Early Cambrian Mollusc Watsonella crosbyi:A Potential GSSP Index Fossil for the Base of the Cambrian Stage 2

The mollusc Watsonella crosbyi was studied on the basis of material from the lower Cambrian Dahai Member of the Zhujiaqing Formation in eastern Yunnan, China and the Pestrotsvet Formation of the Aldan River region in the Siberian Platform. This fossil had been excessively described under different names in the literature, such as Heraultia varensalensis Cobboid, 1935, H. sibirica Missarzhevsky, 1974, Heraultipegma yunnanensis He and Yang, 1982, H. yannanese He and Yang,1982, Watsonella yunnanensis, W. crosbyi Grabau, 1900, etc. Taxonomic revision shows that other species are junior synonyms of W. crosbyi. Analysis of functional morphology implies that W. crosbyi may be rather a heicionelloid than a rostroconch since its univalved conch is untorted endogastric and lacks a rostrum and a true internal pegma. Replicas of the original microstrnctures preserved on the surfaces of phosphatic internal moulds confirm that the shell consists of two layers. The inner layer is lamello-fibrillar, and the outer layer is spherulitic prismatic. The widespread geographical occurrences in both siliciclastic and carbonate rocks of the late Terreneuvian indicate that W. crosbyi is an important index fossil for global correlations and subdivision of the Cambrian Series I （Terreneuvian）.The first appearance datum （FAD） of W. crosbyi is suggested to be a potential GSSP （Global Boundary Stratotype Section and Point） candidate marker for defining the base of the Cambrian Stage 2.

The study of the adductor muscle-shell interface structure in three Mollusc species

The adductor muscle scar（AMS） is the fixation point of adductor muscle to the shell. It is an important organicinorganic interface and stress distribution area. Despite recent advances, our understanding of the structure and composition of the AMS remain limited. Here, we report study on the AMS of three bivalves： Mytilus coruscus,Chlamys farreri and Ruditapes philippinarum. Results showed that there were significant differences among their AMS structures. Both M. coruscus and C. farreri were found to have a columnar layer above the nacreous platelet shell structure at the AMS and this layer was more organized in M. coruscus. There was no distinguishable twolayer structure in R. philippinarum. Atomic force microscopy（AFM） and Fourier transform infrared spectroscopy（FT-IR） results showed that the AMS was much smoother than the nacreous inner shell in all the three species and the AMS had minor different compositions from the nacreous shell layer. SDS-PAGE（sodium dodecyl-sulfate polyacrylamide gel electophoresis） study of the proteins isolated from the interface indicated that there was a 70 k Da protein which seemed to be specifically located to the highly organized columnar AMS structure in Mytilus coruscus. Further analysis of this protein showed it contained high level of Asx（Asp＋Asn）, Glx（Glu＋Gln） and Gly.The special structure and composition of the AMS might play important roles in the stability, adhesion and function at this stress distribution site.

Genome-Wide Scan for Positively Selected Genes in Sessile Molluscs Highlights the Genetic Basis for Their Adaptation to Attached Lifestyle

Molluscs are one of the most diverse groups of animals and exhibit a rich and diverse variety of form and lifestyle. Most molluscs live with a free-moving lifestyle, while some molluscs are sessile. The adaptation to the two distinct lifestyles required complex changes, from molecules to organs, and physiology to morphology. In this study, we conducted a genome-wide scan for positive selection by comparing the available genomes of two sessile molluscs with four free-moving molluscs. A total of 40 genes were identified undergoing positive selection in the sessile molluscs by the branch-site model. Functional characterization showed that they were mainly enriched in two pathways, Oxidative phosphorylation(OXPHOS) and TGF-beta signaling pathway. The unexpected positive selection on OXPHOS genes in sessile molluscs suggests that the adaptation of OXPHOS involves many factors beyond enhancing ATP production. A modified OXPHOS regulatory system may allow sessile molluscs to better cope with biotic and abiotic stresses. Moreover, positively selected genes in TGF-beta signaling pathway probably have played a key role in the patterning of body plans and growth in metazoans. We speculate that these genes are associated with the body structure and organic adaptation to a sedentary lifestyle in sessile bivalve molluscs.

The importance of terrestrial carbon in supporting molluscs in the wetlands of Poyang Lake

Allochthonous organic matter plays an important role in nutrient cycling and energy mobilization in freshwater ecosystems. However, the subsidies of this carbon source in floodplain ecosystems have not yet well understood. We used a Bayesian mixing model and stable isotopes （613C and 815N） of primary food resources and dominant molluscs species, to estimate the relative importance of allochthonous carbon sources for consumers in a representative sub-lake of Poyang Lake during a prolonged dry season. Our study inferred that terrestrial-derived carbon from Carex spp. could be the primary contributor to snails and mussels in Dahuchi Lake. The mean percentage of allochthonous food resources accounted for 35%- 50% of the C incorporated by these consumers. Seston was another important energy sources for benthic consumers. However, during the winter and low water-level period, benthic algae and submerged vegetation contributed less carbon to benthic consumers. Our data highlighted the importance of terrestrial organic carbon to benthic consumers in the wetlands of Poyang Lake during the prolonged dry period. Further, our results provided a perspective that linkages between terrestrial and aquatic ecosystems might be facilitated by wintering geese via their droppings.

Genome-Wide Analysis of the Cyclin-Dependent Kinases(CDK)and Cyclin Family in Molluscs

Cell cycle regulation that plays a pivotal role during organism growth and development is primarily driven by cyclindependent kinases(CDKs)and Cyclins.Although CDK and Cyclin genes have been characterized in some animals,the studies of CDK and Cyclin families in molluscs,the ancient bilaterian groups with high morphological diversity,is still in its infancy.In this study,we identified and characterized 95 CDK genes and 114 Cyclin genes in seven representative species of molluscs,including Octopus bimaculoides,Pomacea canaliculata,Biomphalaria glabrata,Lottia gigantea,Mizuhopecten yessoensis,Crassostrea gigas and Aplysia californica.Genes in CDK and Cyclin families were grouped into eight and 15 subfamilies by phylogenetic analysis,respectively.It should be noted that duplication of CDK9 gene was detected in P.canaliculate,L.gigantea and M.yessoensis genomes,which has never been recorded in animals.It is speculated that duplication may be the main course of expansion of the CDK9 subfamily in the three molluscs,which also sheds new light on the function of CDK9.In addition,Cyclin B is the largest subfamily among the Cyclin family in the seven molluscs,with the average of three genes.Our findings are helpful in better understanding CDK and Cyclin function and evolution in molluscs.

The Clam Cyclina sinensis (Gmelin) Phylogeography Study with 28S rRNA Gene and Potential of Nuclear rRNA Genes in Genetic Assessments of Molluscs

Intraspecific diversity of molluscan species is usually studied based on maternally inherited mitochondrial DNA,from which only part of the evolutionary history can be reflected.Some nuclear ribosomal RNA genes such as 28S rRNA represent poten-tial candidates that can be easily applied in phylogeography because of lacking intraindividual variation.However,considering their low polymorphism,genetic appraisals on whether and how they can be used in population studies are necessary.Here,we applied a short 28S rRNA to assess genetic patterns of the clam Cyclina sinensis along the coast of China and compared the results with a for-mer study based on COI and ITS-1 analyses.The results revealed the 28S rRNA data set was characterized by an extremely low level of variation,with only seven haplotypes defined for 93 individuals.Haplotype and nucleotide diversity for each population was al-most the lowest when compared with the other two markers.However,the distribution of two dominant haplotypes showed clear geo-graphic patterns,and significant population differentiation was revealed between the East China Sea and the South China Sea.These patterns were highly concordant with findings of the former study that populations of C.sinensis were historically separated by land bridges among sea basins.Our study suggested that although the nuclear rRNAs have shortcomings such as low variation,they have advantages including lack of intraindividual variation and high amplification rates.Applying rRNA genes can enrich the toolbox of nuclear markers in molluscan phylogeographic studies.

The Bivalve Mollusc <i>Abra ovata</i>: Role in Succession of Soft Bottom Communities on Newly Flooded Area of the Caspian Sea

The succession of an Abra ovata community that had formed at the flooded area in Sulaksky Bay (the Caspian Sea) since the mid-1980s was investigated. The resident species Abra ovata and Cerastoderma glaucum, the pioneer settlers, were found remaining dominant in the community structure and driving the course of its succession, despite some decrease in settlement density and in the rate of occurrence. It was the tolerance of the Sulaksky pioneer settlers for later colonists (macrophytes, mytilids, crustaceans and other organisms) that determined the development of the first succession stage. The next succession stage in Abra ovata communities of Sulaksky Bay does not quite agree with the pattern typical of solid substrates. On the one hand, the community development supports the tolerance model: the pioneer Abra, in spite of being dominant through all the succession stages, does not oppose the settling of other multiple colonists;on the other hand, it agrees with a facilitation model where the abundance of the original settlers, the grazing species, provokes appearance of sturgeon.

Dynamic of Mangrove Associated Molluscs in Anthropized Areas of the Cameroon Coastline

Due to unabated anthropogenic exploitations, mangrove forests globally are constantly under pressure and degradation, which may result in the reduction of ecosystem functioning and biodiversity. Molluscan fauna, which is one of the main macroinvertebrates that play a major ecological role in nutrient dynamics in mangroves, are sensitive to the changes in their habitat. This survey aims to assess the impact of anthropogenic activities on the diversity of molluscs’ communities in the mangrove forest. Anthropogenic disturbances within 20 sampling sites were valued at six mangrove stands and patched scoring the degree of influence according to vegetation, structure, waste and trampling. Molluscs were caught by hand and counted within 1 × 1 m2 plots placed at three points distant of 50 m established using a straight line transect of 100 m. Upon the 20 sites investigated, five were slightly disturbed, eight moderately disturbed and seven sites were highly disturbed. The mean abundance of molluscs decreased from slightly disturbed areas (172.25 ± 73.09 Ind·m−2) to highly disturbed areas (100.57 ± 62.84 Ind·m−2). Highly disturbed areas have shown lower species richness (R = 1.09 ± 0.15) and diversity (H’ = 2.30 ± 0.31). Human activities in the mangrove forest could particularly have effects on the diversity of molluscs, however, feature potential conservation measures have to be in harmony with the needs of the local population.

The Impact of Pollution on the Bouregreg Estuary （Morocco, Atlantic Ocean）： The Molluscs as an Indicator of Metal Contamination

On the Morrocan Atlantic coast, the estuary of the Bouregreg was submitted to many anthropic effects. After the dam Sidi Mohammed ben Abdellah was built in 1974, the flow became almost null. The waters of the estuary are meant for recreational activities, fishing, but at the same time they receive water collecting domestic and industrial wastewater. The waste in old landfills was not treated and leaked into the river water. The matter gets worse with the action of tides which make it difficult to escape the pollution load （physicochemical, bacteriological, heavy metals, etc.）. The concentrations of heavy metals （Pb, Fe, Cu and Cr） recorded in the sediments are higher than those found in the two molluscs. However, we have found out that Mytilus has accumulated more heavy metals （Cr, Pb and Zn） than Solen marginatus. The Zn makes an exception： It presents a greater concentration in the molluscs （63.015 mg/kg dry weight for Mytilus and 232.736 mg/kg dry weigh for Solen） than in the sediments （57.639 mg/kg）. The amount of these metals exceeds the standard values. The impact of the marine pollution on human health derives from the consumption by humans of heavy-metal polluted molluscs. The detected concentrations of these pollutants are superior to the permissible maximum amounts.

Production of Filler Aggregate from Waste of Bivalves Molluscs Shells

The work presents an experimental study held with shells of molluscs of the species Anomalocardia brasiliana and Tivela mactroides, commonly found in the Northeast coast of Brazil. A local community living from the collection of these animals was the motivation of the work. This community wishes to install an industry for processing these molluscs; however, as government agencies require making an appropriate allocation of discarded shells, the community needs an environmental project of final destination of waste. Thus, the expectation of the work was to obtain a material to be added to Portland cement to act as filler, and also obtain a limestone that can be used as ink, because the material is composed of 80% calcium carbonate. The shells were ground and passed the sieve 325 mesh （0.044 mm）. The material was characterized by X-ray diffraction and X-ray fluorescence. Mortars specimens were prepared with percentages： 0%, 5%, 10%, 15%, 20% and 30% replacement of Portland cement. Two conditions were analyzed： with shells in a raw and burned state. The obtained results confirm the filler material effect, which suggests its use as a partial replacement of cement. However, due to the short silicas＇s concentration, the pozzolanic effect was not observed.

Petroleum hydrocarbon concentrations in eight mollusc species along Tamilnadu coast, Bay of Bengal, India

Eight mollusc species and sediment samples collected from three different stations along Tamilnadu coast, Bay of Bengal, India were analysed for the levels of petroleum hydrocarbons to elucidate the status of the petroleum residues in mollusc meant for human consumption. The concentrations of petroleum hydrocarbons in sediments along Tamilnadu coast varied from 5.04–25.5 μg/g dw （dry weight）. High concentration of petroleum hydrocarbons in the sediment of Uppanar estuary （25.5 ± 1.45 μg/g dw） was perhaps land and marine based anthropogenic sources of this region. The petroleum hydrocarbon residues in eight mollusc species collected from Uppanar, Vellar and Coleroon estuaries varied between 2.44–6.04 μg/g ww （wet weight）. Although the concentration of petroleum hydrocarbons in sediment of the Uppanar region was markedly higher than the background, the petroleum hydrocarbon residues in mollusc collected from Uppanar estuary did not suggest bioaccumulation. The results signified that industrial growth has affected the aquatic environments and regular monitoring will help to adopt stringent pollution control measures for better management of the aquatic region.

Molecular Characterization of the Calvin Cycle Enzyme Phosphoribulokinase in the Stramenopile Alga Vaucheria litorea and the Plastid Hosting Mollusc Elysia chlorotica

Phosphoribulokinase （PRK）, a nuclear-encoded plastid-localized enzyme unique to the photosynthetic carbon reduction （Calvin） cycle, was cloned and characterized from the stramenopile alga Vaucheria litorea. This alga is the source of plastids for the mollusc （sea slug） Elysia chlorotica which enable the animal to survive for months solely by photoautotrophic CO2 fixation. The 1633-bp V. litorea prk gene was cloned and the coding region, found to be interrupted by four introns, encodes a 405-amino acid protein. This protein contains the typical bipartite target sequence expected of nuclearencoded proteins that are directed to complex （i.e. four membrane-bound） algal plastids. De novo synthesis of PRK and enzyme activity were detected in E. chlorotica in spite of having been starved of V. litorea for several months. Unlike the algal enzyme, PRK in the sea slug did not exhibit redox regulation. Two copies of partial PRK-encoding genes were isolated from both sea slug and aposymbiotic sea slug egg DNA using PCR. Each copy contains the nucleotide region spanning exon 1 and part of exon 2 of V litorea prk, including the bipartite targeting peptide. However, the larger prk fragment also includes intron 1. The exon and intron sequences of prk in E. chlorotica and V/itorea are nearly identical. These data suggest that PRK is differentially regulated in V. litorea and E. chlorotica and at least a portion of the V. litorea nuclear PRK gene is present in sea slugs that have been starved for several months.

福建漳江口红树林湿地不同生境软体动物调查分析

为了掌握福建漳江口红树林不同生境条件下软体动物的状况,对漳江口红树林国家级自然保护区内的红树林区、光滩区及互花米草区等不同湿地生境的软体动物种类组成、多样性、密度及生物量进行调查分析。结果表明:福建漳江口红树林国家级自然保护区内的红树林区、互花米草区和光滩区共有软体动物10科14种,其中腹足纲6科10种,双壳纲4科4种;红树林区的软体动物群落和多样性最高,其次是光滩区,互花米草区最低。可见红树林及光滩生境对于维持软体动物多样性具有重要作用,而繁密的互花米草对软体动物不利,应该严格控制互花米草的扩散。

浙江沿岸水域软体动物群落结构分析

根据2019年全年4个航次浙江沿岸海域单船底拖网调查资料,分析了4个季节浙江沿岸海域软体动物的种类组成、优势种及资源密度分布,采用生态多样性指数、物种相似性指数(Js)、群落季节更替指数(AI)和迁移指数(MI)、丰度/生物量比较曲线(ABC曲线)分析了群落物种多样性、动态变化及其稳定性。结果表明:浙江沿岸海域全年共捕获软体动物62种,隶属于3纲,10目,32科。腹足纲(螺类)出现种类30种,占软体动物总种类数的48.39%;头足纲(头足类)出现种类19种,占软体动物总种类数的32.63%;双壳纲(贝类)出现种类13种,占软体动物总种类数的20.98%。软体动物群落优势种为长蛸(Octopus variabilis)、剑尖枪乌贼(Loligo edulis)、棒锥螺(Turritella bacillum)、多钩钩腕乌贼(Abralia multihamatai)和双喙耳乌贼(Sepiola birostrata),优势种的季节变化差异较大。浙江沿岸海域软体动物年平均资源密度为204.94 kg/km2,其中夏季平均资源密度为全年最高,冬季最低,资源密度空间分布特征总体上呈现由北向南逐渐增高的趋势。多样性指数(H′)、丰富度指数(D)及均匀度指数(J′)三种群落多样性指数均不高,软体动物群落多样性水平处于较低水平;物种相似性指数(Js)、群落季节更替指数(AI)和迁移指数(MI)分析,春冬季软体动物群落较夏秋季稳定;根据ABC曲线评估干扰对软体动物群落的影响可得:全年4个季节浙江沿岸软体动物群落均处于中等干扰状态。

贝类性别决定与分化相关基因研究进展

性别决定与分化是生命发育的基本事件,性别决定与分化机制一直是生命科学研究的热点问题。贝类具有雌雄同体、雌雄异体、雄性先熟和性转换等复杂的性别类型,是研究无脊椎动物性别决定与分化机制及其演化进程的理想动物类群。挖掘贝类性别决定与分化调控基因,阐明相关基因的调控作用,对于揭示贝类性别决定与分化的分子机制具有重要意义。本文就贝类性别决定与分化相关基因的研究进展进行了综述,并对该研究领域进行展望,以期为贝类的性别决定和分化机制、生殖操作和遗传改良等研究提供参考。

Helcionelloids from the Cambrian Fortunian of the Northern Yangtze Platform,China

A study of the morphological and microstructural characteristics of helcionelloids from the Nanjiang area(north Sichuan,China)at the northern Yangtze Platform was undertaken,in order to understand their phylogenetic position.Helcionelloids fossils from the Kuanchuanpu Formation of the Changtanhe–Maolinzi section include 7 genera and 11 species.There are distinct differences in the degree of shell bending,the apical morphology and apex position,the outline of the aperture and the height of the shell,all of which constitute important identification features.Although helcionelloid apices exhibit varying degrees of rotation towards the aperture,they do not show any signs of evident distortion.A pair of basally-symmetrical muscle scars are discovered on the shells of helcionelloids(such as Bemella simplex),showing a distinct difference when compared with those of the stem-group gastropod(e.g.,Pelagiella).The prismatic shell layer of helcionelloids has been observed,which are common components in Cambrian molluscs,but differ significantly from the dense layer microstructure found in contemporary molluscs.The microstructures,muscle scars and morphological characteristics demonstrate that helcionelloids represent a stem-group of molluscs.

台湾地区新发生重大外来入侵物种——虎纹非洲大蜗牛的检疫鉴定

虎纹非洲大蜗牛Achatina panthera(Férussac,1832)是近年来台湾地区新发生的重大外来入侵物种,对农林生产和人畜健康构成严重威胁,目前中国内地尚无分布。本文厘清了该蜗牛分类历史和系统学地位,通过核对实物标本结合现有文献,重新描述了虎纹非洲大蜗牛的形态特征,并与近似种的主要形态鉴别特征进行了比对。首次测定该蜗牛的COⅠ基因序列,并建立了分子比对鉴定方法。最后提出了相应的检疫风险管理措施,可为有关部门应对虎纹非洲大蜗牛的入侵提供科学依据。

氨氮对软体动物生长的影响:以铜锈环棱螺为例

为探究氨氮对底栖动物的毒性效应,在位于湖北保安湖的近自然生态系统(单个水域面积约600 m^(2),水深约1.5 m)中开展了为期1年的模拟实验,分析了6个不同氨氮浓度[N25>N_(2)0>N15>N10>N5>N0(对照);0.2-33.7 mg/L]条件下,大型底栖动物(软体动物)群落特征的差异。结果表明:(1)实验系统中采集的软体动物主要为铜锈环棱螺(Bellamya aeruginosa);(2)从B.aeruginosa密度来看,N0、N5、N10和N15处理相差不大[28(0-85)ind./m^(2)],均显著高于N_(2)0和N25处理[5(0-29)ind./m^(2)](P<0.05);(3)从B.aeruginosa生物量来看,N0、N5、N10、N15和N_(2)0处理相差不大[40.0(0-85.5)g/m^(2)],均显著高于N25处理[0.8(0-4.0)g/m^(2)](P<0.05);(4)从B.aeruginosa壳长、壳宽和带壳湿重来看,均是N0处理最低,N_(2)0或N25处理最高;(5)B.aeruginosa密度和生物量与水体氨氮含量呈显著负相关(P<0.05),随分子氨浓度的增加而下降;(6)B.aeruginosa壳长、壳宽和带壳湿重均与分子氨呈显著正相关(P<0.05),随分子氨浓度的增加而上升。以上研究表明,当氨氮浓度高于21.7 mg/L、分子氨高于0.18 mg/L(N15处理年均值)后,对软体动物有明显的毒害作用,尤其对生物数量的增加有明显的抑制作用,但未发现对其个体生长产生负面效应。这可能是因为水中氨氮增加后,促进了藻类的生长,使得软体动物的食物更丰富,有利于其碳水化合物的积累和对氨氮的解毒。此外,水-沉积物界面附近的分子氨浓度比水体表层的略低,可能也是生活在水体底部的软体动物能够耐受更高浓度氨氮的原因之一。以上研究结果可完善氨氮对水生生物毒性的理解,为水体氮管理策略的制定提供一定的科学依据。

我国海水养殖贝类病害发生现状及防控策略

贝类养殖是我国水产养殖业的重要组成部分,在促进经济社会发展、提高就业率、改善人民生活及保护生态环境等方面发挥了重要作用,其经济、社会和生态功能日益凸显。近年来,因环境胁迫和病原侵染引发的海水养殖贝类暴发性病害时有发生,所造成的经济损失巨大,严重阻碍了海水养殖产业的绿色高质量发展。贝类缺乏适应性免疫,且主要养殖于开放或半开放水体,难以通过疫苗注射或环境调控等手段进行病害防控。贯彻“绿色防控”的理念,加快病害预警预报体系建设是海水养殖贝类病害防控的重要发展方向。本文综述了我国海水贝类养殖及病害发生的现状,并结合团队前期研究和病害预警预报工作实践,提出了海水养殖贝类病害防控策略,以期提升我国水产动物疫病防控能力,为保障水产品稳定安全供给、促进水产养殖业绿色高质量发展提供参考。

贝类炎症及其发生机制研究进展

贝类在中国海水养殖业中占据重要地位,养殖贝类病害的频发,严重阻碍了贝类养殖业的可持续健康发展。炎症是机体对刺激的一种防御反应,在抵御病原菌感染中发挥重要作用,但过度的炎症反应会造成机体组织损伤,严重时会引发个体死亡。目前,已经在贝类中观察到了炎症现象,并鉴定出多种炎症细胞因子和炎症相关信号通路。本文围绕贝类炎症细胞因子种类与生物学功能、炎症相关信号通路及炎症反应的形态学特征,总结了近年来贝类炎症研究进展,重点阐述了炎症发生的分子机制,并针对研究中存在的问题,提出不同类型炎症细胞因子的挖掘、炎症细胞因子的免疫学功能及其与不同类型免疫细胞之间的关系等是该领域未来的重点研究方向,以期为推动贝类养殖产业绿色高质量发展提供科学参考。