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;     

OBSERVATIONS ON THE ECOLOGY OF BULINUS (PHYSOPSIS) GLOBOSUS (MORELET), B. (BULINUS) FORSKALII (EHRENBERG) AND LYMNAEA NATALENSIS (KRAUSS) IN RICE SWAMPS IN SIERRA LEONE.

Changes in population of Bulinus globosus, B. forskalii andLymnaea natalensis were studied in four different locationsnamed Sites A, B, C. and D in Bo town Sierra Leone. The snailpopulations and oxygen concentrations of water increased inthe rainy season. The biological oxygen demand did not havesignificant correlation with changes in snail populations inSites B and D. B. globosus was absent from Site A while B. forskaliiwas the predominant snail in Site C. Site D with the highestmean monthly conductivity of 176 µmhos contained 54% whileSite A with a similar reading of 90µmhos contained 1%of all snails found. (Received 22 May 1980;     

双尾蚜属的种类与地理分布

双尾蚜属Diuraphis Aizenberg全世界记录13种,主要分布在古北界和新北界。根据种类丰富度和特有种成分,欧亚大陆的欧洲和中亚为该属蚜虫的现代第一分布中心,北美为第二分布中心。本文提供了该属所有13个种的分种检索表。双尾蚜属蚜虫在中国共有7种,主要分布在蒙新区。它们是：麦双尾蚜Diuraphis noxia (Mordvilko), 害冰麦双尾蚜D. nociva Zhang et Liang,冰草麦蚜D. (Holcaphis) agropyronophaga Zhang, 披碱草蚜D. (Holcaphis) elymophila Zhang, 西方麦蚜D. (Holcaphis) frequens (Walker), 雀麦蚜D. (Holcaphis) bromicola Hille Ris Lambers和绒毛草蚜D. (Holcaphis) holci (Hille Ris Lambers)。对中国种类进行了简要描述。     

GENETIC VARIATION IN SYMPATRIC AND ALLOPATRIC POPULATIONS OF HYBRIDIZING FRESHWATER SNAIL SPECIES(VIVIPARUS ATER AND V. CONTECTUS)

To estimate the geographical extent of introgression, we studiedthe genetic structure of sympatric and allopatric populationsof hybridizing freshwater snail species Viviparus ater and V.contectus in central Europe. Six allozyme loci which were variablein Lake Garda, Italy in a previous study (five nearly diagnosticloci between the two species and one highly polymorphic locusin V. contectus) were analyzed from ten sympatric locationsand four allopatric populations each for the two species. Presumablyintrogressed genes (low allele frequencies) were found fromat least one locus in seven out of the ten sympatric sites.These seven sites covered most of northern Italy. The data indicatethat introgression has occurred from Viviparus contectus toV. ater and vice versa. Therefore, there is a possibility ofwidespread introgression or mosaic zones in nature. However,we cannot rule out that the observed patterns are due to theshared ancestry. V. ater possessed low genetic variation (thejackknifed mean of Wright's F_ST±S.E. over four loci was0.041±0.004). On the other hand, V. contectus showedhigh genetic differentiation (the jackknifed mean of F_ST±S.E. over six loci was 0.546±0.166). Although introgressionmay have caused evolutionary changes in V. ater and V. contectus,it was not strong enough to level out the genetic differencesbetween the two species, which may have originated from isolationamong populations in V. contectus and a past bottleneck eventin V. ater. (Received 21 June 1996; accepted 31 January 1997)     

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)     

THE GONADS OF MARGARITIFERA AURICULARIA (SPENGLER, 1793) AND M. MARGARITIFERA (LINNAEUS, 1758) (BIVALVIA: UNIONOIDEA).

A detailed study of the gonads of two endangered species of thegenus Margaritifera living in the Iberian Peninsula, Margaritiferaauricularia (Spengler, 1793) and Margaritifera margaritifera(Linnaeus 1758), based on macroscopic and histological observationsis presented. In both species, gonadal tissue occurs withinthe visceral mass without a specific location. In hermaphrodite specimens,male and female acini are mixed in the visceral mass but canbe clearly distinguished by detailed macroscopic study. The gonadaltopography and cycle of Margaritifera auricularia is described forthe first time, indicating that the species is a female hermaphroditeand that gametogenesis occurs from December to March. Fiftypercent of Margaritifera margaritifera specimens studied werehermaphrodites and 50% females. (Received 6 March 2000; accepted 5 June 2000)     

BROODING AND NON-BROODING DACRYDIUM (BIVALVIA: MYTILIDAE): A REVIEW OF THE ATLANTIC SPECIES

The Atlantic species of the marine bivalve genus Dacrydium arereviewed, with particular emphasis on their hinge and protoconchcharacters. The basic groundplan of a Dacrydium comprises afunctional primary ligament, a paired series of primary teeth,and a posterior row of secondary teeth separated from the latterby a secondary ligament; this can be transformed into a singleseries either by loss of the secondary ligament and mergingprimary and secondary teeth, or by loss of secondary teeth andligament through paedomorphosis. Twelve species are recognized, of which eleven are illustrated.One abyssal species is not separable morphologically from theIndian Ocean D. speculum Poutiers, 1989 and is new to the Atlantic;four new species (D. wareni, D. dauvini, D. filiferum and D.balgimi) are described; a Caribbean form which is hardly distinctfrom the Eastern Pacific D. elegantu-lum Soot-Ryen, 1955, isdescribed as a new subspecies D. e. hendersoni. The larvae are brooded in D. hyalinum (Mon-terosato, 1875),D. viviparum Ockelmann, 1983 and D. balgimi. The brooding specieshave larger larvae (protoconch 210 to 315 µm long) thanthe non-brooding (protoconch 120 to 150 µm long), andreach a smaller adult size (1.4 to 3 mm instead of 4.5–5mm). A phylogenetic reconstruction is attempted using parsimonyanalysis of hinge and shell characters as well as the brooding/nonbrooding character. (Received 22 October 1996; accepted 28 November 1996)     

THE ROLE OF LYMNAEA AURICULARIA (LINNAEUS) AND LYMNAEA PEREGRA (MULLER) (GASTROPODA: PULMONATA) IN THE TRANSMISSION OF LARVAL DIGENEANS IN THE LOWER THAMES VALLEY

Eleven species of larval digeneans are reported for the firsttime in the UK from the freshwater snail Lymnaea (Radix) auricularia.The latter replaced its congener L. peregra in a gravel pitnear Wraysbury, Berkshire in the Lower Thames Valley and hostedan assemblage of larval digeneans similar to that previouslytransmitted by L peregra. The larval digeneans of L. peregrain small bodies of water in the area were also similar to thosefound in L. auriculania in the gravel pit. This replacementin the role of the host is explained on the basis of morphological,physiological and ecological similarities of the two lymnaeidspecies. (Received 19 February 1992; accepted 27 April 1992)     

EFFECT OF CONTROLLED TEMPERATURES ON GAMETOGENESIS IN THE GASTROPODS PHYSA ACUTA (PHYSIDAE) AND BULINUS TROPICUS (PLANORBIDAE)

The effects of a range of constant temperatures on gametogenesiswere investigated in two freshwater snail species which occursympatrically in the Umsin-dusi River, Natal, South Africa,Physa acuta (invasive) and Bulinus tropicus (endemic). Bothwere shown to be simultaneous hermaphrodites with slight protandry.An increase in temperature accelerated the process of gametogenesisbut P. acuta responded more rapidly to these changes than B.tropicus. This, coupled with the greater fecundity and shorterincubation period of P. acuta, gives it a reproductive advantageover the endemic species, providing a possible explanation forthe invasive's success in rapidly repopulating disturbed riverinehabitats. (Received 16 November 1990; accepted 1 May 1991)     

TAXONOMY AND OCCURRENCE OF DENDRODORIS NIGRA AND DENDRODORIS FUMATA (NUDIBRANCHIA: DENDRODORIDIDAE) IN THE INDO-WEST PACIFIC REGION

The nudibranch Dendrodoris nigra (Stimpson, 1855) has hithertobeen considered as a single, highly poly-chromic species. Ourinvestigations of external morphology, anatomy and colour variationhave revealed more than one species exists. This conclusiongives credibility to the previous discovery of differing developmentalpatterns within D. nigra. Besides D. nigra, we recognise Dendrodorisfumata (Rüppell & Leuckart, 1830) which has three distinguishablecolour forms. The occurrence of D. nigra is confirmed to beextensive, however, the species was not found to be circum-Australianas previously reported. The presence of D. fumata in Australiais confirmed and the species is also reported from Hong Kongand Fiji for the first time. The clear separation of these twospecies and recognition of the different colour forms will permita more accurate picture of their distribution. (Received 15 November 1994; accepted 2 January 1997)     

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)     

POPULATION GENETICS OF A SNAIL SPECIES COMPLEX IN THE BRITISH ISLES: LITTORINA SAXATILIS (OLIVI), L. NEGLECTA BEAN AND L. TENEBROSA (MONTAGU), USING SSCP ANALYSIS OF CYTOCHROME-B GENE FRAGMENTS

The intertidal snail Littorina saxatilis displays a range ofshell morphologies associated with a variety of habitats. Sincemorphology has an environmental and genetic basis, shell-basedtaxonomy may not accurately reflect genetic relationships. Weexplored genetic structure among adjacent populations of L.saxatilis (the robust open-shore type), L. neglecta (the tinybarnacle-dwelling type) and L. tenebrosa (the fragile brackish-watertype), at nine sites in Britain. Using single-strand conformationalpolymorphism analysis of a 375bp fragment of cytochrome-b wefound no evidence of species distinction. In AMOVA tests significantvariation was contained among populations (68%) and among individuals(32%, both P < 0.001), and insignificant variation was foundamong ecotypes. Genetic patterns suggested gene flow among ecotypesover small scales and a strong random input over larger scales. ^* To whom correspondence should be addressed. (Received 27 March 2000; accepted 10 July 2000)     

ANATOMY AND SYSTEMATIC PLACEMENT OF SAYELLA LAEVIGATA (GASTROPODA: PYRAMIDELLIDAE: SAYELLINAE)

The ectoparasitic snail Sayella laevigata was first describedby Orbigny (1842) and first placed in the genus Sayella by Odé (1994) without discussion. This study provides justificationfor this assignment to the genus Sayella Dall, 1885 and to the subfamilySayellinae Wise, 1996. Sayella laevigata possesses an elongatepenis, with subapical swelling tapering to a short terminalnipple, that is characteristic of the genus.     

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)     

THE BIOMPHALARIA HAVANENSIS COMPLEX (GASTROPODA: PLANORBIDAE) IN CUBA: A MORPHOLOGICAL AND GENETIC STUDY

Conchological, anatomical and genetic characteristics werecompared among several populations of the Biomphalaria havanensis complexfrom Cuba and other localities in the Caribbean region. Two morphometricmeasures (height and diameter) distinguished two closely similarmorphs of the shell. The reproductive system also separated thesemorphs, particularly upon comparison of sizes of the penis sheathand the preputium. The two morphological groups differed in9 to 12 fixed alleles according to population. Further allozymicdata analyzed in the present work confirmed this difference.The results strongly support the assumption that the B. havanensis complexincludes two distinct species: B. havanensis, for which thetype locality is the swampy area near the vicinity of Havana,Cuba and Biomphalaria sp. a species which commonly occurs inCuba and in Dominican Republic. The taxonomic identity of Biomphalariasp. is discussed. (Received 28 January 2000; accepted 15 August 2000)     

A NEW GENUS AND SPECIES OF PLANORBIDAE (GASTROPODA: HETEROBRANCHIA: PULMONATA) FROM NORTHERN AUSTRALIA

A new genus and species of Planorbidae, Kessneria papillosa n.gen.and sp. from the Northern Territory, Australia, are described.The new genus is morphologically most similar to Leichhardtia,another genus restricted to Northern Australia, from which itdiffers in a number of important shell and anatomical characters.The shell of the new genus differs from all other planorbidsin having a raised, papillate protoconch, and is also uniqueamongst Australian high-spired genera in being umbilicate and inhaving a sinuate outer lip. (Received 12 May 2000; accepted 25 September 2000)     

Larval trematodes (Digenea) of planorbid snails (Gastropoda: Pulmonata) in Central Europe: a survey of species and key to their identification

A survey of the larval stages (cercariae and metacercariae) of trematodes (Digenea) found in planorbid snails in Central Europe (Austria, Czech Republic, south-east Germany, Hungary, Poland and the Slovak Republic) is presented based on a study of 7,628 snails of 12 species examined between 1998-2006. A total of 34 trematode larval stages, comprising cercariae of 28 species and metacercariae of seven species (one species occurred both as cercaria and metacercaria) of nine families were found in 898 (11.5%) snails of eight species. The dominant cercariae were those belonging to the Rubenstrema exasperatum (Rudolphi, 1819)/Neoglyphe locellus (Kossack, 1910) species complex, Tylodelphys excavata (Rudolphi, 1803) and Echinostoma spiniferum (La Valette, 1855) sensu Nasincová (1992), all from Planorbarius corneus (Linnaeus). Almost the same spectrum of cercariae of the families Echinostomatidae, Plagiorchiidae and Omphalometridae was found in the present study as in previous reports; however, a considerably lower spectrum of cercariae of the families Diplostomidae and Strigeidae was recorded. The most frequent metacercariae were those of Echinoparyphium aconiatum Dietz, 1909, Neoglyphe locellus and Moliniella anceps (Molin, 1859), all occurring mainly in P. corneus. The most heavily infected snail species was P. corneus, followed by Planorbis planorbis (Linnaeus) and Segmentina nitida (Müller). The widest spectrum of trematode species was found in P. planorbis and P. corneus. Forty-two cercariae identified to the species level belonging to 15 families, plus an additional 43 taxa recorded under generic or provisional names, were reported from 11 species of planorbids in previous studies carried out in Central Europe. However, the actual number of trematode species occurring in the planorbid snails is probably much lower, because many, if not most, larval stages reported under provisional names or unidentified to the species level may be conspecific with identified adult forms. A key to the cercariae and metacercariae recorded from planorbids in Central Europe, together with illustrations of those species encountered most frequently in the field, is provided to facilitate identification.     

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)