A REVIEW OF LARVAL DEVELOPMENT IN THE INTERTIDAL LIMPET GENUS SIPHONARIA (GASTROPODA: PULMONATA)

A compilation of distributional and life-history data relatingto mode of larval development is presented for 26 species ofSiphonana, a genus of intertidal pulmonates. Most species depositgelatinous benthic egg masses with two species releasing pelagicegg masses. Fifteen species hatch as planktonic-developing larvae,nine hatch as direct-developing juveniles, and in a furthertwo larvae hatch with both the swimming velar apparatus (associatedwith plank-tonic development) and a crawling foot (associatedwith direct development). Data on mode of larval developmentare interpreted with respect to some adaptive models. Despiteimportant exceptions, there is support for adaptive models basedupon egg capsule size (direct developers hatch from larger eggcapsules) and intertidal distribution (direct developers generallyoccur higher on the shore than planktonic developers). Worldwide,planktonic developers are more widespread than direct-developingspecies, and individual planktonic species have a greater meanlatitudinal range. The evidence for adaptive models relatinglatitudinal distribution to developmental mode is equivocal.There appears to be no clear relationship between body sizeand developmental mode in the genus, although the smallest specieshas direct development and the largest has planktonic development.In most siphonariid subgenera, developmental mode appears tobe constant, but two subgenera contain a mixture of developmentaltypes (Received 1 November 1993; accepted 15 April 1994)     

NOTES ON THE TAXONOMY, SPAWN AND LARVAL DEVELOPMENT OF SOUTH AFRICAN SPECIES OF THE INTERTIDAL LIMPET SIPHONARIA (GASTROPODA: PULMONATA)

The taxonomy of South African Siphonaria is reviewed. We concludethat nine species are valid. These are: S. anneae Tomlin, 1944;S. capensis Quoy & Gaimard, 1833; S. compressa Allanson,1959; S. concinna Sowerby, 1824; S. dayi Allanson, 1959; S.nigerrima Smith, 1903; S. oculus Krauss, 1848; S. serrata (Fischer,1807) and S. tenuicostulata Smith, 1903. Of these, Siphonarianigerrima Smith, 1903, has been incorrectly synonymized withSiphonaria carbo Hanley, 1858, which is not present on SouthAfrican shores. S. aspera Krauss, 1848 is reduced to a juniorsynonym of S. Serrata (Fischer, 1807). Shell characteristicsand mode of larval development are described for these nineSouth African species. All species deposit benthic egg massesand development may be either planktonic with swimming veligerlarvae (S. capensis, S. concinna and S. oculus) or direct, withcrawling larvae emerging from the eggs (S. anneae, S. compressa,S. dayi, S. nigerrima, S. serrata and S. tenuicostulata). (Received 20 November 1992; accepted 24 January 1994)     

VARIATIONS IN INFESTATIONS OF SIPHONARIA CAPENSIS AND S. CONCINNA(PULMONATA) BY LARVAL TREMATODES IN SOUTHERN AFRICA

The prevalence of digenean trematode parasites in Siphonariacapensis (Pulmonata) was examined in populations from 24 sites,and in S. concinna from 10 sites along the coast of southernAfrica from 1989 to 1991. Sporocysts containing cercariae werefound in the digestive gland of both species. To date, two typesof cercaria have been isolated from S. capensis and one typefrom S. concinna, these types possibly representing three distinctspecies of trematode. In approximately 30% of parasitized S.capensis and 10% of parasitized S. concinna the digestive glandwas completely destroyed. In both species of Siphonaria therewas considerable temporal and spatial variation in parasiteprevalence. At some locations up to 40% of S. capensis wereinfected whereas at others, no parasites were found. Prevalenceof trema-todes in S. concinna rarely exceeded 12%. At severalsites the prevalence of infestation within the limpets increasedwith increasing host size. (Received 8 June 1992; accepted 6 July 1992)     

COMPARATIVE SPERMATOLOGY OF FOUR SYMPATRIC SPECIES OF SIPHONARIA (PULMONATA: BASOMMATOPHORA)

The fine structure of the modified sperm and spermatogenesisof four sympatric species of Siphonaria is described. The morphologyof the sperm of all species is very similar. The head, whichis about 6 µm long, is composed of a nucleus with fibrouschromatin capped by an acrosome (about 1 µm long) comprisedof an acrosomal pedestal and apical vesicle. The midpiece hasa mitochondrial derivative which surrounds a single glycogenhelix, posterior to which is a glycogen piece. Although differencesbetween each species exist, the value of sperm morphology forpurposes of taxonomy in this genus is questioned. Comparisonwith other basommatophorans however suggests that sperm morphologymay be of value at a higher taxo-nomic level. The morphologicalchanges that occur during spermatogenesis are similar to thosedescribed for other molluscs with modified sperm, except thatduring early spermiogenesis the Golgi body and smooth endoplasmicreticulum become highly developed. This proliferation of theSER and Golgi occurs at the same time as elongation of the spermatid.Throughout spermatogenesis, the germ cells are closely associatedwith a somatic cell which, because of structural similaritieswith the somatic cell of mammalian seminiferous epithelium,has been termed a Sertoli cell. After the spermatids have beenreleased from the Sertoli cells of the testis, maturation continuesin the hermaphrodite duct where the acrosome reaches its finalsize and glycogen accumulates in the glycogen compartment ofthe mid-piece. (Received 25 April 1990; accepted 1 September 1990)     

NOTES ON THE INTRODUCED TERRESTRIAL PULMONATA (GASTROPODA:MOLLUSCA) OF NEW ZEALAND

The New Zealand Pulmonate fauna contains 22 naturalized terrestrialspecies. For each, a bibliography is given for the New Zealandliterature and comment made on its biology and distribution.Vertigo ovata SAY and Oxychilus draparnaldi (BECK) are newlyrecorded from New Zealand. (Received 11 February 1981;     

CALCIUM PHOSPHATE GRANULES IN THE REPRODUCTIVE SYSTEM OF OXYCHILUS ATLANTICUS (GASTROPODA: PULMONATA)

The presence of connective interstitial cells in the wall ofseveral organs of the distal reproductive system in Oxychilus atlanticusis described by means of scanning electron microscopy (SEM).Connective interstitial cells extend from the distal part of thevas deferens to the penis, being the dominant cell type of large portionsof the epiphallus as well as in the whole penial caecum (=flagellum).These cells are highly mineralized and are characterized bythe presence of large amounts of solid spherules (up to 4 mmin diameter) in their cytoplasm. A semi-quantitative evaluationby X-ray microanalysis demonstrates that calcium and phosphorusare the main elements of the spherules. Their function is unknown,but they could aid in copulation or they could assist the survivalof the transferred spermatozoa. (Received 7 June 1999; accepted 8 September 1999)     

THE ONCHIDIACEA (GASTROPODA, PULMONATA) OF HONG KONG WITH A WORLDWIDE REVIEW OF THE GENERA

The Onchidiacea are a superfamily of mainly marine intertidal,slug-like pulmonates. Twelve genera are recognizable, and theseare redefined. Four of these genera are represented in HongKong, each by a single species, and these are recorded herein.Two of these are new; a third has not been seen since it wasoriginally figured in 1850. ^*Present address: Palmers Sixth-Form College, Grays, Essex. (Received 18 August 1983;     

GEOGRAPHICAL PATTERNS OF GENETIC DIFFERENTIATION IN THE LANDSNAIL HELIX ASPERSA MuLLER (GASTROPODA: PULMONATA)

In order to investigate the initial processes responsible forthe geographical distribution of the Mediterranean landsnailHelix aspersa, populations from 64 locations in Maghreb andin Europe were studied at 17 enzyme loci by both starch andpolyacrylamide gel electrophoresis. Allele frequencies and genotypedistributions were analysed to provide information on populationstructure and genetic differentiation among populations. Valuesof Nei's unbiased (D) and Rogers (R) genetic distances led tothe formation of two main groups, namely Europe-west Algeriaand east Maghreb (average D = 0.182). Such splitting supportedthe pattern of anatomical variation recently described. Twosamples from Morocco were excluded from these groups becauseof an average D = 0.224. Within this Moroccan entity, geneticdivergences did not distinguish the ‘giant’ snailsH. a.maxima from the brownsnails H. a. aspersa. Such biochemicalsimilarities among morphological heterogeneity throws the subspecificstatus of H. a. maxima into question. Values of fixation indicesindicated that the greatest differentiation between samplesoccurred on the Maghreb territory ( = 0.393). The patterns of population differentiation are discussed inrelation to past geological and historical events. Thus, threescenarios, not mutually exclusive, are considered: the disjunctionof populations by plate tectonics during the Tertiary, the formationof geographically isolated populations during the Pleistoceneglacial/interglacial cycle and the possibility of human introductionas early as the Neolithic period. (Received 9 December 1992; accepted 11 November 1993)     

THE LIFE CYCLE, POPULATION DYNAMICS, GROWTH AND SECONDARY PRODUCTION OF THE SNAIL BRADYBAENA FRUTICUM (MULLER, 1774) (GASTROPODA PULMONATA) IN NORTHERN GREECE

The life cycle, population dynamics, growth and secondary productionof the pulmonate land snail Bradybaena fruticum were studiedin northern Greece. The demographic analysis of the populationsof B. fruticum revealed that a) two cohorts exist in the fieldthroughout the year b) the reproductive period started in thebeginning of summer and c) growth was increased during springand autumn. According to von Bertallanffy' method B. fruticum needs 5 yearsto attain its maximum size in the field of 25.40 mm. Mortalityrate increases and life expectancy decreases with increasingage. Net reproductive rate (Ro) was equal to 3. 15 and per capitarate of increase (r^c) was equal to 1. Annual secondary production, calculated by Hynes' size frequencymethod, revealed a mean annual density of 5.9 individuals/m²,a mean standing crop (B) of 8.09 g/m²/year and an annual production(P) of 1.92 ± 0.11g/m²/year. Annual turnover ratio (P/B)was equal to 2.37. (Received 25 May 1989; accepted 17 March 1989)     

WATER-CONTENT OF SLUGS (GASTROPODA:PULMONATA) MAINTAINED IN STANDARDISED CULTURE CONDITIONS

A culture method for mass-rearing slugs is described and thewater-contents of 11 species of slug raised under these conditionsare analysed. The conclusion is drawn that, supplied with anappropriate environment, slugs showed no obvious rhythmic fluctuationsin hydration but exhibited water-contents relatively stablewithin species and presumably maintained by behavioural mechanisms. ^*Present address: Department of Zoology, East Mailing ResearchStation, Maidstone, Kent ME19 6BJ (Received 12 May 1981;     

INFLUENCE OF THE QUINOLIZIDINE ALKALOID CONTENT OF LUPINUS ALBUS (FABACEAE) ON THE FEEDING CHOICE OF HELIX ASPERSA (GASTROPODA: PULMONATA)

Adult Helix aspersa snails were maintained individually forone week in plastic cages with 9 living Lupinus albus plantsas their only food. Among these 9 plants, 3 chemotypes bitter,intermediate and sweet which differed in their alkaloid contentwere equally represented. Each day, the leaf surface grazed and the number of leaves attackedby the snails were recorded for each chemotype and each snail.A consumption/ attack (C/A) ratio was calculated by dividing thesurface grazed (C) by the number of attacks (A). The numberof attacks and the grazed area were positively correlated foreach chemotype during the whole experiment, and the snails atesimilar quantities of lupin each day. After 4 and 6 days ofexperiment, we noticed a rejection of the bitter chemotype infavor of the intermediate and sweet ones respectively. Afterthe 6th day, the surface grazed per attack was significantlyhigher on the sweet chemotype than on the bitter plants. Wehypothesize that rejection of the bitter chemotype might berelated to (i) an alkaloids reaction threshold associated withan increase in the amount of alkaloids in the wounded plantsand/or (ii) aversive ingestive conditioning. (Received ; accepted 16 April 1999)     

POPULATION GENETICS OF LYMNAEA PEREGRA (MULLER) (GASTROPODA: PULMONATA) IN LAKE GENEVA

Using gel electrophoresis, a study was made of genetic exchangeamongst populations of Lymnaea peregra in Lake Geneva. Geneticvariability is high. A within-population heterozygote deficiencyis shown and the role of null alleles as an explanation of thisdeficiency is discussed. High values of gene flow show thatthe inter-population structure is weak. Exchange between populationspropably occurs by both active and passive means. (Received 9 January 1989; accepted 15 August 1989)     

THE INFLUENCE OF INGESTIVE CONDITIONING ON FOOD CHOICES IN THE LAND SNAIL HELIX ASPERSAMULLER (GASTROPODA: PULMONATA: STYLOMMATOPHORA)

An experiment of food choice in one-day-old naïve landsnail Helix aspersa Müller was carried out, involving threephases. First, a training period on a monophagous diet of leafdiscs of Taraxacum officinale or Urtica dioica was given for1, 5, 10, 15 or 30 days. The area of leaf discs consumed byeach snail during this stage was assessed. In the intermediatephase, the animals were not fed for 24hours. Finally, food choicewas tested over 24 hours, when animals could eat leaf discsof each species of plant usedfor training. A coefficient offood preference for Urtica dioica was calculated (UPC = areaof Vrtica leaf disc consumed/area of Urtica and Taraxacum discsof leaves consumed for 24 hours). The length of the training phase did not reduce the percentageof individuals preferring the plant previously consumed. Onthe contrary, after 15 days of monophagous diet, animals formerlyfed on Urtica showed a coefficient of food preference for Urticasignificantly higher than Taraxacum fed animals, and after 30days of training this phenomenon was more pronounced. Thus,during the choice test, snails ate more of the previously eatenplant leaf. Our experiment highlighted the feeding behaviourplasticity of H. aspersa. The significant correlation betweenthe area of Urtica eaten during the training phase and the coefficientof food preference for Urtica is discussed. (Received 10 April 1994; accepted 10 January 1995)     

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;     

THE FINE STRUCTURE AND FUNCTION OF THE SALIVARY GLANDS OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE)

The fine structure of the tubular and acinous salivary glandsof Nucella lapillus (L.) has been studied and some histochemicaland enzyme tests have been carried out. The clusters of subepithelialcells of the tubular glands secrete a glycoprotein composedof chains of tubular macromolecules resembling secretions knownto have adhesive properties which may assist in boring. Thesecretion is rich in disulphide groups, as are many toxins,and is believed to be responsible for the recently demonstratedpharmacological activity of the glands. It is proposed thatflaccid paralysis is induced in prey by envenomation with thissecretion during rasping, after soft parts have been exposedby an ‘anti-predator’ reaction to secretion fromthe hypobranchial gland of Nucella. The secretory vesicles ofboth types of gland cells in the acinous glands have heterogeneouscontents indicating that their secretions are complex. The majorcomponent in those of the mucous cells is an acid mucopolysaccharidetypical of a lubricant or releasing agent. The ciliated basalcells resemble typical enzyme-secreting cells and the majorconstituent of their secretion is a finely granular glycoprotein. (Received 8 January 1990; accepted 5 June 1990)     

STARVATION, DESICCATION AND USE OF ALLOSPERM IN THE HERMAPHRODITE FRESHWATER SNAIL BIOMPHALARIA GLABRATA (GASTROPODA: PULMONATA)

Pairs of albino and pigmented snails were used to test the hypothesisthat the hermaphrodite freshwater gastropod Biomphalaria glabratawas able to conserve and use allosperm, despite periods of desiccationand starvation. In laboratory experiments, lots of twenty snailswere subject to 0, 5, 10, 15 AND 20 days starvation; similarlots of 20 snails were subjected to 0, 2, 4, 6, 8, 10 weeksof desiccation at R.H. 100%. After all periods of starvationand desiccation, albino parents were still producing significantnumbers of pigmented offspring, suggesting preferential cross-fertilizationusing stored allosperm. (Received 30 September 1993; accepted 23 December 1993)     

ASYNCHRONOUS REPRODUCTIVE ACTIVITY IN THE BROADCAST SPAWNER CELLANA CAPENSIS (GMELIN, 1791) (GASTROPODA: PATELLIDAE)

Short-term fluctuations in the reproductive condition of thelimpet Cellana capensis are described. Gravimetric and histologicalanalyses of gonadal development were carried out on samplescollected at 4 day intervals over a 3 month period from theMkambati Nature Reserve, Transkei. The results indicate a distinctlack of reproductive synchrony within the population, whichapplied not only to gametogenic development per se but alsoto spawning activity. Some of the spawning events identifiedduring the study period were more marked than others, thesemay reflect a greater degree of synchronization in activity.Results presented suggest that C. capensis is probably a ‘partial’rather than a ‘complete’ spawner. The implicationsof asynchronous spawning activity for the reproductive successof broadcast spawners are also discussed. (Received 6 December 1988; accepted 15 February 1989)