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Nabq as “A Managed Resource Protected Area” or as “Multiple Use Management Area” is subjected to human activities that influence its biodiversity. Therefore, many field trips from January 2016 to January 2017 were carried out to detect the main activities in Nabq protectorate and their impacts on faunal macro-benthos biodiversity. Four stations representing two major habitats (mangrove and rocky shore) were chosen depending on anthropogenic activities. A total of 112 macro-benthos taxa were recorded in Nabq dominated with Planaxis salcatus, Nerita spp., Barbatia trapezina and Ophiocoma scolopendrina. The anthropogenic activities don't only affect the presence and absence of species, but also influence on the dominance status of species in the investigated stations. El-Rowayseaa and El-Dagal were unaffected stations showing more abundance and diversification than El-Gharkana and El-Monkateaa which were affected mangrove and rocky shore stations, respectively. In conclusion, anthropogenic activities are the main cause of recent changes to the marine biodiversity in Nabq Protected Area and their continuation may cause habitat damage. Keywords: Macro-benthos, Biodiversity, Human activities, Ecotourism, Fishing, Protected areas

Snail Nerita lineata is a snail that lives in the mangrove ecosystem. This snail is also found in the mangrove ecosystem in the Village of Tongke-Tongke, Sinjai Regency, South Sulawesi. This study aims to provide information about the morphometrics of snails N. lineata. This research was conducted for six months, from April to September 2019. There were three research stations, namely A, B, and C, which were grouped according to mangrove age. group A is mangrove ⩾10 years old, group B is mangrove ⩾20 years old, and group C is mangrove which is rove30 years old. Each station uses a large plot measuring 10m x 10m and inside there are four small plots measuring 0.5m x 0.5m. sampling is done every month. Morphometric measurements using a digital caliper with an accuracy of 0.01 mm and weighing using a digital scale with an accuracy of 0.1 gr. Morphometric parameters observed were shell length (SL), shell width (SW), spire height (SpH), columella length (CL), shell opening width (AW), shell opening length (AL), and snail weight (W). Data were analyzed for correlation and Paired Sample Test using SPSS software. Morphometric snails in mangrove groups A, B, and C are not much different. In the mangrove group A, there are several morphometric parameters that are not correlated with each other. In the mangrove groups B and C, the parameters of shell length (SL) and shell width (SW) do not correlate. The results of the Paired Sample Test showed the significant length of snail (SL) between mangrove A and mangrove B and length of snails in mangrove B and mangrove C. None of the results of paired sample test showed significant snail weight.

The size–mass relationships were estimated for four Nerita snail species, viz. N. adenensis, N. longii, N. orbignyana, and N. textilis, collected from the middle and upper intertidal rocky pools of Bandar Lengeh shore line, the northern coast of the Persian Gulf, Iran, during January–April 2015. Estimates of parameter b of the size–mass relationship (W = aLb) ranged between 2.569 (N. adenensis) and 3.205 (N. textilis), while parameter a ranged between 0.0012 (N. textilis) and 0.0047 (N. adenensis). Three of four studied species (except N. textilis) revealed negative allometric relationships. Results could be useful for ecological studies and coastal management activity in future.

Hermit crabs recognize different shell attributes and choose shell size, type, or species to maximize their individual fitness. Aquatic hermit crab species commonly prefer relatively heavy shells species in contrast to semi-terrestrial crabs which prefer lighter shells. Lighter shells favor rapid growth and increase individual fitness because larger individ- ual achieve higher success in intra- and inter-individ- ual competition. In this study, we experimentally measured the daily growth of hermit crabs Calcinus californiensis that were forced to occupy four different shell species with different internal volume to mass ratios (IV/M ratio), and whose sequence in preference is known from previous studies (Cantharus ( Stra- monita ( Columbella ( Nerita). The shell with the highest IV/M ratio (Nerita) favored body growth rate, while the relatively heaviest (lowest IV/M ratios) and most preferred shells (Stramonita and Cantharus) hindered body growth. Our results suggest that in this aquatic hermit crab, the benefits of carrying heavy shells that give better predatory protection exceeded the benefits of rapid growth that can be obtained using lighter, thinner, and less protective shells.

Temperature is a major stressor in the intertidal environment. During emersion, the interaction between physicochemical factors and the external morphology of intertidal organisms results in significant differences between organismal body temperatures and ambient temperatures. Standard temperature loggers do not consider the morphology of the target species and may not serve as effective proxies for body temperatures. Methods such as thermocouples also present their own set of issues, being invasive and potentially damaging. Biomimetic temperature loggers that mimic the organisms of interest are, however, easily deployed in the field and can be used to investigate biological impacts of field temperatures. Due to their high abundance on tropical seawalls and the key ecological roles they play, nerite gastropods (Nerita spp.) were selected as the model organism for the basis of biomimetic “Robonerites”. Here, we discuss the development of Robonerites and present results from field and laboratory tests on their effectiveness and accuracy in measuring the in situ body temperatures of nerites on tropical seawalls. Keywords: Body temperature, Biomimetic sensors, Temperature logger, Intertidal habitats, Nerite snails

Nerita lineata snails are found in the mangrove ecosystem. This snail attaches to the roots of mangroves. This study aims to find the relationship between the length and weight of Nerita lineata’s snails to environmental factors. Sampling was carried out using four plots of 0.5m x 0.5m in a 10m x 10m plot. The research station is 3; station A with mangrove age ⩽10 years, station B with mangrove age ⩽20 years, and station C with mangrove age ⩽30 years. Data were analyzed by regression and t-independent test. The length of the snail that is dominant in the mangrove is 22.27 - 25.57 mm and the dominant weight is 4.93 - 6.09 gr. Salinity and pH of seawater significantly affected the length of N. lineata’s snail shell. Total organic matter significantly affected the weight of N. lineata snails. The average length and weight of N. lineata snails at each research station did not differ.

Sarawak comprises of vast areas of wetland which is the habitat of huge number of edible gastropods. Among the wetland faunal composition, the edible gastropod is one of the important sources of animal protein for the local communities. This diversity of edible gastropod was studied from seven Divisions of Sarawak namely Kuching, Sibu, Mukah, Bintulu, Miri, Limbang and Lawas. Samples were collected from the wet market and catches from local fishermen. A total of 21 species representing 11 families and 16 genera of edible gastropods were identified from Sarawak. Cerithidea spp. was represented by three species while both Nerita and Pomacea were made up of three and two species each. Others were each represented by one single species. Six edible gastropod species belonged to the freshwater habitat while seven and eight species were recorded from brackish and marine habitats, respectively. Cerithidea and Pomacea showed wide geography amongst the Division and also highly distributed. Edible gastropods have high market value in the state of Sarawak and contribute significantly to the livelihoods of the certain indigenous communities in the state.

Describing temporal variation in the foraging behaviour of intertidal gastropods is important to gain an understanding of the environmental conditions that constrain their activity patterns. Foraging behaviour in the tropical gastropod Nerita yoldi was mainly deter- mined by the tidal cycle: individuals foraged when they were awash, or emersed when the rock was wet, migrating downshore to forage and upshore when they returned to refuges. Apart from tidal influences, foraging in N. yoldii also varied with season and tidal state. Indi- viduals were generally more active in summer than in winter and on neap than spring tides; although small-scale daily variation existed. Such temporal variation may be caused by several interacting environmental variables, especially air temperature, pressure and irradi- ance, which influence physical conditions as well as individuals' metabolism. Individual for- aging patterns were also highly labile between seasons: most individuals would stop and remain stationary on the open rock surface in winter, but returned to refuges after foraging in summer, a pattern probably driven by physical stress. The foraging behaviour of N. yoldii, therefore, is predictable on a coarse scale, in terms of when they are active, but highly labile in duration and foraging range, which indicates the importance of local, daily variation in environmental factors controlling foraging on shores that have strong temporal changes in abiotic conditions.

Objective To identify the bioactive potential of crude methanolic extracts of five gastropods and one bivalve collected from the west coast of India (Mumbai coast). Methods Disc-diffusion assay and micro-dilution technique were used to test the bioactive potential of these molluscs against six pathogenic bacteria. Results The crude methanolic extracts of all the molluscs showed significant activity against one or more bacteria tested. Minimum inhibitory concentration of crude methanolic extracts was found in the range of 0.10–0.35 mg/mL against human pathogenic bacterial strains. Hemifusus pugilinus and Nerita sp . extracts were most effective showing activity against all bacterial strains. Hemifusus pugilinus extract exhibited good activity against Vibrio cholerae contrary to earlier reports. Methanolic extract of Gafrarium divaricatum demonstrated considerable activity against both Escherichia coli and Streptococcus pyogenes. Trochus radiatus extract was inactive against all the bacteria tested except Escherichia coli. Euchelus asper extract was active against Klebsiella pneumoniae and Pseudomonas aeruginosa . Conclusions All the molluscs screened exhibited potential activity against one or more bacterial strain. Further work is in progress to isolate the active constituents of the extracts.

Comparative analysis may help elucidate how interacting influences have shaped regional phylogeography. The coasts of southeastern Australia potentially offer an opportunity for such analysis by comparison of southeastern Tasmania and Bass Strait. The latter has been extensively studied but there are fewer phylogeographic studies in southeastern Tasmania and these have mostly shown little evidence of genetic structure. The possibility that snails of the Austrocochlea constricta s.l complex have such structure was investigated here using nuclear and mitochondrial DNA sequences. Similarly to the few known examples of geographically-structured taxa in the region, especially the gastropod genus Nerita, most differentiation in A. constricta s.l. occurs between localities east and west of the Tasman Peninsula. In contrast, Nerita and A. constricta s. l. differ in their phylogeographic structure around Bass Strait. Possible explanations of inter-regional phylogeographic differences include the interaction of breeding season and current variability, whether the geographically partitioned genetic lineages represent intra-specific or species-level divergence and the decoupling of landbridge formation and sea surface temperature at the beginning and end of glacial maxima.

This is the first study to identify and determine the phylogenetics of neritids found in Malaysia. In total, twelve species from the family Neritidae were recorded. Ten species were from the genus Nerita and two species were from the genus Neritina. DNA barcodes were successfully assigned to each species. Although some of these species were previously reported in the region, three are only presently reported in this study. The dendrogram showed Nerita and Neritina strongly supported in their respective monophyletic clades. Phylogenetic positions of some species appeared unstable in the trees. This could be due to the differences in a small number of nucleotides, thus minimizing genetic variation between each specimen and species.

The present work aims to assess the spatial distribution, analyze shell utilization, shell fitness and determine the effect of coexistence of two hermit crabs Calcinus latens and Clibanarius signatus on used shell resources in various habitats on the Red Sea Coast. Also, to determine the choice of shells and investigate the shell species preference of C. latens and C. signatus in the laboratory. The hermit crabs C. latens and C. signatus were found to occupy shells of 39 gastropod species. The most commonly occupied gastropod shells are those belonging to genera Strombus, Nerita, Cerithium and Planaxis. The results showed that crab individuals utilized mainly the shell with elongate aperture. Laboratory experiments showed that two crab species preferred shells of Strombus followed by Cerithium and Nerita when offered shells of nearly similar size (optimal). Crab individuals showed a significant preference for optimal sized shells when given suboptimal shells as an alternative choice. Also, the hermit crabs avoid damaged shells when given a choice of optimal sized damaged shell and optimal sized intact one. In addition, two hermit crab species chose shells of smaller than optimal size when given a choice of damaged optimal sized shells and smaller intact ones. On the other hand, field observations showed that most crab individuals lived in adequate sized shells. The present data conclude that shell selection by hermit crabs C. latens and C. signatus depends mostly on shell internal volume, shell quality and shell aperture size than other factors, because they provide a maximum protection for hermit crabs.

Currently, there are a lot of activities in Sirandah Island, such as tourism activities and deforestation to support the activities. Mangrove forest distruction makes a useable area might have negative effect to mangrove ecosystem itself or mollusc community. This research was conducted on mangrove roots area from February until October 2016. The aim of this research is to know the diversity of Gastropods on the roots of the mangrove. This research was conducted using survey method and purposive sampling method to collecting data. We recorded 8 genera of Gastropods belong to 8 families, named Cerithium, Conus, Ellobium, Littorina, Melongena, Nerita, Cymatium and Turbo. The highest abundance was found in the genus of Littorina with 59.33 individuals/tree. Based on location, abundance ranged from 4.33-60.33 individuals/tree with the highest abundance on mangrove roots of Barringtonia asiatica. Diversity indices of Gastropods on mangrove roots in Sirandah Island ranged from 0.77 to 1.42 which is relative low range.

The effect of shell preference in the wild and field shell experience on choice in laboratory shell-choice experiments by hermit crabs was investigated. The hermit crab Calcinus californiensis prefers one of two different shell species in the wild site where we studied its behavior. The two most occupied gastropod shells were Nerita scabricosta (76%) and Thais biserialis (12%), with the remaining animals occupying a range of other shell species. Hermit crabs, originally collected in Thais and Nerita shells, showed a higher preference for Thais than for Nerita shells. However, shell preference was influenced by previous housing experience in the wild. In addition, the shell adequacy index showed that in the wild females occupy Thais shells relatively larger than the preferred size used under controlled conditions.

Marine biogeographers have long recognized broad east‐west differentiation of marine communities across southern Australia, but few studies have explicitly assessed the site of disjunction or the factors potentially underlying this biodiversity. A recent, detailed phylogeographical and distributional study of the dispersive gastropod genus Nerita revealed an abrupt shift in species abundance across mainland Australia, apparently correlated with the site of an historical vicariant barrier: the Bassian Isthmus. In the current study I provide an independent assessment of this vicariant hypothesis by morphologically analysing over 3000 intertidal Nerita specimens from eight coastal sites around Tasmania. Consistent with the Bassian Isthmus hypothesis, the study reveals a dramatic east‐west disjunction across north-east Tasmania. A survey of marine biogeographical literature reveals several additional examples supporting the east‐west species turnover detected in Nerita . I discuss the role of contemporary oceanographic factors in preserving the biogeographical signature of marine vicariance, even in highly dispersive taxa. Based on recent marine connectivity data, the east‐west disjunction in Nerita taxa can be interpreted as an historic vicariant pattern perpetuated by contemporary oceanographic conditions. The results of this study emphasize the potential importance of considering relative abundance data ‐ rather than just species range data ‐ in marine biogeographical analyses. As the observed disjunction is likely to have broad implications for Australia’s marine biodiversity, it is imperative that conservation biologists incorporate such data in the design of marine protected areas.

Marine species with ranges that span the Indo-Australian Archipelago (IAA) exhibit a range of phylogeographical patterns, most of which are interpreted in the context of vicariance between Indian and Pacific Ocean populations during Pliocene and Pleistocene low sea-level stands. However, patterns often vary among ecologically similar taxa, sometimes even within genera. This study compares phylogeographical patterns in two species of highly dispersive neritid gastropod, Nerita albicilla and Nerita plicata, with nearly sympatric ranges that span the Indo-Pacific. Mitochondrial COI sequences from >1000 individuals from 97 sites reveal similar phylogenies in both species (two divergent clades differing by 3.2% and 2.3%, for N. albicilla and N. plicata, respectively). However, despite ecological similarity and congeneric status, the two species exhibit phylogeographical discordance. N. albicilla has maintained reciprocal monophyly of Indian and Pacific Ocean populations, while N. plicata is panmictic between oceans, but displays a genetic cline in the Central Pacific. Although this difference might be explained by qualitatively different demographic histories, parameter estimates from three coalescent models indicate that both species have high levels of gene flow between demes (2Nem>75), and share a common history of population expansion that is likely associated with cyclical flooding of continental shelves and island lagoons following low sea-level stands. Results indicate that ecologically similar, codistributed species may respond very differently to shared environmental processes, suggesting that relatively minor differences in traits such as pelagic larval duration or microhabitat association may profoundly impact phylogeographical structure.

Cobbled shores in subtropical Japan are small and disturbed by sand transported from terrestrial runoff. How benthic organisms live in such a harsh environment has been seldom studied. On a cobbled shore at Ishigaki Island, the present study investigated the life-history traits of the gastropod, Nerita squamulata Le Guillou 1841. Seasonal quadrat samplings showed that the neritid density decreased when and where sand covered cobbles, indicating impact of sand on the neritid. Monthly frequency histograms of the shell width suggested that the neritid lives less than 2 years and recruits as individuals of 1-4 mm shell width in both May-August and February. With the possible short longevity and frequent recruitments, the neritid population may quickly recover after the disturbance by sand.

The mitochondrial DNA (mtDNA) cytochrome oxidase I (COI) gene has been universally and successfully utilized as a barcoding gene, mainly because it can be amplified easily, applied across a wide range of taxa, and results can be obtained cheaply and quickly. However, in rare cases, the gene can fail to distinguish between species, particularly when exposed to highly sensitive methods of data analysis, such as the Bayesian method, or when taxa have undergone introgressive hybridization, over-splitting, or incomplete lineage sorting. Such cases require the use of alternative markers, and nuclear DNA markers are commonly used. In this study, a dendrogram produced by Bayesian analysis of an mtDNA COI dataset was compared with that of a nuclear DNA ATPS-α dataset, in order to evaluate the efficiency of COI in barcoding Malaysian nerites (Neritidae). In the COI dendrogram, most of the species were in individual clusters, except for two species: Nerita chamaeleon and N. histrio. These two species were placed in the same subcluster, whereas in the ATPS-α dendrogram they were in their own subclusters. Analysis of the ATPS-α gene also placed the two genera of nerites (Nerita and Neritina) in separate clusters, whereas COI gene analysis placed both genera in the same cluster. Therefore, in the case of the Neritidae, the ATPS-α gene is a better barcoding gene than the COI gene.

In Hong Kong, low-shore rock pools support a patchy mosaic of different successional stages of crustose coralline algae. Echinoid and molluscan grazers are abundant in these low-shore rock pools and spatial and temporal variation in grazing pressure is thought to play an important role in structuring these assemblages. Direct records of graze marks using a modified wax-disc method were used to monitor spatial (different pools) and temporal (periods, 3 or 4 days each; spring vs. neap tides; summer vs. winter) variations in grazing pressure. Radula marks of Chlorostoma argyrostoma, Lunella coronata and Nerita albicilla were common in all pools. Grazing pressure was highly variable with tidal state and season but also within these two factors. Lunella and Nerita exerted highest grazing pressure at neap tides during summer, whilst Chlorostoma exerted highest grazing pressure in winter. Although overall patterns of temporal variation were similar and consistent in all pools, there was between pool variation in grazing pressure and individual species showed different patterns. Within the seasonal and tidal variations, large period-to-period differences were found for all species, illustrating small-scale temporal variation. Fine-scale spatial and temporal patterns of variation in grazing pressure of different species, therefore, contribute to the highly dynamic nature of these low-shore rock pools.

Colour-infrared (CIR) imagery was evaluated for its usefulness to test hypotheses about grazing in the intertidal gastropods Nerita atramentosa (Reeve) and Bembicium nanum (Lamarck). Tiles of natural sandstone were placed onto the shore to accumulate micro-algae for a period of 6 weeks. Then, in the laboratory, three replicate tiles were assigned into each of 6 treatments (Nerita and Bembicum at densities of 3 or 6 animals, plus a control and a control for artifacts due to cages). CIR images were acquired before and three times after the animals were placed on the tiles. NIR/red ratio images, which are used to estimate micro-algal biomass, were generated from calibrated CIR data. Nerita at the greater density were more effective at removing microalgae than at the smaller density. The latter were more effective than Bembicium at either density, which did not significantly decrease algal biomass from that in controls. These data are consistent with previous field observations and indicate that CIR imagery is an effective method for testing hypotheses about grazing by intertidal gastropods. D 2005 Elsevier B.V. All rights reserved.

Species of Vetigastropoda (Fissurellidae, Turbinidae, Trochidae) and one species of Neritimorpha (Neritidae) from the Navidad area, south of Valparaiso, and the Arauco Peninsula, south of Concepcion, are described. Among these, the Fissurellidae comprise Diodora fragilis n. sp., Diodora pupuyana n. sp., two additional unnamed species of Diodora, and a species resembling Fissurellidea. Turbinidae are represented by Cantrainea sp., and Trochidae include Tegula (Chlorostoma) austropacifica n. sp., Tegula (Chlorostoma) chilena n. sp., Tegula (Chlorostoma) matanzensis n. sp., Tegula (Agathistoma) antiqua n. sp., Bathybembix mcleani n. sp., Gibbula poeppigii (Philippi, 1887) n. comb., Diloma miocenica n. sp., Fagnastesia venefica (Philippi, 1887) n. gen. n. comb., Fagnastesia matanzana n. gen. n. sp., Calliostoma mapucherum n. sp., Calliostoma kleppi n. sp., Calliostoma covacevichi n. sp., Astele laevis (Sowerby, 1846) n. comb., and Monilea riorapelensis n. sp. The Neritidae are represented by Nerita (Heminerita) chilensis (Philippi, 1887). The new genus Fagnastesia is introduced to represent low-spired trochoideans with a sculpture of nodes below the suture, angulated whorls, and a wide umbilicus. This Miocene Chilean fauna includes genera that have lived at the coast and in shallow, relatively warm water or deeper, much cooler water. This composition therefore suggests that many of the Miocene formations along the central Chilean coast consist of displaced sediments. A comparison with different fossil and Recent faunas from around the Pacific and South America indicates that the vetigastropod and neritid fauna from the Miocene of Chile has only minor affinities with taxa living near New Zealand, Argentina, and the tropical eastern Pacific at that time. q 2004 Elsevier Ltd. All rights reserved.

Samples of mangrove snails Nerita lineata and surface sediments were collected from nine geographical sampling sites in Peninsular Malaysia to determine the concentrations of eight metals. For the soft tissues, the ranges of metal concentrations (μg g(-1) dry weight (dw)) were 3.49-9.02 for As, 0.69-6.25 for Cd, 6.33-25.82 for Cu, 0.71-6.53 for Cr, 221-1285 for Fe, 1.03-50.47 for Pb, and 102.7-130.7 for Zn while Hg as 4.00-64.0 μg kg(-1) dw(-1). For sediments, the ranges were 21.81-59.49 for As, 1.11-2.00 for Cd, 5.59-28.71 for Cu, 18.93-62.91 for Cr, 12973-48916 for Fe, 25.36-172.57 for Pb, and 29.35-130.34 for Zn while for Hg as 2.66-312 μg kg(-1) dw(-1). To determine the ecological risks on the surface habitat sediments, sediment quality guidelines (SQGs), the geochemical indices, and potential ecological risk index (PERI) were used. Based on the SQGs, all the metals investigated were most unlikely to cause any adverse effects. Based on geoaccumulation index and enrichment factor, the sediments were also not polluted by the studied metals. The PERI values based on As, Cd, Cu, Cr, Hg, Pb and Zn in this study were found as 'low ecological risk'. In order to assess the potential health risks, the estimated daily intakes (EDI) of snails were found to be all lower than the RfD guidelines for all metals, except for Pb in some sites investigated. Furthermore, the calculated target hazard quotients (THQ) were found to be less than 1. However, the calculated total target hazard quotients (TTHQ) from all sites were found to be more than 1 for high level consumers except KPPuteh. Therefore, moderate amount of intake is advisable to avoid human health risks to the consumers.

The potential value of the marine prosobranch Nerita saxtilis as an efficient biological monitor to heavy metal pollution in the Red Sea was investigated. Storage ability of lead and cadmium was compared in shell, headfoot and digestive gland of the marine snail N. saxtilis collected from Al-Hamrauin area at El-kuseir (lead, 300.35 +/- 28.53 microg/l, 1,716 +/- 16.14. cadmium 20.01 +/- 1.8 microg/l, 161.72 +/- 21.4 mean +/- S.D. for water and sediment, respectively) relative to that of inhabiting marine water and sediment employing atomic absorption spectrometry to determine the organ with highest capability of heavy metal accumulation. The influence of metal storage on light microscopic structure of that organ was investigated. Also, the ultrastructure localization of storage sites in the same organ was determined employing transmission electron microscopy. The digestive gland was shown to accumulate both metals at conccntrations that are several orders of magnitude higher than those in the surrounding marine water. The bioaccumulation capability of lead and cadmium was ranked in the following order; digestive glandheadfootshell for lead and digestive glandshellheadfoot for cadmium. In spite of its evident highest metal storage capability, no histopathological changes were observed in the digestive gland of that marine prosobranch. Enlarged electron dense vesicles and many granules were observed in ultrathin sections in digestive cells of these snails and are suggested to be the sites of storage of detoxified metals. The results of that finding indicate the possibility of using the marine prosobranch N. saxtilis as biomonitor for heavy metal contaminants in the Red Sea.

International audience; The Southwest Indian Ocean (SWIO) is a striking marine biodiversity hotspot. Coral reefs in this region host a high proportion of endemics compared to total species richness and they are particularly threatened by human activities. The island archipelagos with their diverse marine habitats constitute a natural laboratory for studying diversification processes. Rocky shores in the SWIO region have remained understudied. This habitat presents a high diversity of molluscs, in particular gastropods. To explore the role of climatic and geological factors in lineage diversification within the genus Nerita, we constructed a new phylogeny with an associated chronogram from two mitochondrial genes [cytochrome oxidase sub-unit 1 and 16S rRNA], combining previously published and new data from eight species sampled throughout the region. All species from the SWIO originated less than 20 Ma ago, their closest extant relatives living in the Indo-Australian Archipelago (IAA). Furthermore, the SWIO clades within species with Indo-Pacific distribution ranges are quite recent, less than 5 Ma. These results suggest that the regional diversification of Nerita is closely linked to tectonic events in the SWIO region. The Reunion mantle plume head reached Earth's surface 67 Ma and has been stable and active since then, generating island archipelagos, some of which are partly below sea level today. Since the Miocene, sea-level fluctuations have intermittently created new rocky shore habitats. These represent ephemeral stepping-stones, which have likely facilitated repeated colonization by intertidal gastropods, like Nerita populations from the IAA, leading to allopatric speciation. This highlights the importance of taking into account past climatic and geological factors when studying diversification of highly dispersive tropical marine species. It also underlines the unique history of the marine biodiversity of the SWIO region.

Eighteen species of gastropods were encountered living near and within the large coastal swamps, mangrove forests, intertidal flats and the rocky shore of the Cameroonian coast of the Atlantic Ocean. These represent members of the subclasses Neritimorpha, Caenogastropoda, and Heterostropha. Within the Neritimorpha, representatives of the genera Nerita, Neritina, and Neritilia could be distinguished by their radula anatomy and ecology. Within the Caenogastropoda, representatives of the families Potamididae with Tympano-tonos and Planaxidae with Angiola are characterized by their early ontogeny and ecology. The Pachymelaniidae are recognized as an independent group and are introduced as a new family within the Cerithioidea. Littorinimorpha with Littorina, Assiminea and Potamopyrgus as well as Neogastropoda (Thais) and Heterostropha (Melampus and Onchidium) are described and compared with representatives of the Caribbean and Indo-Pacific province.

Shellfish collection by humans is a form of selective predation, with the larger individuals of a few target species being taken, and can have direct and indirect effects. We investigated the indirect effects of collection by experimental removals of two target species, Cellana tramorerica (Sowerby) and Nerita atramentosa (Reeve) from a rocky shore in south eastern Australia. Removals of single species were compared with the removal of both species and frequent removals were compared against once-off removal events. The removal of Cellana resulted in an increase in micro-algal abundance. This increase was greater where Cellana were frequently removed than where once-off removal of the species occurred. The removal of Cellana also promoted the immigration of adult Cellana, but the overall population was dominated by juveniles. Immigration of juvenile Cellana was high in all cases and was not affected by removals of either target species. The removal of Nerita, whether once-off or frequent, resulted in a decrease in micro-algae, but did not affect the migration of other species. The combined removal of Cellana and Nerita did not affect microalgal abundance, a result that was successfully predicted from the summed effect of the single species removals. In addition, the combined removal had no effect on the abundance of other species. The single and combined removal of these two gastropod species did not influence the species richness at this study site.

Terrestrial hermit crabs (Coenobita compressus (H. Milne Edwards)) on Isabel island, Mexico, prefer Nerita (Ritena) scabricosta (Lanark 1822) over other species of shells. Nerita scabricosta, the lightest species of shell, has the highest internal volume/weight ratio (IV/W ratio) of all species available at the island. Heavier shells (low IV/W ratio) are more costly to carry and may restrain growth. We hypothesized that crabs will search for shells with high IV/W ratios to save energy, and predicted that in every individual shell-exchange crabs will prefer a shell with a higher IV/W ratio. Observations of spontaneous aggressive shell-exchange interactions in nature between crabs carrying preferred shells (with high IV/W ratio) and crabs using less preferred species of shells (low IV/W ratio) support this idea. By inducing individual shell exchanges in the field, we experimentally confirmed the preference for shells with high IV/W ratio, and we also showed that crabs prefer larger shells over those they were bearing. Moving to a larger but not heavier shell may facilitate growth though saving energy that would otherwise be spent in locomotion. High growth rates seem to be advantageous because size is a correlate of fertility, since large males apparently have more access to females, and large females produce larger clutches, thus indicating the possible reproductive benefits for preferred light and large shells.

The concentrations of selected heavy metals (Fe, Pb, Zn, Ni and Cd) were determined in the soft tissues and shells of two mollusc, namely, Nerita lineata and Thais bitubercularis taken from Tanjung Harapan and Teluk Kemang, Malaysia. Samples were collected in April 2012 and analysed using inductively coupled plasma mass spectrometry (ICP-MS). Fe is the most abundant metal in the tissue and shell compared to the rest of the metals. The concentrations of heavy metals in the soft tissues of Nerita lineata taken from Tanjung Harapan follow this order: Fe > Zn > Ni > Cu > Cd while in Thais bitubercularis, the metal concentrations were higher following the order of Fe > Zn > Cu > Ni > Cd. The samples taken from Teluk Kemang were higher and exhibited different trend for both organisms. For Nerita lineata, the concentrations were Fe > Cu > Zn > Ni > Cd > Pb while in the Thais bitubercularis the order was Fe > Zn > Cu > Cd > Ni > Pb. There was evidence of spatial difference where Fe was detected in large amount compared to other metals for both locations. Cd has the potential to be accumulated in Nerita lineata whereas for the T. bitubercularis Cu, Cd, and Zn were accumulated in the soft tissues.

This dataset records the occurrence and inventory of molluscan fauna on Gueishan Island, the only active volcanic island in Taiwan, based on the literature survey and field investigation conducted between 2011 and 2012. The literature review involved seven studies published from 1934 to 2003, which collectively reported 112 species from 61 genera and 37 families of Mollusca on Gueishan Island. Through our field investigation, we identified 34 species from 28 genera and 23 families. Fourteen of these species were new records on Gueishan Island: Liolophura japonica, Lottia luchuana, Nerita costata, Nerita rumphii, Diplommatina suganikeiensis, Littoraria undulata, Solenomphala taiwanensis, Assiminea sp., Siphonaria laciniosa, Laevapex nipponica, Carychium hachijoensis, Succinea erythrophana, Zaptyx crassilamellata, and Allopeas pyrgula. In Total, there are 126 species from 71 genera and 45 families of Mollusca on Gueishan Island. These data have been published through GBIF [http://taibif.org.tw/ipt/resource.do?r=gueishan_island] and integrated into the Taiwan Malacofauna Database (http://shell.sinica.edu.tw/).

Limited literatures exist on fouling organisms attached to mangrove in Ambon Inner Bay (AIB). The purpose of this research is to obtain updated information on fouling organism in this ecosystem. Samplings were carried out in two periods, representing first transition period and west monsoons, at two different locations in AIB (Poka and Kate-kate). Methods used were direct observation and descriptive exploration during sampling. Fouling organisms and mangrove type were identified using identification books. The results obtained indicate that predominant organisms belonged to mollusks and crustacea. Four gastropod species (Littorina scabra, Nerita oualaniens, Terebralia sulcata, Cassidula nucleus) and one bivalve (Saccostrea cucullata) were identified. Clibanarius ambonensis and Cardisoma carnifex were the species identified from crustacea group. Type of mangrove found, either naturally or through replanting program in Poka were Rhizophora apiculata, R. stylosa and Sonneratia alba. There were four different species found in Kate-kate (S. alba, R. apiculata, Ceriops tagal and Aegiceras corniculatum).Keywords: fouling organisms, mangrove ecosystem, Ambon Inner Bay

Long-tailed macaques (Macaca fascicularis) feed opportunistically in many habitats. The Burmese subspecies (M. f. aurea) inhabits coastal areas in southwestern Thailand and Myanmar, and some of their populations have adapted lithic customs for processing encased foods in intertidal habitats. We investigated the diet of such macaques in Laemson National Park, Thailand, and identified the variety of foods they processed with stones. We conducted 36 shore surveys to study tool sites following feeding activity, during which we counted the minimum number of individual (MNI) food items found at each site. We identified 47 food species (43 animals and four plants), from 37 genera. We counted 1,991 food items during surveys. Nearly all were mollusks (n = 1,924), with the small remainder primarily consisting of crustaceans and nuts. The two most common foods, rock oysters (Saccostrea cucullata; n = 1,062) and nerite snails (Nerita spp.; n = 538), composed 80.2% of our sample. Four prey species comprised 83.2% of the sample (MNI = 1,656), S. cucullata (n = 1,062), Nerita chamaeleon (n = 419), Thais bitubercularis (n = 95), and Monodonta labio (n = 80). Macaques selected a wide variety of foods. However, they heavily concentrated on those that were abundant, easy to access, and sufficiently sized. The Burmese long-tailed macaque stone-processed diet, which focuses on intertidal marine prey, differs from Sapajus and Pan, who use stones primarily for encased nuts and fruits. In terms of diversity of foods exploited, coastal stone-based predation by macaques resembles the diet of coastal-foraging humans (Homo sapiens sapiens). Am J Phys Anthropol, 2012.

Factors influencing shell assessment behaviour were studied in the hermit crab, Calcinus tibicen. Visual and chemical presence of potential competition significantly lengthened the duration of shell assessment. Shell genus occupied by the hermit crab also had a significant effect. Those in Astrea shells examined an offered Cerithium shell significantly longer than hermit crabs occupying Gerithium, Pisania, or Nerita shells. Shell deficit, the difference between optimal shell volume for the hermit crab and actual shell volume, did not have a significant effect on the behavior of the hermit crabs occupying Cerithium shells. For those in Pisania shells there was a negative correlation between shell deficit and shell examination; while crabs in Nerita and Astrea shells demonstrated a positive correlation between shell deficit and shell examination. Neither the sex of the individual crab nor the presence of a predator, Calappa flammea, had a significant effect on shell assessment behaviour.

Five gastropod taxa of the family Neritidae in the Ypresian and Bartonian (Eocene) of the Paris and Basse-Loire Basins, are introduced: Cuisenerita gen. nov., Tomostoma angusta sp. nov., Nerita gouetensis sp. nov., Clithon barbei sp. nov., Neritodryas guillioui sp. nov. and Cuisenerita tuberosa sp. nov. New combinations introduced are: Neritodryas dutemplei (Deshayes, 1864) and Neritodryas globosa (J. de C. Sowerby, 1823). This is the earliest record of Neritodryas and the first record for this genus from Europe.

Aim In this study, I examined the relative contributions of geography and ecology to species diversification within the genus Nerita, a prominent clade of marine snails that is widely distributed across the tropics and intertidal habitats. Specifically, I tested whether geographical patterns of speciation correspond primarily to allopatric or sympatric models, and whether habitat transitions have played a major role in species diversification. Location Indo-West Pacific, eastern Pacific, Atlantic, tropical marine intertidal. Methods I used a previously reconstructed molecular phylogeny of Nerita as a framework to assess the relative importance of geographical and ecological factors in species diversification. To evaluate whether recently diverged clades exhibit patterns consistent with allopatric or sympatric speciation, I mapped the geographical distribution of each species onto the species-level phylogeny, and examined the relationship between range overlap and time since divergence using age‐range correlation analyses. To determine the relative contribution of habitat transitions to divergence, I traced shifts in intertidal substrate affinity and vertical zonation across the phylogeny using parsimony, and implemented randomization tests to evaluate the resulting patterns of ecological change. Results Within the majority of Nerita clades examined, age‐range correlation analysis yielded a low intercept and a positive slope, similar to that expected under allopatric speciation. Approximately 75% of sister species pairs have maintained allopatric distributions; whereas more distantly related sister taxa often exhibited complete or nearly complete geographical overlap. In contrast, only 19% of sister species occupy distinct habitats. For both substrate and zonation, habitat transitions failed to concentrate towards either the tips or the root of the phylogeny. Instead, habitat shifts have occurred throughout the history of Nerita, with a general transition from the lower and mid-littoral towards the upper and supra-littoral zones, and multiple independent shifts from hard (rock) to softer substrates (mangrove, mud and sand). Main conclusions Both geography and ecology appear to have influenced diversification in Nerita, but to different extents. Geography seems to play a principal role, with allopatric speciation driving the majority of Nerita divergences. Habitat transitions appear insignificant in shaping the early and recent history of speciation, and promoting successive diversification in Nerita; however, shifts may have been important for respective divergences (i.e. those that correspond to the transitions) and enhancing diversity throughout the clade.

Rates of radular activity were measured in four species of Australian gastropods. The species were Austrocochlea constricta, Bembicium nanum, Cellana tramoserica, and Nerita atramentosa. Work was done in Botany Bay at Cape Banks, NSW, Australia from September 1989 to June 1990. A hydrophone was used to record radular raspings of snails in situ. Averages based on all observations showed Cellana had the fastest rate with 80 rasps/min, and was followed by Austrocochlea (71 rasps/min), Bembicium (57), and Nerita (39). Faster rates were associated with warmer water temperature and smaller body sizes in all species except Bembicium. The potential for these differences in radular activity affecting competitive interactions is discussed.

The concentrations of Cd, Cu, Pb, Zn, Ni and Fe were determined in the gastropod Nerita lineata collected from 15 sites in the west intertidal area of Peninsular Malaysia (shell length 11.5–33.8 mm). The results of the present study showed that metal concentrations in the shells, opercula and soft tissues of N. lineata were distributed differently at different sampling sites. The mean concentrations (μg/g dry weight) of Cd, Cu, Fe, Ni, Pb and Zn in the samples were 2.99, 6.38, 35.05, 23.34, 48.22 and 16.59 in the opercula, 3.15, 5.59, 49.78, 24.18, 48.86 and 7.86 in the shells and 1.03, 2.65, 566.63, 5.85, 92.72 and 92.75 in the soft tissues. All the populations of N. lineata showed similar trends in the accumulation of Cd, Ni and Pb which decreased as follows: shell > operculum > soft tissue, Cu and Zn deceased in the order: soft tissue > operculum > shell and Fe in the order: soft tissue >shell > operculum. In general, higher concentrations of metals were recorded in samples collected from the stations closed to the anthropogenic sites. In particular, snail samples collected from KSAyam accumulated higher Pb concentrations when compared to other sites in the opercula, shells and soft tissues. This may indicate high bioavailability and contamination via Pb of the study site. The snail N. lineata is therefore suggested as a potential biomonitor of bioavailability and contamination of heavy metal in general and Pb in particular for the tropical intertidal area of Peninsular Malaysia.

To determine how historical processes, namely speciation, extinction, and dispersal, have contributed to regional species diversity patterns across the marine tropics, we examined the biogeographical history of a circumtropical genus of intertidal gastropods. A species-level phylogeny of Nerita, representing approximately 87% of extant species, was developed from 1608 bp of mitochondrial (COI and 16S) and nuclear (ATPSα) markers. Phylogenetic relationships generally corresponded to prior classifications; however, comprehensive sampling revealed a number of previously undetected ESUs. Using the resulting tree as a framework, we combined geographical distributions and fossil evidence to reconstruct ancestral ranges, produce a time-calibrated chronogram, and estimate diversification rates. Analyses revealed two monophyletic eastern Pacific + Atlantic (EPA) clades, each of which likely split from an Indo-West Pacific (IWP) sister clade prior to an early Miocene Tethys Seaway closure. More recent diversification throughout the IWP appears to have been driven by both vicariance and dispersal events; EPA diversity has been further shaped by speciation across the Central American Seaway prior to its closure and dispersal across the Atlantic. Despite the latter, inter-regional dispersal has been rare, and likely contributes little to regional diversity patterns. Similarly, infrequent transitions into temperate regions combined with reduced diversification rates may explain low diversity in West and South Pacific clades. Since origination, Nerita diversification appears remarkably constant, with the exception of a lag in the late Eocene–early Oligocene and elevated rates in the late Oligocene–early Miocene. However, a comparison among regions suggested that IWP clades have experienced, on average, higher rates of speciation. Fossil evidence indicates that the EPA likely witnessed greater extinction relative to the IWP. We propose that regional differences in species diversity in Nerita have been largely shaped by differential rates of speciation and extinction.

Phylogeographical disjunctions in high-dispersal marine taxa are variously ascribed to palaeogeographical conditions or contemporary ecological factors. Associated biogeographical studies, however, seldom incorporate the sampling design required to confidently discriminate among such competing hypotheses. In the current study, over 7800 gastropod specimens were examined for operculum colour, and 129 specimens genetically, to test ecological and historical biogeographical hypotheses relating to biogeographical disjunction in the Southern Hemisphere, and to southern Australia in particular. Mitochondrial DNA sequence analysis of the high-dispersal intertidal gastropod Nerita atramentosa in southern Australia (88 specimens; 18 localities) revealed an east-west phylogeographical split involving two highly divergent clades (26.0 +/- 1.9%) exhibiting minimal geographical overlap in the southeast. The eastern clade of Nerita atramentosa is also widespread in northern New Zealand (43 specimens, 10 localities), but no significant genetic differentiation is explained by the Tasman Sea, a 2000-km-wide oceanic barrier. Spatial genetic structure was not detected within either clade, consistent with the species' dispersive planktotrophic phase lasting for 5-6 months. Digital analysis of operculum colouration revealed substantial differences between eastern (tan) and western (black) specimens. Genetic analysis and visual inspection of 88 Australian specimens revealed a completely nonrandom association between mtDNA data and operculum colouration. Independent examination of a further 7822 specimens from 14 sites in southern Australia revealed both colour morphs at all localities, but reinforced the phylogeographical data by indicating a marked turnover in colour morph abundance associated with a palaeogeographical barrier: Wilsons Promontory. This sharp biogeographical disjunction is in marked contrast to the species' high dispersal abilities. The genetic similarity of Nerita morio (Easter Island) and the eastern Australian + New Zealand lineage (1.1 +/- 0.3%) provides further evidence of long-distance dispersal in southern Nerita. Phylogenetic relationships of nine species (four genera) of Neritidae, an almost exclusively tropical gastropod family, are consistent with the hypothesis that southern temperate black nerites comprise a monophyletic radiation.

Since October 1994, a long-term program of Asia/Pacific Mussel Watch: Taiwan Regional Studies has been carried out. The results indicate that trace metal contents in mollusca varied among 30 different species and the environments (water and sediments) along the Taiwan coast. The orders of bioaccumulation of trace metals in mollusca were: Cu (over 200 μg/g), Thais clavigera > Isognomon legumen > Clibanarius rivescens > Crassostrea gigas ; Zn (over 700 μg/g), Moruta granulata > C. gigas > Asiatica cypraea arabica > T. clavigera ; Cd (over 5 μg/g), Trochus hanleyanus > Acanthopleura japonica > Nerita albicilla > Patella flexuosa ; Pb (over 2 μg/g), P. flexuosa > C. gigas > T. hanleyanus > T. clavigera > C. gigas > Capiyulum mitella ; Ni (over 10 μg/g), Meretrix lusoria > Philine sp. > Littoraria scabra > Tridacna squamosa > T. hanleyanus ; Cr (over 30 μg/g), Littoraria undulata > T. hanleyanus > N. albicilla > Nerita chamaelor > M. granulata ; As (over 20 μg/g), Perna viridis > L. scabra ; and Sn (over 5 μg/g), P. viridis > L. undulata > C. mitella > C. gigas . Their seasonal and regional variations as well as their correlation are evaluated and discussed.

Our understanding of the physical factors driving fine-scale structuring of marine biodiversity remains incomplete. Recent studies have hypothesised that oceanography and coastal geometry interact to influence marine biogeographic structure on small spatial scales. The coastal waters of eastern Tasmania, located at the oceanographic interface between two major boundary current systems (the East Australia Current (EAC) and the Leeuwin Current (LC)) represent an informative system for assessing this hypothesis. Parallel biogeographic and oceanographic analyses, focusing on the relative abundance of two widespread, larval-dispersed Nerita gastropods, suggest that the relative influences of the EAC and LC at this interface are modulated by coastal topographical variation. Specifically, east-facing coastalsitesaredominatedbytheEAC-derivedN.melanotragus,whereassouth-facingbaysaredominatedbyLC-derived N.atramentosa.Thesecombinedoceanographicandbiologicaldataimplythatcoastaltopographyandhydrodynamicscan combine to influence the local distributions and abundances of planktotrophic-developing taxa at coastal convergence zones. Additional keywords: boundary current, climate change, connectivity, conservation, dispersal, invasion, marine invertebrate, marine protected areas (MPAs), recruitment.

Diversity of edible mollusc was studied at eight divisions of Sarawak from August 2010 to May 2011. At each division, diversity and number of species were collected from road site selling out lets and local wet markets. Total number of mollusc was comprised of 29 species namely Solen regularies, S. lamarckii, Pharella acutidens, Anadara granosa, Pholas orientalis, Gluconome virens, Circe scripta, Anodonta woodina, Paphia undulata, Amusium pleuronectes, Meretrix meretrix, M. lyrata, Polymesoda bengalensis, P. erosa and P. expansa for bivalve and Cerithidea rizophorarum, C. obtusa, Telescopium telescopium, Clithon retropictus, Nerita articulate, N. chamaeleon, N. albicilla, Ellobium aurisjuda, Trochus radiates, Planaxis sulcatus, Monodonta labio, Turbo crasus, Thais aculate and Melo melo for gastropod. The species number of bivalve was recorded highest (15 species) in mollusc group from Sarawak. Mollusc diversity was found highest (14 species) in Bintulu and lowest (1 species) in the division of Sarikei. From this study, there is a wide chance of research to further explore both on the possibility of commercial value and ecosystem conservation.

Members of the genus Nerita are abundant components of the intertidal fauna in many parts of the world and yet Nerita taxonomy remains unsettled. Here, the relationships among black-shelled Nerita populations from Australia, New Zealand, Norfolk Island, Lord Howe Island, the Kermadec Islands and Easter Island are discussed. Four species are recognised: N. atramentosa Reeve, 1855 from the southern half of Australia; N. melanotragus E.A. Smith, 1884 from eastern Australia, northern New Zealand, Lord Howe Island, Norfolk Island and the Kermadec Islands; N. morio (G. B. Sowerby I, 1833) from Easter Island and the Austral Islands; and N. lirellata Rehder, 1980 from Easter Island alone. These species are of great importance in studies of intertidal community structure and yet two of them have been consistently confused in the ecological and taxonomic literature. Moreover, the relationships among the species are not at all as implied by recent subgeneric classifications; it is argued that all four species should be placed in the subgenus Lisanerita Krijnen, 2002. The superficially similar N. picea Récluz, 1841 is not closely related. An accurate taxonomy of the genus will almost certainly require considerable genetic analysis. The nomenclature for each species is herein established by complete synonymies, and lectotypes for both N. atramentosa and N. melanotragus are selected.

Populations of the intertidal hermit crab Calcinus tibicen were observed in the laboratory and reproductive behaviors recorded. Of the 218 interactions, 68 resulted in copulation(s). Male and female sizes were positively correlated. Male size affected copulation success in a non-linear fashion. In particular, the largest males did not obtain any copulations. This was largely a consequence of the shell species occupied by large individuals; males in Nerita sp and Cittarium pica shells were unsuccessful in courtship. The ability to execute precopulatory rotation of the female was negatively affected by certain shell types. Repeated pairings of individuals suggested some level of individual recognition within the reproductively active population.

The patterns of dispersion of Nerita atramentosa, Bembicium nanum and Cellana tramoserica within two major substrata, the encrusting alga Peyssonelia gunniana and bare rock were analysed from quadrat samples taken at low tide, over 1 year. Distances to the nearest members of each species from random points were analysed to determine spatial patterns of dispersion. The frequencies of nearest neighbours of each species to each animal in the sampled area were analysed to determine the degree of spatial segregation and symmetry in the three species. Nerita atramentosa and Bembicium nanum showed significant aggregated (clumped) dispersion in both substrata. Cellana tramoserica, however, was dispersed at random on Peyssonelia, and regularly dispersed on bare rock. There was no correlation between index of dispersion and density, or time of year, in any species. No useful tests for segregation and symmetry between Cellana and the other two species could be made because of the difference in dispersion of this species. Nerita and Bembicium were significantly segregated on both substrata, indicating that the microhabitat requirements of the two species are different. The two species were symmetrical on both substrata, indicating that there is no tendency for members of one species to be more isolated than members of the other species. Possible explanations of the differences in spatial pattern shown by the three species are discussed, and experimentally testable hypotheses are proposed to clarify the importance of physical and biological factors in the spatial patterns of distribution of the three species.

Populations of three coexisting intertidal gastropods, Nerita atramentosa Reeve, Bembicium nanum (Lamarck) and Cellana tramoserica (Sowerby), were sampled from a shore in Botany Bay, New South Wales, from July 1972 to September 1973. The recruitment and growth rates of each species were analysed from size frequency distributions. Mortality of each age cohort, and longevity, were estimated from analyses of the densities of Nerita atramentosa and Bembicium nanum . Nerita atramentosa showed no significant mortality during the first two years on the shore, but high mortality (at an instantaneous rate of 0.084 deaths/individual/month) after reaching the age of reproductive maturity, which was 20 months from settlement and at a mean shell-length of 13.5 mm. No growth could be detected after reproductive maturity was reached. Longevity of N. atramentosa was estimated as 3–5.5 years. Bembicium nanum juveniles showed higher mortality (at an instantaneous rate of 0.233 deaths/individual/month) than reproductively mature animals (0.060 deaths/individual/month). Reproductive maturity was reached at a mean shell-breadth of 11.0mm, i . e ., about ten months after settlement on the shore. Longevity was estimated as from 4–8 years. Cellana tramoserica showed different growth patterns depending on the time of settlement. The three species showed different patterns of growth and life history relating to variable recruitment (which was demonstrated in all three species) and different rates of mortality of age cohorts.

The archaeogastropod Nerita scabricosta is an abundant and extremely mobile herbivore which occurs from above mean high water through the mid—intertidal zone of exposed rocky areas along the Pacific coast of Panama. It is the principal prey of Purpura pansa, a patchily distributed, high intertidal neogastropod. Both snails exhibit activity patterns and habitat preference which appear to have evolved in response to heavy predation pressure by fish and to harsh physical factors. These behavioral mechanisms restrict movement and limit foraging time for both species, but also result in a cyclic overlap of their distributions. Potential interaction between the two gastropods is thus limited to well defined, discrete periods. Purpura elicits both an escape and an avoidance response in Nerita. The intensity of predation on the nerite by Purpura is lessened by these responses and Purpura appears unable directly to control the abundance of Nerita. However, it is experimentally shown that in a heterogeneous environment, Nerita's distribution is still more restricted and its local abundance further reduced by avoidance responses to temporally stable aggregations of Purpura. These aggregations, centered on specific fish—safe microhabitat, are thus hypothesized to result in the creation of local patches of intertidal substrate which are free from herbivory or disturbance effects by Nerita scabricosta. Evidence from field observations and manipulations is presented to support the hypothesis that in this complex, four trophic level community, a predator—prey interaction between two gastropods can limit potential resource monopolization and affect primary space occupancy.

The highly variable brackish-water snail Clithon oualaniensis (Lesson1831) was first studied in Hong Kong, Ceylon and Malaya-Singapore. Populations within these regions are closely similar, but there are consistent differences between regions. Subsequently, particularly round the Malay Peninsula, orderly changes of variants have come to light. This raises the question of how these have come into being and what is responsible for their apparent stability. Contrary to first impressions, most of the variability of Clithon and of certain species of Umbonium and Nerita is pseudo-polymorphic in nature. Conventional polymorphism seems to make but a small contribution. Quasi-continuous variation and pseudo-polymorphism are essentially the same phenomenon. Both arise by the interaction between polygenic inheritance and environmental conditions. Whether the resulting pheno­types are continuous or discontinuous depends on the developmental physiology of the organs or structures involved and is thus a secondary phenomenon.

Field observations and experiments were conducted on the intertidal gastropod Nerita textilis Gmelin along the Somalian coast to determine if its rhythmical mass-homing includes the detection of durable substrate marking as well as short-term trail-following. The snails' first response to displacement is a zonal orientation compensating for the vertical component of experimental shifting. The homing performance of symmetrically transferred animals supports the hypothesis that a marked area is present in and below the aggregation site, detectable by the homer snails 24 hours after its deposition by spontaneously moving conspecifics. No specific marking of different collective homes resulted from these experiments.

Intraspecific competition for food within and between age-classes of the intertidal grazing gastropod Nerita atramentosa Reeve was investigated using experimental cages on a rock platform in Botany Bay, New South Wales. Adults (mean length 21.0 mm) and juveniles (mean length 12.36 mm) were confined separately and together, at densities of 10, 20 and 50 per cage. The lowest density was the same as the mean density of Nerita on the shore. Cages were maintained for 146 days from November, 1973 to April, 1974. Each animal was numbered and its growth rate recorded over the period of the experiment. Dead animals were replaced by others of the same size to maintain densities, but replacements were not included in analyses. Proportional mortality of each size-class in each cage, growth rates and wet tissue weights at the end of the experiment were analysed. Adult animals did not grow. Growth rate of juveniles decreased with increasing density. Mortality of juveniles was not significantly different at different densities, but mortality of adults increased linearly as density increased. Wet tissue weights of adults and juveniles decreased with increasing density. In adults there was a decrease in weight at densities of 20 and 50 per cage. In juveniles, tissue weight increased with growth, from the start of the experiment except at densities of 50/cage where tissue weight remained constant and growth was absent. For all three factors, there were no differences between the effects of increasing density by additional members of the same age-class or by members of the other age-class. Adults and juveniles have, therefore, identical effects on the growth rates of juveniles, mortality of adults and wet tissue weights of both age-classes. Population density regulation in Nerita is possible, since high densities (e.g., due to increased juvenile recruitment) will cause reduced growth of juveniles and increased mortality of adults, until the densities are lowered. This effect of increased density is compared with intraspecific competition reported in other intertidal gastropods.