Shell Shape Research Articles

Evolutionary trends in trimerellid brachiopods

Non-articulated trimerellides, one minor group among the largest brachiopods, are commonly found in massive monospecific accumulations in Ordovician and Silurian rocks. In this paper, all species of the family Trimerellidae are listed for the first time, and some of them are discussed. They appeared in the Sandbian and became extinct in the Ludlow with an apex of diversification observed, at generic level, during the Katian and at species level, during the Wenlock. Platforms and vaults are the diagnostic morphological characteristics of the trimerellids, and constitute the important basis for generic classification. Individuals with highly raised platforms and deep vaults first appeared in the middle–late Katian, but became the main morphology in the Silurian. Nineteen genera of Trimerellidae are selected in this study, and 30 characters are coded for morphospace and phylogenetic analyses. Based on the morphospace analysis by non-metric multidimensional scaling (NMDS), we have differentiated the morphological characteristics of platforms and vaults into three types (I, II and III). The results of the phylogenetic analysis show a tendency for platforms and vaults to become more prominent in younger genera (from Type I to III). Trimerellids are divided into four morphological groups based on the differences of shell shape or life style. This evolutionary trend of platforms and vaults is reflected in all four morphological groups.

Controlled expansion of shell-shaped Bose–Einstein condensates

Motivated by the recent experimental realization of ultracold quantum gases in shell topology, we propose a straightforward implementation of matter-wave lensing techniques for shell-shaped Bose–Einstein condensates. This approach allows to significantly extend the free evolution time of the condensate shell after release from the trap and enables the study of novel quantum many-body effects on curved geometries. With both analytical and numerical methods we derive optimal parameters for realistic schemes to conserve the shell shape of the condensate for times up to hundreds of milliseconds.

Morphology and taxonomic assessment of eight genetic clades of Mercuria Boeters, 1971 (Caenogastropoda, Hydrobiidae), with the description of five new species

The freshwater snail genus Mercuria is widely distributed in lowland waters across Western Europe, Northern Africa and the Mediterranean islands. Approximately two-thirds of the currently recognised species are described based on their shell morphology, which may vary within species due to biotic and abiotic factors. Recent molecular phylogenies that included numerous previously documented populations recovered 14 species clades, nine of which correspond to nominal species and five, to undescribed taxa. Here, we formally describe the five undescribed taxa as new species and provide morphological descriptions of the shell and other anatomical structures for three of the other inferred clades and for the species M. maceana to elucidate their taxonomic status and assess the utility of morphological characters for species delimitation in Mercuria. Taken together, the morphological and molecular evidence suggest new identifications and synonymies, having implications on the known geographic range of the studied species, including the type species M. similis. Anatomical measurements and geometric morphometric analysis of shell shape revealed no clear differentiation among the species analysed, predicting the importance of molecular data in elucidating the species diversity of the genus.

Collapse of the N=28 shell closure in the newly discovered Na39 nucleus and the development of deformed halos towards the neutron dripline

Halos and changes of nuclear magicities have been extensively investigated in exotic nuclei during past decades. The newly discovered $^{39}\mathrm{Na}$ with the neutron number $N=28$ provides a new platform to explore such novel phenomena near the neutron dripline of the sodium isotopic chain. We study the shell property and the possible halo structure in $^{39}\mathrm{Na}$ within the deformed relativistic Hartree-Bogoliubov theory in continuum. It is found that the lowering of $2p$ orbitals in the spherical limit results in the collapse of the $N=28$ shell closure in $^{39}\mathrm{Na}$, and a well-deformed ground state is established. The pairing correlations and the mixing of $pf$ components driven by deformation lead to the occupation of weakly bound or continuum $p$-wave neutron orbitals. An oblate halo is therefore formed around the prolate core in $^{39,41}\mathrm{Na}$, making $^{39}\mathrm{Na}$ a single nucleus with the coexistence of several exotic structures, including the quenched $N=28$ shell closure, Borromean structure, deformed halo, and shape decoupling. The microscopic mechanisms behind the shape decoupling phenomenon and the development of halos towards dripline are revealed.

How an Ecological Race Is Forming: Morphological and Genetic Disparity among Thermal and Non-Thermal Populations of Aquatic Lymnaeid Snails (Gastropoda: Lymnaeidae)

Hot (geothermal) pools and streams, a specific type of aquatic biotopes having almost worldwide distribution, maintain rich faunas of animals belonging to various taxa. Snails (Gastropoda) represent one of such groups, which form populations in geothermal waterbodies of all continents. Some freshwater snail species produce morphologically distinct hot-water populations, whose rank is often debated (full species or thermal ‘ecotype’, or ‘race’). In this study, we used six species of pond snails (family Lymnaeidae) to investigate the morphological and genetic consequences of infiltration of freshwater snails into geothermal habitats. In particular, we aimed at studying the changes in shell shape and proportions as well as the formation of unique hot-water haplotypes and the occurrence of the latter beyond geothermal waterbodies. All six species studied demonstrate diminutive body size in hot sites accompanied, in four species, by apparent alterations in shell proportions. A phenomenon of phenotypic ‘juvenilization’, when adult and able to reproduce individuals demonstrate shell proportions characteristic for full-grown individuals living under ‘normal’ conditions, is described. Unique ‘thermal’ haplotypes, not found beyond the geothermal sites, were normally restricted to a single locality, and no signs of frequent ‘travels’ of snails from one thermal habitat to another are seen. In the vast majority of cases, these exclusive haplotypes are separated from their ancestors by only a few (1–3) mutational steps, which may indicate their relatively recent origin. We are inclined to relate both size reduction and ‘juvenilization’ to the life-cycle re-adjustment following the penetration of lymnaeids to thermal habitats. The ecological (‘thermal’) intraspecific races of different species, forming in geothermal habitats, exhibit, to a great extent, evolutionary predictability (=convergent evolution; =parallelisms). The dilemma ‘ecological race vs. young species’ in application to the taxonomy of these hot-water populations is briefly discussed.

Variability character of conchological features in the mollusc Gibbulinopsis signata (Mousson, 1873) (Gastropoda: Pupillidae) in Northwestern Uzbekistan

Analysis of the results shows that mollusc of the species Gibbulinopsis signata (Mousson, 1873) from the northwestern region of Uzbekistan exhibits significant variability in conchological characteristics, including variability in shell size, shape, and colour, as well as variations in aperture shape and fittings. Among these characteristics, shell height is found to be the most variable and is recognised as an ecological and biological indicator of mollusc’s adaptability to habitat conditions. The results of molecular analysis, using the sequences of the gene 18S of ribosomal DNA showed that all three populations belonged to the same species.

Genome-wide phylogeography reveals cryptic speciation in the circumglobal planktonic calcifier Limacina bulimoides.

Little is known about when and how planktonic species arise and persist in the open ocean without apparent dispersal barriers. Pteropods are planktonic snails with thin shells susceptible to dissolution that are used as bio-indicators of ocean acidification. However, distinct evolutionary units respond to acidification differently, and defining species boundaries is therefore crucial for predicting the impact of changing ocean conditions. In this global population genomic study of the shelled pteropod Limacina bulimoides, we combined genetic (759,000 single nucleotide polymorphisms) and morphometric data from 161 individuals, revealing three major genetic lineages (FST = 0.29-0.41): an "Atlantic lineage" sampled across the Atlantic, an "Indo-Pacific lineage" sampled in the North Pacific and Indian Ocean, and a "Pacific lineage" sampled in the North and South Pacific. A time-calibrated phylogeny suggests that the lineages diverged about 1 million years ago, with estimated effective population size remaining high (~10 million) throughout Pleistocene glacial cycles. We do not observe any signatures of recent hybridization, even in areas of sympatry in the North Pacific. While the lineages are reproductively isolated, they are morphologically cryptic, with overlapping shell shape and shell colour distributions. Despite showing that the circumglobal L. bulimoides consists of multiple species with smaller ranges than initially thought, we found that these pteropods still possess high levels of genetic variability. Our study adds to the growing evidence that speciation is often overlooked in the open ocean, and suggests the presence of distinct biological species within many other currently defined circumglobal planktonic species.

Microstructure and properties of W[sbnd]Cu composites with low copper content at different sintering temperatures

For the tungsten‑copper composite salt solution prepared using the wet chemical method, micron-sized W-10/15wt.%Cu precursors with hollow spherical shell shape were prepared by spray drying. They were then subjected to hydrogen reduction to obtain irregularly shaped nanoscale W-10/15wt.%Cu composite powders, which were pressed under cold isostatic pressure to obtain high-density green bodies without forming agent and lower pressing force. Different densification processes were carried out at different sintering temperatures, thus remarkably influencing the microstructure and properties of WCu composites. At sintering temperature of 1350 °C, W-10/15wt.%Cu composites reached the maximum relative densities of 97.5 and 98.2 g/cm3, respectively, and exhibited the best thermal and mechanical properties. W-10wt.%Cu composites had a high thermal conductivity (TC) of 195 W/(m·K), coefficient of thermal expansion (CTE) of 6.20 ppm/°C, hardness of 346 HV, and flexural strength of 1146 MPa. W-15wt.%Cu composites also showed excellent performance with TC of up to 208 W/(m·K), CTE of 7.13 ppm/°C, hardness of 328 HV, and flexural strength of 806 MPa. The W-10/15wt.%Cu composites prepared in this study were of great application in the field of electronic packaging.

Effects of different geometric patterns on free form gridshell structures

<p class="JIASSAbstract">Gridshells are commonly known as structures with the shape and rigidity of a double curvature shell consisting of a grid, not a continuous surface. In recent decades, these structures have attracted significant attention. The impact of various geometric patterns on free form gridshell structures is investigated here to demonstrate the necessity of collaboration between structural and architectural characteristics in enhancing structure efficiency. To that goal, a framework is proposed where three shells are first designed, and then six geometric patterns are formed on them. The main factors for evaluation of gridshells are decreasing the steel weight as an economic index and decreasing the displacement as a structural index, also, finite element method is used for structurally analyzing the gridshells, and the generated gridshells are compared to each other based on the mentioned indices. For the optimization process, an approach is suggested to find the most optimum gridshell, then numerical results show the efficiency of the proposed alternative approach.</p>

Geometry and static analysis of thin shells in the form of a diagonal translation surface of the velaroidal type

The author presents the results of a study of the geometry and stress-strain state of a surface with a frame of three flat curves in coordinate planes, which have found application today mainly in the shipbuilding industry. The purpose of the work is to identify from the point of view of the stress-strain state from the action of a constant uniformly distributed load the most optimal shell of a diagonal transfer of a velaroidal type with the same main frame of three superellipses. The static calculation was performed using the SCAD program based on the finite element method, designed to perform strength calculations of various types and purposes of structures. The influence of parametric equations for defining a surface depending on the generative family of the same type of cross sections on the distribution pattern of normal stresses and bending moments is shown. The results obtained can help architects and designers with choosing the shape of shells for new projects.

Land snail diversity in central China: revision of Laeocathaica Möllendorff, 1899 (Gastropoda, Camaenidae), with descriptions of seven new species.

Central China harbors the native dart-sac-bearing camaenids Laeocathaica. The genus is revised and seven new species are proposed based on museum material and newly collected specimens. This work confirmed that most Laeocathaica species have restricted habitats. The comparison of the dart sac apparatus among the dart-sac-bearing camaenid genera indicated the importance of the presence of the proximal accessory sac that might be analogous to the membranous/muscular sac surrounding the proximal dart sac and/or the distal region of the vagina near the atrium, which also plays a significant role in the diagnosis of Laeocathaica species based on its number, symmetry and position on the dart sac. Species with similar shell morphology were studied using geometric morphometric methods to detect variations in shell shape. A molecular phylogenetic analysis based on 16S and ITS2 sequence data of partial Laeocathaica species and many other dart-sac-bearing taxa suggested that Laeocathaica might be monophyletic. Furthermore, the present phylogeny indicated that Stilpnodiscus, Cathaica, Bradybaena, and Pseudobuliminus might be polyphyletic and therefore the taxonomy of dart-sac-bearing camaenids in this region requires a thorough revision. This work reconfirms that the Southern Gansu Plateau is important as a hotspot for malacodiversity conservation on the Chinese mainland.

Natal Philopatry in a Long-Lived Species: The Return of Reproductive River Turtles Marked and Released as Hatchlings

Natal philopatry—the return of an animal to its place of birth to reproduce—can shape population genetics and link essential habitats across generations, yet examples from long-term mark-recapture studies are rare. In this study, we observed 136 nests of Northern Map Turtles at Mount Union, Pennsylvania, between 2000 and 2008 and then individually marked and released 691 hatchling turtles into the Juniata River. During a recent six-year period (from 2017 to 2022), 46 of the hatchling-marked turtles (6.7%) returned to Mount Union as adult females to nest. The ages of these turtles ranged from 11–22 years at first recapture, and their mean age was 17 years. Forty-one hatchling-marked females came from observed nests with known mothers, and remarkably, just four (of 52) mothers produced over half of the returning females. The minimum ages of the oldest female turtles were estimated at 39 years, with reproductive lifetimes of at least 23 years. Our results indicate that a few long-lived Super Moms have made extraordinary contributions to hatchling recruitment and population viability of Northern Map Turtles of the Juniata River. The timing of release also had a significant influence on the probability of a turtle returning, with hatchlings released in May returning at a higher rate than those released earlier in the spring. In addition, morphological characteristics of hatchling-marked females suggest that factors causing shell shape abnormalities in adult turtles have not abated over the past two decades as previously theorized and likely involve exposure of juveniles to contaminants in the Juniata River rather than any maternal influence.

Buckling of an imperfect spherical shell subjected to external pressure

This paper presents numerical results focusing on the buckling behaviour of externally pressurised imperfect spherical shells. The numerical model followed the recommendations of the European Standard EN1993-1-6. A good agreement between the model FE and the experimental results with an average difference of less than 7% was found. The perfect steel spherical shell is then subjected to several imperfection approaches, such as (a) eigenmode imperfection and (b) single load indentation (SLI) imperfection. The eigenmode shape imperfection proves to be the worst imperfection for the externally pressurised spherical shells, yet the SLI is an attractive technique to simulate the realistic imperfection (i.e., dent/dimple). Based on the recommendation of the European Standard EN1993-1-6 for imperfection tolerance, the SLI imperfection was used for the realistic-case imperfection approach for different spherical shell configurations. A lower-bound closed-form empirical formula for a spherical shell under external pressure was proposed for the spherical shell with the single load indentation (SLI). The results show that for a shell shape parameter λ ≥ 10, the EBC provides a much higher knockdown factor compared to the guidelines of NASA SP -8032, Wagner, and lower-bound closed-form empirical formula (the differences are in the range of 48%–56%).

Design and Analysis of a Hemispherical Parallel Mechanism for Forearm–Wrist Rehabilitation

This paper presents a bionic cable-driven mechanism to simulate the motion of human wrist which is suitable for human forearm–wrist rehabilitation. It fulfills workspace of the human forearm–wrist and it can train the joint in active and passive. With three degrees of freedom, it completes the supination/pronation of the forearm, the radial/ulnar deviation, and flexion/extension of the wrist. In addition to the movement of single degree of freedom of the forearm–wrist, it can also complete circumduction of the wrist. The mechanism consists of revolving platform, parallel mechanism, supporting mechanism, and movable table. Especially, in the parallel mechanism, a spring is added between the fixed and moving platform, and the moving platform is designed in the shape of a hemispherical shell. Utilizing the resilient properties of the extension spring and the support of the hemispherical shell, the problem of slack in the cable is solved in this mechanism. Since the spring is a passive component and cannot be calculated directly, a method combining kinematics and statics is proposed to calculate the relationship between the pose of the moving platform and the cable. Meanwhile, the kinematics, statics, and workspace solution of the mechanism are derived. Then, the simulation results demonstrate the accurateness and feasibility of the inverse kinematics and workspace derivation of the mechanism. Finally, the experiments are analyzed to verify the mechanism suitable for forearm–wrist rehabilitation tasks.

Consumer preferences for oyster trait attributes in China: A choice experiment

Consumers are the ultimate value realizers of aquatic germplasm resources. Their choice preferences for a species trait are the endogenous driving force for constructing a long-term utilization mechanism for marine resources. So, this study gauges customer preferences and willingness to pay for various aquatic oyster trait qualities to provide marketable information for oyster breeding. We collected primary data from selected major cities in Shandong Province, China. Based on the choice experiment method, the data were analyzed using a mixed logit model and a latent category model to identify consumer preferences and willingness to pay for oyster trait attributes (shell shape, size, thickness, and color). We find that customer preferences for oyster characteristics vary widely. The highest willingness to pay was for the shell size trait, and the results were still significant after the information intervention. Next, the consumers' preferences for oyster trait attributes also differed between the low-market-value base consumers (70.5%) and the high-market-value market consumers (29.5%). In conclusion, this research offers recommendations from several angles to give breeders focused and practical references in identifying and protecting aquatic germplasm resources.

Evolutionary contingency in lingulid brachiopods across mass extinctions

Morphology usually serves as an effective proxy for functional ecology,1,2,3,4,5 and evaluating morphological, anatomical, and ecological changes permits a deeper understanding of the nature of diversification and macroevolution.5,6,7,8,9,10,11,12 Lingulid (order Lingulida) brachiopods are both diverse and abundant during the early Palaeozoic but decrease in diversity over time, with only a few genera of linguloids and discinoids present in modern marine ecosystems, resulting in them frequently being referred to as "living fossils."13,14,15 The dynamics that drove this decline remain uncertain, and it has not been determined if there is an associated decline in morphological and ecological diversity. Here, we apply geometric morphometrics to reconstruct global morphospace occupation for lingulid brachiopods through the Phanerozoic, with results showing that maximum morphospace occupation was reached by the Early Ordovician. At this time of peak diversity, linguloids with a sub-rectangular shell shape already possessed several evolutionary features, such as the rearrangement of mantle canals and reduction of the pseudointerarea, common to all modern infaunal forms. The end Ordovician mass extinction has a differential effect on linguloids, disproportionally wiping out those forms with a rounded shell shape, while forms with sub-rectangular shells survived both the end Ordovician and the Permian-Triassic mass extinctions, leaving a fauna predominantly composed of infaunal forms. For discinoids, both morphospace occupation and epibenthic life strategies remain consistent through the Phanerozoic. Morphospace occupation over time, when considered using anatomical and ecological analyses, suggests that the limited morphological and ecological diversity of modern lingulid brachiopods reflects evolutionary contingency rather than deterministic processes.

First record and description of three new species in the land snail genus Diplommatina Benson, 1849 (Caenogastropoda, Diplommatinidae) from Satun Province, Thailand

The micro land snail genus Diplommatina (family Diplommatinidae) is widely distributed in Southeast Asia and includes many endemic species. Three new species of Diplommatina are described from Satun Province in southern Thailand. Diplommatina bulonensissp. nov., D. laemsonensissp. nov. and D. prakaiphetensissp. nov. are distinguished from other species in the genus by their shell size and shape, the number of radial ribs on the penultimate whorl, the number of whorls, and features of the peristome. The agreement between phylogenetic tree based on analyses of COI and 16S sequences and comparative morphology support the delineation of these new species which, when compared to related species, belong to well-differentiated clades. The K2P distance between any of the three new species and other Diplommatina species included in the molecular phylogenetic analysis was at least 5.5% in COI and 3.9% in 16S. Two of the three new species (D. prakaiphetensissp. nov. and D. bulonensissp. nov.) are apparently endemic to Prakaiphet Hill and Bulon Pai Island, respectively. Additionally, we documented a new regional record for D. naiyanetri in Satun Province. These new species and records contribute to the knowledge of Thailand’s land snail biodiversity and highlight the need of conservation protections for regional karst habitats.

Feasibility Study of Laser-Assisted Incremental Forming for Carbon Fiber Reinforced Thermo Plastic Based on 3D-CAD Data

A three-dimensional (3D) printer can be used to form various shapes in a single process. However, shell shape formation is difficult because of the low adhesion strength between the layers in 3D printing, and sufficient stiffness cannot be maintained. Therefore, the authors focused on laser-assisted incremental forming, which enables the formation of shell shapes from sheet materials, and used carbon fiber reinforced thermo plastic (CFRTP) for the samples. In the study, a laser-assist incremental forming system based on 3D computer-aided design (CAD) data was developed. The system comprises computer-aided manufacturing (CAM) system, which generates a tool path based on CAD data and evaluates the formability between the CAD data and 3D-scanned data, including alignment compensation. The feasibility of the developed system was demonstrated through a set of forming experiments.

We Made It in Venice! But Then …? Reversing Notions of Center and Periphery

We Made It in Venice! But Then …? Reversing Notions of Center and Periphery

Species identification of the mud snails <i>Batillaria multiformis</i> and <i>B. attramentaria</i> by PCR-RFLP method—the advantages of two restriction enzymes—

The habitats of Batillaria multiformis (Near Threatened species) and Batillaria attramentaria are often overlapping on a mudflat, and young individuals of two Batillaria snails were difficult to identify by shell morphology. This is one of the causes that the study, such as population dynamics of two Batillaria species, did not advance. Recently, species identification by DNA analysis for B. multiformis and B. attramentaria was developed using a PCR-RFLP method. However, using only one restriction enzyme and universal primer may lead to misidentification. Therefore, this study examined a more precise method using two restriction enzymes for the PCR-RFLP technique. The mitochondrial DNA gene encoding cytochrome c oxidase subunit I (COI) was amplified, and two restriction enzymes, PstI and HinfI, were selected for this method. The number and position of bands after the agarose gel electrophoresis enable us to identify the two Batillaria species. After the effectiveness of this method was confirmed by adult B. multiformis and B. attramentaria that had each typical shell shape, young Batillaria snail samples that were difficult for morphological identification were identified by this PCR-RFLP method. We proved that the proposed PCR-RFLP identification method is simple and reliable in identifying the morphologically similar B. multiformis and B. attramentaria.