Interior Of Shell Research Articles

Multiple predatory drill holes in Cardiolucina (Bivalvia: Lucinidae): Effect of conchiolin sheets in predation

The origin of multiple drill holes in the lucinid bivalve Cardiolucina okinawaensis ( Noda, 1988) from the upper Pliocene Shinzato Formation is discussed. These holes are thought to be produced by predatory naticid gastropods. The valve of C. okinawaensis often bears more than one drill hole, none or only one of which is completely penetrated. The holes are countersunk stepwise and often have a flat bottom when they are incompletely penetrated. Analyses of shell microstructure and growth pattern in the Pliocene C. okinawaensis and modern Cardiolucina quadrata reveal unique shell episodic growth that results in the secretion of discretely distributed, blocky prismatic myostraca and thin conchiolin sheets within the shell. The conchiolin sheets seem to have been produced in each growth unit and spread broadly along the interior shell surface to a varying extent, so that the shells have many conchiolin sheets in fully-grown individuals. Like corbulid bivalves, the conchiolin sheets prevent drilling predation effectively and therefore result in multiple incomplete drill holes. Observations of nine fossil and eight modern Cardiolucina species reveal that all the species examined have almost the same episodic growth pattern with C. okinawaensis and have varying numbers of conchiolin sheets. The conchiolin sheets have an effective function to retard the naticid drilling predation among the fossil and modern Cardiolucina species. However, the absence of any spatial and temporal trend in the number of conchiolin sheets, and the higher number of conchiolin sheets in larger species seem to suggest that the presence of conchiolin sheets in the Cardiolucina species is an example of exaptation rather than of adaptation to the naticid drilling predation.

Revision of Camarotoechia radiata Nalivkin (Brachiopoda, Rhynchonellida) from the Famennian of Novaya Zemlya

The shell interior of the rhynchonellid brachiopod Sinotectirostrum radiatum (Nalivkin) is studied for the first time. The description of this species is emended. The internal and external features of three species are analyzed to confirm their validity: S. radiatum, S. banffense (Warren), and S. arcticum Yudina. A new subspecies, S. banffense rachmanovense subsp. nov., and a new species, S. hayminense, are described. The genus Pseudosinotectirostrum Yudina, 1991 is treated as a subgenus of Sinotectirostrum Sartenaer, 1961.

Studies of the over-rotating BMPV solution

We study unphysical features of the BMPV black hole and how each can be resolved using the enhancon mechanism. We begin by reviewing how the enhancon mechanism resolves a class of repulson singularities which arise in the BMPV geometry when D--branes are wrapped on K3. In the process, we show that the interior of an enhancon shell can be a time machine due to non-vanishing rotation. We link the resolution of the time machine to the recently proposed resolution of the BMPV naked singularity / "over-rotating" geometry through the expansion of strings in the presence of RR flux. We extend the analysis to include a general class of BMPV black hole configurations, showing that any attempt to "over-rotate" a causally sound BMPV black hole will be thwarted by the resolution mechanism. We study how it may be possible to lower the entropy of a black hole due to the non-zero rotation. This process is prevented from occurring through the creation of a family of resolving shells. The second law of thermodynamics is thereby enforced in the rotating geometry - even when there is no risk of creating a naked singularity or closed time-like curves.

Radiation from a source embedded in a two-layer coating of a spherical shell

Analysis of the acoustic field generated by a small source embedded in a viscoelastic layer encapsulating a spherical shell gives rise to several analytical difficulties not encountered in the classical problem of a point source in the surface of a rigid sphere. The present investigation addresses a double layer configuration in which the layer closest to the shell is acoustically soft, whereas the outer layer, in which the source is embedded, has an impedance that matches that of the surrounding fluid, water. The analysis is carried out by treating the layers as dissipative fluids, while classical Love theory describes the interior shell. The analysis employs spherical harmonic expansions for each medium, which is known as Mie series analysis in related studies of electromagnetic scattering from coated series. Like the electromagnetic problem, computational difficulties associated with the occurrence of spherical Bessel functions of complex argument arise, but the remedies used there require modification.

Stable isotope evidence for identification of chemosynthesis-based fossil bivalves associated with cold-seepages

Fossil evidence of chemosynthesis-based organisms has so far been circumstantial and completely based on association of fossilized organisms with 13C-depleted authigenic carbonates. In this study, the stable isotopic signatures of preserved organic matter, conchiolin, in the fossil shell interior were used to obtain additional evidence for chemosynthesis-based bivalves, since the carbon, nitrogen, and sulfur isotopic compositions of soft tissues can distinguish chemosynthesis-based animals from marine photosynthesis-based animals. The carbon and nitrogen isotopic compositions of both soft tissues (the mantle) and conchiolin from modern chemosynthesis-based bivalves belonging to the genera Calyptogena and Bathymodiolus had small difference (Δ 13C conchiolin-mantle ≤ + 3‰, Δ 15N conchiolin-mantle ≤ − 1‰ with the exception of − 7.5‰ for a Calyptogena specimen). Sulfur isotope compositions of the conchiolin from Calyptogena whose lifestyle is almost entirely infaunal were significantly depleted in 34S, while epifaunal Bathymodiolus showed relatively small differences between the δ 34S values of chonchiolin and soft tissues. Thus, a systematic difference in sulfur isotope compositions has not been observed for chemosynthesis-based bivalves (Δ 34S conchiolin-mantle = − 16.1 to + 2.6‰). Moreover, we were able to extract conchiolin from fossil bivalves to determine its isotopic compositions. The δ 13C and δ 15N values of the conchiolin obtained from the fossil Vesicomyidae were − 28.5 and − 1.4‰, respectively. The δ 13C and δ 15N values of lost soft tissues were estimated at approximately − 31‰ and − 1‰, respectively, by subtracting the Δ conchiolin-mantle values determined for modern soft tissues and conchiolin (Δ 13C conchiolin-mantle = + 3‰, Δ 15N conchiolin-mantle = − 1‰). Such values are expected for clams harboring thioautotrophic symbionts, suggesting that the fossil was dependent on chemosynthesis during its lifetime. In contrast, the carbon and nitrogen isotopic ratios of the conchiolin from the fossil Mytilidae were − 23.1‰ and + 4.2‰, respectively. The estimated δ 13C and δ 15N values of its lost soft tissues were approximately − 26‰ and + 5‰, respectively. These values are depleted in 13C and 15N relative to non-symbiont bearing marine organisms suggesting that this fossil likely supported chemosynthetic and/or methanotorophic symbionts and was also dependent on photosynthetically derived organic matter. Our study provides additional and more direct evidence for putative chemosynthesis-based bivalves, whether or not they harbor symbionts.

Structures of small Pd–Pt bimetallic clusters by Monte Carlo simulation

Segregation phenomena of Pd–Pt bimetallic clusters with icosahedral and decahedral structures are investigated by using Monte Carlo method based on the second-moment approximation of the tight-binding (TB-SMA) potentials. The simulation results indicate that the Pd atoms generally lie on the surface of the smaller clusters. The three-shell onion-like structures are observed in 55-atom Pd–Pt bimetallic clusters, in which a single Pd atom is located in the center, and the Pt atoms are in the middle shell, while the Pd atoms are enriched on the surface. With the increase of Pd mole fraction in 55-atom Pd–Pt bimetallic clusters, the Pd atoms occupy the vertices of clusters first, then edge and center sites, and finally the interior shell. It is noticed that some decahedral structures can be transformed into the icosahedron-like structure at 300 and 500 K. Comparisons are made with previous experiments and theoretical studies of Pd–Pt bimetallic clusters.

Precipitation of aragonite by calcitic bivalves in Mg-enriched marine waters

To understand the relative importance of biological versus physicochemical control over biomineralization, we have tested if the chemical composition of the medium (i.e., the Mg/Ca ratio) can change the mineralogy of mollusk shells. The shells of mollusks are made of calcite and/or aragonite, which are by far the most common CaCO3 polymorphs. Several species of bivalves with predominantly calcitic shells have been cultivated in artificial seawater with a Mg/Ca molar ratio within the range of 8.3–9.2, well above the present value for seawater (5.2). Four out of six species used (the scallop Chlamys varia, the oyster Ostrea edulis, the saddle oyster Anomia ephippium and the mussel Mytilus edulis) survived long enough to secrete significant amounts of calcium carbonate. The deposits (sometimes extensive) formed on the interior shell surfaces were predominantly aragonitic. Three individuals of C. varia also increased their length by adding new shell at the margin. Contrary to the internal shell deposits, these margins were high-Mg calcite. This implies that the marginal mantle is able to exert a more strict control on the secreted mineral phase than the mantle facing the internal shell surface. This is the first report on an in vivo experimentally forced switch in bivalve shell mineralogy, from calcite to aragonite due to a change in water chemistry.

Exotic hard clam in Tokyo Bay identified as Mercenaria mercenaria by genetic analysis

An exotic hard clam has been observed in Tokyo Bay since the mid-1990s, which has been morphologically identified as Mercenaria mercenaria. The authors have determined 444-bp partial nucleotide sequences of mitochondrial DNA (mtDNA) 16S rRNA gene of 31 hard clam individuals collected in three locations of Tokyo Bay. Phylogenetic analysis indicated all individuals to be M. mercenaria. Two shell interior colorations (white or purple) were observed, but no relationships between the colorations and mtDNA haplotypes were detected. Frequency of clam individuals having white or purple shell significantly differed among locations, which was accompanied by heterogeneous amounts of acid-volatile sulfides and organic matter and mud ratio.

Generalized ammonoid hydrostatics modelling, with application to Intornites and intraspecific variation in Amaltheus

A numerical procedure for calculating the buoyancy, apertural orientation and rotational stability of ammonoids can accommodate noncircular apertures and allometries. The hydrostatic properties of the Triassic oxyconic ammonite Intornites nevadanus were estimated from measured coiling parameters, body chamber length and digitized whorl section. The calculations indicate close to neutral buoyancy. The orientation of the aperture is 33 degrees from the horizontal, and the stability index relatively high at 0.054. Unlike for many other ammonites, these values are comparable to those of Nautilus, suggesting a similar nektobenthic lifestyle. An apertural interior shell callus does not contribute to stability in this genus, and its function remains unknown. In Amaltheus margaritatus, hydrostatic properties and body chamber length vary significantly as a result of intraspecific variation in shell shape. Covariation between septal spacing and whorl shape can be given a functional explanation in terms of hydrostatic properties. Buckman's second law of covariation between ribbing and sutural complexity can possibly be thought of in terms of heterochrony.

A model for linear dragging

We try to carry over, as closely as possible, the well-known results for rotational dragging (Thirring, Brill and Cohen) to dragging due to linearly accelerated masses. To this end, a spherical, charged mass shell is linearly accelerated by a (weak) external, axisymmetric and dipolar charge distribution. It is shown that the interior of this (Reissner–Nordström-like) shell stays flat. The dragging of neutral test particles inside the shell, defined by their acceleration, scaled by the overall acceleration of the (rigid) shell, is calculated for the weak field case for a highly massive but weakly charged shell and for the general strong field case. The results compare favourably with the corresponding results for rotational dragging.

An Effective Method for Preparing Polymer Nanocapsules with Hydrophobic Acrylic Shell and Hydrophilic Interior by Inverse Emulsion Radical Polymerization

An Effective Method for Preparing Polymer Nanocapsules with Hydrophobic Acrylic Shell and Hydrophilic Interior by Inverse Emulsion Radical Polymerization

Differential taphonomy of modern brachiopods (San Juan Islands, Washington State): effect of intrinsic factors on damage and community‐level abundance

The differences in shell structure and population turnover between organic-poor, impunctate (Hemithiris) and organic-rich, punctate brachiopod (Terebratalia) in a mixed-bottom, siliciclastic setting (San Juan Islands, WA) lead to different taphonomic damage and fidelity with respect to community-level abundance in death assemblages. In comparing shell interiors of similar-sized specimens, Terebratalia is predominantly affected by fibre detachment and shows almost no microbioerosion at the SEM scale; whereas, Hemithiris shows less marked fibre detachment at the SEM scale and is more intensely affected by microbioerosion both at SEM and light microscope (LM) scales. Fibre detachment related to rapid, microbially-induced organic matter decay appears to be the main destructive process acting on Terebratalia. Higher bioerosion levels in Hemithiris at SEM and LM scales are probably related to a combination of a low maceration rate and a preferential settlement by borers. From their vastly different abundances in life assemblages it can be deduced that Terebratalia produces dead shells at a much higher rate than Hemithiris. Therefore, the proportion of altered Terebratalia, relative to Hemithiris, is expected to be decreased due to its higher production of recently dead cohorts. That Terebratalia is also characterized by high damage levels shows that differential population turnover alone is not responsible for the differences in taphonomic damage. This shows that organic-rich and organic-poor shells are characterized by differential post-mortem durability. Although very few Hemithiris are present in the life assemblages, high durability ensures its relative over-representation in death assemblages. Terebratalia is not strongly under-represented in death assemblages, despite its high destruction rate, because of large production of recently dead shells. Even with the biasing effect of differential durability, the good fidelity reported in previous live-dead studies can be enhanced by higher population turnover of numerically dominant taxa, leading to constant input of recently dead shells into death assemblages.

A new cornulitid genus from the Silurian of Gotland, Sweden

A new genus and species Septalites septatus gen. et sp.n. of a possible cornulitid is described from the Silurian of Gotland. The new genus resembles Conchicolites in having a smooth tube interior with multiple septa, but differs in the greater number of septa and microlamellar tube structure. Most of the shell interior (about 3/4) is filled with the septa. S. septatus shares several features with Cornulites and tentaculitids, but it differs in lacking pseudopuncta and an annulated tube interior. It is affiliatiated with the Class Tentaculita Bouãek (1964) because of micro-lamellar tube structure and the presence of septa.

The costs of being bored: Effects of a clionid sponge on the gastropod Littorina littorea (L)

Mollusc shells provide a major defense against predators, but changes in shell properties may alter the effectiveness of this defense. An endolithic boring sponge, Cliona sp., infests many shells of the gastropod Littorina littorea in the southern Gulf of Maine. Cliona excavates ramifying chambers within the shell but does not affect tissue directly. Field surveys showed that 22–83% of snails were infected with Cliona at the Isles of Shoals; the prevalence of infection declined with increasing tidal height and increased with increasing snail size. We also investigated potential costs to L. littorea of infection by Cliona. L. littorea appeared to respond to sponge boring by laying down additional material on the interior of the shell, which reduced interior shell volume and was associated with smaller dry body mass for a given shell length. Biomechanical studies showed that sponge boring weakened shells: the mean compressive force required to break severely bored L. littorea was 29% lower than that required to break unbored snails. Cliona infection increased vulnerability of snails to predation by the crab, Cancer borealis Stimpson, which attacks molluscs by crushing or peeling shells. Unlike uninfected snails, predation risk did not decline with increasing size in bored L. littorea. In addition, bored snails were generally crushed by the crab, regardless of snail size, whereas large unbored snails could only be attacked by peeling. Thus, costs to L. littorea of Cliona boring included the following: (1) increased vulnerability to predation due to structural changes in the shell; (2) reduction or elimination of the size-refuge advantage; and (3) a potential decrease in growth and fecundity due to diversion of energy to supplemental interior layers to the shell and the consequent reduction in interior shell living space and body mass.

Pressure screening in the interior of primary shells in double-wall carbon nanotubes

The pressure response of double-wall carbon nanotubes has been investigated by means of Raman spectroscopy up to $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. The intensity of the radial breathing modes of the outer tubes decreases rapidly but remain observable up to $9\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, exhibiting a behavior similar (but less pronounced) to that of single-wall carbon nanotubes, which undergo a shape distortion at higher pressures. In addition, the tangential band of the external tubes broadens and decreases in amplitude. The corresponding Raman features of the internal tubes appear to be considerably less sensitive to pressure. All findings lead to the conclusion that the outer tubes act as a protection shield for the inner tubes whereas the latter increase the structural stability of the outer tubes upon pressure application.

Characteristics of Trapping Various Organophosphorus Pesticides with a Ferritin Reactor of Shark Liver (Sphyrna zygaena)

A reactor is composed of liver ferritin of Sphyrna zygaena (SZLF) and an oscillating bag. A reactive procedure for trapping various organphosphorus pesticides (OPs) with the SZLF reactor in the flowing water is described in detail, showing the maximal trapping numbers of 28 +/-1.0 dichlorovos/SZLF, 42 +/- 1.0 dimethoate/SZLF, and 55 +/- 1.0 methamido-phos/SZLF determined by a improved spectrophotometric method in 12 h. In addition, it is found that the OP numbers trapped by the reactor increase along with the incubation time and its concentration increment in the flowing water (or seawater), respectively. This trapping capacity is considered to depend on the composition of amino acids on the surface of the ferritin shell interior rather than the available volume within the shell. A novel pathway for trapping various OPs with the ferritin is suggested in reference to unstable characteristics of the protein subunits. We claim that the ferritin reactor will be employed to monitor the contamination level of various OPs in the flowing water continuously.

Euendoliths and cryptoendoliths within late Middle Cambrian brachiopod shells from North Greenland

Traces of an association of microscopic endoliths are described within the shell wall and internal cavity of phosphatic brachiopods with conjoined valves from the Holm Dal Formation (late Middle Cambrian) of Peary Land, central North Greenland. Ridged galleries which also penetrate early diagenetic, phosphatised, fibrous crusts on the shell interior are borings excavated by a multifilamentous euendolith. Meshworks of strands crossing the shell interiors are phosphatised encrustations seemingly originally deposited as radiating, acicular, aragonite crystals on cryptoendolithic filaments prior to their degradation. The Greenland fossils closely resemble a present day association of calcified green algae from recent Bermuda reefs, but were probably produced by Cyanobacteria.

Supernova Remnants in the Magellanic Clouds. IV. X‐Ray Emission from the Largest Supernova Remnant in the Large Magellanic Cloud

We present the first X-ray detection of SNR 0450-70.9, the largest known supernova remnant (SNR) in the Large Magellanic Cloud. To study the physical conditions of this SNR, we have obtained XMM-Newton X-ray observations, optical images and high-dispersion spectra, and radio continuum maps. Optical images of SNR 0450-70.9 show a large, irregular elliptical shell with bright filaments along the eastern and western rims and within the shell interior. The interior filaments have higher [S II]/Hα ratios and form an apparent inner shell morphology. The X-ray emission region is smaller than the full extent of the optical shell, with the brightest X-ray emission found within the small interior shell and on the western rim of the large shell. The expansion velocity of the small shell is ~220 km s-1, while that of the large shell is ~120 km s-1. The radio image shows central brightening and a fairly flat radio spectral index over the SNR. However, no point X-ray or radio source corresponding to a pulsar is detected, and the X-ray emission is predominantly thermal. Therefore, these phenomena can be most reasonably explained in terms of the advanced age of the large SNR. Using hydrodynamic models combined with a nonequilibrium ionization model for thermal X-ray emission, we derived a lower limit on the SNR age of ~45,000 yr, well into the later stages of SNR evolution. Despite this, the temperature and density derived from spectral fits to the X-ray emission indicate that the remnant is still overpressured and thus that the development is largely driven by hot gas in the SNR interior.

Examination of the atomic pair distribution function (PDF) of SiC nanocrystals by in-situ high pressure diffraction

X-ray and neutron diffraction experiments were performed on nanocrystalline SiC with the average grain diameters of 7, 12, and 16nm subjected to isostatic pressure. Under pressure the interatomic distances undergo a complex, non-monotonic changes which were correlated with the compression of the SiC lattice determined from the Bragg scattering. The results indicate the presence of non-uniform distribution of stresses between the interior and surface shell of the nanograins. The present results lend a strong support to the concept of a core-shell model of nanocrystals.

Spatially extended K iλ7699 emission in the nebula of VY CMa: kinematics and geometry

Long-slit echelle spectra reveal bright extended emission from the K I lambda7699 resonance line in the reflection nebula surrounding the extreme red supergiant VY Canis Majoris. The central star has long been known for its unusually-bright K I emission lines, but this is the first report of intrinsic emission from K I in the nebula. The extended emission is not just a reflected spectrum of the star, but is due to resonant scattering by K atoms in the outer nebula itself, and is therefore a valuable probe of the kinematics and geometry of VY CMa's circumstellar environment. Dramatic velocity structure is seen in the long-slit spectra, and most lines of sight intersect multiple distinct velocity components. A faint ``halo'' at large distances from the star does appear to show a reflected spectrum, however, and suggests a systemic velocity of +40 km/s with respect to the Sun. The most striking feature is blueshifted emission from the filled interior of a large shell seen in images; the kinematic structure is reminiscent of a Hubble flow, and provides strong evidence for asymmetric and episodic mass loss due to localized eruptions on the star's surface.