SPATIAL PATTERNS OF SHELL SHAPE OF THREE SPECIES OF CO-EXISTING LITTORINID SNAILS IN NEW SOUTH WALES, AUSTRALIA

The shape and relative weight of the shell have been shown tovary intraspecifically and interspecifically in a number ofspecies of gastropods, including many different littorinids.These differences give rise to different shell forms in differenthabitats. In those species which have non-planktotrophic development,differences in shell form among shores have been usually explainedin terms of natural selection because exposure to waves supposedlyfavours light shells with large apertures, while predation bycrabs on sheltered shores favours elongated, thick shells withsmaller apertures. Differences in shell shape among speciesfound at different heights on the shore have been explainedin terms of resistance to desiccation and temperature. Suchvariables would tend to act on a relatively broad-scale, i.e.causing differences among heights on a shore or among shores.Rates of growth, which might vary at much smaller scales withina shore, have also been shown to affect the shapes of many shells. In this study, the shape and relative weight of shells of threespecies of co-existing littorinids (Littorina unifasciata, Bembiciumnanum and Nodilittorina pyramidalis) were measured. These speciesall haveplanktotrophic development and they are found on manyshores where there is no evidence that they are preyed uponby crabs. Before explanations of shell shape are proposed, itis necessary that patterns of variation, within different partsof ashore and among different shores are clearly documented.These patterns were measured at a number of different spatialscales within and among replicate shores with different amountsof wave exposure. Large and small specimens were included toallow intraspecific comparisons among snails of different sizesfound at different heights on the shore. The results showedsignificant differences among shores in shape and relative weightof shells, but these differences could not be explained by exposureto waves. In addition, snails of different sizes and differentspecies did not show the same patterns although they were collectedfrom the same sites. Importantly, the shell shape of Liuorinaunifasciata varied significantly among sites at approximatelythe same height within a shore. These differences could notbe clearly correlated with density, mean size nor exposure towaves. The only consistent pattern was a decrease in relativeaperture size in specimens living higher on the shore. Modelsthat have commonly been proposed to explain shape and relativeweight of shells in other species of gastropods are not adequateto explain the small- and large-scale variation of the measurementsdescribed here. It is proposed that any selective advantageof shell morphology and the effects of any variables on thedevelopment of shell morphology in these species can only beidentified after appropriately designed and replicated fieldexperiments. (Received 4 March 1994; accepted 13 September 1994)     

POPULATION GENETICS OF EUROPEAN ANODONTINAE (BIVALVIA: UNIONIDAE)

Enzyme electrophoresis was used to study population geneticsand molecular differentiation of European Anodontmae. The existenceof two genera (Anodonta Lamarck 1799 and Pseudanodonta Bour-guignat1876) is supported by the number of diagnostic loa (4) and Net'sD > 0.463 in all cases. In western and central Europe thereare two species of Anodonta, A. anatina (Linnaeus 1758) andA cygnea (Linnaeus 1758) while two other taxa of still uncertainrank were identified in the Mediterranean area. An estimatedmedium level of gene flow and pronounced genetic differentiationbetween-the taxa support this view. Data on genetic distancessuggest that the diversification of European Anodontinae tookplace in the middle-late Pleistocene (Received 15 August 1995; accepted 5 February 1996)     

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)     

RADULAR PRODUCTION RATES IN TWO SPECIES OF LACUNA TURTON (GASTROPODA: LITTORINIDAE)

The molluscan radula is a dynamic organ, both in terms of itsuse and production. New rows of teeth are constantly producedat the posterior end of the radula, while older, worn teethare shed anteriorly, producing a dynamic equilibrium. We useda cold-shock to mark the radular ribbon and measure tooth rowproduction rates in two gastropod species, Lacuna vincta (Montagu)and L. vanegata Carpenter. We found that the average tooth rowproduction rate at 10–11°C did not differ betweenthese two species, and was 2.94 (SE = 0.002) rows per day forLacuna vincta and 2.97 (SE = 0 002) for L. vanegata Inter-individualvariability in production rate was very low, and was correlatedwith shell length, smaller individuals had slightly higher productionrates. The total length of the radular nbbon varied greatlyamong individuals, ranging from 47 to 94 (2.57 to 5.68 mm) rowsin L vincta and 53 to 99 rows (2.80 to 7.14 mm) in L vanegata,and was only somewhat correlated with the length of the shelLThis great variability will result in large differences amongindividuals in the time it takes to replace the radula totally,from 14.96 to 35.44 days in L vincta and from 17 43 to 39 69days in L. vanegata. (Received 1 September 1995; accepted 20 November 1995)     

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)     

A NEW OVOVIVIPAROUS SPECIES OF TECTARIUS (GASTROPODA: LITTORINIDAE) FROM NIUE, SOUTH PACIFIC, WITH A MOLECULAR PHYLOGENY OF THE GENUS

A new ovoviviparous littorinid gastropod, Tectarius (Echininiopsis)niuensis, from Niue, west of the Cook Islands, is described.This is distinguished from the only other ovoviviparous memberof the genus, T. (E.) viviparus (Rosewater, 1982) from the MarianaIslands, here redescribed in detail. The new species is remarkabletor its high-level habitat in the littoral fringe on wave-exposedkarstic limestone cliffs, for its variation in shell shape accordingto tidal level, shell colour polymorphism, calcified operculumand penis with a single mamilliform penial gland. In a cladisticanalysis of morphological characters, including single representativesof each of the three other subgenera of Tectarius (Tectarius,Echininus, Tectininus), these two ovoviviparous species appearas sister-taxa. This is confirmed by a molecular phylogeneticanalysis of the same species, based on the sequence of a portionof the 16S ribosomal RNA mitochondrial gene. Neither analysisunequivocally confirms the monophyly of Tectarius. The divergenceof DNA sequences within Tectarius suggests that the genus arosein the Upper Cretaceous, much earlier than the oldest (UpperEocene) fossils. Only 4 of the 175 species of Littorinidae areknown to be ovoviviparous (with brooding through metamorphosis)and the possible adaptive significance of this type of developmentis discussed. Hitherto, its rarity had been explained by earlyextinction of poorly-dispersed brooding taxa. However, ovoviviparitymay have persisted in Echininiopsis for at least 35 millionyears, and has not precluded colonization of islands 6300kmapart. (Received 17 September 1996; accepted 15 November 1996)     

SYSTEMATIC REVISION OF PATELLOIDA PYGMAEA (DUNKER, 1860) (GASTROPODA: LOTTIIDAE), WITH A DESCRIPTION OF A NEW SPECIES

Patelloida pygmaea (Dunker) and its closely allied species,P. heroldi (Dunker) and P. conulus (Dunker) have caused nomenclaturalconfusion because of their variable shell morphology and distinctivehabitats. According to current nomenclature, these species ofPatelloida have been synonymized and treated as one specieswith two ecological forms. Patelloida pygmaea lives on the shellof Crassostrea gigas (Ostreidae), P. pygmaea form heroldi occurson intertidal rocks on sheltered shores and P. pygmaea formconulus is found on the shell of Batillaria multiformis (Batillariidae).Their taxonomic relationships and possible species status are,however, unclear. Using two mitochondrial genes (fragments ofCOI and 16S ribosomal RNA; total 1192 sites), we analysed 88specimens of P. pygmaea, P. pygmaea form heroldi and P. pygmaeaform conulus from 37 localities in East Asia. In the resultingmolecular phylogenetic trees, the specimens of Patelloida fallinto four clades with high bootstrap probabilities; these cladescorrespond taxonomically to P. pygmaea, P. conulus, P. heroldiand a fourth previously unrecognized taxon, Patelloida ryukyuensisn. sp., described here. A minimum-spanning network for 29 uniquemitochondrial COI haplotypes obtained from 45 specimens in thesame bay in central Japan form three distinct clusters, consistingof P. pygmaea, P. conulus and P. heroldi, respectively. Thissuggests that reproductive isolation has been established betweeneach group. A detailed examination of radular and shell morphologiesof the four taxa clarifies the morphological distinction betweenthese species. The four species form a rather young clade inthe genus Patelloida that diverged during the Pliocene. Theyprovide an example of habitat segregation in a restricted marineenvironment. (Received 21 December 2004; accepted 11 March 2005)     

Atebbania Bernasconii, a New Genus and Species from Subterranean Waters of the Tiznit Plain, Southern Morocco (Gastropoda: Hydrobiidae)

The new genus Atebbania is described for a new hydrobiid species,A. bernasconii, which lives in groundwaters of southern Morocco.Of the Hydrobiidae genera with known shell and anatomy Moitessieriais the closest to Atebbania. The two share the following characters:shell elongate; teleoconch surface with evident microsculpture;seminal receptacle absent. Atebbania is distinguished from Moitessieriaby: shell ovate; penis with a) apical stylet, b) one lobe bentdownward on left (inner) side and c) penial duct running nearthe right (outer) side; posterior end of foot indented. Atebbaniabernasconii n. sp., lives in a limited area, the Tiznit plainin southern Morocco. Other stygobiont hydrobiids from otherareas of Morocco are currently being studied. None of them appearsto be closely related to A. bernasconii or to the species ofMoitessieria (Received 10 February 1998; accepted 30 April 1998)     

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)     

RELATIONSHIPS BETWEEN SHELL SHAPE, WATER RESERVES, SURVIVAL AND GROWTH OF HIGHSHORE LITTORINIDS UNDER EXPERIMENTAL CONDITIONS IN NEW SOUTH WALES, AUSTRALIA

The shell morphologies of the highshore littorinids, Littorinaunifasciata Gray and Nodilittorina pyramidalis (Quoy & Gaimard)have previously been shown to vary at a variety of spatial scales,including among replicate sites at the same height, from heightto height and from shore to shore. In this study, the relationshipsbetween morphology of the shell, the reserves of water heldwithin the shell, the size of the foot and survival on differentshores and rates of growth in different habitats were examinedfor L. unifasciata and, to a lesser extent, N. pyramidalis.Reserves of water were not consistently related to size or shapeof the shell, but did increase as relative weight of shell increased.This may be due to the relatively smaller body providing moreinternal volume for extra-corporeal water. Water reserves andthe amount of free water held in the shell were also not relatedto loss of water or survival during extended periods of emersion.Although the shape of the shell on sheltered and exposed shoreswas correlated with size of the foot, with the snails on anexposed shore having larger apertures and feet than those ona sheltered shore, transplant experiments did not show differentialmortality between morphs from the different shores. All translocatedand transplanted snails disappeared from the exposed shore ata greater rate than from the sheltered shore, but this was probablydue to the snails dispersing out of the experimental areas ratherthan due to mortality. Therefore, many of the large-scale modelsthat have previously been used to describe patterns of shellshape in intertidal gastropods do not appear to be importantin these highshore littorinids. Finally, field experiments ongrowth of juvenile L. unifasciata indicated that rate of growth,largely governed by opportunity to feed rather than type andquantity of food, is the most likely explanation for the small-and large-scale patterns of shell shape that have been previouslydescribed in this species. (Received 22 October 1996; accepted 19 February 1997)     

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)     

GENETIC AND CONCHOLOGICAL COMPARISON OF SNAILS (HELIX ASPERSA) DIFFERING IN SHELL DEPOSITION OF LEAD

Populations of snails inhabiting areas with different historiesof Pb contamination differed in their deposition of Pb in shellrelative to soft tissues. Genetic variation, measured usingisozymes, was not related to Pb history nor geographic distancebetween populations. Shell characteristics were significantlydifferent among sites; shell dry weight was strongly relatedto soil calcium levels. Shells of snails from areas with longhistories of Pb contamination were significantly more robust(greater shell width/shell height ratio) than snails from otherlocations. H. asprsa adaptation to Pb contamination may involvesignificant changes in shell characteristics but these do notcorrelate with genetic traits assessed with allozymes (Received 29 December 1994; accepted 15 October 1995)     

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;     

THE ANATOMY OF CYLINDROTIS QUADRASI FORM OKINAWA ISLAND, JAPAN AND THE SUBFAMILIAL POSITION OF THE GENUS CYLINDROTIS MOLLENDORFF, 1895 (ARCHAEOPULMONATA: ELLOBIIDAE)

Cylindrotis quadrasi Mollendorff, 1895, the type species ofthe ellobiid genus Cylindrotis, was collected from Okinawa Island,southwest Japan. This is the first record of C. quadrasi inJapan and the third in the world. The anatomical charactersof this species, i.e. shell, head-foot, pallial cavity, radula,stomach, reproductive system, and central nervous system, aredescribed in detail for the first time. The significance ofthese observations is discussed and the subfamilial positionof Cylindrotis is reconsidered. Cylindrotis was included inthe Pythiinae, the most primitive group of the Ellobiidae, basedon the conchological characters alone. However, the male andfemale tracts of the reproductive system are entirely separated,and other internal organs exhibit highly derived conditions.Accordingly, Cylindrotis is transferred from the Pythiinae tothe Ellobiinae. Among the genera of the latter subfamily, Cylindrotisseems to be allied to Blauneria Shuttleworth, 1854 and LcucophytiaWinckworth, 1949. (Received 1 February 1993; accepted 7 June 1993)     

REMOTE BIOMINERALIZATION IN DIVARICATE RIBS OF STRIGILLA AND SOLECURTUS (TELLINOIDEA: BIVALVIA)

Deposits composed of aragonite prisms, which were formed afterthe outer shell layer, have been found at the posterior steepslopes of divaricate ribs in two species of Strigilla and anothertwo of Solecurtus. These prisms have their axes oriented perpendicularto the outer shell surface and differ in morphology from fibresof the surface-parallel composite prisms forming the outer shell.They display crystalline features indicating that, unlike crystalsforming the outer shell surface, their growth front was free,unconstrained by the mantle or periostracum. These particulardeposits are called free-growing prisms (FGPs). In these generathe periostracum is clearly not the substrate for biomineralizationand, upon formation, does not adhere to the steep slope of ribs,but detaches at the rib peak and reattaches towards the posterior,just beyond the foot of the posterior scarps of ribs. In thisway, a sinus or open space developed between the internal surfaceof the periostracum and the outer shell surface along each steeprib slope. These spaces could remain filled with extrapallialfluid after the mantle advances beyond that point during shellsecretion. FGPs grow within this microenvironment, out of contactwith the mantle. Other species with divaricate ribs do not developFGPs simply because the periostracum adheres tightly to both ribslopes (which are never so steep as in Solecurtus and Strigilla).FGPs constitute one of the rare cases of remote biomineralizationin which aragonite is produced and direct contact with the mantlenever takes place. (Received 22 November 1999; accepted 20 February 2000)     

SPERM AND SPERMIOGENIC ULTRASTRUCTURE IN THE MATHILDIDAE WITH A REVIEW OF SPERM MORPHOLOGY AND ITS SYSTEMATIC IMPORTANCE IN THE ARCHITECTONICOIDEA (GASTROPODA)

The ultrastructure of spermiogenesis and spermatozoa is examinedfor the first time in the heterogastropod family Mathildidae(Mathilda brevicula Bavay and Mathilda sp.). Mathildid spermatozoaexhibit the following features: (1) an ovoid acrosomal vesicleshowing curved dense layers basally and underlain by a thincurved plate; (2) a solid, rod-shaped nucleus showing a shallowbasal invagination (nucleus helically keeled in Mathilda sp.);(3) a midpiece composed of a 9+2 axoneme, 9 thick and periodicallybanded coarse fibres (associated with the axonemal doublets)and a continuous mitochondrial derivative; (5) glyco-gen piececomposed of the axoneme surrounded by dense granules; (6) andend piece (paddle-shaped terminally). Results of the study demonstratethat mathildids share the same key sperm and spermi-ogenic featuresobserved in the Architectonicidae. The monophyly of the Architectonicoidea,established by previous authors on anatomical grounds, is thereforeconfirmed using sperm morphology. Spermatozoa of the two mathildidsinvestigated lack the periodically banded midpiece structuresseen in investigated species of Architectonica (A. pcrspectiva(Linnaeus), A. perdix (Hinds)), Heliacus (H. (Heliacus) variegatus(Gmelin)) and Pseudotorinia (P. laseronorum (Iredale)) therebyresembling most closely the spermatozoaof Philippia lutea (Lamarck)and Psilaxis oxytropis (A. Adams) which also lack suchbandedstructures. Given the widely accepted primitive status of theMathildidae within the Architectonicoidea, the genera Philippiaand Psilaxis may prove to be relatively basal rather than advancedgenera within the Architectonicidae. Thi: view needs to be testedby examination of sperm morphology in other genera of the Architectonicidaeand also the basal mathildid genus Tuba sensu lato (= Gegania+ Tubena). Such information will be vital in any future cladisticstudy of the Architectonicoidea. (Received 16 June 1994; accepted 6 February 1995)     

Recent bivalve molluscs of the genus Calyptogena (Vesicomyidae)

The genus Calyptogena (Bivalvia: Vesicomyidae) comprises highlyspecialized bivalves living in symbiosis with sulphur-oxidizingbacteria in reducing habitats. In this study, the genus is revisedusing shell and anatomical features. The work is based on typematerial, as well as on the extensive collection of vesicomyidsobtained during twelve expeditions to the Pacific and IndianOceans. Nine Recent species are ascribed to the genus Calyptogena,four of which are new: C. pacifica Dall, 1891, C. fausta Okutani,Fujikura & Hashimoto, 1993, C. rectimargo Scarlato, 1981,C. valdiviae (Thiele & Jaeckel, 1931), C. gallardoi Sellanes& Krylova, 2005, C. goffrediae n. sp., C. starobogatovin. sp., C. makranensis n. sp. and C. costaricana n. sp. Thecharacteristic features of Calyptogena are: shell up to 90 mmin length, elongate-elliptical or elongate; presence of escutcheon;presence of broad posterior ramus (3b) of right subumbonal cardinaltooth as well as right posterior nymphal ridge; absence of pallialsinus as a result of attachment of intersiphonal septal retractorimmediately adjacent to ventral surface of posterior adductor;absence of processes on inner vulva of inhalant siphon; presenceof inner demibranch only, with descending and ascending lamellaewith interlamellar septa not divided into separate tubes. Themost closely related taxa to Calyptogena are probably the genusIsorropodon Sturany, 1896, and the group of species representedby ‘Calyptogena’ phaseoliformis Métivier,Okutani & Ohta, 1986. These groups have several charactersin common, namely absence of pallial sinus, presence of singleinner pair of demibranchs and absence of processes on innervulva of inhalant siphon. The worldwide distribution of thegenus Calyptogena suggests that methane seeps at continentalmargins are the major dispersal routes and that speciation waspromoted by geographical isolation. Recent species diversityand fossil records indicate that the genus originated in thePacific Ocean. Sufficient data to discuss the distribution atspecies level exist only for C. pacifica, which has a remarkablynarrow bathymetric range. Published studies on the physiologyof C. pacifica suggest that adaptation to a specific geochemicalenvironment has led to coexisting vesicomyid genera. The bacteria-containinggill of C. pacifica and other Calyptogena species is one ofthe most specialized in the family Vesicomyidae and may reflectthese ecological adaptations. (Received 23 December 2005; accepted 3 April 2006)