THE MORPHOLOGICAL EXPRESSION OF IMPOSEX IN NUCELLA LAPILLUS (LINNAEUS) (GASTROPODA: MURICIDAE)

The prosobranch gastropod Nucella lapillus exhibits imposex(occurrence of male parts in addition to the female genitalduct) in response to tributyltin (TBT) pollution. Six stageswith three different types in the first three stages and twotypes in the last two stages can be distinguished and are documentedwith SEM-photographs for the first time. Furthermore, nine additionalalterations to the genital tract are shown. As a consequence of TBT exposure in early life stages a sexchange might occur. The oogenesis is suppressed and supplantedby spermatogenesis. The results are two observed specimens witha male genital tract (with a testis) and different female parts.Anatomical and histological details are given here. If TBT-expositionoccurs later, the vagina is replaced by a small prostate glandor the vaginal opening is occluded by proliferating tissue. The two established indices for PSH monitoring (VDS and RPS)in muricid gastropods are discussed. It is shown that the VDSis the more valid parameter. (Received 2 January 1991; accepted 1 March 1991)     

THE ONTOGENY OF THE PLEUREMBOLIC PROBOSCIS IN NUCELLA LAPILLUS (GASTROPODA: MURICIDAE)

The ontogeny of the proboscis in Nucclla lapillus was investigatedusing light and scanning electron microscopy. The proboscis develops by elongation of the body wall surroundingthe mouth, whilst the rhynchocoel is formed by imagination ofthe body wall surrounding the proboscis. Elongation of the snoutduring development of the proboscis results in the anteriormovement of the anterior oesophagus and part of the mid-oesophagus(the valve of Leiblein) which is drawn through the circum-oesophagealnerve ring. The acinous salivary glands and the radular sacalso come to lie anterior to the nerve ring. The mid-oesophagealgland of Leiblein and the glandular dorsal folds are not drawnthrough the nerve ring, and develop behind it. The anterioroesophagus elongates at a later stage of development to producethe oesophageal length required for extension of the adult proboscis.Modifications to this sequence of events, or changes in therate of growth of the various parts of the foregut, might accountfor the differences between the neogastropod and neotaenioglossanpleurembolic proboscis. The intraembolic proboscis found inthe Conoidea and the Pseudolivoidea may have been derived viaa modification of the developmental sequence which producesthe muricoidean pleurembolic proboscis. (Received 10 May 1996; accepted 15 August 1996)     

SEXUAL DIMORPHISM OF NUCELLA LAPILLUS (GASTROPODA: MURICIDAE) IN NORTH WALES, UK

Multivariate statistical methods were employed to examine sexualdimorphism in size and shape of Nucella lapillus collected from 16sheltered sites along coasts of Anglesey and the Lleyn Peninsula, NorthWales, UK. Females were significantly larger than males in overallsize; among 12 relative measures of shell shape, two ratios (shellwidth/shell length and aperture length/shell length) were significantlydifferent between males and females, but these differences usuallydecreased with increasing age (shell length). The observed hypoallometricdimorphism could be a result of selection on increased femalefecundity, which may be positively correlated with shell sizein N. lapillus as in other gastropod species. (Received 22 November 1999; accepted 10 April 2000)     

TROPHIC ROLES OF CO-OCCURRING SPECIES OF DRUPA (GASTROPODA: MURICIDAE) AT ENEWETAK ATOLL

Diets in nature differed significantly among three species ofthe gastropod genus Drupa (Muricidae: Thaidinae) on a windward,seaward reef platform at Enewetak Atoll, Marshall Islands. Nereidand eunicid polychaetes and vermetid gastropods were the mostimportant prey organisms. D. morum ate mainly Perinereis, Ceratonereisand eunicids; D. ricinus ate mainly Ceratonereis in protectedsites and Dendropoma near the exposed outer reef edge. Sizeof Drupa was correlated with that of vermetid but not polychaeteprey. The results are compared with data from studies of otherpredators on the same prey species at Enewetak, and with J.D. Taylor's data on the diets of Drupa species elsewhere inthe Indo-Pacific region. ^*Present address: Department of Zoology, University of California,Berkeley, California 94720. (Received 4 February 1989; accepted 6 March 1989)     

中国海结螺属四新纪录(腹足纲,骨螺科)

在对中国科学院海洋研究所历年来采集的骨螺科Muricidae标本进行整理分类时,共鉴定出结螺属Morula12种,其中4个中国新纪录：1）刺猬结螺Morula（M.）echinata（Reeve,1846）;2）紫结螺Morula（M.）purpureocincta（Preston,1909）;3）石优美结螺Morula（H.）lepida（Houart,1994）;4）白优美结螺Morula（H.）ambrosia（Houart,1994）.     

FEED PREFERENCES OF NUCELLA CRASSILABRUM AND JUVENILE CONCHOLEPAS CONCHOLEPAS (GASTROPODA: MURICIDAE) FROM A ROCKY SHORE IN SOUTHERN CHILE

The feeding preferences of two molluscan predators, Nucellacrassilabrum and Concholepas concholepas, from southern Chilewere studied by means of laboratory and field experiments. Bothpredators preferred Semimytilus algosus to Perumytilus purpuratus.Small C. concholepas selected mussels less than 5 mm, similarsized N. crassilabrum preferred individuals of 5-10 mm. LargerC. concholepas did not consume mussels above 10 mm whereas largeN. crassilabrum preferred the 15-20 mm size but also took musselsup to 30 mm. Individuals rarely consumed more than one musselin a 7 day period. Both predators consumed the barnacle Chthamalusscabrosus, larger items being taken more frequently than smallerones. Field experiments confirmed laboratory results, but barnacleconsumption was 30% higher in the field. Although considerabledietary overlap is evident between these two predators, thereare clear differences in their selection of prey species andsizes. This might provide a mechanism for reducing competitionwhich may result from changes in prey abundance. (Received 17 July 1990; accepted 28 August 1990)     

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)     

EARLY STAGES OF THE ENCAPSULATED DEVELOPMENT OF NUCELLA LAPILLUS (LINNAEUS) (GASTROPODA, MURICIDAE)

The intertidal muricid gastropod Nucella lapillus (Linnaeus)develops entirely within an egg capsule up to the juvenile stage.This study investigates how the embryos have adapted to theabundance of their own yolk (protolecith) and extraembryonicnutrients (nurse eggs, capsule fluid) during five stages ofearly organogenesis The pretorsional preveliger uses protolecith and albumen asnutritive resources. The main portion of the protolecith isstored in the large unequal macro-mere 4D, which is interpretedto be an adaptation to the large content of its own yolk andpersists beyond the ingestion stage. The transitory storageof protolecith makes the predominant resorption of the nutritiveeggs possible. The stomodaeum develops early as an ectodermalinvagination and opens into an anterior buccal part and a posterioroesophageal part. The radular sac is of early pretorsional origin.Some prospective endodermal structures (midgut and hindgut)first become apparent by their histological differentiation During ingestion the differentiation of midgut and cephalopodiumis arrested. The extremely thin epithelium of the midgut surroundsthe swallowed nurse eggs The last stage, an early veliger, has developed all essentialorgans as rudiments, except the coelomic derivates and the pallia]organs. The hindgut opens by a proctodaeal invagination (anus).The embryo undergoes further torsional displacement (Received 20 August 1987;     

荔枝螺属一新种记述(腹足纲,新腹足目,骨螺科)

笔者在整理浙江沿海荔枝螺属Thais Roeding,1798标本时,经形态分类方法和分子生物学方法鉴定发现1新种,即大渔荔枝螺Thais(Stramonita)dayunensis sp.nov.,隶属于腹足纲、前鳃亚纲、新腹足目、骨螺科、红螺亚科、荔枝螺属、Stramonita亚属.文中对新种的形态特征和栖息环境进行了记述,并与近似种进行了比较讨论.     

PRELIMINARY INVESTIGATIONS OF THE ECOLOGY OF THE INTERTIDAL PREDATORY GASTROPOD LEPSIELLA VINOSA (LAMARCK) (GASTROPODA MURICIDAE)

Lepsiella vinosa\ (Lamarck), a common intertidal predatory gastropod,was studied in two zones on an exposed rocky shore in Victoria(Australia). Those from the Mussel Zone in the mid-shore primarilyate one species of mussel and had a faster rate of energy consumptionthan those from the Littorinid Zone in the high-shore, whichmainly ate one species of littorinid gastropod. Shell length,growth rate and size-specific body weight of L. vinosa wereall significantly greater in the Mussel Zone. Egg capsules ofL. vinosa from the Mussel Zone contained significantly moreeggs and more potential hatchlings per capsule than those fromthe Littorinid Zone although there were no significant differencesin the sizes of eggs or hatchlings between zones. These differencesbetween the two zones were correlated to the greater consumptionof energy by L. vinosa in the Mussel Zone and were discussedin relation to the absence of dispersive larvae in this species ¹Present address: Department of Zoology, Monash University,Clayton, Victoria, 3168, Australia ²Present address: School of Biological Sciences, Carslaw Building,F07, University of Sydney, N.S.W., 2006, Australia. Addresseefor reprints. (Received 2 June 1987;     

COPULATION AS FEMALES AND USE OF ALLOSPERM IN THE FRESHWATER SNAIL GENUS BULINUS (GASTROPODA:PLANORBIDAE)

Each of 8 snails in 2 groups of Bulinus (Physopsis) globosus,1 group raised in isolation and 1 group raised in community,were paired for 14 consecutive days with a male-acting partnersnail. In each group, the experimental snails, which were notallowed to act as males, were able to copulate as females onapproximately 94% of the days paired. Two copulations as female,with the same male partner, occurred on 50% of the days thatthe snails were paired, in the 2 groups combined. Non-receptivefemale behaviour by the experimental snails occurred frequently,and copulation was prevented by such behaviour during 6 pairings,3 in each group. Young B. (P.) africanus first copulated as females when theywere 31–33 days old. The accessory sex glands of the femalereproductive tracts of these young female-acting snails containedmoderate to large amounts of secretion. B. (P.) africanus, which were raised in pairs, laidcross-fertilizedeggs in isolation for an average of 76 days, and 1559 eggs/snailwere deposited before cross-fertilization ceased. Cross-fertilizedeggs were produced for as long as 120 days. After 1 copulation as female, virgin B. (P.) africanus laidcross-fertilized eggs for an average of 78 days and deposited3654 eggs/snail before crossfertilization ceased. Cross-fertilizedeggs were produced for as long as 113 days. After 2 copulationsas female, 1 copulation on each of 2 consecutive days, virginB. (P.) africanus laid cross-fertilized eggs for an averageof 102 days and produced 4397 eggs/snail before cross-fertilizationceased. Cross-fertilized eggs were produced for as long as 123days. Snails which were homozygous for an allele governing mantlepigment pattern were raised with a partner which was homozygousfor a different pigment pattern. Young produced in a 4-day periodafter the snails were isolated were 100% heterozygous. The snailswere then rearranged into pairs with a partner of the same genotypefor 4 days, during which time 26% of the young produced werehomozygous. The snails were again isolated for 4 days, and 49%of the young produced during this 4-day period were homozygous.The results of this experiment strongly suggest that multipleoutcrossing occurred. In B. (P.) africanus, stored allosperm were used to fertilizeeggs after 1, 4 and 7 weeks of starvation; after 1 and 4 weeksof 15°C low temperature and 4 weeks of 15°C + 4 weeksof 10°C low temperature; and after 1 and 4 weeks of desiccation.After 8 weeks of desiccation, 2 of 3 surviving snails reproducedby self-fertilization and 1 snail did not reproduce. Too fewsnails survived 8 weeks of desiccation for a conclusion to bereached on the ability of allosperm to survive. (Received 1 June 1984;     

PREDATOR-PREY INTERACTIONS BETWEEN LEPSIELLA (BEDEVA) PAIVAE (GASTROPODA: MURICIDAE) AND KATELYSIA SCALARINA (BIVALVIA: VENERIDAE) IN PRINCESS ROYAL HARBOUR, WESTERN AUSTRALIA

On a sandy beach at Shoal Bay in Princess Royal Harbour, Albany,southwestern Western Australia, lives a small muricid gastropodthat feeds virtually monotonically on the overwhelmingly dominantresident bivalve Katelysia scalarina. Lepsiella paivae livesburied in the sand and attacks its prey within it. Because ofits small size (<13 mm shell height), bivalve prey isalso small and this study demonstrates a preference for K. scalarinaof 5 mm shell length, i.e. juveniles. Laboratory experimentsalso suggested a possible preference for attack of the rightvalve. Lepsiella paivae can and does, however, attack largerprey (up to 15 mm shell length), but cannot consume themcompletely. A second visit to Princess Royal Harbour in theAustral winter, when there was no juvenile K. scalarina present,showed L. paivae to be attacking at the sand surface, also bydrilling, the small (<4 mm) gastropod Hydrococcus brazieri(Hydrococcidae). SEM studies of experimentally determined drillholes of L. paivae show them to be of variable form, some straightsided, others bevelled (like a naticid) and <500 µmin diameter. On this sheltered Southern Ocean beach, therefore,L. paivae has specialized to attack juvenile bivalves by burrowingafter them. It can, however, attack other species opportunisticallyon the sand surface when seasonally favoured juvenile bivalveprey are not present. (Received 8 January 2005; accepted 16 March 2005)     

A COMPARATIVE STUDY OF CHROMOSOMES IN FOUR SPECIES OF THEODOXUS (GASTROPODA: NERITIDAE)

Karyological analysis was performed on Theodoxus baeticus (Lamarck,1822), T. valentina (Graells, 1846), T. velascoi (Graells, 1846)and T. fluviatilis (Linne, 1758), collected from freshwaterbodies of eastern Spain. Cells possessing diploid chromosomenumbers of 2n 5 25 were most common in the tissues of males,whilst 2n 5 26 was most prevalent in females. The sixth pairof chromosomes had only one homologue in mitotic cells of males,indicating the XO/XX sex-determining mechanism. The absolutelength of chromosomes ranged from 1.65 to 6.33 mm. The relativesizes of chromosomes varied from 3.92 to 13.33% of the totalhaploid set length. In all species chromosome pairs no. 1, 4,7-13 were composed of metacentric, pairs no. 5 and 6of submetacentricchromosomes. Pairs no. 2 and 3 were submetacentric, subtelocentricor submeta- subtelocentric according to the species studied.There were significant differences (P, 0.05) among the relativelength, as well as centromeric indices of different chromosomepairs across the species. Karyological differences were greatestbetween T. fluviatilis and three other Theodoxus species. (Received 6 March 2000; accepted 8 May 2000)     

EVOLUTIONARY HISTORY OF NORTHERN HEMISPHERE NUCELLA (GASTROPODA,MURICIDAE): MOLECULAR,MORPHOLOGICAL, ECOLOGICAL,AND PALEONTOLOGICAL EVIDENCE

By combining data from a variety of sources we explore patterns of evolution and speciation in Nucella, a widely studied genus of shallow-water marine neogastropods. We present a hypothesis of phylogenetic relationships for all of the currently recognized species of northern hemisphere Nucella, based on an analysis of 718 base pairs of nucleotide sequence from the mitochondrial cytochrome b gene. The order of appearance of species in the fossil record is congruent with this hypothesis. The topology of the inferred phylogeny of Nucella, coupled with ecological, morphological, and fossil evidence, was used to address three main questions: (1) At what time and by which route was the North Atlantic invaded from the North Pacific compared to prior studies of the trans-Arctic interchange? (2) Do patterns of molecular variation within species corroborate the importance of climatic cycles in driving speciation in north temperate marine animals? (3) Was radiation in the direction of increased or decreased ecological specialization, body size, or vulnerability to predation? Molecular evidence confirmed that the sole North Atlantic species, N. lapillus, arose from a North Pacific ancestor. Biogeographic and paleontological evidence supported the dispersal of Nucella, and perhaps other interchange species, via the Eurasian Arctic. Rather intriguingly, the linkage of N. lapillus to a western as opposed to eastern Pacific clade, and the biogeographic origins of the eastern Pacific species, parallel closely similar patterns observed in another genus of rocky-shore gastropods, Littorina. This congruence, in conjunction with information on the climatic and geographic histories of the region, as well as the geographic arrangement of mtDNA haplotypes within Nucella species, supports a model of speciation in Nucella driven by cycles of climatic amelioration and deterioration that began during the Miocene. Calibrations from the fossil record of Nucella suggest that third position transitions and transversions accrue at a rate of 3–4% and 0.5% respectively per million yr. This supports an early participation by Nucella in the trans-Arctic interchange, as suggested by paleobiogeographic studies. Consistent with the unstable taxonomic history of species of Nucella, we found few nonmolecular traits to be phylogenetically informative. Among North Pacific species, more recently derived species (N. canaliculata and the N. emarginata clade) were more ecologically specialized (narrower diet and habitat range). Consistent with extensive intraspecific variation, shell traits were quite labile evolutionarily: neither overall size nor development of antipredatory traits exhibited consistent evolutionary trends over the history of the genus. Nurse eggs (unfertilized eggs consumed by developing embryos) were an ancestral trait that was lost evolutionarily in the two clades that also exhibited increased body size, suggesting that these two life-history traits may be coupled. The reduced number of chromosomes in N. lapillus is clearly a derived state and is consistent with White's (1978) observations on chromosome evolution in other clades.     

COMPETITIVE GRAZERS AND THE PREDATORY WHELK LEPSIELLA FLINDERSI (GASTROPODA: MURICIDAE) STRUCTURE A MUSSEL BED (XENOSTROBUS PULEX) ON A SOUTHWEST AUSTRALIAN SHORE

On a southwest Australian exposed rocky shore within King GeorgeSound, the predatory muricid Dicathais orbita was observed feedingnon-selectively on an array of sessile prey, including Austromegabalanusnigrescens, Galeolaria caespitosa, Patelloida nigrosulcata,Serpulorbis sipho, Siphonaria sp. and the mussel Xenostrobuspulex. On a more sheltered, contiguous, platform of the same shore,however, a mat of Xenostrobus pulex occurred which was beingpredated by another muricid, Lepsiella flindersi. X. pulex occupieda wide vertical range on this shore. Higher-zoned, supralittoral,individuals were small and occurred as clusters in crevicesand pits in the rock. A mat of mussels in the lower eulittoralzone was heavily predated by the drilling L. flindersi whichattacked selectively the largest individuals. Between, in thehigh eulittoral, the mussel bed was formed into patches whichwere isolated by the grazing activities of an array of herbivorousgastropods. Recruitment here by X. pulex was to the patch edgesand the grazer's habits of clustering against them, furtherkept them discrete. Little predation by L. flindersi occurredat this shore level. The Xenostrobus pulex community was, therefore, highly structureddown the shore sequentially by: (a), physiological stresses;(b), competitive grazing pressures and (c), predation. (Received 2 February 1998; accepted 5 January 1999)