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1.
The marine bivalved Brachiopoda are abundant throughout the geological record and have apatitic (CaPO4-rich) or calcitic (CaCO3-rich) shells. Vesicles covering the larval valves of living apatitic-shelled discinids contain tablets of silica. The tablets are cemented into close-packed mosaics by spherular apatite in glycosaminoglycans. They are usually lost as vesicles degrade but leave imprints on the underlying apatitic shell. Similar imprints ornament larval surfaces of some of the earliest Paleozoic apatitic-shelled brachiopods and may also be indicators of siliceous biomineralization. 相似文献
2.
The California mussel Mytilus californianus records with high fidelity annual temperature variations of nearshore waters in the oxygen isotope composition of its shell. The onset and termination of upwelling events (and metabolic activity) are recorded in the associated carbon isotope signal, and the magnitude and timing of upwelling can be estimated. The method has implications for studying the history of upwelling and the life history of living and fossil mollusks and for analyzing shell midden deposits. 相似文献
3.
Norton SF 《Science (New York, N.Y.)》1988,241(4861):92-94
In contrast to the diets of other cottid fishes and most teleosts, the diet of Asemichthys taylori is dominated by gastropod mollusks. Access to this underused prey appears to be made possible by morphological speializations of the neurocanium that allow Asemichthys to puncture the shells of its prey during mastication. Unpunched, the shell and operculum act as a barrier to digestion; more than 40% of the unpunched gastropods emerged alive in the feces. Asemichthys adjusted its punching behavior in an apparently adaptive way; other prey lacking such barriers to digestion were rarely punched. The ability of some shelled invertebrates to avoid digestion may make them less desirable as prey for many fishes that cannot masticate this kind of prey. The ability of shelled mollusks to survive in the digestive tracts of vertebrates may provide a dispersal mechanism for otherwise sedentary species. 相似文献
4.
Stanley SM 《Science (New York, N.Y.)》1969,166(3905):634-635
Oblique and chevron-like ridges on the shell surfaces of certain burrowing bivalve mollusks grip the sediment during shell-rocking movements to aid in sediment penetration. These ridges (characterized by steep dorsal slopes and gentle ventral slopes) have evolved through convergence in several families in association with particular behavioral and ecological traits. 相似文献
5.
Phosphatized univalves, recovered from the Lower Cambrian ( approximately 530 million years old) Qiongzhusi Formation in southern China, are recognized as early instars belonging to bradoriid ostracodes whose later instars are bivalved. The univalved form is the primitive larval character for shell-secreting crustaceans, although most post-Cambrian ostracodes bypassed this developmental phase. The univalved-bivalved transition during early on-togeny represents an important evolutionary event in ostracodes, with implications for crustacean classification, and implies that the ostracode ancestor achieved this bivalved capacity before the appearance of mineralized skeletons during the "Cambrian explosion." 相似文献
6.
为了实现吊耳法养殖虾夷扇贝Patinopecten yessoensis的钻孔作业自动化,对扇贝左壳定向方法进行了研究。提出了利用扇贝左右壳曲率不同的形状特征,通过控制扇贝的入水速度和角度,在水中实现左壳定向的方法。结果表明：扇贝在水中运动时,左右两壳所受的压力不同,扇贝在流体压力差和重力的作用下实现左壳朝上。在入水速度为1.0～1.5 m/s、入水角度为-30°～60°、水槽直径为60 cm、槽深为26 cm以上的条件下,将扇贝投入静水中,可实现左壳朝上定向;扇贝在水中完成定向所需时间为0.42～0.45 s。该法既可避免机械振动和碰撞对扇贝的损伤,又能减少因加工过程中扇贝在空气中暴露对其生长的影响。 相似文献
7.
A discrete, calcareous layer that binds the foliated calcite of the oyster's shell to the organic ligament in the hinge is reported, apparently for the first time. This layer is ultrastructurally, and generally mineralogically, different from the underlying foliated calcite, and is named the ligostracum. 相似文献
8.
[目的]探讨矿化基因、贝壳和珍珠经济性状之间的相关关系。[方法]选择47个培育优质珍珠的马氏珠母贝,测量贝壳的壳宽、壳高、壳长、绞合线长、总壳重、左壳重、珠层厚度及珍珠的直径、重量、珠层厚度,并分析矿化基因msi60在外套膜内缘组织的相对表达量,珍珠经济性状和贝壳经济性状之间的相关关系。[结果]珍珠的珠层厚度、珍珠直径和珍珠重量3个经济性状均与受体贝贝壳的壳宽、壳长、总壳重和左壳重呈显著相关,推测育珠贝的生长状况在一定程度上影响珍珠的培育;msi60在外套膜内缘的相对表达量与珍珠重量之间存在相关性(P=0.059),贝壳和珍珠的珍珠层厚度存在显著相关性(P=0.019),推测在马氏珠母贝中,贝壳的矿化和珍珠的矿化可能具有共同的上游调控元件。[结论]msi60在形成贝壳珍珠质层的外套膜内缘组织中的基因表达量与珍珠的经济性状相关。该研究为马氏珠母贝生物矿化分子机制的研究提供基础资料。 相似文献
9.
海南野生长肋日月贝形态性状与重量性状的通径分析 总被引：3，自引：0，他引：3
[目的]了解长肋日月贝的重量性状与一般性状的关系。[方法]以海南海区捕捞的野生长肋日月贝,壳长（69．720±1．309）mm为样本,对其壳长、壳高、壳宽、铰合线长及重量性状体重、软体部重、闭壳肌重和生殖腺重进行通径分析。[结果]4个形态性状对体重和闭壳肌的直接影响依次为：壳高〉壳宽〉铰合线长〉壳长。壳高对体重和闭壳肌重的决定系数分别为：0．106929和0．203401．壳长对体重和闭壳肌重的决定系数分别为：0．027225和0．001521。4个重量性状之间,闭壳肌重对体重有极显著的正效应（通径系数0．912^＊＊）,其次为生殖腺重（通径系数0．087^＊＊）。[结论]为深入探讨长肋日月贝的种质资源保护和人工育苗提供了理论依据。 相似文献
10.
11.
武昌南湖圆背角无齿蚌雌蚌繁殖特征的研究 总被引：7，自引：0，他引：7
研究了武昌南湖圆背角无齿蚌繁殖习性 ,该蚌为雌雄异体 ,雌雄性比为 1∶1 .1 61 5,各月、各龄雌雄性比与其自然性比有显著的适合性 ;1 龄性成熟 ,4～ 8月中旬为繁殖期 ,5月为繁殖高峰期 ,产卵适宜水温为 1 9.9～ 30 .8℃ ,繁殖高峰期的平均水温为 2 3℃ ;平均怀胚量约 6.8× 1 0 5,5月怀胚率最高 ,达82 .46%。卵细胞分批成熟 ,分批排放 ;育儿囊中的钩介幼虫大小 (壳长×壳宽×绞合部宽 )为 1 78μm× 1 57μm× 1 2 2 μm。 相似文献
12.
Stable isotopic and shell-growth banding studies of the symbiont-bearing giant clam Tridacna maxima reveal the existence of two growth phases related to sexual maturity that can be discerned in the shells of extinct and extant mollusks. The changeover from the first to second growth phase at an age of approximately 10 years is accompanied by a decrease in rate of calcification and suggests a reordering of energy priorities between biomineralization and reproduction. The carbon-13 to carbon-12 ratio of Tridacna maxima is systematically depleted relative to symbiont-barren mollusks, making it possible to determine the importance of algal-molluscan symbiosis to the functional morphology and paleoecology of mollusks in the geologic record. 相似文献
13.
M Stuiver 《Science (New York, N.Y.)》1968,162(857):994-997
Freshwater lake marl and mollusks from Indiana show variations in ratios of oxygen-18 to oxygen-16 of a few per mil during the Postglacial. For the last 9000 years these variations are about 1 per mil for properly selected lake sediments. Thus the oxygen isotope composition of atmospheric precipitation appears relatively stable over this interval, indicating stationary atmospheric circulation patterns over the Great Lakes region. A reduction in oxygen-18 content around 10,000 years ago corresponds with the climate change indicated by pollen profiles. Large systematic differences were found between carbon-13 and oxygen-18 content of marl and mollusks. 相似文献
14.
Phosphorite concretions have been detected in the kidneys of two widespread species of mollusks, Mercenaria mercenaria and Argopecten irradians, which have relatively high population densities. These concretions are the first documentation of the direct biogenic formation of phosphorite grains. The concretions are principally amorphous calcium phosphate, which upon being heated yields an x-ray diffraction pattern which is essentially that of chlorapatite. These concretions appear to be a normal formation of the excretory process of mollusks under reproductive, environmental, or pollutant-induced stress. Biogenic production of phosphorite concretions over long periods of time and diagenetic change from amorphous to crystalline structure, coupled with secondary enrichment, may account for the formation of some marine phosphorite desposits which are not easily explained by the chemical precipitation-replacement hypothesis. 相似文献
15.
Specimens of the small bivalved animal Fordilla troyensis Barrande from New York State show that this fossil is the oldest known pelecypod mollusk and not a conchostracan arthropod. This finding extends the range of the class Pelecypoda backward in time from the Early Ordovician (about 495 million years ago) to the Early Cambrian (about 540 to 570 million years ago). The morphology of Fordilla troyensis suggests that it lived infaunally and that it was ancestral to the pelecypod subclasses Heteroconchia and Isofilibranchia. 相似文献
16.
徐德才 《江西农业大学学报》1996,18(2):234-237
对单自由度系统和两个自由度系统连接点进行分类分析两构件在连接点上的速度，第一类连接点是两构件以铰链相连，这类连接点，两构件在连接点上具有相同的速度，第二类连接点，两构件不是以铰链相连，连接点随构件的运动而变化，此类连接点，两构件在连接点具有不同的速度。 相似文献
17.
Molluscan phylogeny: the paleontological viewpoint 总被引：1，自引：0，他引：1
Stasek (1) theorized that the extant mollusks are the progeny of three separate lineages that separated before the phylum was well established. He wrote that no known intermediate forms, fossil or living, bridge the "enormous gaps between any two of the three lineages," and therefore treated each as a separate subphylum. These subphyla are (i) the subphylum Aculifera Hatscheck 1891, containing only the class Aplacophora, derived from the most primitive ancestors of the Mollusca; (ii) the subphylum Placophora von Jhering 1876, containing only the class Polyplacophora, and emphasizing the pseudometamerism of its more advanced premollusk ancestor; and (iii) the subphylum Conchifera Gegenbaur 1878, containing the Monoplacophora and the other classes derived from it. We point out that the Polyplacophora may be derived from the Monoplacophora instead of a more primitive ancestral stock. We also suggest that the Conchifera can be separated into two major lineages, each worthy of the rank of subphylum. The fossil record indicates that the Monoplacophora gave rise to the Gastropoda, Cephalopoda, Rostroconchia, and possibly Polyplacophora, and that the Pelecypoda and Scaphopoda are derived from the Rostroconchia. These last three classes thus form a lineage that diverged from the Monoplacophora in the Early Cambrian. They emphasized a shell form that in all groups is primitively open at both ends, allowing the gut to remain relatively straight, with an anterior mouth and posterior anus. They became burrowing (infaunal) deposit or filter feeders. We coin the term Diasoma (through-body) for the subphylum containing these three classes (Rostroconchia, Pelecypoda, and Scaphopoda). The remaining three classes (Monoplacophora, Gastropoda, and Cephalopoda) emphasize a conical univalved shell, usually twisted into a spiral. The relatively small single aperture forces the anus to lie close to the mouth, and the gut is bent into a "U." Most are surface-dwelling (epifaunal) grazers or carnivores. We coin the name Cyrtosoma (hunchback-body) for the subphylum containing these three classes. Strictly speaking, the cyrtosomes are the ancestors of the diasomes but, in fact, both subphyla appeared and began to diversify within a few million years in the Early Cambrian. Note added in proof: After proofs were corrected we were informed that the new genus Opikella (40) is preoccupied by (Opikella = Oepikella) Thorslund 1940, an Ordovican ostracod. We rename the mollusk genus Oepikila. 相似文献
18.
The origin and possible antiquity of faunas at deep-sea hydrothermal vents and seeps have been debated since their discovery. We used the fossil record of seep mollusks to show that the living seep genera have significantly longer geologic ranges than the marine mollusks in general, but have ranges similar to those of deep-sea taxa, suggesting that seep faunas may be shaped by the factors that drive the evolution of life in the deep sea in general. Our data indicate that deep-sea anoxic/dysoxic events did not affect seep faunas, casting doubt on the suggested anoxic nature and/or global extent of these events. 相似文献
19.
框架—剪力墙结构目前在建筑结构中应用较广,现有二维平面力学计算模型现阶段仅根据有无连梁划分为两种结构体系,只要存在连梁简化为刚结体系,否则将作为铰结体系,显然这两种简化无法真实反映其受力情况。本文提出介于两者之间的框架—剪力墙弹性铰结体系,考虑楼板对连梁刚度的增强作用,用连梁刚度来进行结构体系的划分。按不同的结构体系进行内力计算、设计差异较大,本文建立框架—剪力墙弹性铰结体系,使此类结构的内力分析计算、结构构件设计能更好地反映其实际工作状态,对该类结构的理论分析是一个较大的补充。 相似文献
20.
本实验对自然种群青蛤的壳色进行了观察和分析;将亲贝分为白壳群体和紫壳群体分别进行人工繁育,对F1壳色分离情况进行了统计和分析;分析了泥质、粉沙质和细沙质不同底质对F1壳色表达的影响。结果表明:(1)F1出现了4种壳色类型,两群体间相同壳色个体百分率差异均显著(P﹤0.01),F1壳色出现相同于亲本的纯化,说明青蛤白、紫壳色能够真实遗传;(2)青蛤紫色壳色的深浅明显受到底质的影响,泥质使壳色变淡并降低了紫壳个体百分率,沙质底则利于紫色壳色的表达,其中细沙质与泥质差异达到显著性水平(P﹤0.05),但底质影响力不超过遗传能力的1/4;(3)紫壳群体F1的紫壳个体百分率达70%以上,接近未分离亲贝18.71%的4倍,使紫壳个体得到显著纯化,为选育纯紫壳品系或群系创造了条件。 相似文献