Symmetrical Shell Research Articles

The first healed injury in a hyolith operculum.

The Palaeozoic sediments of the Barrandian area are globally well-known as a classic example of rocks characterised by an abundant skeletal marine fauna, including well-preserved remains of hyoliths. Several tens specimens of malformed invertebrates such as trilobites, cephalopods and gastropods have been collected and documented from Cambrian to Devonian clastic sediments and carbonates in this area. However, no malformed hyolith specimen has yet been recorded. Hyoliths are Palaeozoic animals with small calcium carbonate shells composed of the conch (= oblong, conical and bilaterally symmetrical shell of diverse cross section and aperture at its wide end) and the operculum (= cap closing the conch aperture). Here we describe an operculum showing regeneration after non-lethal predatory attack in the Ordovician hyolith Elegantilites custos. This is the first record of regeneration in a hyolith operculum that has been repaired after a failed durophagous attack. Epibenthic/infaunal predatory echinoderms, such as ophiuroids, are considered as potential culprits.

Shell morphology and size distribution of Turbo spp in Sepanjang Beach by shell collecting: An Initial Survey

Turbo spp. in Sepanjang Beach, Gunung Kidul, Indonesia, are at risk of depletion due to their popularity for consumption and decoration. Protecting this species demands sustainable management practices. This initial survey aimed to examine the shell morphology, size distribution, and shell growth patterns of Turbo spp. at Sepanjang Beach, Indonesia, to establish baseline data for future research. A total of 233 shells were collected randomly and analyzed for morphological parameters. Shell dimensions exhibited variations in size, shape, color, and whorl features. Shells ranged from 7.59 to 60.96 mm in length and 7.47 to 52.43 mm in width. Operculum dimensions varied from 3.14 to 29.75 mm in length and 3 to 22 mm in width. Size frequency distributions highlighted a peak at 30-35 mm shell length. The right-skewed size distribution indicated a prevalence of smaller individuals, possibly influenced by the environmental and genetic factors. Positive correlations between shell and operculum dimensions suggested an isometric growth pattern, implying symmetrical shell development. These insights are crucial for developing effective conservation strategies for Sepanjang Beach. Further research, including species genetics, size at first gonadal maturity, and environmental influences, is recommended for a comprehensive understanding of Turbo spp. sustainability in the region.

Effect of polyhedral oligomeric silsesquioxanes with different structures on dielectric and mechanical properties of epoxy resin

AbstractPolyhedral oligomeric silsesquioxane (POSS) is a hybrid material composed of an organic substituent shell and inorganic skeleton core. To study the influence of different shells and cage‐shaped cores on dielectric and mechanical properties, four kinds of epoxy resin composites (EPs) fabricated with 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), DOPO‐containing polyhedral oligomeric silsesquioxane (DOPOPOSS), octaphenyl polyhedral oligomeric silsesquioxane (OPS), and epoxy phenyl polyhedral oligomeric silsesquioxane (EPOSS) with the addition of 5 and 10 wt% were prepared, respectively. The dispersion, transparency, glass transition, dielectric, mechanical tensile, flexural, and impact properties of these epoxy resins were studied. Dielectric constant and loss of EPs were significantly reduced through introduction of three POSSs owing to their inherent hollow cores, and dielectric constant of the resins was further decreased with additional increase. Compared with three POSSs, DOPOPOSS had the best compatible shell, and its composites exhibited favorable transparency similar to pure EP and the obvious reduction in dielectric constant and loss, due to its nano‐dispersion in matrix. EPOSS was dispersed in a perfect spherical shape and uniformly embedded in matrix, and the composites showed good mechanical tensile, flexural, and impact strength. OPS was disorderly dispersed in resins, but its eight phenyl rings symmetrical shell had the advantage of nonpolar molecule structure, which endowed epoxy resin lower dielectric loss over the high‐frequency range (105–106 Hz). Compared with DOPOPOSS, DOPO was effective in reducing dielectric constant and loss of epoxy resin due to its reactive addition, however, it decreased the glass transition temperature, mechanical tensile, flexural, and impact strength of epoxy resin either.

Meisterfeldia bitsevi-new testate amoeba of the family Cryptodifflugiidae Jung, 1942 (Amoebozoa: Arcellinida) from the tree hollow in the urban park (Moscow, Russia) with a key to species of the genus Meisterfeldia.

The new testate amoeba species Meisterfeldia bitsevi is described from the linden-tree trunk hollow in the urban park in Moscow (Russia). New species is characterized by elongated ovoid bilaterally symmetrical shell, which is laterally not compressed. The shell is composed of proteinaceous material without mineral particles. Almost circular subterminal aperture is placed on ventral side. The key to the species of the genus Meisterfeldia is developed.

Muscle scars, mode of life and systematics of Pollicina (Mollusca) from the Ordovician of Baltica

Pollicina is a distinctive, but uncommon, univalved mollusc originally described from the Middle Ordovician (Darriwilian Stage) of the Baltic. The slender, bilaterally symmetrical shell expands slo ...

Natural history clues to the evolution of bivalved gastropods (Mollusca: Gastropoda: Sacoglossa: Juliidae)

Bivalved gastropods (family Juliidae) are a pan-tropical group of small, green, extraordinary gastropods with a symmetrical clam-like shell. Only a single species of Juliidae has been reported in Malaysia, Berthelinia singaporensis Jensen, 2015, feeding on multiple species of siphonous green algae in the genus Caulerpa. In spite of a baseline expectation for megadiversity in this region, including 13 recorded species in the genus Caulerpa from two small field sites studied here, B. singaporensis appears to be a relative generalist without preferences among available Caulerpa spp. that occur in suitable (micro)habitats. The life cycle of Juliidae includes univalve, coiled larvae that transform to bivalved adults. In the presence of Caulerpa, swimming veligers rapidly settle and begin feeding; in a later, terminal metamorphosis, the larval operculum is shed, and the teleoconch shell field splits to form a second, right valve of the adult bivalved form. By three days after hatching, settled larvae achieve a fully functional bivalved shell with a working hinge. Both veligers and adults produce an unusual elastic mucous tether to maintain attachment to the substratum or food plant. These animals are dependent on Caulerpa for their entire life cycle; so, adults occupy environments where dislodgement may be a substantial risk. In the adult, bivalved, form, the gastropod can withdraw completely into its shell and close the valves while maintaining the byssus-like tether. This arrangement, enabling the gastropod to be simultaneously anchored to the food plant and protected within the shell, suggests that being able to use a byssus is the most plausible adaptive explanation for the evolution of the bivalved form within gastropods.

Morphological and molecular aspects of Ceratomyxa ghannouchensis n. sp. and C. pallida Thélohan 1894 infecting the bogue, Boops boops (l.)

ABSTRACTWe report herein the molecular and morphological characteristics of two myxozoan parasites, Ceratomyxa ghannouchensis n. sp. and Ceratomyxa pallida Thélohan, 1894 infecting the gallbladder of the bogue, Boops boops (Linnaeus, 1758) in the Gulf of Gabès off the Tunisian coast. Mature myxospores of C. ghannouchensis were stubby with a convex anterior end and almost straight to slightly concave posterior one. Mature myxospores measured 5.8 ± 0.4 (5–7) µm in length and 11.7 ± 0.3 (11–13) µm in thickness. Valves were unequal in size with one occasionally tapering to a greater degree than the other. The polar capsules were equal in size, spherical in shape and measured 2 ± 0.2 (1.8–2.8) µm in diameter. Infection with C. pallida occurs as spherical to elongated mono-, di- or trisporic plasmodia floating in the bile. Mature myxospores were crescent-shaped with two symmetrical shell valves with rounded edges. The myxospores measured 6 ± 0.5 (5–7) µm in length and 28.5 ± 2.5 (26–33) µm in thickness. The polar capsules were spherical, equal in size and measured 3 ± 0.3 (2.7–3.3) µm in diameter. Based on the SSU rDNA partial sequence, C. ghannouchensis n. sp. and C. pallida appeared in the same subclade with Ceratomyxa leatherjacketi and Ceratomyxa tunisiensis.www.zoobank.org/urn:lsid:zoobank.org:pub:0DE35680-A3C9-45BA-B29B-0B7462CA7A43

Hyoliths with pedicles illuminate the origin of the brachiopod body plan.

Hyoliths are a taxonomically problematic group of Palaeozoic lophotrochozoans that are among the first shelly fossils to appear in the Cambrian period. On the basis of their distinctive exoskeleton, hyoliths have historically been classified as a separate phylum with possible affinities to the molluscs, sipunculans or lophophorates-but their precise phylogenetic position remains uncertain. Here, we describe a new orthothecide hyolith from the Chengjiang Lagerstätte (Cambrian Series 2 Stage 3), Pedunculotheca diania Sun, Zhao et Zhu gen. et sp. nov., which exhibits a non-mineralized attachment structure that strikingly resembles the brachiopod pedicle-the first report of a peduncular organ in hyoliths. This organ establishes a sessile, suspension feeding ecology for these orthothecides and-together with other characteristics (e.g. bilaterally symmetrical bivalve shell enclosing a filtration chamber and the differentiation of cardinal areas)-identifies hyoliths as stem-group brachiopods. Our phylogenetic analysis indicates that both hyoliths and crown brachiopods derived from a tommotiid grade, and that the pedicle has a single origin within the brachiopod total group.

Self-assembly of lattices with high structural complexity from a geometrically simple molecule.

Here we report an anomalous porous molecular crystal built of C-H···N-bonded double-layered roof-floor components and wall components of a segregatively interdigitated architecture. This complicated porous structure consists of only one type of fully aromatic multijoint molecule carrying three identical dipyridylphenyl wedges. Despite its high symmetry, this molecule accomplishes difficult tasks by using two of its three wedges for roof-floor formation and using its other wedge for wall formation. Although a C-H···N bond is extremely labile, the porous crystal maintains its porosity until thermal breakdown of the C-H···N bonds at 202°C occurs, affording a nonporous polymorph. Though this nonporous crystal survives even at 325°C, it can retrieve the parent porosity under acetonitrile vapor. These findings show how one can translate simplicity into ultrahigh complexity.

Robust assembly of aromatic molecules

Microporous Crystals Organic materials can exhibit high porosity, but the structures often collapse or decompose at high temperatures. Yamagishi et al. synthesized an aromatic molecule that bears a symmetrical outer shell of three dipyridylphenyl wedges and crystallized it from highly dielectric solvents. Porous crystals formed with complex pore-wall structures that resulted from labile C–H⋯N bonds and van der Waals forces. Despite the weakness of these interactions, the porous structure was stable up to 202°C and could be recovered after collapse by exposure to solvent vapor. Science , this issue p. [1242][1] [1]: /lookup/volpage/361/1242?iss=6408

Structural Foams of Biobased Isosorbide-Containing Copolycarbonate

Isosorbide-containing copolycarbonate (Bio-PC) is a partly biobased alternative to conventional bisphenol A (BPA) based polycarbonate (PC). Conventional PC is widely used in polymer processing technologies including thermoplastic foaming such as foam injection molding. At present, no detailed data is available concerning the foam injection molding behavior and foam properties of Bio-PC. This contribution provides first results on injection-molded foams based on isosorbide-containing PC. The structural foams were produced by using an endothermic chemical blowing agent (CBA) masterbatch and the low pressure foam injection molding method. The influence of weight reduction and blowing agent concentration on general foam properties such as density, morphology, and mechanical properties was studied. The test specimens consist of a foam core in the center and compact symmetrical shell layers on the sides. The thickness of the foam core increases with increasing weight reduction irrespective of the CBA concentration. The specific (mechanical) bending properties are significantly improved and the specific tensile properties can almost be maintained while reducing the density of the injection-molded parts.

Detection of Zn Atoms on Ferritin by Annular Dark-Field cryo-STEM

Metal ions play essential roles in many aspects of biological chemistry, including oxygen transport, enzyme catalysis, and maintenance of biopolymer integrity. Cryo-electron microscopy is in principle sensitive to metal ions due to the stronger Coulomb potential relative to surrounding light elements, but conventional defocus phase contrast may not be the ideal approach to visualization. In tomography even small gold nanoparticles (<5 nm) are difficult to identify.We explore the alternative modality of scanning transmission EM (STEM), recently applied to cryo-microscopy and tomography. Annular dark-field STEM provides a quantitative image contrast based on atomic scattering, and has been exploited most effectively for mass measurements of macromolecules. Angular resolution of the scattering can provide further information to distinguish relatively heavy and light elements; in materials science this is known as Z contrast. We ask whether cryo-STEM can detect the presence and location of metal ions in protein complexes.Ferritin proteins forms a nearly spherical, highly symmetrical 3D shell structure by self-assembly of 24 polypeptide subunits. Ferritins bind iron as the primary physiological substrate, but also other metals. Zn binds to ferritin at precise ferroxidase sites within the structure. Taking advantage of these properties, we used cryo-STEM to identify Zn ions within the protein structure. Images were processed by single-particle alignment and averaging. Even in very small datasets, Zn stands out clearly at the predicted binding sites. The data provide an experimental measure of the signal contribution from single Zn atoms in cryo-STEM. This is key to understanding atomic detection of metals in 3D macromolecular and cellular contexts, as well as to use of synthetic metal tags as specific molecular labels.

Shell galaxies as laboratories for testing MOND

Tests of MOND in elliptical galaxies are relatively rare because they often lack kinematic tracers in the regions where MOND effects are significant. Stellar shells observed in many elliptical galaxies offer a promising way to constrain their gravitational fields. Shells appear as glowing arcs around the host galaxy, with radii observed up to ∼100 kpc. The stars in axially symmetric shell systems move in nearly radial orbits. The radial distributions of shell locations and the spectra of stars in shells can be used to constrain the gravitational potential of their host galaxy. The symmetrical shell systems, being especially suitable for these studies, occur in approximately 3% of all early-type galaxies. Hence, if we overcome several problems (e.g., multiple shell generations present in the system, shells missed by observations, blurry shell edges, dynamical friction during the merger), the shells substantially increase the number of ellipticals in which MOND can be tested up to large radii. In this paper, we review our work on shell galaxies in MOND. We summarize Bílek et al. (Astron. Astrophys. 559, A110 (2013)), where we demonstrated the consistency of shell radii in an elliptical NGC 3923 with MOND, and Bílek et al. (arXiv:1404.1109. 2014), in which we predicted a giant (∼200 kpc), yet undiscovered shell of NGC 3923. We explain the shell identification method that was used in these two papers. We further describe the expected shape of line profiles in shell spectra in MOND, which is very special because of the direct relation of the gravitational field and baryonic matter distribution (Bílek et al. 2014, in preparation).

Stress Analysis of the Thin-Walled Vessels

This article focuses on the analysis of stresses within a thin-walled vessel. Focused on rotary symmetrical shell, boundary faults arising at the junction of the cylindrical part of the vessel and its bottom are monitored. The bottom of the vessel is designed in three variants and obtained values of stresses are compared. From the obtained results it is possible to assess which form of the bottom is preferred.

The gravitational self-energy of a spherical shell

According to Einstein’s mass-energy equivalence, a body with a given mass extending in a large region of space, will get a smaller mass when confined into a smaller region, because of its own gravitational energy. The classical self-energy problem has been studied in the past in connection with the renormalization of a charged point particle. Still exact consistent solutions have not been thoroughly discussed in the simpler framework of Newtonian gravity. Here we exploit a spherically symmetrical shell model and find two possible solutions, depending on some additional assumption. The first solution goes back to Arnowitt, Deser and Misner (1960). The second is new. When applied to a spherical shell of a given “bare” mass M0, both solutions lead to a vanishing “renormalized” mass for a vanishing radius R of the shell. As a consequence the condition for the existence of a Newtonian black hole will never be met for finite R . When applied to the e.m. mass of a pure static electric charge the second solution yields a new vanishingly small value (10−55cm) for the classical electron radius.

Dynamics of the Himalayan singing bowl

The singing bowl, commonly known as the Tibetan or Himalayan singing bowl, is an idiophone indigenous to many Asian cultures. Singing bowls are usually made of brass, which is hammered into a nearly symmetrical hemispherical shell and then hand-turned on a lathe. A sound is produced by either striking the bowl or rubbing the surface with an excitation stick referred to as a puja. We report on an investigation of the sound generation mechanism of the singing bowl, with an emphasis on understanding the origin of the sound created by the stick-slip excitation mechanism that occurs while rubbing the bowl with the puja. It is shown that both the radial and tangential motion of the puja experience exponential gain during the excitation process, and the feedback mechanism required to produce this behavior is discussed. A slow oscillation in the sound produced by the bowl is explained by the dominance of a single vibrational mode that rotates at the angular speed of the puja.

Elastoplastic Instability of the Double-Arc Ring-Stiffened Cylindrical Shell

The elastoplastic instability of the symmetrical double-arc ring-stiffened cylindrical shell was analyzed. The critical pressure was obtained for small deflection elastoplastic buckling of the cylindrical shell under hydrostatic pressure. The critical pressure for large deflection buckling of the cylindrical shell with initial geometric imperfections was determined under hydrostatic pressure by using nonlinear large deformation theory. The effects of hoop equivalent wave number, initial geometric imperfection and the central angle of circular arc on buckling mode and critical pressure of double-arc ring-stiffened cylindrical shell were analyzed. The results showed that the hoop equivalent wave number of arc cylindrical shell had an main effect on the critical pressure of the structure, designed equivalent hoop wave number of double-arc cylindrical shell should not be approach to the hoop wave number corresponding to minimum critical pressure, and the central angle of circular arc had less effect on critical pressure of the structure.

Blasting Off on an Actin Comet Tail

Blasting Off on an Actin Comet Tail

Geometrically nonlinear numerical procedure for Saint-Venant's problem for a symmetrical elastic shell with a closed contour and circular axis

An original numerical procedure of treating Saint-Venant's problem for toroidal-like shells under pressure and bending moment is suggested. Its peculiarity consists in that the loading and displacement parameters are separated into two groups: the first one describes the ring-like transverse deformation of the shell cross section, while the second the beam-like axial deformation of the latter. One of them is considered separately in the sequential iteration procedure while the other is reckoned to be known. After each step of calculation, the parameters considered to be known are made more exact. A lot of the well-known problems widely presented in the literature are considered. Among them are: (1) Karman's problem, which explains the ovalization of the cross section and the enlarged flexibility of a pipe bend as compared to a straight pipe under bending; (2) the so-called pressure reduction effect when the internal pressure prevents ovalization, which is a demonstration of the influence of the geometrical nonlinearity even at small displacements; (3) Brazier's effect, which deals with nonlinearly enlarged ovalization of an initially straight elastic pipe with an increase in the bending moment. The main advantage of the method is that it allows analyzing a toroidal shell of arbitrary cross section with a variable wall thickness. As an example, a toroidal shell with two long symmetrical axial cracks is considered, where cracks are modeled as the jumps of the contour angular displacement whose values are related to the crack depth.

Measuring Fluctuating Asymmetry in Plastron Scutes of Yellow-bellied Sliders: the Importance of Gender, Size and Body Location

The use of fluctuating asymmetry (FA) estimates in animal research is increasing, but most studies thus far have focused on birds, amphibians and insects. Turtles have bilateral shell scutes that can be easily measured with modern imaging techniques and, therefore, should serve as ideal candidates for FA research, although identifying the most appropriate characters to measure must first be determined. With this issue in mind we undertook the current project to assess levels of plastron scute asymmetry in a common freshwater turtle species, specifically examining the level of variation among scutes and the effects of age (size) and gender on our estimates of scute FA. We photographed 86 museum specimens of adult yellow-bellied sliders, Trachemys scripta (32 males, 54 females) and used image analysis software to measure their carapace lengths and absolute differences in left-right surface areas of plastron scutes. We found that scutes varied in the degree of FA, but the magnitude of the variation tended to be higher among males and there was higher FA in general in the forward-most plastron scutes. We also found that scute asymmetry increased with carapace size, indicating that turtle shells become increasingly asymmetrical with age. This may be the result of adjacent scutes growing against each other over time, leading to random flux in symmetrical growth, or from age-related bioaccumulation of pollutants, which could interfere with normal symmetrical shell production.