INTRASPECIFIC AND INTERSPECIFIC VARIATION IN SHELL MORPHOLOGY OF BIOMPHALARIA PFEIFFERI (KRAUSS, 1848) AND HELISOMA DURYI (WETHERBY, 1879) FROM MOSHI, TANZANIA, ANALYSED BY MORPHOMETRIC STUDIES

Helisoma duryi, a planorbid snail species, which is a potentialbiological control agent of the intermediate hosts of schistosomiasis,was introduced in an irrigation scheme (T.P.C.) in northernTanzania in 1972. The species has been present at T.P.C. since,and during a snail survey in January 1981, a great variationin the shell morphology of H. duryi, ranging from typical H.duryi forms to forms resembling Biomphalaria pfeifferi, theintermediate host of Schistosoma mansoni in the area, was observed.The Biomphalaria- Wkc forms of H. duryi could constitute anentire population but also occasionally occurred in populationsof typical H. duryi. This study was undertaken to determine whether simple shellmeasurements, or ratios between some of these could be usefulin discriminating between H. duryi and B. pfeifferi. Followingparameters were considered: shell height, shell diameter, diameterof the umbilicus, ratio between shell height and diameter ofthe umbilicus, and the number of whorls. (Received 29 July 1983;     

FOOD PREFERENCES AND DIETARY OVERLAP BY TERRESTRIAL SNAILS IN LOGOS AREA (EDESSA, MACEDONIA, NORTHERN GREECE)

Among the five coexisting species of snail in Edessa (N. Greece),Bradybaena fruticum and Helix lucorum dominated in density andbiomass in comparison with Xeropicta arenosa, Monacha cartusianaand Cepaea vindobonensis. Resting places of each species inrelation to plant cover and diet preferences are examined seasonallyand throughout a year. Discriminant analysis for the annualdata showed that 83% of the snail group species could be differentiatedby the plants on which they were attached. Each snail specieswas usually found sitting on one of the most abundant plants.Cepaea preferred to sit on and eat senescent material even inspring time and Bradybaena green material. In spring, the snailsdid not consume plant material in proportion to the occurrenceof those plants but they usually did so in summer and in autumn.Hedera helix was not consumed even when it was abundant. Inspring and autumn the snails had consumed plants to which theywere found attached, but in summer they did not. (Received 9 August 1993; accepted 14 February 1994)     

GENETIC AND MORPHOLOGICAL VARIATION OF POPULATIONS BELONGING TO THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA; PLANORBIDAE) IN SOUTH WESTERN ZIMBABWE

Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.29–0.80among populations from Plumtree and expected heterozygosity(H_e) from 0.02–0.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998)     

LIFE CYCLE AND HABITAT SHIFT OF THE TROCHID SNAIL DILOMA SUAVIS (PHILIPPI) WITHIN INTERTIDAL MUSSEL ZONES

The life cycle of the trochid snail Diloma suavis (Philippi, 1849),was studied on an intertidal rocky shore at Shirahama, Wakayama Prefecture,where two mytilid bivalves, Septifer virgatus (Wiegmann) andHormomya mutabilis (Gould), formed vertically contiguous musselbeds in the upper-middle and lower zones, respectively. At lowtide in April, the snail density increased with decreasing shoreheight and was greatest at the middle level of the H. mutabilisbed. Then, the density decreased towards the lower littoralfringe. Newly settled juveniles smaller than 2 mm in shell heightappeared abundantly in late summer and autumn within algal turfon the lower shore. As snails grew larger than 2 mm, they appearedwithin the gaps of the H. mutabilis bed and the S. virgatusbed. They increased in size monotonically towards the next summer,but rate of growth in shell height tended to be great in autumnand small in winter. Seasonal change in the density of snailsfound within the gaps of the mussel beds was remarkable during athree year period, increasing from autumn to winter and then decreasingtowards next summer. Reproduction occurred in summer, and adultsnails disappeared by September. It is thus suggested that this specieshas a one year lifespan and shows a habitat shift from algal turfto the gaps of the mussel beds with growth. (Received 12 October 1998; accepted 2 March 1999)     

DREPANOTREMA NORDESTENSE (LUCENA, 1953) (PULMONATA: PLANORBIDAE): A NEW RECORD FOR THE BOLIVIAN ALTIPLANO AND ITS DIFFERENTIATION BY MORPHOLOGY AND ENZYMES

In 1995, a small planorbid snail new for the Northern Bolivian Altiplanowas discovered in several temporary ditches. Conchological andanatomical characteristics of this snail are similar to thoseof Drepanotrema nordestense (Lucena 1953), a tropical planorbid snailreported from the northeastern region of Brazil. A comparative studywas carried out with the closely related species D. aeruginosumfrom Puerto Rico and Guadeloupe using morphological (shell andanatomy of the reproductive system) and genetic (allozyme) markers.This study confirmed a clear distinction between the two species.Several malacological surveys have been carried out in the NorthernBolivian Altiplano since the first field trip by D'Orbigny in1835, the last one in 1975. That D. nordestense and relatedspecies were not reported in these earlier surveys may indicatea relatively recent introduction. (Received 6 March 2000; accepted 1 June 2000)     

THE COURTSHIP OF EUGLANDINA ROSEA FERUSSAC

Courtship of Euglandina rosea commences with trail followingculminating in the pursuing snail mounting the shell of thepursued from the rear. A vigorous head waving display then occursand is terminated after about 15 min by a short quiescent periodduring which the lower animal turns its head to face its ownshell. Copulation takes place whilst one snail is still mountedon the shell of the other, but in a head to head position broughtabout by the twisting of the neck of the lower animal. It lastsup to four hours. (Received 24 April 1984;     

Variation in adult shell morphology and life-history traits in the land snail Oreohelix cooperi in relation to biotic and abiotic factors

In this study, we explore factors influencing variation in adultshell morphology and life-history characteristics (offspringsize and number) in the ovoviviparous land snail, Oreohelixcooperi, from the Black Hills, South Dakota and Wyoming, USA.To date, no study of shell morphology and life-history characteristicsin ovoviviparous land snails has included a combination of datasetsincluding genetic data, life-history traits, shell morphologyand multiple environmental factors. We report that differencesin shell size among populations are strongly related to meanannual temperature (and the highly correlated variable elevation)and population density (measured as shell density). In addition,shell size varies among populations, despite an apparent lackof population genetic differentiation. Common factors thoughtto influence adult shell size, like precipitation and calciumlevels, do not have a significant effect in this study. Adultsize strongly influences per-clutch reproductive output, withlarger snails having larger and more offspring. As mean annualtemperature and shell density affect adult shell size, theyalso indirectly affect per-clutch output. The results suggestthat a large portion of the life-history variation in O. cooperiis environmentally induced, as has been found in oviparous landsnails and brooding freshwater bivalves. (Received 20 July 2006; accepted 10 January 2007)     

HYDROBIIDAE (GASTROPODA: HYDROBIOIDEA) FROM THE RIBEIRA VALLEY, S.E. BRAZIL, WITH DESCRIPTIONS OF TWO NEW CAVERNICOLOUS SPECIES

Potamolithus karsticus n. sp. and Potamolithus troglo-bius n.sp., two Brazilian aquatic cavesnails (Gastropoda: Hydrobiidae),are described. P. troglobius is blind and depigmented, and isthe first stygobiontic snail to be described from Brazil Additionally, specimens of Potamolithus ribeirensis Pilsbry,1911 were collected near the type locality for comparison withthe new cave species (Received 2 December 1993; accepted 20 June 1994)     

SHELL STRENGTH OF COLOUR MORPHS OF THE MANGROVE SNAIL LITTORARIA PALLESCENS

The load required to break shells of the snail Littor-aria pallescens(Philippi) (Gastropoda: Littorinidae) has been established.Mass increases more than proportionally with size. Size forsize, relatively heavy shells are thicker than relatively lightones, and the thicker shells are stronger. Three samples fromdifferent localities differ significantly in strength. Littorariapallescens is polymorphic for shell colour. It is shown thatin two of the three samples, both from Papua New Guinea, individualsof the dark morph are significantly heavier and stronger thanthose of the yellow morph, while there is no difference betweenmorphs in the third sample, from Thailand. In the sample withthe most robust shells the dark individuals are stronger, massfor mass, than yellows. Thus, colour morph is sometimes, butnot always, associated with differences in shell characteristicswhich are likely to affect fitness. Where there is a difference,the dark morph is estimated to be on average about 22% strongerthan the yellow morph. The difference between morphs is smallcompared with the large variation in shell characters associatedwith size. (Received 20 May 1992; accepted 22 June 1992)     

AGE DETERMINATION OF ARIANTA ARBUSTORUM (L.) (PULMONATA) BASED ON GROWTH BREAKS AND INNER LAYERS

The pulmonate snail Arianta arbustorum from the Swiss Alps wasaged using thin sections of the shell margins cut from markedindividuals. Shell layers at the apertural lip and growth breaksin the juvenile can give a reliable estimate of age. (Received 16 May 1986;     

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)     

Excavation of Boreholes by the Gastropod, Urosalpinx: An Analysis by Light and Scanning Electron Microscopy

Penetration of shell by the muricid gastropod, Urosalpinx cinereafollyensis, is accomplished by successive alternating periodsof (a) chemical activity by the accessory boring organ (ABO), and (b) rasping by the radula. This paper reports on the functionsof the radula and of the ABO in producing the characteristicgeometry of the borehole, andon the effects of radular teethand of the ABO secretion on the microscopic anatomy of the surfaceof the borehole during the process of shell-boring. Radulae of U. c. follyensis and the surfaces of incomplete boreholesin the shell of Crassoslrea virginica, Mytilus edulis, and Myawere examined by means of light and scanning electron microscopy.Hardness tests of radular teeth andshell of prey demonstratedthat marginal teeth are harder than rachidian teeth, and thatthe range of hardness of rachidianteeth overlaps that of thethree species of shell. Rasping is carried out by two, occasionallythree, of the five rachidiancusps. Rasping patterns are shallowand asymmetric. Rachidian teeth are worn to the base with use;marginal teeth wear onlyslightly as they are employed mainlyin feeding. The distance between the tips of rachidian cuspscorresponds with the interval between the parallel cusp tracesrasped by them in shell. During each rasping period, snailsscrape off about 1/10 to 1/5 of the surface of the chemicallytreated area of the bottom of the borehole. Dissolution of shell is accomplished by secretion from the secretorydisk of the ABO. With each application of the ABO,most or allof the radular marks of the previous rasping period are erasedby solution of a thin layer of shell. The pattern of etchingis specific for each of the species of shell studied. In oysterand mussel shell, initial solubilization occurs through theorganic, non-mineralized, prism sheaths, exposing prismaticforms shown by other workers to be distinctive for these species,and then proceeds into the organic-calcareous structure of individualprisms. Etching of Mya shell revealed no fundamental prismaticform. Shell-penetration includes dissolution of both organiccomplexes and CaCO₃ crystals. Shell-boring by this snail is principally a chemical process,and the geometry of the borehole is generally a reflection ofthe morphology of the ABO.     

Complementary Association of an Endophytic Red Alga and a Shell-encrusting Green Alga

Endophytic filaments of a red alga in the shell-encrusting greenalga Pseudulvella consociata S. & G. collected from subtidaland intertidal habitats in the San Juan Islands, WashingtonState, U.S.A., have been identified as Audouinella sparsa (Harvey)Dixon. The association appears to be complementary. Pseudulvella consociata, Audouinella sparsa, alage, Rhodophyta, Chlorophyta, endophyte     

Ecological Aspects of Some Coral-Boring Gastropods and Bivalves of the Northwestern Red Sea

More than 17 molluscan species were obtained from burrows incoral substrata at Al-Ghardaga (Hurghada on maps) on the RedSea coast, six of which in particular bore into livingcolonies.The species reported in this paper belong to the families Mytilidae,Coralliophilidae, and Gastrochaenidae. The direction of boringin living corals is to the outside, the borers keeping pacewith the growing coral layer to maintain their burrows open.Coral growth is generally of a higher rate than that of borers,and burrows are accordingly mostly much larger than their inhabitants.There is evidence in such cases that burrows form initiallyby growth of coral around the settling young. Boring of Lithophagaspecies is mostly due to the abrasive action of the shell whichmoves straight and posteroventrally without any rotation. Incoralliophilids,boring is also executed mechanically by the turning movementsof the shell. Boring in dead coral is directed inwards, andburrows are nearly as large as the borers. The latter avoidthe blocking of their burrows (e.g., by a living coral incrustation)either by great siphonal extension (Rocellaria) or the freeends of the shell may be strengthened to maintain the capabilityof boring in the opposite direction (Lithophaga laevigata).Both L. luevigata and Modiola chmamomeus bore mainly mechanicallyby the rocking movements of the shell. Chemical boring is stilla possibility,particularly in the posterior narrow region ofburrows of Modiola lodging the extended pallial siphons whichare deprived of any effective mechanical devices for boring.Therole of boring algae in rarefying bored coral material hasalso to be included as an indirect chemical factor.     

INTERACTIONS BETWEEN SOIL BACTERIA AND THE MOLLUSCAN ALIMENTARY TRACT

The alimentary tract is a major site of interaction betweenan animal's ecosystem and its physiology. It may be intermittentlyor permanently populated by microorganisms from its environmentthat could be beneficial or pathogenic in their influence. Thebacterial populations of the snail (H. aspersa) and the woodlouse(O. asellus) have therefore been estimated in terms of colonyforming units. gm body weight^–1. The bacteria in the snailappear to be similar to those found in soil and show wide resistanceto antibiotics. The main types are gram negative rods tentativelyidentified as belonging to Pseudomonas, Xanthomonas, Acinobacter,Vibrio and Enterobacteriaceae. Some gram positive and endosporeforming bacteria of Bacillus, Staphylococcus and Micrococcusspp were also present. The numbers of bacteria increase towardsthe posterior of the alimentary tract although the numbers inthe digestive gland are more constant. An artificial diet is described that can be used to feed snailsand study the effects of known amounts of additives. When starvedor kept under clean conditions the bacterial population of thesnail gut falls and the thickness of the alimentary tract decreases.All the indications are that the bacteria in the alimentarytract of the snail are indiscriminately accumulated from thenatural environment and are transient populations. (Received 7 June 1989; accepted 24 July 1989)     

IN VITRO RECALCIFICATION OF ORGANIC MATRIX OF SCALLOP SHELL AND SERPULID TUBES

Organic matrix was isolated from the shell of the bivalve Argopectenirradians by decalcification. The capacity of the matrix toinitiate formation of crystals similar in form and orientationto the crystals of normal shell was investigated. Decalcifiedshell matrix placed in an inorganic recalcification solutioninitiated the formation of elongate crystals in parallel arrangementcorresponding to the parallel orientation observed in the matrixfibers and similar to the orientation of the long crystals innormal shell. The detailed form of the crystals deposited invitro was different from that of the normal shell crystals.Electron diffraction analysis of remineralized matrix demonstratedthat the material was calcite, the mineral of normal shell. In contrast, the calcareous tube of the serpulid Hydroides dianthushas crystals lacking uniform arrangement and a matrix whichdoes not have a well-oriented structure. The decalcified tubematrix was recalcified and the mineral posited showed some evidenceof normal orientation. The results demonstrate that matrices of Argopecten shell andHydroides tube can induce crystal formation in vitro. Sincethe soluble matrix would be expected to be removed during decalcification,the observed in vitro effects apparently involve the insolublematrix. (Received 19 June 1984;     

Evidence for an outcrossing reproductive strategy in the hermaphroditic heterobranch gastropod Valvata utahensis (valvatidae), with notes on the genetic differentiation of V. utahensis and V. humeralis

The hermaphroditic aquatic heterobranch Valvata utahensis isa federally endangered snail endemic to the Snake River corridorin southern Idaho, USA. Although an appreciable understandingof molluscan taxonomic diversity has been established withinthis ecosystem, little is currently known about the ecologyand life history of many individual species (V. utahensis included).In this study, we used a combined analysis of mitochondrialand nuclear genetic variation within V. utahensis to infer thepredominant mode of reproduction (selfing vs outcrossing) withinnatural populations of this species. Results of this analysisindicated that outcrossing is likely a common reproductive strategy.We discuss our results in the context of conservation and managementefforts for this endangered species. Furthermore, in the courseof performing our investigations, we frequently collected specimensthat were tentatively identified as V. humeralis. Given thatlittle genetic work has previously been performed within thegenus Valvata, we compared genetic data from V. utahensis withdata from V. humeralis to determine whether molecular data supportedmorphological evidence that these two taxa are distinct evolutionaryentities. Results of our analyses clearly revealed strong patternsof genetic differentiation between these two taxa and confirmedthe presence of two sympatric Valvata species within the SnakeRiver system. (Received 25 January 2006; accepted 20 April 2006)     

Early Shell Formation During Molluscan Embryogenesis, with New Studies on the Surf Clam, Spisula solidissima

Shell formation in molluscs begins early in embryogenesis duringsome stage of archenteron formation. Ultrastructural informationon early formation of external shells is available from onlya few bivalves and gastropods. Secretion of the very first shellmaterial by shell field epithelial cells is preceded by an invaginationof the dorsal ectoderm in the region of the shell field. A centuryago, this invagination was termed the "shell gland." As a secretoryfunction for this invagination has not yet been demonstratedand as the term "shell gland" has taken on various meaningsin the literature, the invagination will be referred to as theshell field invagination. The opening into the shell field invaginationseems to be circular in gastropods and elongate in bivalves.Accordingly initial organic shell material seems to form a ringin gastropods and a saddle in bivalves. As in adult molluscs,shells of pre-metamorphic molluscs are composed of both organicand inorganiccomponents. Ultrastructural data from bivalvesand gastropods indicate that the initial organic shell materialis secreted just outside the shell field invagination (acrossthe pore). Initial inorganic shell materials have not been localizednor their pathway traced into or through any pre-metamorphicmolluscs. New SEM and TEM data show that the invagination inthe bivalve Spisula solidissima is composed of a wide outerregion and very narrow inner region with the first shell materialforming at the junction between the two. This is unlike ultrastructuraldata available for other species. Many sections give the falseimpressions that: 1) the shell field invagination is closedto the outside and, 2) that the first organic shell materiallines the innermost region of the invagination. It is not clearwhether the cells of the outer invagination in this speciesare shell field cells. It is suggested that they are not.     

SURFACING AND WATER LEAVING BEHAVIOUR OF THE FRESHWATER PULMONATE SNAILS LYMNAEA PEREGRA (MULLER), BIOMPHALARIA GLABRATA (SAY) AND BULINUS JOUSSEAUMEI (DAUTZENBERG)

Surfacing and water-leaving behaviour (quitting) of aquaticpulmonate snails was investigated in the laboratory. Regressioncoefficients of surfacing rate per hour for 16 snails in 200cm³ of water were 1.28 for L. peregra, 1.35 for B. glabrata(albino form), 0.47 for B. glabrata (pigmented form) and 0.17for B. jousseaumei. Disturbance, snail size and conditioningof the water were relatively unimportant factors; water volumeadjusted by depth was also unimportant up to 50 mm depth. Importantfactors controlling surfacing appeared to be population density,time of year, temperature, water volume adjusted by perimeterand dissolved oxygen concentration. The response to the latterwas not clear and both B. glabrata and L. peregra orientatedalmost as well to a nitrogen/water interface as to an air/waterinterface. Water-quitting regressed on volume, which had beenadjusted by perimeter variation, revealed a curvilinear relationshipfor B. glabrata, with maximum quitting at 1 snail per 7cm³ (1snail per 14cm of climbable perimeter). L. peregra showed anegative exponential curve, with maximum quitting at 1 snailper 3 cm³ of water (1 snail per 8 cm of climbable perimeter).These data could be relevant to design and management of irrigationchannels where bilharzia might occur. (Received 28 November 1990; accepted 22 October 1991)