FIELD OBSERVATIONS ON FEEDING OF THE LAND SNAIL HELIX ASPERSA MULLER

Feeding of the land snail Helix aspersa (Müller) was observedat monthly intervals. Three natural populations in Galicia (NW-Spain)were studied. At two sites only a few plants constituted thebulk of the diet and in spring the snails' diet had the highestdiversity (H'). In the third population feeding and distributionof Helix aspersa (Müller) were observed in a small plotwith permanent patches of Urtica dioica. Nearly one half offeeding snails fed upon Urtica dioica. Most of the other observations wereon Mentha suaveolens, Ranunculus repens and Gramineae. The diversity ofthe snails' diet showed seasonal variation with the maximumin the autumn months. Comparison between the availability ofthe different plant species and their contribution to the snails'diet showed that the snails did not eat at random; Urtica dioicawas eaten much more than expected from its occurrence and grasseswere strongly under-represented in the snails' diet. Temporalchanges of availability were significantly correlated with the amountseaten in the case of Urtica, but not for the other food plants.The distribution of the snails in the plot was significantlycorrelated with that of Urtica. Chemical analyses of the foodplants revealed Urtica as the species with the higher protein,ash and calcium contents. The strong preference of Helix aspersafor Urtica dioica could be explained by the value of Urticaas food or by its suitability as habitat for the snails. The largestproportions of green material in the snails' diet occurred inthe spring and juveniles ate more green material than adultsin the three populations. (Received 16 March 1998; accepted 30 November 1998)     

THE INHERITANCE OF DIVERGENT MITOCHONDRIA IN THE LAND SNAIL, CEPAEA NEMORALIS

The mitochondrial genomes of Cepaea nemoralis can differ widelybetween individuals in the same population. Various hypothesishave been proposed to account for this diversity, includingunusually fast evolution and the retention of deep lineagesin sub-divided populations. Another possibility is that pulmonatemitochondria are inherited in the doubly uniparental mode, asin Mytilus, allowing separate maternal and paternal lineagesto coexist. In Mytilus, separate lineages may differ by as muchas 20% and may pre-date the origin of the species carrying them. Until now, mitochondrial inheritance has not been studied inany molluscan group except the bivalves. I have investigatedit in C. nemoralis through a series of matings, and assayedindividuals for evidence of heteroplasmy. In five matings, mitochondrialinheritance was maternal, and no heteroplasmic individuals weredetected. The maintenance of the divergent haplotypes can notbe explained by doubly uniparental inheritance. (Received 30 April 1999; accepted 6 July 1999)     

VARIATION IN SNAIL SPECIES WIDESPREAD ON PORTO SANTO, MADEIRAN ARCHIPELAGO

Shell variation has been studied in two widespread land snailsfrom Porto Santo, Madeiran archipelago: the helicid speciesor species complex Heterostoma paupercula (Lowe) and the clausiliidspecies Boett-geria lowei Albers. Samples were collected fromthe mainland and the offshore islets from sea level to the highestaltitude. Shell size, colour and presence or absence of penstometeeth were scored in H. paupercula and some individuals weredissected to examine genitalia. Shell size and rib number werescored in B. lowei. In B. lowei size declines and rib number increases with altitude.In H. paupercula samples from sandy locations have a largershell size and a higher frequency of pale colour than thosefrom non-sandy locations. On average, sandy sites have a loweraltitude than non-sandy ones, however, so that these two variablesare confounded. The survey shows that shell characters of akind used in taxonomy are subject to variation associated withecology, this must be borne in mind when assessing present-daytaxa and morphological change through the fossil sequence. Thedata for H. paupercula support the conclusion that it is a singlespecies variable in shell characters and polymorphic for hemiphally. ⁴Present address for Gao Gaixt Biology Department, Shanxi EducationalCollege, Taiyuan, Shanxi, P.R.China (Received 27 February 1995; accepted 27 August 1995)     

OBSERVATIONS ON THE POPULATION DYNAMICS OF SNAIL HOSTS FOR SCHISTOSOMES IN THE DELTA OF THE SENEGAL RIVER BASIN

Between 1987 and 1990, snail surveys were carried out in theSenegal River Basin at Lampsar, in a natural ‘marigot’,and at Richard Toll, in an irrigation canal. Lymnaea natalensis.Bulinus guernet^* and B.forskalii, were regularly found at boththe sites. Bulinus globosus/jousseaumei and B. umbilicatus wereonly present at Lampsar. A decrease of the snail density wasobserved during the rainy season at Lampsar. The recent appearanceof Biomphalaria pfeifferi at Richard Toll is discussed. Thedata show that adult B. pfeiffert are present in the main irrigationcanal all through the year. Consequently parasite transmissionwill be possible throughout the year as well. (Received 23 October 1991; accepted 20 May 1992)     

A COMPARATIVE STUDY OF THE MORPHOLOGY OF THE PULMONATE SNAIL PSEUDOTACHEA LITTURATA (PFEIFFER) AND OTHER SPECIES OF PSEUDOTACHEA, IBERUS AND CEPAEA

A population of Pseudotachea litturata (Pfeiffer, 1851) fromTarifa (Càdiz, Spain) has been studied. The morphologicalresults are compared with those from P. splendida, Iberus gualtierianus,I. alonensis, I. marmoralus, I. guiraoanus and four speciesof the genus Cepaea using, as an exploratory method, the Wagnerparsimony procedure and 18 characters of the shell, genitalsystem and karyotype have been analysed. According to this methodit seems that the taxonomical position of P. litturata in thegenus Pseudotachea is confirmed, and agrees with the phylogeneticalrelationships in this group of species. The genus Cepaea seemsto be well established, although two species groups can be distinguished:C. nemoralis—C. hortensis and C. syluatica—C. vindobonensis.These differ mainly in chromosome number, diverticulum lengthand degree of shell polymorphism. Although the present resultsdo not allow us to clarify the current taxonomical problemswithin the genus Iberus, the species studied seem to belongto a natural group (Received 15 September 1987; accepted 1 January 1988)     

ASPECTS OF THE LIFE CYCLE, POPULATION DYNAMICS,GROWTH AND SECONDARY PRODUCTION OF THE EDIBLE SNAIL HELIX LUCORUM LINNAEUS, 1758 (GASTROPODA, PULMONATA) IN GREECE

This paper examines the biology and ecology of Helix lucorumL. which lives in mainland Greece, as well as its growth andsecondary production. A demographic study revealed that (a)3 cohorts exist at any time during the year (when adults ofall generations belong to the same cohort) (b) egg-laying andhatching occur during the months of July and August respectively,(c) the most rapid growth takes place during spring. Study ofH. lucorum genitalia in relation to age showed that the snailsaxe sexually mature 3 years after hatching, when the largestdiameter of their shell (D) is equal to or greater than 35 mm Von Bertallanffy's method suggests that Helix lucorum may liveup to 14 years or more in order to reach its possible maximumsize (48.80 mm) The study of relative growth of D in relation to P_s (peristomesurface) of Helix lucorum shows that D grows faster than P_swhen D12.50 mm; juveniles change their growth rate when theirD arrives at 22.05 mm, and growth becomes slower when adultsarrive at 36.27 mm Annual secondary production calculated by the size frequencymethod gave a mean annual density of 3.39 individuals per m²,a mean annual crop (biomass) of 4.04 g-m^–2 and an annualproduction (P) of 5.02 g · m^–2. The annual turnoverratio (P//b) is equal to 1.24 (Received 23 June 1987;     

HAEMOCYTES OF THE FRESHWATER SNAIL VIVIPARUS ATER (GASTROPODA, PROSOBRANCHIA)

Morphological and functional characteristics of the haemocytesof Viviparus ater were studied. Only one cell type occurs inthe haemolymph: the spreading haemocyte. These cells have thesame functions as blood cells belonging to the spreading typefound in other gastropods. It is also suggested that the spreadinghaemocytes represent the ancestral cell responsible for defencemechanisms. (Received 18 May 1988; accepted 19 August 1988)     

PLASTICITY OF THE LIFE CYCLE OF XEROPICTA DERBENTINA (KRYNICKI, 1836), A RECENTLY INTRODUCED SNAIL IN MEDITERRANEAN FRANCE

Xeropicta derbentina (Krynicki, 1836), a native of Eastern MediterraneanEurope, was introduced to southeastern France during the 1940sand is now widely spread across Provence. In summer it aggregateson plants, making its populations clearly visible. However,its life cycle within the Mediterranean basin is poorly documented.While X. derbentina in its native area exhibits an annual lifecycle, this species has been found in Provence to have a bienniallife cycle. Moreover, in southeastern France, field studieswithin a restricted area show variations in demographic structure.In consequence, the life cycle of X. derbentina and the demographicpatterns observed require clarification. Five populations withvarious demographic structures were studied over 1 year in thesame location, i.e. under the same climatic conditions. Thefield study was complemented by laboratory observations on mating,egg-laying and hatching. Xeropicta derbentina appears to bea semelparous species, with an annual life cycle being foundon four plots. The reproductive period begins at the end ofsummer and lasts until the beginning of winter. First egg-layingoccurs within 1 week after mating and lasts up to 30 days. Hatchingtakes place 15–20 days after egg-laying. Xeropicta derbentinapossesses multiple mating and egg-laying sessions, involvingsuccessive hatching. Populations are mainly characterized bytwo growth stages, the first in spring when newly-hatched snailsevolve into juveniles, and the second in late summer when theyreach maturity. However, on the highest density plot, a bienniallife cycle is observed for some newly-hatched snails that showan interrupted growth during summer and evolve into juvenilesonly in the second autumn. Moreover, this life cycle not onlyvaries among plots but also at a 1-year interval within plots.Hence, the life span of X. derbentina is between 12 and 20 months,but can be extended up to 30 months according to whether hatchingoccurs early or late and whether they survive the first andsecond winters. Xeropicta derbentina is thus able to have variousgrowth speeds and life spans, and appears to switch from anannual life cycle to a biennial cycle in response to populationdensity or climatic conditions. (Received 8 October 2004; accepted 15 December 2004)     

TAXONOMIC REVIEW OF THE TREE SNAIL AMPHIDROMUS ALBERS, 1850 (PULMONATA: CAMAENIDAE) IN THAILAND AND ADJACENT AREAS: SUBGENUS AMPHIDROMUS

Extensive series of Amphidromus Albers, 1850 were collectedfrom low-altitude areas (30–500 m above sea level)in Thailand, Laos, Malaysia, Singapore and Indonesia between1993 and 2004. Data on shell colour, genital and spermatophoremorphology, and radular structure are presented. Five speciesof Amphidromus (Amphidromus) are reviewed, of which four occurin Thailand. Intraspecific variation between populations ofAmphidromus (Amphidromus) atricallosus (Gould, 1843) is considered;three subspecies are accepted and a new subspecies described.Subspecies of A. (A.) inversus (Müller, 1774) and A. (A.)schomburgki (Pfeiffer, 1861) are reconsidered, and a new subspeciesof the latter is described. A dichotomous key to the speciesand subspecies of Amphidromus (Amphidromus) in Thailand is provided. (Received 7 May 2004; accepted 31 March 2005)     

ASPECTS OF LIFE CYCLE, POPULATION DYNAMICS, GROWTH AND SECONDARY PRODUCTION OF THE PULMONATE SNAIL CEPAEA VINDOBONENSIS (FERUSSAC, 1821) IN NORTHERN GREECE

The life cycle, population dynamics, growth and secondary productionof the land snail C. vindobonensis were studied in northernGreece. Demographic analysis of the populations of C. vindobonensisrevealed that a) three cohorts were present in the field throughoutthe year, b) the reproductive period started in late April-Mayand the newly hatched snails appeared in the beginning of June,and c) increased growth rates were observed during spring andearly summer, but also during autumn for the newly hatched snails. According to von Bertalanffy's method C. vindobonensis needs7 years to attain its maximum size measured in the field. Mortalityrate is very high during the first year of life, while lifeexpectancy is higher during the second year of life and decreasesafterwards. Net reproductive rate (R_o) was equal to 3.1 andthe finite capacity for increase (antilog_er_c) was equal to 1. Estimated annual secondary production with Hynes' frequencymethod revealed a mean standing crop (B) of 0.99 g/m²/year anda production (P) of 1.3 ± 0.11 g/m²/year. Annual turnoverratio (P/B) was equal to 1.31. (Received 7 April 1997; accepted 2 October 1997)     

WATER EXCHANGE, TEMPERATURE TOLERANCE, OXYGEN CONSUMPTION AND ACTIVITY OF THE NAMIB DESERT SNAIL, TRIGONEPHRUS SP.

Water exchange, temperature tolerance and oxygen consumptionof the snail, Trigonephrus sp., from the southern Namib desertof Namibia were examined and related to activity. At 25°Cand 15% R.H. mean water loss and food and water uptake were5.95 mg. day^–1 and 630 mg.day^–1, respectively. Bodytemperature tracked sand temperature. Snails tolerated sandtemperatures as high as 45°C. Mean ± S.D. oxygenconsumption rates were 32.0 ± 2.94 µlO₂.g totalbody mass^–1.h^–1 at 15°C, when the snails wereactive, and 11.27 µlO₂.g total body mass^–1.h^–1at 25°C, when the snails were inactive. These values are2-6 times lower than those recorded for the similarly sizedmesic snail, Helix aspersa. Activity experiments indicated thatlow ambient temperatures and high humidities were favoured bythe snails. This, together with the burying behaviour of thesesnails during high temperatures, suggests that they limit stressby restricting activity to physiologically-favourable periods,even though more-extreme conditions may be tolerated. (Received 7 June 1990; accepted 20 November 1990)     

CONSUMPTION OF AMPHIPODS BY THE NEW ZEALAND LAND SNAIL WAINUIA URNULA (PULMONATA: RHYTIDIDAE)

An unusual carnivorous diet was documented for the rhytididsnail Wainuia urnula urnula (Pfeiffer) from the southern North Island,New Zealand. Eighty-two percent of 315 samples of faeces or gutcontents contained remains of landhoppers (Crustacea: Amphipoda).Earthworms (Oligochaeta) were the second most common food typeidentified, but occurred in only 4 percent of samples. In the laboratory,W. urnula urnula captured landhoppers by rapidly everting theTVU-section odontophore beneath the prey and immediately drawingit into the mouth in a single action. Diet samples from the allopatriccongeners W. edwardi (Suter) (n 5 51) and W. clarki Powell (n5 7) contained no remains of landhoppers, and these snails didnot eat landhoppers in the laboratory. The diet of these specieswas dominated by earthworms. The subspecies W. u. nasuta ateboth earthworms and amphipods with similar frequency (n 5 40).Individual teeth on the radula of W. urnula urnula had a simpleblade-like cusp like other Wainuia species, but there were fewerteeth per row and fewer rows on the whole radula than in otherspecies. W. u. nasuta had a similar number of rows of teethto W. clarki and W. edwardi, but the number of teeth per rowwas intermediate between these species and W. u. urnula. Recordsof pulmonate species preying on arthropods are rare, yet inthe case of W. urnula this specialization has been accompaniedby minimal morphological change. (Received 22 December 1998; accepted 11 March 1999)     

ROLE OF FOOD IN MASS CULTIVATION OF THE FRESHWATER SNAIL INDOPLANORBIS EXUSTUS, VECTOR OF ANIMAL SCHISTOSOMIASIS

For the mass cultivation of the tropical freshwater snail, Indoplanorbisexustus, primary intermediate host of animal schistosomiasis,three foods, spinach, sheep's liver and a synthetic food (M/sHindustan Lever's rat food) were evaluated. The effect of thesefoods on growth, sexual maturity, fecundity and mortality isconsidered in this study. It is concluded that synthetic foodis ideal for breeding and sheep's liver for the maintenanceof mass cultures of this snail. revised 27 August 1985;     

LIFE HISTORIES, DENSITY AND BIOMASS IN A WOODLAND SNAIL COMMUNITY

Data, based on 8 monthly sets of random samples, are presentedon the life histories, densities and biomass of snail populationsin a mixed deciduous wood with moderately rich soil. Discus rotundatus, Oxychilus helveticus, O. cellarius and Trichiahispida have approximately annual life cycles, with rather littlepost-reproductive survival. Aegopinella nitiduta and Cochlodinalaminata take two years to reach maturity, and adults of thelatter may survive for several years. Breeding seasons are prolonged,but annual species peak in the autumn. Density does not vary much with season. Mean annual densityof all species combined (37.m^–2) is much lower than thoserecorded for similar woods elsewhere, but the estimate of meanannual standing crop (175 mg ashfree dry weight m^–2) doesnot show the same discrepancy. Comparisons reveal that the maincause of low density is the absence or rarity of several verysmall litter-dwelling species which have little effect on overallbiomass, and reasons for this are discussed. (Received 27 January 1981;     

DISTRIBUTION OF THE SCHISTOSOME VECTOR SNAIL, BIOMPHALARIA STRAMINEA (PULMONATA: PLANORBIDAE) IN HONG KONG

Biomphalaria straminea (Dunker) is a snail intermediate hostof Schistosoma mansoni Sambon which has invaded Hong Kong inrecent years from its home range in Brazil. This study examinesits distribution pattern in terms of habitat type and hydrologicalfactors. The data revealed very strong colonizing power, bothin terms of number of sites occupied as well as numerical dominanceat these sites. An inability to colonize lotic habitats mayhave been related to low levels of dissolved minerals and nutrientsbut the effect of current speed on colonization has yet to beresolved. Principal component analysis revealed that hydrological factorsimportant for colonization included high levels of dissolvedcalcium, magnesium, iron, chloride, total nitrogen, sulphateand phosphate. pH had only a secondary effect. The significanceof these findings is discussed with special reference to thelikelihood of introduction of B. straminea elsewhere, and possiblemanagement strategies. (Received 16 December 1988; accepted 12 February 1989)     

GROWTH, MORTALITY, AND FEEDING RATES OF THE SNAIL HELIX ASPERSA AT DIFFERENT POPULATION DENSITIES IN THE LABORATORY, AND THE DEPRESSION OF ACTIVITY OF HELICID SNAILS BY OTHER INDIVIDUALS, OR THEIR MUCUS

When reared at high densities, young Helix aspersa show lessshell growth, even if waste products are removed. They alsofeed less, and show increased mortality. It is suggested thatthese effects are linked to reduced activity. Juveniles showreduced activity in the presence of adults or their mucus. Mucusof adult Cepaca nemoralis also depresses the activity of bothadult and young Helix and Cepaea. ^* Present Address: Unit Zoologi, Universiti Kebangsaan Malaysia,Jalan Pantai Baru, Kuala Lumpur, West Malaysia. (Received 12 May 1981;     

PATTERNS OF SEXUAL ROLES ADOPTED BY THE SCHISTOSOME-VECTOR SNAIL BIOMPHALARIA GLABRATA (PLANORBIDAE)

Relatively little is known about the mating behaviour of hermaphroditefreshwater snails, many of which transmit the Schistosoma trematodesamong humans in developing countries. Knowledge of the breedingbiology of these snails could help in the design of schistosomecontrol programmes, as well as possibly contributing to ourunderstanding of the evolution of simultaneous hermaphroditismin animaL. Here we describe an experiment investigating thepatterns of sexual roles adopted by the Schistosoma mansoni-vectotsnail, Btmphalaria glabrata. During observations on groups offreely interacting snails, no individuals copulated significantlymore often in the male than in the female role, or vice versa.Only one individual showed a pattern of alternating sexual rolesover successive matings that differed significantly from a randomsequence of roles. There was no evidence for reciprocal copulationwith one particular partner, either between consecutive matings(unless they were temporarily isolated from other snails) orbetween non-consecutive matings (separated by copulations withother conspccifics). We discuss these results in the contextof sex allocation and ESS mating strategy theories. ^*Present address (or correspondence 1 G VERNON. Bioscan (UK).Standingford House, Cave Street, St. Clements, Oxford OX4 IBA. (Received 5 October 1995; accepted 6 November 1995)     

POPULATION DYNAMICS OF THE FRESHWATER SNAIL BIOMPHALARIA PFEIFFERI IN EASTERN ZAIRE

The population dynamics of the freshwater snail Biomphalariapfeifferi, an intermediate host of the parasitic worm Schistosomamansoni, was studied in the Virunga stream in Eastern Zaïre. Methods are developed to estimate age-specific survivorshipfrom regular quadrat-sampling data without assuming a constantmortality rate, and to approximate age-specific fecundity whenthe fecundity function is known in the laboratory. The population dynamics in the field was found to be very differentfrom that in the laboratory: it is basically discontinuous,with one main generation per year; a massive mortality occursafter hatching; fecundity is reduced considerably; and thereare marked seasonal variations in both survivorship and fecundity.Time-dependent demographic parameters were estimated by monthinstead of by cohort. They show that the environmental conditionsare favourable to an increase of the population only duringa short period of the year. The intrinsic rate of natural increase,r, was found to be well correlated with the changes in egg density. The environmental factors determining the population dynamicsin the Virunga are discussed; current speed seems critical. (Received 4 February 1987;     

ROBERTSIELLA SILVICOLA, A NEW SPECIES OF TRICULINE SNAIL (CAENOGASTROPODA: POMATIOPSIDAE) FROM PENINSULAR MALAYSIA, INTERMEDIATE HOST OF SCHISTOSOMA MALAYENSIS (TREMATODA: DIGENEA)

A new species of pomatiopsid gastropod, Robertsiella silvicola,is described from Perak, peninsular Malaysia. The encapsulationof the ducts of the bursa copulatrix complex, short (wide) spermathecalduct and penial stylet indicate that this is a species of Robertsiella.Robertsiella silvicola is distinguished from other Robertsiellaby its small size, the lack of pronounced spiral macrosculptureon the shell, and the nature of the stylet. Robertsiella silvicolais found in water bodies ranging from small, spring-fed, first-orderstreams to tiny trickles of water draining off forested hillsides.This species appears restricted to limestone areas in the foothillsof the mountain chains of Kedah and Perak States, West Malaysia.It appears to be a highly compatible intermediate host for theparasitic blood fluke Schistosoma malayensis Greer, Ow-Yang& Yong, 1980 that infects humans and other mammals in Malaysia. (Received 15 September 2004; accepted 21 March 2005)     

UPTAKE OF ACETATE BY NEOTRICULA APERTA (GASTROPODA: POMATIOPSIDAE), THE SNAIL HOST OF SCHISTOSOMA MEKONGI IN THE LOWER MEKONG BASIN

All three races of Neotricula aperta, an epilithic, schistosometransmitting, snail of the Mekong and Mul rivers of NortheastThailand and southern Laos, were found to take up acetate froma dilute solution. After 48 h incubation the mean specific netuptake rates (µmol^–1 g^–1 h^–1), from750 µM acetate, were: 1.86, -race; 1.39, ß-raceand 3.25, y-race. Over 48 h the snails were able to achievereductions in the ambient acetate concentration of up to 60%.Incubations under bacteriostatis suggested that bacteria arenot involved in the uptake of acetate by N. aperta. The uptakecharacteristics conform to the Michaelis-Menten model. The transportconstants, J_max (µmol^–1 g^–1 h^–1) andK_t (µM) were 1.10 and 102 respectively (-race). Racialdifferences in uptake characteristics are discussed in relationto micro-habitat differences. HPLC indicated concentrations of acetate in y-N. aperta microhabitatsof around 325 µM. This suggests a pool size sufficientto satisfy only 6% of the snail's basal metabolic rate (BMR).Levels within the epilithic aufwuchs, however, are probablyhigh enough to provide for more than 50% of the BMR. The possible role of acetate in the energy metabolism of N.aperta is discussed. Short-chain carboxylic acids (such as acetate),arising from the decomposition of the aufwuchs, could representsources of fermentable organics that may be taken up by N. apertasnails and used to supplement their nutrition during times offood shortage. However, further investigations involving ¹⁴C-labellingtechniques are required. The findings of this investigationhave implications for the chemical ecology and life-cycle ofN. aperta. (Received 16 June 1994; accepted 28 July 1994)