Groups Of Snails Research Articles

Latitudinal variation of freeze tolerance in intertidal marine snails of the genus Melampus (Gastropoda: Ellobiidae).

Abstract Low temperatures limit the poleward distribution of many species such that the expansion of geographic range can only be accomplished via evolutionary innovation. We have tested for physiological differences among closely related species to determine whether their poleward latitudinal ranges are limited by tolerance to cold. We measured lower temperature tolerance (LT50) among a group of intertidal pulmonate snails from six congeneric species and nine locales. Differences in tolerance are placed in the context of a molecular phylogeny based on one mitochondrial (cytochrome oxidase subunit I) and two nuclear (histone 3 and a mitochondrial phosphate carrier protein) markers. Temperate species from two separate lineages had significantly lower measures of LT50 than related tropical species. Range differences within the temperate zone, however, were not explained by LT50. These results show that multiple adaptations to cold and freezing may have enabled range expansions out of the tropics in Melampus. However, northern range limits within temperate species are not governed by cold tolerance alone.

Patterns of land-snail succession in Central Europe over the last 15,000 years: main changes along environmental, spatial and temporal gradients

Land snail shell assemblages have been used since the pioneering days of palaeoecology to describe Quaternary environmental changes. Despite the many advantages of this proxy, it has recently been rather overlooked. There are more than 300 mollusc successions from localities throughout the Czech and Slovak Republics, making this a globally unique archive. We selected 91 of these successions for radiocarbon dating and further detailed processing. Based on analyses of 828 mollusc assemblages we found a significant increase in both total species richness and number of forest species since the Lateglacial, with a decrease in both after the Middle Holocene. In contrast, the opposite response was found for open-country species and the proportion of xerophilous species. The proportion of forest and open-country species reversed at the Pleistocene/Holocene transition (approx. 11,500 cal yrs BP). Changes in species richness were rather stable across the study area and at different elevation, contrary to changes in species composition. MDS ordination based on presence/absence data show four main patterns of species composition associated with the number of forest species in a sample, position of site along the west–east direction, the proportion of hygrophilous species and, finally, with the age of the mollusc assemblage. The number of forest species indicates the main pattern of changes in the composition of Central European land snail assemblages from the Lateglacial to the present. We confirmed the application and temporal stability of ecological groups of snails as a useful tool for reconstruction of the terrestrial palaeoenvironment.

Comparative evaluation of haemagglutination potential of haemolymph from two species of giant African land snails (Archachatina marginata and Achatina achatina)

A comparative study was conducted to evaluate haemagglutination potential in the haemolymph of two species of giant African land snails (Archachatina marginata and Achatina achatina). Three liveweight groups of snails (<100 g, 101–150 g and >150 g) were used with 4 replicates per liveweight per species for haemagglutination assay (HA). The effect of aestivation on haemagglutination potential was also evaluated. Erythrocytes (2%) from cattle, sheep, goat and chicken were used for HA assay. Results showed that agglutinin-like substances that agglutinate erythrocytes of sheep, goat, cattle and chicken were present in the haemolymph of the two species of giant African land snails. Effect of species was found to be significant (P < 0.001) on haemagglutination titre. Haemolymph of A. marginata, had higher haemagglutination titre than that of A. achatina across the three liveweight groups used in this study. Snail liveweight had no significant effect (P > 0.05) on agglutinin content of the haemolymph in both species. Agglutination level depended on the source of erythrocyte used. Sheep erythrocyte recorded the highest haemagglutination titre, followed by goat, cattle, and chicken in that order. To our knowledge, this is the first evidence that Giant African land snails (GALS) haemolymph contain agglutinins as previously reported for Helix species. This evidence may be the basis for its survivability in the wild and thus establish the use of GALS for African herbal medicinal applications.

Radiation and decline of endodontid land snails in Makatea, French Polynesia.

The family Endodontidae Pilsbry, 1895comprised one of the most diverse groups of indigenous land snails of Pacific Islands. However, due to anthropogenic degradation of their habitats and predation by or competition with introduced species, most members of the family are now extinct or severely endangered. Based on limited and sporadic collections, the endodontidfauna of the raised coral island of Makatea in the western Tuamotu Archipelago was known to consist of four valid species, Mautodontha (Mautodontha) daedalea (Gould, 1846), Kleokyphus callimus Solem, 1976, K.hypsus Solem, 1976and Pseudolibera lillianae Solem, 1976, the last three of which were endemic. To these, we add 18 new species based on a reappraisal of museum collections and analysis of abundant new material collected in 2005: M. (M.) domaneschii, M. (M.) virginiae, M. (M.) harperae, M. (Garrettoconcha) aurora, M. (G.) occidentalis, M. (G.) temaoensis, M. (G.) makateaensis, M. (G.) passosi, M. (G.) spelunca, K. cowiei, P. solemi, P.matthieui, P. cookei, P. aubertdelaruei, P.extincta, P.paraminderae, P. elieporoii, and P. parva. The recently collected material also revealed new information on the morphology, intraspecific variation and distribution of the four previously known species, which are here revised and re-described. With 22 recognized taxa, the radiation of endodontidsin Makatea is second in species richness only to that of Rapa Iti in the Austral Islands, from where 24 endodontidshave been described. Despite intensive field work in Makatea in 2005, only M.(M.)daedaleawas found alive. All other Makatean endodontidswere represented solely by empty and worn shells and are probably extinct.

Nitric oxide is necessary for long-term facilitation of synaptic responses and for development of context memory in terrestrial snails

Correlated electrophysiological and behavioral experiments in the snail Helix lucorum were conducted to investigate the contribution of nitric oxide (NO) to synaptic plasticity during withdrawal reflex and aversive context memory development. Time, stimulation frequency and number of tetani/electrical shocks were determined in vitro and in vivo. In isolated brain preparations, nerve tetanization accompanied by bath application of serotonin induced long-term facilitation (LTF) of the excitatory postsynaptic potential (EPSP) in withdrawal interneurons. Bathing with either the NO-synthase inhibitor N-omega-nitro-L-arginin (L-NNA) or the NO-scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide (PTIO) before the tetanization prevented tetanus-induced long-term increase of EPSP.Withdrawal interneurons are key elements in the network underlying aversive behavior, with LTF considered the basis for aversive learning. We hypothesized that L-NNA injections in free-behaving snails could influence aversive learning. Snails were trained for 1 or 5days to remember the context in which they were shocked. In one-day training experiments, the snails received 5 electrical shocks in one context. Different groups of snails were sham-injected or L-NNA-injected before or after training. After training, the sham-injected groups demonstrated a significant increase in behavioral responses compared to the L-NNA-injected groups. On the following day, only sham-injected snails demonstrated altered behavioral responses, but no associative context differences were observed. These results correlated with the electrophysiological results. In another series of experiments, the snails received electrical shocks for 5days. Testing on the second day after training demonstrated that the sham-injected group maintained selective aversive context memory, whereas the L-NNA-injected snails were not different between the two contexts.Together these results demonstrated that inhibition of NO synthesis prevents memory formation and influences synaptic plasticity in the withdrawal interneurons that underlie the behavioral changes. This suggests that NO influences the behavior via regulation of synaptic plasticity.

A nomenclator of extant and fossil taxa of the Valvatidae (Gastropoda, Ectobranchia).

A compilation of all supra- and (infra-) specific taxa of extant and fossil Valvatidae, a group of freshwater operculate snails, is provided, including taxa initially described in this family and subsequently classified in other families, as well as names containing errors or misspellings. The extensive reference list is directly linked to the available electronic source (digital view or pdf-download) of the respective papers.

Genotoxicity of cadmium chloride in the marine gastropod Nerita chamaeleon using comet assay and alkaline unwinding assay

This paper presents an evaluation of the genotoxic effects of cadmium chloride (CdCl2 ) on marine gastropod, Nerita chamaeleon following the technique of comet assay and the DNA alkaline unwinding assay (DAUA). In this study, the extent of DNA damage in gill cells of N. chamaeleon was measured after in vivo exposure to four different concentrations (10, 25, 50, and 75 µg/L) of CdCl2 . In vitro exposure of hydrogen peroxide (H2 O2 ; 1, 10, 25, and 50 µM) of the gill cells showed a significant increase in the percentage tail DNA, Olive tail moment, and tail length (TL). Significant changes in percentage tail DNA by CdCl2 exposure were observed in all exposed groups of snails with respect to those in control. Exposure to 75 µg/L of CdCl2 produced significant decrease in DNA integrity as measured by DAUA at all duration with respect to control. In vivo exposure to different concentrations of CdCl2 (10, 25, 50, and 75 µg/L) to N. chamaeleon showed considerable increase in DNA damage as observed by both alkaline comet assay and the DAUA. The extent of DNA damage in marine gastropods determined by the application of alkaline comet assay and DAUA clearly indicated the genotoxic responses of marine gastropod, N. chamaeleon to a wide range of cadmium concentration in the marine environment.

Plio‐Pleistocene out‐of‐Australia dispersal in a camaenid land snail

AbstractAimCamaenidae are amongst the most diverse land snail groups in Southeast Asia and Australasia, but their phylogeny and biogeography are poorly understood. The monophyly and biogeographical origin of the Australian species has remained uncertain. Being reported from north‐western Australia as well as from the Lesser Sunda Islands, the genus Rhagada is crucial to our understanding of camaenid biogeography. By resolving the phylogeny of Rhagada, we aim to uncover spatial and temporal patterns of its diversification at the interface between Oriental and Australian biogeographical regions.LocationNorth‐western Australia, Lesser Sunda Islands.MethodsWe implemented Bayesian and maximum likelihood methods to generate the most complete mitochondrial phylogeny of Rhagada land snails to date. Divergence times of clades were estimated by employing a relaxed molecular clock and two internal calibrations from fossil and tectonic data. Ancestral areas of clades were inferred using character history reconstruction based on parsimony, as implemented in Mesquite.ResultsRhagada clustered into eight well‐supported clades that are restricted to certain geographical areas. Species from the Kimberley, Western Australia, formed the earliest branching clades. A single Lesser Sunda clade was sister to a radiation in the Western Australian Pilbara. Molecular age estimates placed the evolutionary origin of Rhagada between the late Miocene and early Pleistocene, and dispersal from Western Australia onto the Lesser Sunda Islands in a period between the mid‐Pliocene and early Pleistocene.Main conclusionsThe camaenid Rhagada originated in the Kimberley and subsequently expanded its range through the Pilbara and into the Shark Bay area, probably during the late Pliocene and mid‐Pleistocene. From the Kimberley, Rhagada snails colonized the Lesser Sunda Islands probably not before 1.9 Ma following emergence of the youngest islands, which may have acted as ‘stepping stones’. Over‐sea dispersal might have occurred during the mid‐Pleistocene when lowered sea levels facilitated faunal exchange across the region.

Growth rate of the intermediate snail host Galba truncatula influences redial development of the trematode Fascioloides magna

A total of 850 pre-adult Galba truncatula (shell height, 4mm), originating from four French snail populations differing in shell height at the adult stage (from 6.5 to 12mm), were individually subjected at 20°C to single-miracidium infections with Fascioloides magna. At day 75 post-exposure, the surviving snails were dissected, and rediae and cercariae were counted. Snail groups differed in shell growth during the experiment: from 1.8±0.4mm in group A up to 4.0±1.1mm in group D. The prevalence of F. magna infection, the numbers of free rediae and cercariae significantly increased together with increasing growth of infected snails during the experiment. Group A produced 1-6 first-generation rediae per snail and the mean daughter redia production ranged from 7.5 second-generation rediae (when a single first generation per snail developed) to 2.3 (6 first-generation rediae per snail). In contrast, up to ten first-generation rediae were noted in group D, and each mother redia gave daughter rediae with averages ranging from 1.5 (ten first-generation rediae per snail) to 13 (a single first generation per snail). In conclusion, the development of F. magna in G. truncatula exhibited both inter- and intrapopulation variability, where the development of rediae and cercariae was positively correlated with snail growth.

Effect of starvation and hibernation on the values of five biomarkers of general and specific stress using the land snail Eobania vermiculata

Values of five biomarkers related to cell stress or pollution were evaluated in tissues of the land snail Eobania vermiculata under starvation or hibernation conditions. The biomarkers applied were lysosomal membrane stability in digestive gland cells (LMS) or in haemocytes (neutral red retention assay (NRR)), acetylcholinesterase activity (AchE; EC 3.1.1.7), metallothionein content (MTs), and cyclic AMP content (cAMP). Three groups of snails were studied that were kept under starvation, hibernation and normal conditions, respectively. The results indicated statistically lower values of LMS and NRR in snails kept under starvation or hibernation compared to control ones. Higher values of AChE activity were measured in snails under hibernation compared to controls. MT contents were statistically higher in snails under starvation compared to controls. Measurement of cAMP contents showed no significant differences among the tested groups. The values of the first four biomarkers may be affected by factors other than pollution, such as starvation or hibernation. Therefore, these factors should be taken into consideration when biomonitoring studies are performed in time intervals of hibernation or starvation.

Genotoxicity of Nicotiana tabacum leaves on Helix aspersa

Tobacco farmers are routinely exposed to complex mixtures of inorganic and organic chemicals present in tobacco leaves. In this study, we examined the genotoxicity of tobacco leaves in the snail Helix aspersa as a measure of the risk to human health. DNA damage was evaluated using the micronucleus test and the Comet assay and the concentration of cytochrome P450 enzymes was estimated. Two groups of snails were studied: one fed on tobacco leaves and one fed on lettuce (Lactuca sativa L) leaves (control group). All of the snails received leaves (tobacco and lettuce leaves were the only food provided) and water ad libitum. Hemolymph cells were collected after 0, 24, 48 and 72 h. The Comet assay and micronucleus test showed that exposure to tobacco leaves for different periods of time caused significant DNA damage. Inhibition of cytochrome P450 enzymes occurred only in the tobacco group. Chemical analysis indicated the presence of the alkaloid nicotine, coumarins, saponins, flavonoids and various metals. These results show that tobacco leaves are genotoxic in H. aspersa and inhibit cytochrome P450 activity, probably through the action of the complex chemical mixture present in the plant.

Anthropogenic extinction of Pacific land snails: a case study of Rurutu, French Polynesia, with description of eight new species of endodontids (Pulmonata).

Faunistic surveys are fundamental in the conservation of land mollusks, particularly as a means of achieving accurate estimates of species richness and levels of extinction of endangered taxa. The family Endodontidae comprises one of the most diverse groups of indigenous land snails of Pacific Islands. Due to anthropogenic degradation of their habitats, most members of the family are now extinct or severely endangered. In Rurutu, French Polynesia, 11 species of Endodontidae were previously described (10 endemics), but only 1 is known to have been extant during the first half of the 20th Century. Extensive collections made in Rurutu in 2003 recovered only empty shells of these 11 species, as well as of an additional 8 endemic species of endodontids not known to previous investigators: Australdonta oheatora sp. nov., A. anneae sp. nov., A. sibleti sp. nov., A. florencei sp. nov., A. pakalolo sp. nov., A. teaae sp. nov., Minidonta boucheti sp. nov. and M. bieleri sp. nov. The radiation of endodontids in Rurutu was thus much larger than previously envisaged. However, we hypothesize that all species of the family are now extinct in the island.

Ecological speciation in an island snail: evidence for the parallel evolution of a novel ecotype and maintenance by ecologically dependent postzygotic isolation

Speciation is the process by which reproductive isolation evolves between populations. Two general models of speciation have been proposed: ecological speciation, where reproductive barriers evolve due to ecologically based divergent selection, and mutation-order speciation, where populations fix different mutations as they adapt to similar selection pressures. I evaluate these alternative models and determine the progress of speciation in a diverse group of land snails, genus Rhagada, inhabiting Rosemary Island. A recently derived keeled-flat morphotype occupies two isolated rocky hills, while globose-shelled snails inhabit the surrounding plains. The study of one hill reveals that they are separated by a narrow hybrid zone. As predicted by ecological speciation theory, there are local and landscape level associations between shell shape and habitat, and the morphological transition coincides with a narrow ecotone between the two distinct environments. Microsatellite DNA revealed a cline of hybrid index scores much wider than the morphological cline, further supporting the ecological maintenance of the morphotypes. The hybrid zone does not run through an area of low population density, as is expected for mutation-order hybrid zones, and there is a unimodal distribution of phenotypes at the centre, suggesting that there is little or no prezygotic isolation. Instead, these data suggest that the ecotypes are maintained by ecologically dependent postzygotic isolation (i.e. ecological selection against hybrids). Mitochondrial and Microsatellite DNA indicate that the keeled-flat form evolved recently, and without major historical disruptions to gene flow. The data also suggest that the two keeled-flat populations, inhabiting similar rocky hills, have evolved in parallel. These snails provide a complex example of ecological speciation in its early stages.

Snails and their trails: the multiple functions of trail‐following in gastropods

Snails are highly unusual among multicellular animals in that they move on a layer of costly mucus, leaving behind a trail that can be followed and utilized for various purposes by themselves or by other animals. Here we review more than 40 years of experimental and theoretical research to try to understand the ecological and evolutionary rationales for trail-following in gastropods. Data from over 30 genera are currently available, representing a broad taxonomic range living in both aquatic and terrestrial environments. The emerging picture is that the production of mucus trails, which initially was an adaptation to facilitate locomotion and/or habitat extension, has evolved to facilitate a multitude of additional functions. Trail-following supports homing behaviours, and provides simple mechanisms for self-organisation in groups of snails, promoting aggregation and thus relieving desiccation and predation pressures. In gastropods that copulate, trail-following is an important component in mate-searching, either as an alternative, or in addition to the release of water- or air-borne pheromones. In some species, this includes a capacity of males not only to identify trails of conspecifics but also to discriminate between trails laid by females and males. Notably, trail discrimination seems important as a pre-zygotic barrier to mating in some snail species. As production of a mucus trail is the most costly component of snail locomotion, it is also tempting to speculate that evolution has given rise to various ways to compensate for energy losses. Some snails, for example, increase energy intake by eating particles attached to the mucus of trails that they follow, whereas others save energy through reducing the production of their own mucus by moving over previously laid mucus trails. Trail-following to locate a prey item or a mate is also a way to save energy. While the rationale for trail-following in many cases appears clear, the basic mechanisms of trail discrimination, including the mechanisms by which many snails determine the polarity of the trail, are yet to be experimentally determined. Given the multiple functions of trail-following we propose that future studies should adopt an integrated approach, taking into account the possibility of the simultaneous occurrence of many selectively advantageous roles of trail-following behaviour in gastropods. We also believe that future opportunities to link phenotypic and genotypic traits will make possible a new generation of research projects in which gastropod trail-following, its multitude of functions and evolutionary trade-offs can be further elucidated.

Effects of Echinostoma caproni miracidia dose on the neutral and polar lipids of Biomphalaria glabrata as determined by high-performance thin-layer chromatography

The effects of a 5 versus 25 miracidia exposure of Echinostoma caproni on the lipid composition of Biomphalaria glabrata was studied using high performance thin layer chromatography (HPTLC)-densitometry. A 50 miracidia dose was not used because such a high level of exposure caused severe snail mortality by 3 weeks post-exposure (PE). Lipids were determined in the digestive-gland gonad complex (DGG) of the exposed snails and in the uninfected matched controls at 2 and 4 weeks PE. Extraction of lipids from DGGs was carried out by the Folch method with chloroform-methanol (2:1), and extracts were analyzed on Analtech HPTLC-HLF pre-adsorbent silica gel plates with measurement of separated bands using a CAMAG Scanner 3. For neutral lipids the mobile phase was petroleum ether-diethyl ether-glacial acetic acid (80:20:1) and the detection reagent was 5% ethanolic phosphoric acid, and for polar lipids chloroform-methanol-deionized water (65:25:4) mobile phase and 10% cupric sulfate in 8% phosphoric acid detection reagent were used. No significant differences in the concentrations of free sterols, free fatty acids, triacylglycerols, phosphatidylcholine, and phosphatidylethanolamine were seen at 2 weeks PE in any of the groups. At 4 weeks PE, the free fatty acid concentration increased significantly in the snails exposed to 25 miracidia compared to that of the 5 miracidia/snail group or the controls. Elevation of the free fatty acid fraction in the high dose snail group suggested that some changes occurred in the lipid metabolism of the snails in that group as a function of miracidia dose.

Survival of Larval and Cyst Stages of Gordiids (Nematomorpha) After Exposure to Freezing

Hairworms infect terrestrial arthropods and are 1 of the most understudied groups of parasites. Recently, life cycles of 2 gordiids (Paragordius varius and Paragordius obamai) have been domesticated in the laboratory. We tested the viability of laboratory reared and post-frozen larval and cyst stages of the North American gordiid, P. varius , frozen at -80 C for 7 mo, and the viability of field collected and post-frozen cysts of the African (P. obamai) and North American ( P. varius ) gordiid frozen at -20 C for 2 mo. All snails exposed to post-frozen or control P. varius larvae became infected with cysts, and there was no significant difference in prevalence or mean intensity of cysts among control or experimental snail groups. As with larvae, no significant differences were observed in prevalence or mean intensity of emerging worms from crickets infected with post-frozen or control P. obamai or P. varius cysts. All female P. obamai and P. varius worms from control and post-frozen cyst infections laid eggs and larvae hatched from some of these eggs. Survival and cyst formation of P. varius larvae exposed to different combinations of drying and/or freezing temperatures indicated that gordiid larvae have the ability to survive drying and freezing, but survival significantly increases during freezing at lower temperatures. The major contribution of our study is the demonstration that gordiid larval and cyst stages can survive freezing temperatures to infect and develop in the next host.

Seasonal variation in abiotic factors and ferulic acid toxicity in snail‐attractant pellets against the intermediate host snail Lymnaea acuminata

Laboratory evaluation was made to access the seasonal variations in abiotic environmental factors temperature, pH, dissolved oxygen, carbon dioxide, electrical conductivity and ferulic acid toxicity in snail-attractant pellets (SAP) against the intermediate host snail Lymnaea acuminata in each month of the years 2010 and 2011. On the basis of a 24-h toxicity assay, it was noted that lethal concentration values of 4.03, 3.73% and 4.45% in SAP containing starch and 4.16, 4.23% and 4.29% in SAP containing proline during the months of May, June and September, respectively, were most effective in killing the snails, while SAP containing starch/proline + ferulic acid was least effective in the month of January/February (24-h lethal concentration value was 7.67%/7.63% in SAP). There was a significant positive correlation between lethal concentration value of ferulic acid containing SAP and levels of dissolved O2 /pH of water in corresponding months. On the contrary, a negative correlation was observed between lethal concentration value and dissolved CO2 /temperature of test water in the same months. To ascertain that such a relationship between toxicity and abiotic factors is not co-incidental, the nervous tissue of treated (40% and 80% of 24-h lethal concentration value) and control group of snails was assayed for the activity of acetylcholinesterase (AChE) in each of the 12 months of the same year. There was a maximum inhibition of 58.43% of AChE, in snails exposed to 80% of the 24-h lethal concentration value of ferulic acid + starch in the month of May. This work shows conclusively that the best time to control snail population with SAP containing ferulic acid is during the months of May, June and September.

Paramphistomum daubneyi: characteristics of infection in three lymnaeid species

Experimental infections of two South American lymnaeids (Lymnaea neotropica and L. viatrix var. ventricosa) with Paramphistomum daubneyi were carried out to determine if these snail species could sustain larval development of this digenean and, if so, to specify their potential for cercarial production. A French population of Galba truncatula infected and raised according to the same protocol served as controls. In both experiments, prevalence of P. daubneyi infections in snails did not significantly differ from each other. In snail groups evaluated for cercarial shedding (first experiment), a significantly lower number of shed cercariae was noted for L. neotropica, while those from G. truncatula and L. v. ventricosa did not differ significantly from each other. Dissection of infected snails at day 65 post-exposure at 20 °C (second experiment) found significantly lower burdens of P. daubneyi rediae and cercariae in the bodies of L. neotropica than in those of G. truncatula and L. v. ventricosa. Compared to total cercarial production observed in dissected snails, the percentage of cercariae which exited from snails was 75.6% for G. truncatula, 21.6% for L. neotropica, and 91.4% for L. v. ventricosa. This last species seems to be a good candidate for metacercarial production of P. daubneyi.

Lymnaea neotropica and Lymnaea viatrix, potential intermediate hosts for Fascioloides magna

Experimental infections of two South American lymnaeid populations with Fascioloides magna were carried out to determine whether these snails may sustain larval development of this digenean and, if so, to quantify their potential for cercarial production. The reference group was a French population of Galba truncatula infected and raised according to the same protocol. According to the internal transcribed sequence (ITS)-1 segment of their genomic rDNA, these South American populations were identified as Lymnaea neotropica (origin, Argentina) and Lymnaea viatrix var. ventricosa (origin, Uruguay). In the snail groups followed for cercarial shedding, longer prepatent periods and lower numbers of shed cercariae were noted in South American lymnaeids. In other snails dissected at day 65 post-exposure, the redial and cercarial burdens of F. magna found in the bodies of L. neotropica and L. v. ventricosa were significantly lower than those noted in G. truncatula. Compared to the total cercarial production noted in the dissected snails, the percentage of cercariae that exited from snails was 51.3% for G. truncatula, 32.2% for L. neotropica and 46.8% for L. v. ventricosa. The two South American species of snails can thus be considered as potential intermediate hosts of F. magna.

CATALOGUE OF THE NOMINAL TAXA OF MESOAMERICAN PACHYCHILIDAE (MOLLUSCA: CAENOGASTROPODA)

The caenogastropod family Pachychilidae Troschel, 1858 is a monophyletic group of freshwater snails that is distributedin the tropical regions of the world, where they exhibit high levels of endemism at the species and generic levels. Thereare many uncertainties regarding generic affiliation and species names in the Mesoamerican Pachychilidae owing to theirrelatively variable shells, the lack of distinctive anatomical features and the intricate taxonomic histories. In an attempt toconsolidate the knowledge of this taxon in the Neotropics, we provide here a catalogue of all available names of theMesoamerican pachychilid fauna, laying the foundation for future taxonomic revisions. Primary types were located for 56species-group taxa, and lectotypes for 22 nomina were designated. 102 nominal taxa of Mesoamerican pachychilids wereoriginally described. We consider that six of these taxa belong to other cerithioidean families. Two nomina are consideredto be unnecessary replacement names (Melania renovata Brot, 1862; Pachychilus tristrami Crosse &amp; Fischer, 1892). Twotaxa are South American species that were incorrectly associated with Mesoamerican taxa (Pachychilus laevissimus sensuReeve, 1860; Melania laevissima var. decollata Brot, 1875). The exact type locality of Pachycheilus dalli Pilsbry, 1896and Melania mexicana were identified, and we accept Pachychilus hinkleyi (Marshall, 1920) as replacement name of the invalid Sphaeromelania hinkleyi Marshall, 1920.