Fine structure of acrosome biogenesis and of mature sperm in the bivalve molluscs<Emphasis Type="Italic"> Glycymeris</Emphasis> sp. (Pteriomorphia) and<Emphasis Type="Italic"> Eurhomalea rufa</Emphasis> (Heterodonta)

Proacrosomal vesicles form during the pachytene stage, being synthetized by the Golgi complex in Glycymeris sp., and by both the Golgi and the rough endoplasmic reticulum in Eurhomalea rufa. During early spermiogenesis, a single acrosomal vesicle forms and its apex becomes linked to the plasma membrane while it migrates. In Glycymeris sp., the acrosomal vesicle then turns cap-shaped (1.8 μm) and acquires a complex substructure. In E. rufa, proacrosomal vesicles differentiate their contents while still at the premeiotic stage; as the acrosomal vesicle matures and its contents further differentiate, it elongates and becomes longer than the nucleus (3.2 μm), while the subacrosomal space develops a perforatorium. Before condensation, chromatin turns fibrillar in Glycymeris sp., whereas it acquires a cordonal pattern in E. rufa. Accordingly, the sperm nucleus of Glycymeris sp. is conical and elongated (8.3 μm), and that of E. rufa is short and ovoid (1.1 μm). In the midpiece (Glycymeris sp.: 1.1 μm; E. rufa: 0.8 μm), both species have four mitochondria encircling two linked orthogonal (Glycymeris sp.) or orthogonal and tilted (30–40°; E. rufa) centrioles. In comparison with other Arcoida species, sperm of Glycymeris sp. appear distinct due to the presence of an elongated nucleus, a highly differentiated acrosome, and four instead of five mitochondria. The same occurs with E. rufa regarding other Veneracea species, with the acrosome of the mature sperm strongly resembling that of the recent Mytilinae. Electronic Publication     

Relationships between broodstock condition,oocyte quality,and 24 h D-larval survival during the spawning season of the pullet carpet shell Venerupis corrugata (Gmelin, 1791)

Abstract

Venerupis corrugata is commercially exploited in Europe. Over-fishing and recruitment failure is causing the decline of its populations and stock sustainability. Knowledge of this species reproduction is paramount to establish hatchery production of juveniles for restoring natural beds. This work aimed to find a relationship between broodstock condition, oocyte quality, and viability of 24 h D-larvae. Adult specimens were induced to spawn by thermal stimulation. From each female, oocytes were taken for biochemical analyses (proteins, total lipids, and carbohydrates), and the remaining oocytes were fertilized. The 24 h D-larval yield was calculated after embryo incubation. Spawning in the hatchery with ‘wild’ broodstock was possible for a long period, however, subsequent larval viability varied according to oocyte quality. Two distinct periods of spawning were recorded: in January/March, with a higher number of oocytes released, and in June/July with a lower response to the spawning stimulation, however with greater success in 24 h D-larval survival. The condition index of broodstock and the total lipids of oocytes released can be used as benchmarks for estimating the success of D veliger larvae.     

<Emphasis Type="Italic">Pearl</Emphasis>, a Novel Family of Putative Transposable Elements in Bivalve Mollusks

Abstract While genome sequencing projects have discovered numerous types of transposable elements in diverse eukaryotes, there are many taxa of ecological and evolutionary significance that have received little attention, such as the molluscan class Bivalvia. Examination of a 0.7-MB genomic sequence database from the cupped oyster Crassostrea virginica revealed the presence of a common interspersed element, CvA. CvA possesses subterminal inverted repeats, a tandemly repeated core element, a tetranucleotide microsatellite region, and the ability to form stable secondary structures. Three other less abundant repetitive elements with a similar structure but little sequence similarity were also found in C. virginica. Ana-1, a repetitive element with similar features, was discovered in the blood ark Anadara trapezia by probing a genomic library with a dimeric repeat element contained in intron 2 of a minor globin gene in that species. All of these elements are flanked by the dinucleotide AA, a putative target-site duplication. They exhibit structural similarity to the sea urchin Tsp family and Drosophila SGM insertion sequences; in addition, they possess regions of sequence similarity to satellite DNA from several bivalve species. We suggest that the Crassostrea repetitive elements and Ana-1 are members of a new MITE-like family of nonautonomous transposable elements, named pearl. Pearl is the first putative nonautonomous DNA transposon to be identified in the phylum Mollusca.     

Molluscan fauna of Gueishan Island,Taiwan

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/).     

Environmental variability at the phosphoglucose isomerase locus in the genus Chlamys

Two geographically and reproductively isolated populations each of Chlamys opercularis and of Chlamys varia are compared with respect to polymorphism at the phosphoglucose isomerase (PGI) locus. One population of C. varia is further sub-divided into sub-littoral and inter-tidal samples. From the results it is inferred that PGI is a dimeric molecule, controlled by five alleles in C. varia and by at least four alleles in C. opercularis. acting at a single locus. The alleles recognised for C. opercularis have identical electrophoretic mobility as four of those seen in C. varia. The two populations of C. varia are remarkably similar, as were their habitats. However, the sub-littoral sample does show a lesser degree of homozygosity than the inter-tidal sample of the same population. The two populations of C. opercularis differ significantly and represent two separate and identifiable ‘races’. C. varia exhibits a much greater degree of genetic variability than the deep sub-littoral species, C. opercularis indicating that a more stable environment regulates a more monomorphic species.     

Un nouveau Cycloconchide (Mollusca Bivalvia) du Llanvirn inférieur (Ordovicien) des Monts de Tolède (Espagne)

A new Cycloconchid, designated Ananterodontaoretanica, has been collected from the Lower Llanvirn (Montes de Toledo). The only known specimen is described and compared with several genera of Ordovician Cycloconchids, the validity of which is briefly discussed.     

Taphofacies analysis of recent shelly cheniers (beach ridges), northeastern baja california,Mexico

Summary This report presents the results of taphofacies analyses of shelly cheniers (mollusk-dominated lag-concentrations) from the tidal flats of northeastern Baja California, Mexico. The three generations of moderm (formed during last 70 years), submodem (younger than 1,500 BP), and subfossil (5,000–2,000 BP) cheniers can be distinguished by their position relative to the shoreline, their topography, and the radiocarbon-age of their shells. The generations differ in the duration and complexity of their taphonomic history. Sixty-one samples from nine localities were collected to test the utility of the taphofacies approach for studying chenier-type shell deposits. The three chenier generations, although all dominated by the bivalve molluskMulinia coloradoensis, differ significantly in their taxonomic composition due to taphonomic and/or biologic factors. The taphofacies analysis included 4,334 specimens ofM. coloradoensis described by nine taphonomic variables. Univariate analysis of those variables indicated that the shells that accumulated in the cheniers are little-affected by biological processes (bioerosion, encrustation), and moderately affected by physical processes (fragmetation, cracking, peeling, edge preservation). Only the luster features of shells (external luster, internal luster, and internal features) vary substantially and consistently with chenier age —a result of subaerial weathering. Multivariate taphofacies analysis discriminates the three generations of cheniers even when the poorly preservable luster variables are excluded from the analysis. This suggests that taphofacies discrimination is possible for fossil cheniers. The shells collected from the chenier surface have substantially poorer preservation than shells from the subsurface, indicating that taphonomic degradation in the chenier plain environment is a surface phenomenon. Chenier plain shelly assemblages are taphonomically distinct from assemblages formed in other marine environments: they have a very low frequency of macroscopically recognizable bioerosion and encrustation. The existence of preservable taphonomic differences between the cheniers that differ in their age (i.e., duration of preburial history), suggests that fossil lag concentrations may be useful in detecting incompleteness gradients along stratigraphic boundaries. A ‘taphonomic clock’—a correlation between a ‘time-sincedeath’ and shell preservation—was found only for luster features, taphonomic attributes that are unlikely to be preserved in the fossil record.     

广东东海岛与硇洲岛海域底栖贝类物种多样性及其地理分布

海洋底栖贝类是海洋底栖动物区系的重要组分之一, 也是影响海洋生态系统和海洋底质环境的关键类群之一。粤西岸段地处南海北部, 海洋底栖贝类物种丰富, 但却是我国海洋底栖贝类区系调查最为缺乏的区域之一, 严重妨碍了我国近海底栖动物地理区系区划工作的开展。东海岛与硇洲岛海域是粤西岸段中底栖贝类历史研究相对较多的地区, 也是揭示南海北部底栖动物地理格局的关键地区。本文基于中山大学地理科学与规划学院2021-2023年间在东海岛与硇洲岛潮间带及近海海域采集的底栖贝类标本的鉴定, 结合中国科学院南海海洋研究所馆藏标本记录及已发表文献中记载物种的整理, 更新了该海域的底栖贝类名录, 并对各物种在东亚大陆近海的地理分布类型进行了分析。本研究共采集贝类标本2,600余号, 分属73科144属207种, 其中38种为东海岛与硇洲岛海域新记录。结合中国科学院南海海洋研究所馆藏标本及历史文献资料记录的物种, 至本研究为止, 东海岛与硇洲岛海域共记录底栖贝类115科330属602种, 为目前南海北部大陆岸段海洋底栖贝类物种数最多的地区。区系成分上, 热带性暖水种占26.2%; 热带-亚热带性暖水种占49.3%; 余下24.4%为广温性种。地理格局上, 有89.0%的种类在海南岛也有分布记录, 80.2%的种类在北部湾也有分布记录, 粤东岸段有分布记录的种类也占80.2%。研究结果表明, 东海岛与硇洲岛海域的底栖贝类区系十分丰富, 热带性特征明显, 且与海南岛的联系最为密切, 在南海北部近海底栖生物地理区划上可考虑同海南岛划入同一生物地理地区。基于本文结果及近年来的南海北部底栖生物相关研究, 我们推测雷州半岛及琼州海峡对南海北部底栖生物扩散及生物地理格局的影响程度很有可能被高估了。本研究丰富了雷州半岛东侧海域的底栖贝类区系, 为开展整个南海北部的底栖生物地理格局与区系区划工作提供了数据支持。     

Sticky bivalves from the Mesozoic: clues to the origin of the anomalodesmatan arenophilic system

Arenophilic glands represent the only molluscan example of multicellular organs solely concerned with adhesion of foreign particles to the external surfaces of an organism. The glands are exclusive to the bivalve clade Anomalodesmata, but do not occur in all component taxa, having been declared absent in a number of families, including Pholadomyidae. This paper records and describes for the first time the arenophilic apparatus of Pholadomya candida G. B. Sowerby I, 1823, and demonstrates that secretion from these glands is at times preserved in the fossil record. In P. candida , arenophilic glands in the middle mantle folds discharge their products on top of the shell as the animal grows, forming radial lines of secretion that comprise a meandering main strand and numerous thin threads projecting in tufts. The arrangement is similar to that of other families, corroborating the hypothesis that the glands are a synapomorphy of crown-group anomalodesmatans. Instances of preserved secretion in fossil Pholadomya , ranging in age almost to the initial appearance of the genus in the Late Triassic, suggest that fossilized arenophilic secretion may aid systematic studies of problematic fossil groups traditionally included in Anomalodesmata.     

Distribution of Acid Proteinase Activity in Molluscs

Acid proteinases with an optimum around pH 3 were demontrated in various tissues of 12 molluscan species. Enzymes strongly inhibited by pepstatin were predominant and the molecular weights of those from two species were in the region of 38,000–68,000, suggesting that they were cathepsin D-type proteinases.     

广西凤山、西林等地中三叠统上部双壳类分带研究

讨论广西西部中三叠统上部的双壳类生物地层序列,建立5个化石带;并附述黔南和滇东南晚三叠世1个双壳类带.这些带自下而上为:(1) Daonella (Longidaonella) producta-D. americana 带,属晚安尼早中期;(2) D. moussoni 高峰带,属晚安尼晚期;(3) D. rieberi-D. indica 带,属早拉丁期;(4) D. kotoi-D. jilongensis 带,属晚拉丁早期;(5) Halobia subcomata-D. varifurcata带,属晚拉丁晚期;(6) H. rugosoides-H. bifurcata 带,属早卡尼期.文内简要描述了各带的主要标志化石23种.     

Shell Beds as paleoecological puzzles: A case study from the Upper Permian of the Paraná Basin, Brazil

Summary Microstratigraphic, sedimentological, and taphonomic features of the Ferraz Shell Bed, from the Upper Permian (Kazanian-Tatarian?) Corumbataí Formation of Rio Claro Region (the Paraná Basin, Brazil), indicate that the bed consists of four distinct microstratigraphic units. They include, from bottom to top, a lag concentration (Unit 1), a partly reworked storm deposit (Unit 2), a rapidly deposited sandstone unit with three thin horizons recording episodes of reworking (Unit 3), and a shell-rich horizon generated by reworking/winnowing that was subsequently buried by storm-induced obrution deposit (Unit 4). The bioclasts of the Ferraz Shell Bed represent exclusively bivalve mollusks.Pinzonellaillusa andTerraia aequilateralis are the dominant species. Taphonomic analysis indicates that mollusks are heavily time-averaged (except for some parts of Unit 3). Moreover, different species are time-averaged to a different degree (disharmonious time-averaging). The units differ statistically from one another in their taxonomic and ecological composition, in their taphonomic pattern, and in the size-frequency distributions of the two most common species. Other Permian shell beds of the Paraná Basin are simílar to the Ferraz Shell Bed in their faunal composition (they typically contain similar sets of 5 to 10 bivalve species) and in their taphonomic, sedimentologic, and microstratigraphic characteristics. However, rare shell beds that include 2–3 species only and are dominated by articulated shells preserved in life position also occur. Diversity levels in the Permian benthic associations of the Paraná Basin were very low, with the point diversity of 2–3 species and with the within-habitat and basin-wide (alpha and gamma) diversities of 10 species, at most. The Paraná Basin benthic communities may have thus been analogous to low-diversity bivalve-dominated associations of the present-day Baltic Sea. The ‘Ferraz-type’ shell beds of the Paraná Basin represent genetically complex and highly heterogeneous sources of paleontological data. They are cumulative records of spectra of benthic ecosystems time-averaged over long periods of time (10²–10⁴ years judging from actualistic research). Detailed biostratinomic reconstructions of shell beds can not only offer useful insights into their depositional histories, but may also allow paleoecologists to optimize their sampling designs, and consequently, refine paleoecological and paleoenvironmental interpretations.     

Tromelinodonta nov. gen., bivalve lyrodesmatide (Mollusca) de l'Arenigien (Ordovicien inférieur)

A new generic taxon from the Lower Ordovician,Tromelinodonta, is introduced in the family Lyrodesmatidae (Bivalvia). This new genus is based on the species T. armoricana (De Tromelin & Lebesconte, 1876); it has an intermediate dentition between this of Noradonta with lateral posterior crenulated teeth and this of Lyrodesma with a fan-shaped disposition of the cardinal crenulated teeth; its phylogenetic signification is shortly discussed.     

砂质潮间带自由生活海洋线虫对缺氧的响应——微型受控生态系研究

以青岛砂质潮间带自由生活海洋线虫为研究对象,建立微型受控生态系,研究缺氧对海洋线虫群落结构和垂直分布的影响,以及环境复氧后海洋线虫群落的恢复能力。研究结果显示,海洋线虫是耐低氧的小型底栖动物类群,可通过垂直迁移来耐受缺氧造成的不利条件。但是,海洋线虫通过主动迁出而耐受缺氧条件的特性具有种的区别。研究中Pseudosteineria sp1、Rhynchonema sp1等海洋线虫通过向有氧环境的主动迁移耐受缺氧条件;Thalassironus sp1却可通过自身耐受机制抵御缺氧条件,在缺氧生境中仍能保持较高的丰度。此外,研究结果显示,当表层海洋线虫暴露于缺氧环境时,其总丰度显著降低,种类组成发生改变。Pseudosteineria sp1对缺氧环境较为敏感,可暂时性地离开沉积物进入水层;而沉积物溶解氧恢复正常后,该种可以重新回到沉积物中。Daptonema sp1成熟个体及其幼龄个体对缺氧均具有较高的耐受性,是缺氧群落的绝对优势种。D.sp3则表现出对缺氧环境较高的敏感性。环境恢复正常,线虫群落丰度及多样性增加,Neochromadora sp1和Spilophorella sp1等具有机会种的特点,首先表现出丰度和繁殖能力的增加。但是线虫群落种类组成在受测时间内并未能完全恢复,群落结构的恢复需要更长的时间。