Clam Species Research Articles

Characteristics of cytochrome C oxidase subunit I gene in giant clam from Wakatobi National Park Waters, Indonesia

Characteristic of cytochrome C oxidase subunit I (COI) gene in giant clam from Wakatobi National Park Waters was studied to detect the specific nucleotide and show the relationship among species of giant clams. Sample collection was conducted around Wangi-wangi, Kaledupa, and Tomia waters. Genomic DNA was extracted from clam mantle tissue of two generas, and amplified by PCR method. We obtained nucleotide size of 522 bp for genus Tridacna (T. crocea, T. maxima) and 708 bp for genus Hippopus (H. hippopus). There were 52 specific nucleotide for the clams (included T. gigas and T. squamosa from GenBank data). T. crocea, T. gigas, T. squamosa, T. maxima, and H. hippopus had 2, 3, 9, 2, and 36 sites, respectively. Reconstruction phylogenetic tree using Neighbour Joining of 476 bp COI gene sequences showed that all species of giant clams were monophyletic.

A report of 42 unrecorded bacterial species isolated from fish intestines and clams in freshwater environments

Nine fish and one clam species were collected from freshwater environments in Korea, including four lakes, two streams, and the Nakdong River, to investigate the host-associated bacteria. Hundreds of bacterial strains were isolated from the samples using a cell sorter and a dilution plating method. After identification of the bacterial strains using 16S rRNA gene sequences, 42 strains with greater than 98.7% sequence similarity with validly published species were determined to be unrecorded bacterial species in Korea. These strains were phylogenetically diverse and assigned to four phyla, six classes, 17 orders, 27 families, and 32 genera. At the genus level, the unrecorded species were classified as Corynebacterium, Mycobacterium, Mycolicibacterium, Gordonia, Williamsia, Modestobacter, Brachybacterium, Sanquibacter, Arthrobacter, and Mycolicibacterium of the class Actinobacteria; Empedobacter, and Flavobacterium of the class Flavobacteriia; Fictibacillus, Psychrobacillus, Cohnella, Paenibacillus, Rummeliibacillus, Enterococcus, and Vagococcus of the class Bacilli; Aquamicrobium, Paracoccus, and Sphingomonas of the class Alphaproteobacteria; Achromobacter, Delftia, and Deefgea of the class Betaproteobacteria; and Aeromonas, Providencia, Yersinia, Marinomonas, Acinetobacter, and Pseudomonas of the class Gammaproteobacteria. The 42 unrecorded species were subjected to further taxonomic characterization using gram staining, cellular and colony morphological determination, biochemical analyses, and phylogenetic analyses. This paper provides detailed descriptions of the 42 previously unrecorded bacterial species.

Multiplex species-specific PCR identification of native giant clams in the South China Sea: A useful tool for application in giant clam stock management and forensic identification

In an effort to develop molecular tools for giant clam species identification, this study reveals the usefulness of a multiplex species-specific PCR for the reliable, rapid and low-cost identification of five giant clam species found in the South China Sea: Hippopus hippopus, Tridacna maxima, Tridacna derasa, Tridacna squamosa and Tridacna noae. We used the mitochondrial COI gene for marker development. Five reverse primers and a common forward primer were designed to generate five different size species-specific PCR fragments. These six primers were combined in a multiplex PCR to enable identification of five giant clam species in a single reaction. This molecular approach provides a simple and rapid identification of the giant clam species from the South China Sea, thus increasing the efficiency and quality of giant clam stock management, protecton and forensic identification by reducing the risk of wrong species identification.

Levels of PAHs, PCBs, and toxic metals in Ruditapes philippinarum and Donax trunculus in Marmara Sea, Turkey.

The manila clam Ruditapes philippinarum and the wedge clam Donax trunculus are economic bivalve species which constitute an important part of the natural bivalve beds in the Marmara Sea, Turkey. Toxic chemicals such as, dioxins, dioxin-like polychlorinated biphenyls (PCBs), polycyclic hydrocarbons (PAHs), and toxic metals are recognized as important health risk factors that threaten public health via food or directly in the environment. In the present study, we aimed to determine and monitor levels of these toxic chemicals in both clam species, R. philippinarum and D. trunculus, between 2013 and 2017. According to the results, maximum levels of dioxins, PAHs, and toxic metals (lead, cadmium, mercury) during the period were determined as 0.18 pg g-1 , 2.43 mg kg-1 , and 0.44-0.53-0.1 mg kg-1 , respectively. The level of contaminants in both clam species were determined to be below the threshold or tolerable daily intake values established by the European Commission, European Food Safety Authority (EFSA), and Food and Agriculture Organization/World Health Organization (FAO/WHO). Seasonal fluctuations were observed to be similar in both species and also in seasons, but elevated levels of PCBs and PAHs were detected in warmer months during the period. As a consequence, toxic chemicals in both clam species were found at low concentrations in this study from the point of view of public health concerns; however, the contaminants should be closely monitored in the future due to their elevated levels in samples. © 2020 Society of Chemical Industry.

Survey of Tetrodotoxin in New Zealand Bivalve Molluscan Shellfish over a 16-Month Period.

Tetrodotoxin (TTX) is a heat-stable neurotoxin typically associated with pufferfish intoxications. It has also been detected in shellfish from Japan, the United Kingdom, Greece, China, Italy, the Netherlands and New Zealand. A recent European Food Safety Authority (EFSA) scientific opinion concluded that a level of <0.044 mg TTX/kg in marine bivalves and gastropods, based on a 400 g portion size, does not result in adverse effects in humans. There have been no reports of human illness attributed to the consumption of New Zealand shellfish containing TTX. To obtain a greater understanding of its presence, a survey of non-commercial New Zealand shellfish was performed between December 2016 and March 2018. During this period, 766 samples were analysed from 8 different species. TTX levels were found to be low and similar to those observed in shellfish from other countries, except for pipi (Paphies australis), a clam species endemic to New Zealand. All pipi analysed as part of the survey were found to contain detectable levels of TTX, and pipi from a sampling site in Hokianga Harbour contained consistently elevated levels. In contrast, no TTX was observed in cockles from this same sampling site. No recreationally harvested shellfish species, including mussels, oysters, clams and tuatua, contained TTX levels above the recommended EFSA safe guidance level. The levels observed in shellfish were considerably lower than those reported in other marine organisms known to contain TTX and cause human intoxication (e.g., pufferfish). Despite significant effort, the source of TTX in shellfish, and indeed all animals, remains unresolved making it a difficult issue to understand and manage.

Abundance and harvest strategy of three species of clam (Bivalvia: Veneridae) located in new fishing banks in the Gulf of California

Clams of the family Veneridae in northwest Mexico have traditionally been exploited by small-scale fisheries. Despite their socioeconomic importance for coastal communities in the region, most catch zones are currently in decline due to a lack of harvest control regulations that would impede the depletion of local fishing banks. In Puerto Libertad, in the northern reaches of the Gulf of California, banks of commercially unexploited clam species, including Megapitaria aurantiaca, M. squalida and Dosinia ponderosa, were discovered. The adequate management and exploitation of these banks requires developing basic knowledge regarding the abundance of the species and establishing reference points to determine clear, simple harvest regulations. The goal of this study was to identify population abundance in these banks and ascertain the parameters of the life history of the species found there in order to propose a harvest strategy that will allow the sustainable exploitation of this resource. A total of 288 transects were conducted in the two clam banks to identify species density. Abundance was determined using a geostatistical method. The relative cohort biomass-at-length was estimated to evaluate the effect of different lengths of first capture on the remaining biomass. Based on these data, two harvest control regulations were proposed: a maximum catch (Cmax) of 10% of the total estimated biomass, and a minimum optimal catch size (Lc). The abundance estimates were M. squalida (266,293–381,881 individuals); D. ponderosa (2,779,100–3,455,597); and M. aurantiaca (408,783–447,391). The harvest control regulations proposed are: M. squalida, Cmax = 2.98 t and Lc = 50.33 mm; D. ponderosa, Cmax = 49.67 t and Lc = 103.44 mm; and M. aurantiaca, Cmax = 15.87 t and Lc = 80.85 mm. These results are important as reference information for implementing harvest strategies in clam-fishing banks, and as a contribution to the management and sustainable exploitation of fisheries in the region.

TRACE METALS IN TWO WILD POPULATIONS OF THE SQUALID CALLISTA CLAM (Megapitaria squalida) IN THE SOUTHEASTERN GULF OF CALIFORNIA, MEXICO

The squalid callista clam (Megapitaria squalida) is a popular raw seafood item for human consumption; however, as a filter feeder, this clam accumulates heavy metals from natural and anthropogenic sources. The concentrations of copper (Cu), cadmium (Cd), chromium (Cr), nickel (Ni), lead (Pb), zinc (Zn), arsenic (As), and mercury (Hg) in sediments and the soft tissues of M. squalida from two sites on the southeastern coast of the Gulf of California, Mexico, were evaluated from April 2016 to April 2017 on a monthly basis. The metal concentrations in sediments from both sites did not exceed the Mexican and international regulations. Concentrations of Cd and Pb in the clams from Altata bay (2.49 and 5.68 µg/g dw, respectively) and Agiabampo bay (2.38 and 5.54 µg/g dw, respectively) exceeded the permissible limits recommended by Mexican sanitary regulations, thus representing a threat to human health. The higher values of Cd, As, and Hg obtained for the biota sediment accumulation factor in both sampling areas indicate that squalid callista is a strong accumulator of these metals. The metal burdens in sediments and M. squalida soft tissues are influenced by chemicals from agriculture and aquaculture, as well as urban sewage disposal near both sites. This study brings useful information on metal bioaccumulation in one of the most important commercial clam species on the Pacific coast.

The Role of Temperature on the Impact of Remediated Water towards Marine Organisms

Marine organisms are frequently exposed to pollutants, including trace metals, derived from natural and anthropogenic activities. In order to prevent environmental pollution, different approaches have been applied to remove pollutants from waste water and avoid their discharge into aquatic systems. However, organisms in their natural aquatic environments are also exposed to physico-chemical changes derived from climate change-related factors, including temperature increase. According to recent studies, warming has a negative impact on marine wildlife, with known effects on organisms physiological and biochemical performance. Recently, a material based on graphene oxide (GO) functionalized with polyethyleneimine (PEI) proved to be effective in the remediation of mercury (Hg) contaminated water. Nevertheless, no information is available on the toxic impacts of such remediated water towards aquatic systems, neither under actual nor predicted temperature conditions. For this, the present study assessed the toxicity of seawater, previously contaminated with Hg and remediated by GO-PEI, using the clam species Ruditapes philippinarum exposed to actual and a predicted temperature conditions. The results obtained demonstrated that seawater contaminated with Hg and/or Hg+GO-PEI induced higher toxicity in clams exposed to 17 and 22 °C compared to organisms exposed to remediated seawater at the same temperatures. Moreover, similar histological and biochemical results were observed between organisms exposed to control and remediated seawater, independently of the temperatures (17 and 21 °C), highlighting the potential use of GO-PEI to remediate Hg from seawater without significant toxicity issues to the selected marine species.

Effects of Waterborne Cadmium Exposure on Its Internal Distribution in Meretrix meretrix and Detoxification by Metallothionein and Antioxidant Enzymes

Cadmium (Cd), one of the most toxic metals found in inshore sediments of China, is a persistent environmental contaminant capable of exerting irreversible toxic effect on aquatic organisms and their associated ecosystems. Although Cd is known to be toxic to marine animals, the underlying mechanism of this toxicity is not clear. In this study, Meretrix meretrix, a commercially and ecologically important species of clam, was exposed to different concentrations of cadmium chloride (0, 1.5, 3, 6, 12 mg L-1) for 5 days, and the levels of Cd accumulation, antioxidant enzyme activity and expression of metallothionein (MT) in the hepatopancreas, gill, foot and mantle were evaluated. The results revealed a sharp increase in Cd accumulation in the tissues in response to increased Cd2+ concentrations in the water, and significant differences in Cd accumulation were observed among the different tissues. Increased Cd2+ level in the tissues also led to a significant increase in malonaldehyde (MDA) content, caused by increased lipid peroxidation. The activities of superoxide dismutase (SOD) and catalase (CAT) also increased, peaking at different Cd2+ concentrations, depending on the tissue. Glutathione peroxidases (GPx) activity in the gill and mantle initially increased, but then decreased with increasing external Cd2+ concentration. In the hepatopancreas and foot, GPx activity was inhibited by Cd2+, even at low concentrations. Furthermore, Cd2+ also stimulated the expression of MT in all four tissues. However, the levels of reduced glutathione (GSH) andoxidized glutathione (GSSG) in the gill and mantle, as well as the GSH/GSSG ratios in all four tissues decreased with increasing external Cd2+ concentrations. Taken together, the results suggested that in M. meretrix, response to the toxic effect of Cd2+ might occur through a combination of mechanisms, which involve both enhanced antioxidant enzyme activities and the ability to bind and sequester Cd2+ via cysteine-rich molecules such as GSH and MT, both of which would eventually lead to the reduction of heavy metal-induced oxidative stress.

The morphological variance Polymesoda erosa and Polymesoda expansa (Mollusc; Corbiculidae) in the Laguna Segara Anakan, Cilacap, Indonesia

There are two species of mangrove clam (Polymesoda erosa and Polymesoda expansa) belong to family Corbiculidae). Morphological variance between Polymesoda erosa and Polymesoda expansa is important to study detail in order to make understand taxonomy study of family Corbiculidae. The research purpose is to study detail abaut the morphological of Polymesoda erosa and Polymesoda expansa . Randomly sampling was used to get samples of mangrove clam. There are three sites of sampling to take mangrove clam such as Panikel, Klaces and Ujung Alang. According to the research sampling, Polymesoda erosa from Panikel, Klaces and Ujung alang has same ratio value between LCT/SL is 0.16 ± 0.035. Whereas, for P. expansa has value LCT/SL 0.14 ± 0.025. Furthermore, P. erosa has value VPM/SL 0.32 for three location (Panikel, Klaces, and Ujung Alang ). The value of VPM/SL for P. expansa is 0.30 ± 0.02 for three location (Panikel and Ujung Alang). . In conclusion, different species of mangrove clam is difference value ratio of LCT/SL and VPM/SL.

Interspecific and Intrashell Stable Isotope Variation Among the Red Sea Giant Clams

AbstractThe Gulf of Aqaba is home to three giant clam species with differing ecological niches and levels of photosymbiotic activity. Giant clams grow a two‐layered shell where the outer layer is precipitated in close association with photosymbiont‐bearing siphonal mantle, and the inner layer is grown in association with the light‐starved inner mantle. We collected 39 shells of the three species (the cosmopolitan Tridacna maxima and T. squamosa, as well as the rare endemic T. squamosina) and measured carbon and oxygen isotope ratios from inner and outer shell layers, to test for differences among species and between the layers of their shells. T. squamosina records higher temperatures of shell formation as determined by oxygen isotope paleothermometry, consistent with its status as an obligately shallow‐dwelling species. However, the known negative fractionation imparted on tissue carbon isotopes by photosymbiotic algae did not produce measurable offsets in the carbonate δ13C values of the more symbiotic T. squamosina and T. maxima compared to the more heterotrophic T. squamosa. Across all species, outer shell layers recorded mean growth temperatures 1.8°C higher than corresponding inner layers, which we propose is a function of the high insolation, low albedo microenvironment of the outer mantle, and potentially the activity of the symbionts themselves. Population‐wide isotopic sampling of reef‐dwelling bivalve shells can help constrain the ecological niches of rare taxa and help reconstruct their internal physiology.

High density of Tridacna crocea in Rita Island, Puerto Princesa City, Palawan, Philippines

In spite of being a protected species in the Philippines, the Tridacna crocea or crocus clam, the smallest among eight known giant clam species in the country, is getting rare in most reef areas of Palawan. However, a high density of this species has recently been noted in Rita Island, Ulugan Bay. A total of 44 photos with known dimensions having a total area of 13.26 m2 suitable habitats with clams were analyzed for size structure and density of T. crocea. In total, 215 T. crocea were noted with 84.91 (±25.6) mm average shell length (±sd). The average density (±sd) was 16.22 (±15.75) individual (ind)∙m-2 but the clams had occurred up to 17 individuals in 0.28 m2 or 59.91 ind∙m-2. This high density of T. crocea could be due to suitable environment and the absence of exploitation within the vicinity of the island resort. The importance of other resorts in biodiversity conservation may be investigated.

Fishery management and spatial variation of giant clam stocks: lessons from New Caledonia

Giant clams have been over-exploited throughout their wide geographical range in the Indo-Pacific. Marine reserves could be one tool to potentially safeguard broodstock, but their effect on giant clam abundance and the differential benefits of lagoon reserves compared to barrier reef reserves is still unclear. We assessed abundances of four species of giant clams across 20 barrier reef and 30 lagoon reef sites across 600 km of coastline in New Caledonia using stratified underwater visual censuses. Tridacna maxima was the most common species. T. derasa was significantly more abundant in marine reserves than at sites open to fishing, but there was no effect of marine reserves on total abundance pooled across the four species. T. squamosa was significantly more abundant on barrier reefs, while Hippopus hippopus was found solely on lagoon reefs. National data from fisher logbooks shows a marked reduction in commercial catches of giant clam following implementation of daily catch limits of 5 giant clams per vessel per trip. Despite small daily bag limits of 2 giant clams per recreational fisher per trip, the recreational catch appears to be significant and much greater than the commercial catch. The utility of marine reserves on giant clams appears to be species specific, and might be diminished for the group as a whole by the concomitant protection of their natural predators. Both lagoon and barrier reef sites should be included in reserve networks. Our data suggest that daily boat/trip limits are an effective output control, at least for commercial fishers, but might not safeguard giant clams if recreational fishers are numerous. Further fishery restrictions on the less common species might be needed to ensure their persistence in the Indo-Pacific.

Two evolutionary units on the South American razor clam Ensis macha (Bivalvia: Pharidae): genetic and morphometric evidence

The patterns of genetic and phenotypic diversity in marine life are the result of different geological and ecological processes. We analyzed the pattern of genetic and morphometric variation of the razor clam Ensis macha along its entire geographic distribution. This species is one of the most important shellfish resources of South America. To uncover the genetic variation across this species, we used sequences of the COI mitochondrial gene and of 856 nuclear orthologs. To describe morphological variation in the shape of the shell, we used elliptic Fourier analysis followed by multivariate statistics. Two main genetic lineages were found, designated as Northern and Southern clades. This genetic distinction is concordant with a biogeographic transition along the Pacific coast of Southern South America, which is also known for other taxa. Based on the genetic distance between the two lineages, each lineage can be considered an incipient species. Morphological approaches revealed similar results, though there was no strict concordance between the morphometric and the genetic results. Geological history and ecological processes could both be responsible for the variation across the range of E. macha. In particular, fragmentation and isolation between populations may have favored genetic diversification, while the environment may have molded the variation shell shape. Lastly, our results have important implications for fisheries management, to preserve biological diversity of the world’s southernmost razor clam species.

Hatchery culture of European clam species (family Veneridae)

Aquaculture and capture production of clam species have great economic value in Europe. The production is dominated by the introduced species, Manila clam, Ruditapes philippinarum, which has displaced some of the native species of clams. In Europe, landings of autochthonous clams have decreased in the recent years due to overfishing, failure in recruitment, abiotic stress and diseases. Due to aforementioned factors, seed production in hatcheries has become essential to ensure the sustainability of the fisheries and aquaculture production of European native clams. Many studies have focused on the different steps involved in hatchery rearing, but the volume of seed of native species produced in commercial hatcheries is still relatively low in comparison to the exotic Manila clam. Presently, in European hatcheries, seeds from only two native species, Ruditapes decussatus and Venerupis corrugata, are produced at industrial scale. The present review analyses the state of hatchery culture of European native clam species, and the aims are to transfer information to the industry and identify critical gaps that might be impeding the development of hatchery production.

Metabarcoding reveals distinct microbiotypes in the giant clam Tridacna maxima

BackgroundGiant clams and scleractinian (reef-building) corals are keystone species of coral reef ecosystems. The basis of their ecological success is a complex and fine-tuned symbiotic relationship with microbes. While the effect of environmental change on the composition of the coral microbiome has been heavily studied, we know very little about the composition and sensitivity of the microbiome associated with clams. Here, we explore the influence of increasing temperature on the microbial community (bacteria and dinoflagellates from the family Symbiodiniaceae) harbored by giant clams, maintained either in isolation or exposed to other reef species. We created artificial benthic assemblages using two coral species (Pocillopora damicornis and Acropora cytherea) and one giant clam species (Tridacna maxima) and studied the microbial community in the latter using metagenomics.ResultsOur results led to three major conclusions. First, the health status of giant clams depended on the composition of the benthic species assemblages. Second, we discovered distinct microbiotypes in the studied T. maxima population, one of which was disproportionately dominated by Vibrionaceae and directly linked to clam mortality. Third, neither the increase in water temperature nor the composition of the benthic assemblage had a significant effect on the composition of the Symbiodiniaceae and bacterial communities of T. maxima.ConclusionsAltogether, our results suggest that at least three microbiotypes naturally exist in the studied clam populations, regardless of water temperature. These microbiotypes plausibly provide similar functions to the clam host via alternate molecular pathways as well as microbiotype-specific functions. This redundancy in functions among microbiotypes together with their specificities provides hope that giant clam populations can tolerate some levels of environmental variation such as increased temperature. Importantly, the composition of the benthic assemblage could make clams susceptible to infections by Vibrionaceae, especially when water temperature increases.Dmya7RRvZemunHrBwHskoDVideo abstract.

Cytotoxicity of New Zealand surf clam extracts against hormone sensitive cancer cell lines

The cytotoxicity of three species of New Zealand (NZ) surf clam extracts was investigated in three hormonal cancer cell lines. Four extracts from each clam species were used: water, ethanol, petroleum ether (pe), and ethyl acetate (ea). The last three of these extracts significantly induced apoptosis via caspase cascades and cell cycle arrest. This was observed, for example, in the percentages of early apoptotic cells in Storm shell extracts with PC-3, MCF-7, and SiHa, with 30, 31, and 35%, respectively, at 400 μg∙ml-1. Cells incubated for 72 h led to the induction of arrest in the S- and G2-M phases. Previous analysis showed that pe and ea extracts from NZ clams were rich in lipids, and current indications based on fractional efficacy, pointed to a lipid soluble bioactive compound. This study provided a basis for further development of NZ clam extracts for treatment, or as a supplement, for positively affecting prostate, breast, and cervical cancers.

Biochemical and physiological responses of two clam species to Triclosan combined with climate change scenario

Ocean acidification and warming are among the man-induced factors that most likely impact aquatic wildlife worldwide. Besides effects caused by temperature rise and lowered pH conditions, chemicals of current use can also adversely affect aquatic organisms. Both climate change and emerging pollutants, including toxic impacts in marine invertebrates, have been investigated in recent years. However, less information is available on the combined effects of these physical and chemical stressors that, in nature, occur simultaneously. Thus, this study contrasts the effects caused by the antimicrobial agent and plastic additive, Triclosan (TCS) in the related clams Ruditapes philippinarum (invasive) and Ruditapes decussatus (native) and evaluates if the impacts are influenced by combined temperature and pH modifications. Organisms were acclimated for 30 days at two conditions (control: 17 °C; pH 8.1 and climate change scenario: 21 °C, pH 7.7) in the absence of the drug (experimental period I) followed by a 7 days exposure under the same water physical parameters but either in absence (unexposed) or presence of TCS at 1 μg/L (experimental period II). Biochemical responses covering metabolic, oxidative defences and damage-related biomarkers were contrasted in clams at the end of experimental period II. The overall picture showed a well-marked antioxidant activation and higher TCS bioaccumulation of the drug under the forecasted climate scenario despite a reduction on respiration rate and unaltered metabolism in the exposed clams. Since clams are highly consumed shellfish, the consequences for higher tissue bioaccumulation of anthropogenic chemicals to final consumers should be alerted not only at present conditions but more significantly under predicted climatic conditions for humans but also for other components of the marine trophic chain.

A new pill clam from an unusual habitat: the interstitial Pisidium interstitialis n. sp. (Bivalvia: Sphaeriidae) from southwestern and Central Germany

AbstractA new species of pill clam, Pisidium interstitialis n. sp. (Bivalvia: Sphaeriidae), is described from wet meadows bordering a small creek in the Odenwald, southwestern Germany, and from a similar habitat in the Thuringian Schistic Mountains, Central Germany. It can be differentiated from the known European Pisidium species on the basis of shell morphology and DNA sequence data for the mitochondrial cytochrome c oxidase subunit I and 16S rRNA genes. Despite critical evaluation of a large number of potential names from the current synonymies of morphologically similar Pisidium species, no available name was found. Pisidium interstitialis n. sp. is most similar to P. personatum Malm, 1856, and P. casertanum (Poli, 1791), both of which occur syntopically with the new species. Typical specimens of the new species can be readily identified on the basis of shell morphology. However, P. personatum and P. casertanum are morphologically highly variable, so that occasional overlap in conchological characters between these two species and P. interstitialis n. sp. does occur. Although these three taxa co-occur, microhabitat analyses using a special sampling technique showed that P. interstitialis n. sp. exhibits an exclusively interstitial lifestyle, living outside open water bodies. While other Pisidium species may live in the interstitial water of semi-terrestrial habitats, this is the first time that an exclusively interstitial lifestyle has been observed for Pisidium and this may explain why P. interstitialis n. sp. has remained undiscovered for so long. To date, despite the examination of large quantities of Central European samples of Pisidium, the new species is only known from the two areas reported in our study. It seems likely that further surveys will show that P. interstitialis n. sp. has a wider and more continuous distribution.

Extensive cryptic diversity of giant clams (Cardiidae: Tridacninae) revealed by DNA-sequence-based species delimitation approaches with new data from Hainan Island, South China Sea

AbstractAccurate species delimitation is important, especially for endangered species. As one of the most conspicuous bivalve taxa, giant clams are threatened throughout their geographic range. Many phylogeographic studies have revealed strong population structure among giant clams in the Indo-Pacific, suggesting cryptic diversity within these species. However, less attention has been paid to their identification and delimitation. In this study, we assembled a comprehensive dataset of mitochondrial cytochrome c oxidase subunit I (COI) sequences for Tridacna species, focusing on new sequences from Hainan Island in the South China Sea and previously published ones from Japan, Taiwan, Singapore, the Philippines, Indonesia, Australia, the Solomon Islands and the Red Sea. Three nominal species, Tridacna crocea, T. squamosa and T. noae, were recognized at Hainan Island on the basis of distance-based DNA barcoding, with mean interspecific K2P distances of 10.6–24.7% for seven Tridacna species (T. crocea, T. squamosa, T. noae, T. maxima, T. mbalavuana, T. derasa and T. gigas). The most abundant species, T. noae, represents the first record of this species from Hainan Island. Using a combination of phylogenetic and DNA-based species delimitation analyses (automatic barcode gap discovery, generalized mixed Yule coalescent and Bayesian Poisson tree processes), we found strong support for a total of 13 operational taxonomic units (OTUs) for the seven nominal Tridacna species. These results, coupled with the fact that each OTU occupies different regions in the Indo-Pacific, strongly suggest multiple cryptic species of giant clams. Our findings point to the need for taxonomic revisionary work on giant clams throughout the Indo-Pacific; such work will have important conservation implications.