einer daraus resultierenden erhohten Mortalitat der Weibchen und eine massive Stimulation der Ei- und Gelegeproduktion charakterisiert. Bei den Experimenten ergab sich eine LOEC von 48,3 ng/l, eine NOEC von 7,9 ng/l und eine EC10 von 13,9 ng/l. Superweibchen traten auch bei den drei anderen untersuchten Schneckenarten auf, doch wurden bei diesen wahrscheinlich aufgrund artspezifischer Unterschiede in der Anatomie der Genitaltrakte keine Eileitermissbildungen gefunden. Bei Potamopyrgus antipodarum loste BPA in einem 9-wochigen Experiment (nominaler Konzentrationsbereich: 1 bis 100 μg/l) eine vermehrte Bildung von Embryonen wahrend der sexuellen Ruhephase aus. Fur den Versuch ergab sich eine invertiert Uformige Konzentrations-Wirkungsbeziehung. Die 3-monatige Exposition von Nassarius reticulatus erfolgte uber kunstliche Sedimente (nominaler Konzentrationsbereich: 10–1000 μg/kg TG). BPA zeigte bei dieser Art konzentrationsabhangig eine uterotrophe Wirkung, die sich in einer signifikanten Vergroserung und Gewichtszunahme der akzessorischen Eileiterdrusen auserte. Adulte Nucella lapillus wurden uber einen Zeitraum von 3 Monaten aquatischen Nominalkonzentrationen von 1–100 μg BPA/l ausgesetzt. Die Superweibchen waren bei dieser Art ebenfalls durch vergroserte akzessorische Geschlechtsdrusen und eine verstarkte Eibildung gekennzeichnet. Zusatzlich loste die Testsubstanz aber auch bei den Mannchen charakteristische Veranderungen aus: Der Anteil fortpflanzungsfahiger Tiere mit reifen Spermien in der Vesicula seminalis ging ebenso zuruck wie die Ausdehnung von Penis und Prostata. Auch bei dieser Spezies wurden bereits bei der niedrigsten Testkonzentration statistisch signifikante Effekte im Vergleich zur Kontrolle ermittelt (LOEC ≤ 1 μg BPA/l; NOEC < 1 μg BPA/l). Die Ergebnisse zeigen, dass Vorderkiemerschnecken bereits bei erheblich niedrigeren BPA-Konzentrationen als andere systematische Gruppen des Tierreichs negative Effekte zeigen. Daher ist zum Schutz der aquatischen Lebensgemeinschaften und vor dem Hintergrund der derzeit auf EU-Ebene stattfindenden Risikobewertung fur BPA eine Berucksichtigung der vorgestellten Resultate zu fordern.

Isolation and characterization of di‐ and trinucleotide microsatellites in the freshwater snail Potamopyrgus antipodarum

AbstractThe freshwater prosobranch snail Potamopyrgus antipodarum is an important model system for studying the maintenance of sexual reproduction in its native New Zealand. Since introduction to the UK in the 1850s, the species has spread throughout Europe and recently the USA. We present the first microsatellites for P. antipodarum. Using two isolation protocols, which are qualitatively compared, we have developed PCR primers for three di‐ and four trinucleotide microsatellites. All loci proved to be polymorphic, when screened for variability in several UK populations. These markers should be of considerable utility in future population and ecological genetics studies of this species.

Some rare larval trematodes of prosobranch snails, Semisulcospira spp., in the Lake Biwa drainage system, central Japan

A total of 17 737 individuals of prosobranch snails, Semisulcospira spp., were collected from Lake Biwa and its tributaries, central Japan, from 1995 to 1999. They were examined for trematode larvae. One species of Aspidogastrea and 28 species of Digenea were detected. This paper briefly describes five of the 28 digeneans: a tetracotyle metacercaria from S. niponica, Cercaria A (cystophorous cercaria) from S. reticulata, Cercaria B (echinostomatid cercaria) from S. libertina, Cercaria C (magnacauda cercaria) from S. niponica and Cercaria D (mutabile cercarium) from S. nakasekoae. They were rare and every one of them was obtained from one snail only once.

THE LIFE CYCLE, POPULATION DYNAMICS, GROWTH AND SECONDARY PRODUCTION OF BITHYNIA GRAECA (WESTERLUND, 1879) (GASTROPODA) IN LAKE KERKINI, NORTHERN GREECE

The life cycle, population dynamics, growth and secondary production of the freshwater prosobranch snail Bithynia graeca (Westerlund 1879) were studied in the artificial Lake Kerkini (Serres, Northern Greece) where water volume and depth fluctuate dramatically. B. graeca faces deterministic and stochastic aspects of this environment. Growth and reproduction were studied for two populations, one being covered by the water almost throughout the year and the other not. B. graeca is a semelparous annual freshwater snail whose life expectancy decreased with increasing age. Maturity was attained 4 months earlier for the first population. Reproduction took place in spring. The majority of adults died after egg-laying. Growth rate was rapid during spring, and activity ceased during winter. B. graeca is a prosobranch snail whose short turnover time (77.9 and 84.3 days) was similar to that seen in freshwater pulmonate snails. Productivity was assessed in two ways, by a size frequency method and by using cumulative biomass. Observed values, for the two methods respectively, were for mean biomass 18.53 and 22.8 g dry body weight/m 2 , for annual production (P) 86.81 and 88.38 g dry body weight/m 2 or 9.56 gC/m 2 ·year respectively, and for annual turnover ratio (P/B ‐ ) 4.68 and 3.87/year. Net reproductive rate Ro was 2.99 and per capita rate of increase (rc) was 0.091.

Age distribution, growth, and lifetime copulation frequency of a freshwater snail, Clithon retropictus (Neritidae)

AbstractClithon retropictus is a prosobranch snail species that reproduces in freshwater but spends its veliger period in the sea. The age distribution of this snail was investigated at three sites along Takase River in Japan by counting annual growth lines on their shells. Also, copulation performance was examined using sheaths of spermatophores stored in the bursa copulatrix of females. A mark–recapture census demonstrated that the number of growth lines was a good indicator of the age of a snail. The maximum number of growth lines was 20, suggesting that this species is one of the most long‐lived freshwater gastropods. All the populations were female biased; the growth rate was higher and the life span was longer in females. Because spermatophore sheaths received by a female remained in her bursa copulatrix without being digested or discharged, the number of spermatophores implies her lifetime number of copulations. The number ranged from 0 to 91 and increased with age. Comparisons of population demonstrated that the average age was older, and the lifetime copulation number was significantly lower, at the upper stream site. These findings suggest that upstream migration had occurred only when the snails were very young and that copulation had been suppressed at the upstream site. The observed shorter longevity in males and the female‐biased sex ratio are thought to be a result of the high cost paid by the male in multiple copulation.

Interclonal variation in the acute and delayed toxicity of cadmium to the European prosobranch gastropod Potamopyrgus antipodarum (Gray).

The lethal responses of three European clones--A, B, and C-of the prosobranch snail Potamopyrgus antipodarum to acute cadmium exposure were examined by the use of a conventional LC50 test and a delayed toxicity test. The questions addressed were: (1) Are there differences in susceptibility (LC50 values and uniformity of response) among the three European clones of P. antipodarum? (2) Are the patterns of differences in susceptibility among clones observed in the LC50 test also observed for the delayed toxicity test? (3) Is there concordance in the ranking of susceptibility among clones under acute cadmium exposure and under chronic cadmium exposure? The results showed that the widths of the tolerance distribution differed among clones. Clones A and B had a steeper slope than clone C (for clone A the difference was marginally significant), which indicates that individuals from clones A and B showed a more uniform response to acute lethal cadmium stress than individuals from clone C. On the basis of the measured differences in LC50 values, clone A individuals showed the highest tolerance to acute cadmium (LC50 value: 1.92 mg Cd L(-1)) followed by clone B (LC50 value: 1.29 mg Cd L(-1)) and clone C (LC50 value: 0.56 mg Cd L(-1)). Clone C was significantly less tolerant than clones A and B. The delayed toxicity test showed a similar pattern to the LC50 test with regard to tolerance differences among clones; however, mortality continued following transfer to clean water, indicating that cadmium was lethal at much lower concentrations than indicated by the conventional LC50 test. Results of the LC50 test and the delayed toxicity test in the present study were in general agreement with results from chronic cadmium exposure experiments (Jensen et al. [2000] Ecol Appl [submitted]), i.e., the least susceptible clone A in the acute cadmium exposure test was also the least susceptible clone in the chronic cadmium exposure test. Based on the dramatic differences between the LC50 and the cadmium exposure concentrations causing delayed toxicity, we suggest that the potential for delayed toxicity should be given greater consideration in ecotoxicity testing.

Effects of endocrine disruptors on prosobranch snails (Mollusca: Gastropoda) in the laboratory. Part III: Cyproterone acetate and vinclozolin as antiandrogens.

The effects of suspected endocrine disrupting chemicals on freshwater and marine prosobranch species were analysed in laboratory experiments. In this last of three publications, the responses of the fresh water snail Marisa cornuarietis and of two marine prosobranchs (Nucella lapillus, Nassarius (Hinia) reticulatus) to the antiandrogenic model compounds cyproterone acetate (CPA) and vinclozolin (VZ) are presented. The snails were exposed to nominal CPA concentrations of 1.25 mg/L alone and simultaneously to a potent synthetic estrogen (ethinylestradiol), androgen (methyltestosterone) or an indirectly acting xeno-androgen (tributyltin) in experiments with adult specimens and in a life cycle test for 12 months. Marisa and Nucella were furthermore exposed to nominal concentrations of 0.03-1.0 microgram VZ/L for up to 5 months. The antiandrogens induced a number of biological responses in all three species. The length of the penis and of accessory male sex organs (e.g., penis sheath, prostate) were significantly reduced. For Marisa, this effect occurred only in sexually immature specimens and was reversible as the males attained puberty. Typical androgen-mediated responses (imposex development, delayed spermatogenesis, tubulus necrosis of the testis with orchitis and Leydig cell hyperplasia) were partially or totally suppressed by a simultaneous administration of CPA. In the two marine species even adult, sexually mature males responded to antiandrogens with a reduction of the male sex organs and an advancement of the sexual repose phase. The results for CPA and VZ are compared with the effects of an exposure to xeno-estrogens (bisphenol A, octylphenol) and xeno-androgens (triphenyltin, tributyltin) in the same species. Each group of endocrine disruptors induces a characteristic set of toxicological effects in prosobranch snails which can be used as endpoints in an organismic invertebrate test for the identification of endocrine mimetic test compounds. Estrogens cause primarily an induction of superfemales resulting in an increased female mortality by the enhancement of spawning mass and egg production. The main effects of androgens are a virilization of females by imposex development and a marked decrease of the fecundity. Compared with estrogens and androgens, the antiandrogen responses seem to be less drastic and might have--in contrast to the two other disruptor classes--no biologically significant effects at the population level.

Effects of an exotic bivalve mollusc on benthic invertebrates and food quality in the Ohio River

Effects of zebra mussels (Dreissena polymorpha) on populations of amphipods (Gammarus fasciatus) and prosobranch snails (Lithasia obovata) and on nutritional quality of benthic organic matter were examined in 20 artificial streams receiving Ohio River water and containing either mussels or small gravel. Twenty individually-marked snails were placed in each trough, and streams were allowed to colonize with other benthic species for 28 days.

Aspects of ecology and conservation of sympatric, prosobranch snails in a large river

We examined factors influencing distribution of prosobranch snails with field surveys, lab substrate-choice and movement experiments, and outdoor artificial stream experiments manipulating current, substrate and temperature. Restriction of Lithasia obovata to shallow, isolated rock patches and the more continuous distribution of Pleurocera canaliculatum on diverse substrates (shallow to deep water) seem related to food availability, predator vulnerability, wave resistance and dispersal abilities. Shallow, rocky habitats favored by the relatively fragile-shelled Lithasia maximize the more nutritious, epilithic microalgal food while minimizing wave displacement (firmer substrate) and exposure to molluscivorous fish inhabiting deeper waters. The broader distribution of the heavily-armored Pleurocera is attributed mostly to greater dispersal abilities (e.g. via deep water, gravel pathways), prevalence in more substrate types, and resistance to fish predators, but their relatively small foot may account for low densities in very shallow, wave-swept habitats. Lithasia is vulnerable because of its restriction to isolated, shallow rocky habitats, inability to reach deeper gravel dispersal pathways, and greater susceptibility to cold temperatures (slowing colonization of other habitats). Impoundments increase this threat by blocking inter-reach dispersal and hindering intra-reach dispersal through siltation. Pleurocera's survival is threatened by biofouling from zebra mussels which are more prevalent in depths inhabited by this species.

Standard Metabolic Rate in Gastropoda Class

Abstarct—The relationship between oxygen consumption and soft tissue weight in the Gastropoda class (according to the obtained and published data) is expressed by the equation with coefficientsa = 0.71 and k = 0.78. Prosobranch and pulmonate snails have similar levels of oxygen consumption. Opisthobranch snails have higher oxygen consumption. No relationship has been revealed between the metabolic rate (coefficient a) and climatic zone of the gastropod habitat.

Phylogenies inferred from mitochondrial gene orders-a cautionary tale from the parasitic flatworms.

[Extract] Mitochondrial genomes have been used in numerous studies to investigate phylogenetic relationships among eukaryotes at many levels (e.g., Smith et al. 1993; Boore et al. 1995; Boore, Lavrov, and Brown 1998). In recent years, the arrangement of genes in the mitochondrial genome has been regarded as a powerful record of historical relationships (Boore 1999). Changes in mitochondrial gene order are infrequent, even over considerable spans of time (Boore 1999), and are unlikely to exhibit homoplasy. Our research has focused on the relationships between two groups of human blood flukes within the genus Schistosoma. Our investigations on the mitochondrial genomes of these worms revealed striking divergences in mitochondrial gene order within the genus. The schistosomes are among the most significant parasites of humans in the developing world. The disease they cause, schistosomiasis, is second only to malaria in public health importance, affecting some 200 million people in 75 countries and giving rise to severe morbidity or mortality in tens of millions. Recent molecular studies (Barker and Blair 1996) have demonstrated that the deepest split in the genus is between East the Asian species utilizing prosobranch snail hosts and the African species utilizing pulmonate snails. The depth of this split has led some authors to propose an early Tertiary divergence (Despres et al. 1992). Species closely allied with the African group also occur in the Middle East, India, and parts of Southern Asia. One African species, Schistosoma mansoni, was probably introduced into the Americas by the slave trade during the 18th and 19th centuries (Despres, Imbert-Establet, and Monnerot 1993). The Asian group contains fewer recognized species, and these are found primarily in East Asia (the Philippines, China, Malaysia, Indonesia, Cambodia, and Laos). There is a growing realization that African and East Asian schistosomes differ in many biological attributes, including morphological characters, infectivity to snails, range of definitive hosts, growth rates, egg production, prepatency periods, pathogenicity, and immunogenicity (McManus and Hope 1993). We expected our investigations of mitochondrial genomes in these two groups of species to provide more evidence of their phylogenetic distance. However, we were startled by the remarkable differences in mitochondrial gene order which came to light between the two groups and which we report here.

Plagioporus sinitsini (Digenea : Opecoelidae): a one-host life cycle.

Adult Plagioporus sinitsini occur within daughter sporocysts voided with the feces of prosobranch snails Elimia symmetrica in Basin Creek, North Carolina. These worms produced eggs containing active miracidia while still in the snail. Adults in snails and adults in rosyside dace, Clinostomus funduloides, collected from the same stream were indistinguishable morphometrically. Adults in snails develop from cotylocercous cercariae sequestered in daughter sporocysts that pass through the metacercaria stage. These observations, and previous study in Michigan, suggest that the life cycle of P. sinitsini has 3 potential pathways, i.e., a 3-host life cycle involving molluscan, arthropod, and piscine hosts, a 2-host life cycle involving only molluscan and piscine hosts, and a 1-host life cycle involving only the snail host. The truncated life cycles do not appear to be the result of paedomorphosis.

Effects of endocrine disruptors on prosobranch snails (Mollusca: Gastropoda) in the laboratory. Part I: Bisphenol A and octylphenol as xeno-estrogens.

The effects of suspected endocrine disrupting chemicals on freshwater and marine prosobranch species were analysed in laboratory experiments. In this first publication, the responses of the freshwater snail Marisa cornuarietis and of the marine prosobranch Nucella lapillus to the xeno-estrogenic model compounds bisphenol A (BPA) and octylphenol (OP) are presented at nominal concentration ranges between 1 and 100 micrograms/L. Marisa was exposed during 5 months using adult specimens and in a complete life-cycle test for 12 months. In both experiments, the xeno-estrogens induced a complex syndrome of alterations in female Marisa referred to as "superfemales" at the lowest concentrations. Affected specimens were characterised by the formation of additional female organs, an enlargement of the accessory pallial sex glands, gross malformations of the pallial oviduct section resulting in an increased female mortality, and a massive stimulation of oocyte and spawning mass production. The effects of BPA and OP were comparable at the same nominal concentrations. An exposure to OP resulted in inverted U-type concentration response relationships for egg and spawning mass production. Adult Nucella from the field were tested for three months in the laboratory. As in Marisa, superfemales with enlarged accessory pallial sex glands and an enhancement of oocyte production were observed. No oviduct malformations were found probably due to species differences in the gross anatomical structure of the pallial oviduct. A lower percentage of exposed specimens had ripe sperm stored in their vesicula seminalis and additionally male Nucella exhibited a reduced length of penis and prostate gland when compared to the control. Because statistically significant effects were observed at the lowest nominal test concentrations (1 microgram BPA or OP/L), it can be assumed that even lower concentrations may have a negative impact on the snails. The results show that prosobranchs are sensitive to endocrine disruption at environmentally relevant concentrations and that especially M. cornuarietis is a promising candidate for a future organismic invertebrate model to identify endocrine-mimetic test compounds.

Effects of endocrine disruptors on prosobranch snails (Mollusca: Gastropoda) in the laboratory. Part II: Triphenyltin as a xeno-androgen.

In laboratory experiments the effects of suspected endocrine disrupting chemicals on freshwater and marine prosobranch species were analysed. In this second of three publications the responses of the freshwater ramshorn snail Marisa cornuarietis and of two marine prosobranchs (the dogwhelk Nucella lapillus and the netted whelk Hinia reticulata) to the xeno-androgenic model compound triphenyltin (TPT) are presented. Marisa and Nucella were exposed via water (nominal concentrations 5-500 ng TPT-Sn/L) and Hinia via sediments (nominal concentrations 50-500 micrograms TPT-Sn/kg dry wt.) for up to 4 months. Female ramshorn snails but not the two marine species developed imposex in a time and concentration dependent manner (EC10 4 months: 12.3 ng TPT-Sn/L) with a comparable intensity as described for tributyltin. TPT reduced furthermore the fecundity of Marisa at lower concentrations (EC10 4 months: 5.59 ng TPT-Sn/L) with a complete inhibition of spawning at nominal concentrations > or = 250 ng TPT-Sn/L (mean measured +/- SD: > or = 163 +/- 97.0 ng TPT-Sn/L). The extension of the pallial sex organs (penis with accessory structures and prostate gland) of male ramshorn snails and dogwhelks were reduced by up to 25% compared to the control but not in netted whelks. Histopathological analyses for M. cornuarietis and H. reticulata provide evidence for a marked impairment of spermatogenesis (both species) and oogenesis (only netted whelks). The test compound induced a highly significant and concentration independent increase in the incidence of hyperplasia on gills, osphradia and other organs in the mantle cavity of N. lapillus indicating a carcinogenic potential of TPT. The results show that prosobranchs are sensitive to endocrine disruption at environmentally relevant concentrations of TPT. Also, M. cornuarietis is a promising candidate for a future organismic invertebrate system to identify endocrine-mimetic test compounds.