Evaluation of the use of transplanted Nassarius reticulatus (Linnaeus, 1758), in monitoring TBT pollution,within the European Water Framework Directive

The European Water Framework Directive (WFD) requires monitoring programmes, to establish a coherent and comprehensive overview of ecological and chemical water status. Recently and within this context, the use of biomarkers has been proposed for incorporation into WFD monitoring programmes. In the present study, cages have been used to transplant (ranging between 14 and 75 days) adults of the dogwhelk Nassarius reticulatus in relation to a gradient of tributyltin (TBT) pollution; this is in order to evaluate its usefulness within the WFD monitoring programmes. Only the most polluted site (close to a shipyard) shows evidence of TBT contamination effects. As such, it may be concluded that the use of caged transplants with N. reticulatus (adults) is useful only for areas of high TBT pollution. Thus, within the European WFD context, this approach is generally not useful for surveillance and operational monitoring, but has some potential in investigative monitoring.     

TBT effects on the female genital system of Littorina littorea: a possible indicator of tributyltin pollution

Specimens of the prosobranch Littorina littorea (L., 1758) collected along the East Frisian North Sea coast in summer 1993 exhibited alterations of the pallial oviduct termed as intersex in response to tributyltin (TBT) pollution. The range of TBT body burden was between 150.9 and 1289.5 μg as Sn kg⁻¹ (dry wt.). Five stages of intersex development (0–4) could be distinguished and are documented with scanning electron micrographs. In stages 2–4, which can be found in the direct vicinity of harbours and marinas, the morphological malformations of the oviduct inhibit successful copulation and capsule formation, resulting in sterilization. The intersex index (ISI, calculated as the average intersex stage of a population) and the average prostate length of females were used as parameters for the determination of intersex intensities in the populations. Both indices show significant and positive correlations to the TBT body burden of L. littorea and are promising parameters for TBT biomonitoring. A comparison of TBT bioconcentration factors with populations from England and France indicates that the threshold concentration for intersex development is in the range of 15 ng TBT as Sn/l. Morphometric analyses of the midgut gland revealed no significant differences between sampling stations. In the ovary a retardation and blockage of maturation (atresia) was observed in populations close to harbours. Lytic processes in ovary follicles were observed not only at TBT exposed sites but also at reference stations.     

Comparison of imposex response in three Prosobranch species

A comparative study of the three gastropod species Nucella lapillus (L.), Ocenebra erinacea (L.) and Hinia (Nassarius) reticulata (L.) reveals that Nucella is the most TBT sensitive species while Hinia is the least sensitive. Of the two imposex indices VDSI and RPSI, good interspecies correlations were obtained only for VDSI. The three species can be considered as complementary not only in terms of their ecology but also for their levels of sensitivity. Indeed, Nucella and Ocenebra are useful test species at TBT concentrations below 2 ng Sn 1⁻¹ while Hinia is the more appropriate species at higher TBT levels. For the first time, two sterilised Hinia females are recorded. This sterilization does not seem to be due to proliferation of vas deferens tissue in the vaginal opening and further investigation is needed to find intermediary VDS stages between stage 4⁺ and sterilization. Studies using Nucella show that the use of narcotization in imposex analysis leads to an underestimation of RPSI compared with non-narcotization methods. Indeed, narcotization straightens the penis and increases its length when compared with non-narcotized animals, but this increase is proportionally higher in males than in females.     

Imposex and butyltin burden in Bolinus brandaris (Mollusca, Gastropoda) and sediment from the Tunisian coast

The present study aimed at analyzing the imposex incidence and the presence of butyltins namely tributyltin (TBT) with its di- and mono-substituted metabolites in Bolinus brandaris whole tissues and in surface sediments at seven sites from the Tunisian coast during one campaign in May 2010. Butyltin levels were evaluated using isotope dilution GC–MS. Except the population collected from Zarat site, imposex was found in snails from the remained six sites with a maximal incidence and sterility (closure of the vaginal opening) registered in Carrier bay. Both imposex indices VDSI and RPLI showed a positive correlation with tissue concentrations of TBT. Total butyltin concentrations in sediments were higher in sites located in the vicinity of shipping areas with levels of TBT high enough to cause environmental concern if there is no legislative restriction and enforcement for the sale and use of these chemicals in Tunisia. These results further confirmed that B. brandaris is a good bioindicator of butyltin pollution in the studied areas. In addition, this study provided recent and new data on sediment butyltin concentrations that could serve for long-term monitoring of TBT pollution in Tunisia and the Mediterranean Sea.     

Modelling the influence of nutrient loads on Portuguese estuaries

The effects of implementing Directive 91/271/EEC of 21 May 1991 (Waste Water Treatment Plan Directive) and Directive 91/676/EEC of 12 December (Nitrates Directive) are analysed in 7 Portuguese estuaries (Minho, Lima, Douro, Mondego, Tagus, Sado and Guadiana) and two coastal lagoons (Ria de Aveiro and Ria Formosa), with a modelling approach. MOHID Water Modelling System was used to perform simulations with three nitrogen load scenarios for each system: a reference scenario, a 50% nitrate removal by agriculture scenario and another with a 100% nutrients removal by waste water treatment plants (WWTP). It is shown that the interaction between hydrodynamic and ecological processes is an important feature to study trophic problems in estuaries. Ecological processes such as primary production only occur inside the system if the residence time of water is high enough to enable organismal activity and if the adequate conditions are found (e.g. light, nutrients, temperature). From the model results it is possible to conclude: (i) in systems with short residence time a reduction in nutrient load will only produce a decrease in nutrient transit and will not affect the system’s global ecological status (e.g. Douro Estuary); (ii) in systems with long residence time the effects will range from significant, when primary production is mostly limited by nutrients (e.g. Ria de Aveiro), to non-significant, when primary production in the system is light-limited (e.g. Tagus Estuary).     

Direct and indirect effects of predation,herbivory and surface rugosity on mussel recruitment

Summary The predatory gastropod Nucella lapillus, commonly preys upon the mussel, Mytilus edulis, and is thought to control the distribution and abundance of mussels on the rocky shores of New England, USA. In this study, done in Maine, USA, not only the presence of Nucella lapillus but also the roughness of the experimental surface and the presence of the herbivorous gastropod, Littorina littorea, were manipulated. Four types of surfaces were used as recruitment substrata for mussels: smooth bare granite, aggregations of the barnacle, Semibalanus balanoides, fiberglass resin castings of smooth bare granite and resin castings of aggregations of S. balanoides. To ensure that caged N. lapillus were not starving, barnacles were provided as alternative prey. Experiments showed no detectable effect of N. lapillus on the recruitment of M. edulis. Mussel recruitment was enhanced by surface rugosity and depressed by the activities of L. littorea. Analysis of covariance, using the number of algal species as the covariate, suggested that L. littorea reduced the number of newlyrecruited mussels by removing algae that provided recruitment sites, but no manipulations were done to test this conjecture. It is likely that previous reports of N. lapillus controlling mussel abundance are attributable to N. lapillus preying upon barnacles, which increase surface rugosity and enhance mussel recruitment. Review of literature on feeding preferences of N. lapillus supports this view. When handling times and prey availability are taken into account, Nucella shows a clear preference for barnacles over mussels.     

M-AMBI derived from taxonomic levels higher than species allows Ecological Status assessments of benthic habitats in new geographical areas

Under the Water Framework Directive (WFD) benthic Ecological Quality Ratios (EQRs) are important tools for assessing Ecological Status (ES) of coastal and transitional waters. Calculation of the Multivariate-AZTI Marine Biotic Index (M-AMBI) EQR is based on the proportions of sensitive and stress tolerant benthic invertebrate species, number of species and Shannon–Wiener diversity. The sensitivity of many tropical/sub-tropical taxa has not yet been determined, presenting a barrier to the direct transfer of WFD EQRs, and the ideas underpinning them, to the management of coastal waters beyond Europe. To overcome this we examine using higher taxonomic level data with M-AMBI.Before applying such approaches to assessing ES in new geographical regions it is essential to determine the effects of using higher taxonomic level data on M-AMBI in areas where the tool was developed. To this end, we use macrofaunal data from three well studied sites in north-western Europe to examine the effects of using taxonomic level data higher than species on M-AMBI. Using the European datasets M-AMBI ES classification was shown to be robust to changes in taxonomic level data. We test the suitability of family-level M-AMBI for assessing ES in subtropical Hong Kong waters. Family level M-AMBI was useful in detecting stress in Hong Kong, where it successfully detected temporal and spatial shifts in ES in response to seasonal hypoxia and salinity variability, and anthropogenic organic enrichment.     

Imposex expression in Hexaplex trunculus from the North Tunis Lake transplanted to Bizerta channel (Tunisia)

Adult specimens of the muricid gastropod Hexaplex trunculus were collected from their natural habitat: the Lake Club station located in the North Tunis Lake, a sampling site characterized by the absence of shipping activity and an imposex incidence of 12.9%. These specimens were transplanted to a sampling site with intense shipping traffic: the Bizerta channel, where a preliminary survey detected an imposex incidence of 100%. The transplanted specimens were tagged prior to release and periodical recaptures were made every 60 days during a study period of 8 months (from July 2004 to March 2005) in order to compare the imposex development between both sampling sites. After 5 months of exposure in the Bizerta channel, all transplanted females were affected by imposex (with the development of an incomplete male genital tract). Microscopic examinations showed that imposex begun by the development of a small portion of vas deferens located halfway between the expected position of the future penis and the vagina. The imposex indices used in this study were the imposex frequency (I (%)), the vas deferens sequence index (VDSI), the relative penis length index (RPL), the average female penis length index (FPL) and the average female vas deferens length (VDL). All these indices increased in the transplanted population as compared to the population from the original sampling site, but VDSI and VDL were considered the best indices to assess the environmental pollution by tributyltin (TBT) and its deleterious effects in H. trunculus.     

Transcriptomics and in vivo tests reveal novel mechanisms underlying endocrine disruption in an ecological sentinel,Nucella lapillus

Anthropogenic endocrine disruptors now contaminate all environments globally, with concomitant deleterious effects across diverse taxa. While most studies on endocrine disruption (ED) have focused on vertebrates, the superimposition of male sexual characteristics in the female dogwhelk, Nucella lapillus (imposex), caused by organotins, provides one of the most clearcut ecological examples of anthropogenically induced ED in aquatic ecosystems. To identify the underpinning mechanisms of imposex for this ‘nonmodel’ species, we combined Roche 454 pyrosequencing with custom oligoarray fabrication inexpensively to both generate gene models and identify those responding to chronic tributyltin (TBT) treatment. The results supported the involvement of steroid, neuroendocrine peptide hormone dysfunction and retinoid mechanisms, but suggested additionally the involvement of putative peroxisome proliferator–activated receptor (PPAR) pathways. Application of rosiglitazone, a well‐known vertebrate PPARγ ligand, to dogwhelks induced imposex in the absence of TBT. Thus, while TBT‐induced imposex is linked to the induction of many genes and has a complex phenotype, it is likely also to be driven by PPAR‐responsive pathways, hitherto not described in invertebrates. Our findings provide further evidence for a common signalling pathway between invertebrate and vertebrate species that has previously been overlooked in the study of endocrine disruption.     

An assessment of tributyltin contamination in the North Atlantic using imposex in the dogwhelk Nucella lapillus (L.) as a biological indicator of TBT pollution

Summary

Surveys of imposex in the dogwhelk Nucella lapillus suggest that most parts of the north Atlantic are free of TBT contamination at biologically significant levels. Imposex was absent or poorly developed at the large majority of sites, including coasts adjacent to major shipping lanes passing through Pentland Firth, the Minches and North Channel. There were “hot-spots” of TBT pollution at ports and harbours along the northeast coast of England but, with the exception of the stretch of coast which includes the major ports of Hartlepool and Teesside, impacts were highly localised. The severity of imposex has declined dramatically during the past decade in those areas for which there are comparative data from earlier surveys. This can presumably be attributed to the success of regulations prohibiting the use of TBT-based antifoulants on vessels <25 m in length.     

Effects of tributyltin (TBT) and testosterone on the female genital system in the mesogastropodLittorina littorea (Prosobranchia)

Experiments were performed with the mesogastropodLittorina littorea on Helgoland, in Roscoff, and in the laboratory in order to evaluate the reaction of the female genital system to TBT, an environmental toxicant. The snails were either injected with 50 or 100 ng tributyltin (TBT) soluted in ethanol or exposed to artificial sea water treated with 5, 50, 100, and 200 ng TBT/l, and 33 ng testosterone/l. The duration of the experiments was either four or eight weeks. None of the analysed femaleL. littorea showed signs of imposex. Compared to results for the control groups, the size of the female glandular complex was significantly reduced if the pre-experimental toxication was already high, as is the case in snails collected around Helgoland. TBT-related gland complex reduction occurs also in femaleL. littorea from other sampling sites. In addition, injection of ethanol also causes a decrease in gland size. The experimental results demonstrate that the distal female genital system responds with significantly lower sensitivity to TBT than that of other prosobranchs. This behaviour is ascribed to the lack of an androgen receptor at the ovipositor. The results further strengthen the case of the extreme rarity of imposex described for femaleL. littorea in natural habitats. However, strong TBT-toxication may affectL. littorea populations significantly because of increasing masculinization of the females, which reduces reproduction ability.     

Reference conditions and WFD compliant class boundaries for phytoplankton biomass and chlorophyll-a in Alpine lakes

The intercalibration (IC) exercise is a key element in the implementation of the Water Framework Directive (WFD) in Europe. Its focus lies on the harmonization of national classification methods to guarantee a common understanding of ‘Good Ecological Status’ in surface waters. This article defines reference conditions and sets class boundaries for deep (mean depth >15 m, IC lake type L-AL3) and moderately deep (mean depth 3–15 m, IC lake type L-AL4) Alpine lakes >0.5 km². Data were collated from each of the five EU member states included in the Alpine Geographical Intercalibration Group (Alpine GIG: Austria, France, Germany, Italy and Slovenia). Hydro-morphological, chemical and biological data from 161 sites (sampling stations) in 144 Alpine lakes over a period of seven decades were collated in a database. Based on a set of reference criteria, 18 L-AL3 and 13 L-AL4 reference sites were selected. Reference conditions were defined using a combined approach, based on historical, paleolimnological and monitoring data in conjunction with trophic modelling and expert judgement. Reference values and class boundaries were set for annual mean total biomass (biovolume), and then derived for annual mean chlorophyll-a using a regression between the two parameters. In order to allow for geographical differences within the Alpine GIG and to facilitate the inclusion of the broadly defined common IC types and national lake types, ranges were defined for each reference value. Range of reference values are 0.2–0.3 mg l^?1 (L-AL3) and 0.5–0.7 mg l^?1 (L-AL4) for total biovolume and 1.5–1.9 μg l^?1 (L-AL3) and 2.7–3.3 μg l^?1 (L-AL4) for chlorophyll-a. Depending on lake type and variable, the ecological quality ratios (EQR) for setting the class boundaries lie between 0.60 and 0.75 for the high/good class boundary and between 0.25 and 0.41 for the good/moderate class boundary. The response of sensitive phytoplankton taxa along a nutrient gradient and the occurrence of ‘undesirable conditions and secondary effects’ as defined in the WFD was used to validate the class boundary values, which are thus considered to be compliant with the requirements of the WFD.     

The invertebrate species index (ISI) for streams in southeast Queensland,Australia

The invertebrate species index (ISI) is a new biotic index to assess stream health in southeast Queensland, Australia, using benthic macroinvertebrates. The index aims to refine stream monitoring, in particular for eutrophication, as nutrient input is a major stressor of streams in the region. Biotic indices previously used for the region were based on sensitivity scores for macroinvertebrate families and orders, and were valid for all streams across the continent. The ISI is based on species level and tailored to the specific traits of southeast Queensland, thus yielding an increased level of detection of biological change. This will improve monitoring of environmental impact on a regional and local scale. The ISI is a site-specific index calculated as the weighted average (WA) of species’ sensitivity scores (S₁₀), with a species-specific indicator weight (W) and the abundance (A) of each species used as weights. S₁₀ scores for 203 species of benthic macroinvertebrates ranging from 10 (species most sensitive to pollution) to 1 (tolerant of excessive pollution) were derived by means of WA regression and calibration using site scores representing an environmental impact gradient. W measures the indicator strength of the species, and was derived from the weighted standard deviation of the S₁₀. The initial site scores for the WA modeling were derived using canonical correspondence analysis (CCA) to ordinate the sites along a gradient associated with 12 abiotic variables. The data on benthic macroinvertebrates are based on 212 quantitative samples collected in wadeable freshwater streams in southeast Queensland. Two major stream types, (1) small creeks, mainly of uplands and (2) larger streams and rivers of lowlands, were recognised for the region, and for both types the ISI range representing reference condition was established. These reference conditions can be used to establish ecological quality ratios by comparing observed to expected indices and to define ecological quality classes. The ISI is the first biotic index for streams in Australia that uses sensitivity scores and indicator weights for macroinvertebrate species. There is a growing trend in Australia to identify stream macroinvertebrates to species level and to study their specific traits and ecological requirements. The reasons for this are manifold; assessing and monitoring stream health is only one of them. For most regions of Australia, no common ground exists, so far, on how to use species data for stream health assessment. The new biotic index fills this gap for southeast Queensland in providing a standard for the use of species level data in stream health assessment.     

Comparing macroinvertebrate indices to detect organic pollution across Europe: a contribution to the EC Water Framework Directive intercalibration

With the EC Water Framework Directive (WFD) the ecological status of a water body is defined by comparing the observed biological community composition present with near-natural reference conditions. The ecological status is then classified into five quality classes (high, good, moderate, poor and bad). It is of great importance that `good ecological status' has the same meaning within the European Union, since water bodies not measuring up to these standards have to be improved. Therefore, the Ecological Quality Ratios (EQR) at high-good, and good-moderate quality class boundaries will be intercalibrated. Each country has to report physical, chemical, and biological data from two sites at each of these boundaries and since most data exist for benthic macroinvertebrates, this quality element will be of great importance in the intercalibration process. The aim of this study was therefore to compare the results of different benthic macroinvertebrate metrics used to assess the impact of organic pollution (including eutrophication) (one of the major human impacts on European streams). A selection of the data sampled in the AQEM project was evaluated, where benthic macroinvertebrate- and abiotic data from four countries (Austria, the Czech Republic, Portugal and Sweden) and seven `stream types' were included. An organic pollution (including eutrophication) gradient was defined using Principal Component Analysis and the boundaries for high-good and good-moderate ecological status set by the partners from each country were used to define arbitrary class boundaries. The Average Score Per Taxon (ASPT) was well correlated with the stress gradient in most stream types, whereas the Saprobic Index worked clearly better than ASPT in those countries (Austria and the Czech Republic) where macroinvertebrates are generally identified to lower (species) as opposed to a higher (genus or family) level of identification. Defining harmonised class boundaries is difficult; this process has to consider the natural differences between stream types (e.g. in the reference values of metrics) but has to eliminate different perceptions of ecological quality.     

Predatory behaviour of juvenile shore crab Carcinus maenas (L.)

Juvenile shore crabs Carcinus maenas (L.) were observed feeding on rock barnacles Semibalanus balanoides (L.) on a Bay of Fundy rocky shore. This previously unreported predatory behaviour was further investigated in the laboratory. When given a choice of three common and abundant gastropods, Nucella lapillus (L.), Littorina littorea (L.), and Littorina obtusata (L.), and the rock barnacle Semibalanus balanoides, juvenile shore crabs of both sexes ate mainly barnacles and consumed proportionately more barnacles than gastropods compared with adults, which ate mainly gastropods. The rock barnacle is an abundant and readily available food source which may be important in sustaining the juvenile crab through periods of moults and rapid growth. As the shore crab attains a certain age (size), it must forage lower on the shore as gastropods become more important in its diet.     

The influence of mantle cavity fluid on the aerial oxygen consumption of some intertidal gastropods

The intertidal gastropods Gibbula cineraria (L.), Nucella lapillus (L.), and Littorina littorea (L.) have been investigated. Animals that had attached to a plastic surface under sea water were exposed to air and rapidly frozen. Fluid was found to be retained within the mantle cavity in contact with the gill. For each species the weight of the mantle cavity fluid retained in air was related to the whole weight of the animal. There was no significant difference between the weight of fluid held by animals in the laboratory and that held by animals on the shore 2 h after aerial exposure. The oxygen consumption of inactive individuals in air was measured by two techniques which did not produce significantly different results. The aerial oxygen consumption of all three species was lowered by the loss of mantle cavity fluid. This also reduced the temperature coefficient. A correlation is suggested between a large weight of mantle cavity fluid, the presence of a gill in the mantle cavity and a large reduction in oxygen consumption upon the loss of fluid.     

Morphological effects of tributyltin (TBT) in vitro on the genital system of the mesogastropodaLittorina littorea (Prosobranchia)

This ultrastructural study investigates the pathological changes in the penial, the sperm groove and the glandular cushion epithelium in maleLittorina littorea (Mesogastropoda) related to TBT (tributyltin) contamination. The results are compared with those onOcinebrina aciculata (Neogastropoda), which shows a wide range of cell changes in the penis epithelia of male and imposex affected females. The investigation of the different penis epithelia ofL. littorea revealed that the cells analysed show a low sensibility towards TBT. The cells display normal metabolism. Certain atypical structures like swelling microvilli and cristae which tend to lie parallel to the long axis in the mitochondria, were detected as pathological effects.     

TBT-induced imposex in marine neogastropods is mediated by an increasing androgen level

Tributyltin (TBT) exposure at different concentrations (5, 60, and 100 ng TBT as Sn/l) induces a concentration- and time-dependent imposex (=pseudohermaphroditism) development in femaleNucella lapillus andHinia reticulata. In both species the average imposex stage, termed as vas deferens sequence (VDS) index, and the average female penis length increases with increasing TBT concentration and duration of TBT exposure. Testosterone added at a concentration of 500 ng/l induces a faster and more intensive imposex development compared to that induced by the TBT concentrations used in the present experiments. Radioimmunological determination of endogenous steroid content reveals increasing testosterone titres in female gastropods exposed to TBT which correlate with the TBT concentration used and the duration of the experiment. The most marked and highest increase of the endogenous testosterone level is exhibited by females, of both species exposed to testosterone. Simulataneous exposure to TBT and to the antiandrogen cyproterone acetate which suppresses imposex development completely inN. lapillus and reduces imposex development strongly inH. reticulata proves that the imposex-inducing effects of TBT are mediated by an increasing androgen level and are not caused directly by the organotin compound itself. Further-more, TBT-induced imposex development can be suppressed in both snails by adding estrogens to the aqueous medium. These observations suggest that TBT causes an inhibition of the cytochrome P-450 dependent aromatase system which catalyses the aromatization of androgens to estrogens. The increase of the androgen content or the shift of the androgen-estrogen balance in favour of androgens induces the development of pseudohermaphroditism in marine prosobranchs. Artificial inhibition of the cytochrome P-450 dependent aromatase system using SH 489 (1-methyl-1,4-androstadiene-3,17-dione) as a steroidal aromatase inhibitor and flavone as a nonsteroidal aromatase inhibitor induces imposex development inN. lapillus as well as inH. reticulata.     

Genetic diversity of two Portuguese populations of the pullet carpet shell Venerupis senegalensis, based on RAPD markers: contribution to a sustainable restocking program

The pullet carpet shell Venerupis senegalensis (=V. pullastra) is a commercially important species in Portugal, Spain, France, and Italy. In Portugal, this species was once abundant in the Ria Formosa (southern Portugal). However, in the early 1980s, its abundance declined dramatically due to overfishing. In order to reverse this negative trend, the genetic sustainable management of the wild stocks of V. senegalensis should be performed by promoting successful restocking actions and the development of an aquaculture commercial production program of this species. In order to find the best broodstock for aquaculture purposes and therefore minimize the deleterious effects of hatchery practices, we analyzed the genetic diversity of the natural population to be restocked (Ria Formosa) but also of another potential genetically close population (Ria de Aveiro) by RAPD. Similar and substantive percentage of polymorphic loci, effective number of alleles, Nei’s gene diversity, and Shannon’s diversity index was found within both populations. This high genetic variability within populations suggests that they might have a gene pool with sufficient genetic plasticity to support changes in the environmental conditions. Analyses of population genetic structure also revealed a small genetic differentiation between the two populations. The high genetic variability of the natural population to be restocked makes it the preferential broodstock for aquaculture purposes. However, the Ria de Aveiro population could also be a viable alternative, due to its genetic plasticity and the genetic similarity of both populations. The results of this study can be useful to the sustainable management of wild stocks as well as in promoting successful restocking actions based on aquaculture production.     

Cercaria sevillana n sp,a new cercaria (Digenea: Microphallidae) from Nassarius reticulatus (L) (Mollusca: Prosobranchia) in Portugal

Cercaria sevillana n. sp. (Digenea: Microphallidae) was discovered infecting the gonads and digestive gland of the prosobranch Nassarius reticulatus (L.) (Nassariidae) collected from the Ria de Aveiro, Portugal. Cercariae were obtained by natural emission and were studied under a differential interference contrast microscope and scanning electron microscope (SEM). C. sevillana n. sp. is identical to the cercaria found by Dolgikh (1965) in the same mollusc host from the Black Sea, but erroneously named C. misenensis Palombi, 1940, which is a parasite of Cerithium rupestre Risso, 1826 (Cerithiidae). Cercaria sevillana n. sp. can be distinguished from C. misenensis by its tail being shorter than the cercarial body, as well as by differences in the pattern of penetration glands the size and shape of the stylet and excretory vesicle, and its behavioural pattern. An unusual structure of the tail of this new cercaria was observed by SEM; it is characterised by the presence of annular folded membranes arranged as overlapping flounces around its central axis. This resembles the traditional skirts of the women of Seville. Such a morphological feature of the tail has not been previously observed, but may be a feature of many microphallid cercariae.