THE RELATIONSHIP BETWEEN SHELL INJURIES, SHELL THICKNESS AND HABITAT CHARACTERISTICS OF THE INTERTIDAL SNAIL LITTORINA RUDIS MATON

The hypothesis that risk of shell injury from crab predationand crushing by boulders and stones is important in the selectionof shell thickness in the intertidal gastropod Littorina rudisMaton was tested using data from 24 populations from Britain.Although there was an obvious relationship between the incidenceof shell injuries and both the distribution of crabs and substratummobility, there was no correlation between risk of shell injuryand shell thickness. This is probably accounted for by between-habitatvariations in energy levels which may vary independently ofcrab density and substratum mobility. ^*Present address: Department of Biology, University of Essex,Wivenhoe Park, Colchester C04 3SQ (Received 23 May 1977;     

INTER AND INTRA-SPECIFIC VARIATION OF THE SHELL OF TWO SPECIES OF THE TROPICAL FRESHWATER SNAIL BELLAMYA (MOLLUSCA: PROSOBRANCHIA)

Shell variation in two species of the tropical freshwater snailBellamya from two different habitats, was studied. The variation of the shell features studied, which includedthe shell width, spire height, aperture height and aperturewidth, were found to be related to shell height. Furthermore,significant difference in the shell shape was found not onlybetween the two species but also between males and females ofeach species. (Received 18 August 1983;     

THE YELLOW PIGMENT CELLS OF HYDROBIA ULVAE (PENNANT) (MOLLUSCA : PROSOBRANCHIA)

The distribution of yellow pigment cells in the veliger larvaeand post-metamorphic snails of Hydrobia ulvae has been recorded.The number of cells increases with the size of the snail andthe pigment is characteristic of the foot of the veliger larva,and the foot, mantle, tentacles and penis of adult snails. Thecells contain numerous, double membrane-bound vesicles and havea highly granular cytoplasm. The absorption spectra of acetoneand methanolic HC1 extracts show single peaks at 337 and 392nm respectively, while chloroform extracts show peaks at 249,274 and 283 nm with an inflexion at 293 nm. The pigment hasa pale green fluorescence in ultraviolet light. The resultsof feeding and starvation experiments using larval and post-metamorphicsnails lead to the hypothesis that the pigment is a waste productof metabolism which is stored in the vesicles of the cells (Received 3 January 1979;     

PHENOTYPIC DIFFERENTIATION IN LITTORINA SAXATILIS OLIVI (MOLLUSCA, PROSOBRANCHIA) IN A SMALL AREA ON THE SWEDISH WEST COAST

The Littorina saxatilis species-complex exhibits two distinctmorphs in the area investigated. Differences in shell morphologyand number of penial glands are statistically significant (P<0.02)between populations from exposed and sheltered habitats. However,in intermediate environments intermediate specimens as wellas typical specimens of both morphs are found. The differencesare considered intraspecific and at least partly geneticallydetermined, and possible selection pressures responsible arediscussed. (Received 8 February 1981;     

THE EGG MASS OF LITTORINA OBTUSATA AND LACUNA PALLIDULA (GASTROPODA : PROSOBRANCHIA)

The egg masses of Littorina obtusata and of Lacuna pallidulahave been compared with regard to size, shape, egg number, eggsize and substratum. The structure and histochemistry of thespawn of the two species has been investigated and observationson the laying process in L. obtusata are also recorded. ^* Present address: Portway School, Penpole Lane, Shirehampion,Bristol, BS11 0EB. (Received 12 October 1977;     

FUNCTIONAL MORPHOLOGY OF THE RECTUM IN THE MARINE GASTROPOD LITTORINA SAXATILIS (OLIVI) (PROSOBRANCHIA:LITTORINOIDEA)

The ultrastructure of the rectum of the marine prosobranch gastropod,Littorina saxatilis suggests that it may have an additionalrole to the voiding of faecal pellets. It consists of two epitheliallayers, separated by a blood space. The inner epithelial layeris greatly folded and consists of metabolically highly activecells containing a wide variety of inclusions, and showing evidenceof secretory activity at their luminal surfaces. The outer epitheliumcontains a greater diversity of cell types, also with a largenumber of different inclusions present. Unlike some other prosobranchgastropods, a distinct rectal gland is absent in L. saxatilis.The entire rectal epithelium is glandular, and it appears thatthe rectal epithelial cells produce a number of secretions.This may indicate a role in absorption, the removal of materialfrom the blood, or the addition of a final covering to the faecalpellets. (Received 6 February 1989; accepted 6 March 1989)     

THE GENETIC RELATIONSHIPS OF THREE TAXA IN THE LITTORINA SAXATILIS SPECIES COMPLEX (PROSOBRANCHIA: LITTORINIDAE)

Three species in the Littorina saxatilis complex (the ovoviviparousL. saxatilis and the two oviparous species L. arcana and L.nigrolineata) were screened for the products of up to 22 lociusing gel elec-trophoresis. Analysis of allele frequencies andderived genetic distances showed that, with rare exceptionsin L. saxatilis and L. arcana, conspecific populations clusteredtogether. Sympatric pairs of populations showed significantdifferentiation at many polymorphic loci. The results confirmedthe biological reality of the three taxa, and did not suggestthe existence of any previously unrecognized species. The speciesare genetically closely related to each other, with Nei geneticdistances ranging from 0.035 to 0.083. (Received 24 October 1989; accepted 18 April 1990)     

AN ANALYSIS OF SHELL SHAPE VARIATION IN THE PAINTED TOPSHELL CALLIOSTOMA ZIZYPHINUM (L.) (PROSOBRANCHIA: TROCHIDAE

Littoral and sublittoral Calliostoma zizyphinum (L.) from fourteensites around Ireland are compared by a new method of shell shapeanalysis. The apparatus used is described and results show clearvariation between populations. It is also used to show similaritybetween the variegated and white morphs found in StrangfordLough. Patterns of growth are shown to be largely in responseto the habitat conditions encountered at each site. The meanapical angle of each population is shown to be of great importancein distinguishing populations of topshells, as it varies withthe relative exposure of each site. (Received 30 July 1986;     

CONTRIBUTION OF GENETIC AND ENVIRONMENTAL FACTORS TO SHELL SHAPE VARIATION IN THE LOTIC SNAIL SEMISULCOSPIRA REINIANA (PROSOBRANCHIA: PLEUROCERIDAE)

The genetic and environmental factors affecting shell shapein the freshwater snail Semisulcospira reiniana at Takahashiin Kyoto, central Japan, were studied by means of a rearingexperiment and field observations. Shell shape was characterizedby three parameters; W (whorl expansion rate), T (whorl translationrate), and S (roundness of generating curve). Estimated heritabilitieswere low in all three parameters and the largest component ofthe great shell variation in the Takahashi population was environmentalvariance, suggesting that the main source of shell variationwas phenotypic modulation, in response to the external environment.In the field, snails that were active in fast currents had largerW and smaller T, that is, a larger body whorl and a lower spire,than snails in slow currents. Substratum conditions relatedto T in resting periods although its cause was unclear. Mechanismsare suggested which in the absence of selection of genetic variationcould cause and maintain shell variation in S. reiniana in differentmicrohabitats. (Received 8 March 1996; accepted 3 November 1997)     

EMBRYONIC ABNORMALITIES IN POPULATIONS OF LITTORINA SAXATILIS (OLIVI) (GASTROPODA: PROSOBRANCHIA) IN THE WHITE SEA

The incidence of abnormally developing embryos in brood pouchesof females was studied in five populations of Littorina saxatilisliving under different salinity conditions. The proportion ofabnormals decreased during embryonic development. Age of femaleand infection with the ciliate Protophrya ovi-cola had no effecton the frequency of abnormals. The proportion of abnormal eggs(PAE) increased at the end of the reproductive season; a similartrend was found for the proportion of abnormal veligers (PAV)although it was not always significant. The proportion of abnormaljuveniles (PAJ) showed no seasonality. The increase of PAE coincidedwith decrease of water temperature in September. Environmentalsalinity was significantly correlated with frequency of abnormalsin L. saxatilis populations: the highest values of PAV and PAJwere observed in estuarine population (salinity range 5–8%),intermediate in populations living under conditions of 10–20%osalinityand lowest in control populations (23–24%). Itis suggested that critical salinity (sensu Khle-bovich, 1974)(approximately 8–10%) may also be a crucial point forstability of embryonic development in the White Sea populationsof L. saxatilis. (Received 28 June 1994; accepted 28 November 1994)     

EVIDENCE FOR PREDATION AS A FACTOR IN DETERMINING SHELL COLOR FREQUENCIES IN A MANGROVE SNAIL LITTORINA SP. (PROSOBRANCHIA: LITTORINIDAE)

It was hypothesized that in Littorina populations living on Avicennia marina in Moreton Bay, Queensland, yellow shelled individuals are at a selective advantage over other shell colors and that this advantage is due to differential selection by predators. Yellow shelled individuals were more likely to be recaptured than others, indicating a higher survival rate of yellows. When predation was restricted on ten mangrove trees, the apparent advantage of yellow shells was removed. After 18 months, the relative frequency of yellow shelled individuals was significantly lower on experimental trees than on control trees. A combination of selection for crypsis and for the less common morph is suggested as the mechanism maintaining the high levels of variation in this species.     

SYSTEMATIC REVISION OF THE EPIMENIIDAE (MOLLUSCA: SOLENOGASTRES)

The species of Epimeniidae (Solenogastres: Cavi-belonia) arecompared and revised according to available type material. Structuresof particular interest include the differentiation of the foregut,the pharyngo-buccal nervous system and the blood cells. Sevenspecies are recognized in the family. Of these, six are placedin the genus Epimenia: E. australis (Thiele) (synonym Dinomeniaverrucosa Nierstrasz), E. ohshimai Baba, E. arabica Salvini-Plawen& Benayahu, and the three new species E. babai from offKyushu, Japan (synonym E. verrucosa in Baba 1939–1951),E. allohaemata from off Korea and E.indica from the Maldives. E. vixinsignis Salvini-Plawen is transferred to Epiherpia gen.nov. (Received 2 February 1996; accepted 19 September 1996)     

EFFECTS OF WOUNDING BY THE HERBIVOROUS SNAILS LITTORINA SITKANA AND L. SCUTULATA (MOLLUSCA) ON GROWTH AND REPRODUCTION OF THE INTERTIDAL ALGA FUCUS DISTICHUS (PHAEOPHYTA)1

Small (3–7 cm long) Fucus distichus ssp. edentatus (de la Pyl.) Pow. Plants were tagged at three sites in which densities of the herbivorous snails Littorina sitkana and L. scutulata ranged from 367–4690 animals · M^-2. From April–August 1986, the growth rate, degree of wounding, and reproductive status of individual thalli were monitored at 2–4 week intervals. Grazer-inflicted damage to the thalli varied within and among sites. Mean growth rates at the site with low densities of littorines were about twice those at the site with intermediate densities and about four times those at the high density site. At the site with high densities of littorines, F. distichus growth rates were negatively correlated with the degree to which the plants were wounded. There appeared to be no correlation of grazer density with F. distichus survivorship. Thalli at the site with few herbivores tended to reproduce earlier and at a larger size than did those at the other two sites. In all three areas, only thalli that had received little damage from herbivores became reproductive. By lowering growth rates and delaying reproduction in F. distichus, grazing by littorine snails can potentially cause variation in reproductive output among individual thalli.     

GEOGRAPHICAL VARIATION OF SHELL MORPHOLOGY IN CYPRAEA ANNULUS (GASTROPODA: CYPRAEIDAE)

Macro- and microgeographic variation of shell morphology inCypraea annulus was studied. Surveys of phenotypic variationin 19 populations from the Indian and West Pacific Oceans revealeda significant positive relationship between average seawatertemperature and callus thickness. In contrast, juvenile shellsize after maturation had no significant relationship with seawatertemperature. Research on within-population variation in OkinawaIsland indicated that shell morphology is correlated with someecological factors such as temperature and algal abundance.Both juvenile shell size and callus thickness decreased withincreasing density of individuals. These microgeographical patternssuggest that ecophenotypic variation, rather than genetic differentiation,causes the latitudinal clines in shell morphology that havebeen reported in several cypraeid species. (Received 18 November 2004; accepted 8 April 2005)     

VARIATION IN THE OCCURRENCE OF ABNORMAL EMBRYOS IN FEMALES OF THE INTERTIDAL GASTROPOD LITTORINA SAXATILIS OLIVI

The incidence of abnormally developed embryos within the brood-pouchof female L. saxatilis was very variable, ranging from 0–100%of embryos being abnormal. A minor part of the total variationwas attributed to between-shore variation, while 82% reflectedwithin sample differences between females. Possible factorsresponsible for the variation in embryo abnormality shown bythis and other investigations, are discussed and it is concludedthat genetic rather than non-genetic factors are important. (Received 8 November 1983;     

A GENETIC ANALYSIS OF SYMPATRIC SUBPOPULATIONS OF THE SIBLING SPECIES LITTORINA SAXATILIS (OLIVI) AND LITTORINA ARCANA HANNAFORD ELLIS

A detailed analysis of shell characteristics (four parameters)and allozyme allele frequencies (eight to nine polymorphic loci)of sympatric Littorina saxatilis and Littorina arcana subpopulationsfrom Filey Brigg on the east coast of England supports theiridentification as closely related but separate species. Oneenzyme system, esterase-2, was nearly species diagnostic. Resultswere generally comparable with an earlier study of the two speciesfrom East Lothian, Scotland. Littorina saxatilis was again foundto be more variable than L. arcana. (Received 14 December 1983;