The world’s tiniest land snails from Laos and Vietnam (Gastropoda, Pulmonata, Hypselostomatidae)

Two new, extremely small land snail species, Angustopila coprologos Páll-Gergely, Jochum & Hunyadi n. sp. and Angustopila psammion Páll-Gergely, Vermeulen & Anker n. sp. are described from northern Vietnam and northern Laos, respectively. The former is characterized by a rough surface sculpture and bears tiny mud granules arranged in a pattern of radial lines on its shell surface. The latter species is the new global record-holder of the tiniest land snail title, with a shell width of 0.6–0.68 mm and a shell height of 0.46–0.57 mm. These measurements surpass the former records of Angustopila pallgergelyi and Acmella nana.

Determination of error of sector location of subterrene stabilizing section based on coordinate control data

Results of the study of actual accuracy of the stabilizing section shell of the prototype subterrene are presented. The problem of experimental verification of the assumptions made in modeling is formulated. The research described in the article was carried out on the basis of experimental data obtained by coordinate control of the shell of the prototype subterrene. Data analysis was carried out by mathematical modeling of the surface of the shell of the stabilizing section as a whole and the surfaces of each individual sector. The obtained mathematical models are based on the approximation of sets of points obtained in the process of coordinate control by cylindrical surfaces. The article shows that at least a significant part of the deviations of the geometric shape of the section shell (from 30.3 to 52.3%) is explained by errors in the location of the sectors and errors in their radii. On the basis of the performed modeling, absolute values of the corresponding errors and actual values of the dimensions and deviations were determined. Studies confirmed the possibility of ensuring the specified accuracy of the shell surface when implementing the assembly technology used in a pilot production. At the same time, the proximity of actual deviations to maximum permissible values can lead to problems in ensuring the stable quality of subterrene case products in mass production. Correlation analysis of coordinate control data and statistical analysis of the series of residuals of developed models were carried out. Correlation analysis confirmed the dependence of deviations of experimental points on their cylindrical coordinates, which confirms the significance of the error in the location of the sectors in deviations from the geometric accuracy of the shell.

On in-plane drill rotations for Cosserat surfaces

We show under some natural smoothness assumptions that pure in-plane drill rotations as deformation mappings of a C 2 -smooth regular shell surface to another one parametrized over the same domain are impossible provided that the rotations are fixed at a portion of the boundary. Put otherwise, if the tangent vectors of the new surface are obtained locally by only rotating the given tangent vectors, and if these rotations have a rotation axis which coincides everywhere with the normal of the initial surface, then the two surfaces are equal provided they coincide at a portion of the boundary. In the language of differential geometry of surfaces, we show that any isometry which leaves normals invariant and which coincides with the given surface at a portion of the boundary is the identity mapping.

Microbiome divergence of marine gastropod species separated by the Isthmus of Panama

The rise of the Isthmus of Panama ~3.5 mya separated populations of many marine organisms, which then diverged into new geminate sister species currently living in the Eastern Pacific Ocean and Caribbean Sea. However, we know very little about how such evolutionary divergences of host species have shaped their microbiomes. Here, we compared the microbiomes of whole-body and shell-surface samples of geminate species of marine gastropods in the genera Cerithium and Cerithideopsis to those of congeneric outgroups. Our results show that the effects of the Isthmus on microbiome composition varied among host genera and between sample types within the same hosts. In the whole-body samples, microbiome compositions of geminate species pairs in the focal genera tended to be similar, likely due to host filtering, although the strength of this relationship varied among the two groups and across similarity metrics. Shell-surface communities show contrasting patterns, with co-divergence between the host taxa and a small number of microbial clades evident in Cerithideopsis, but not Cerithium. These results suggest that (i) the rise of the Isthmus of Panama affected microbiomes of geminate hosts in a complex and clade-specific manner and (ii) host-associated microbial taxa respond differently to vicariance events than the hosts themselves.

Flow-induced surface crystallization of granular particles in cylindrical confinement

An interesting phenomenon that a layer of crystallized shell formed at the container wall during an orifice flow in a cylinder is observed experimentally and is investigated in DEM simulation. Different from shear or vibration driven granular crystallization, our simulation shows during the flow the shell layer is formed spontaneously from stagnant zone at the base and grows at a constant rate to the top with no external drive. Roughness of the shell surface is defined as a standard deviation of the surface height and its development is found to disobey existed growth models. The growth rate of the shell is found linearly proportional to the flow rate. This shell is static and served as a rough wall in an orifice flow with frictionless sidewall, which changes the flow profiles and its stress properties, and in turn guarantees a constant flow rate.

DEFORMATION AND BUCKLING ANALYSIS OF SHALLOW CONICAL SHELLS BASED ON IMPROVED MODEL OF WIND LOAD USING ENVIRONMENT ANSYS

The process of deformation and buckling of shallow thin-walled elastic conical shells has been investigated for the case of significantly non-uniform stress-strain state due to the action of wind load based on improved model of pressure application schema to the surface of shallow shell and for hinged hedge of border. An improved model of wind load was based on data presented in terms [5, 6] and was a logical continuation of previous investigation of wind action on shallow conical shells based on model of first approach [3]. Deformation and buckling process investigation has been carried out using software ANSYS which effectivity was approved by the fact of being used by NASA for its aerospace projects. A model of shallow conical shell has been made using four-corner finite element SHELL 281 with 8 nodes that let us obtain not only symmetrical relatively to the axis of rotation buckling form but an asymmetrical too. Two types of computation have been made during numerical modeling – linear bifurcation computation with determination of linear pressure qcr value and corresponding to it buckling form, and computation of geometrically non-linear problem of deformation with determination of limit pressure qlim and corresponding buckling form. Obtained buckling forms have been compared to the deformed shape of shell surface when aerodynamic computations have been carried out using software ANSYS. An estimation analysis has been made for case of application of improved model of wind load in comparison to the previous investigation according to the values of baring capacity and buckling shape coherence during resolution of static tasks and comparison to the results of aerodynamic solution. An analysis of base parameter influence has been carried out for the model of first approach and current improved model according to the bearing capacity value and local extremums on schema of pressure intensity distribution of wind load. Specific moments of deformation process computations based on improved model using environment ANSYS have been mentioned and of further analysis on the basis of improved model with it specifics have been given too.

A norovirus uses bile salts to escape antibody recognition while enhancing receptor binding.

Noroviruses, members of the Calicivirus family, are the major cause of epidemic gastroenteritis in humans, causing ∼20 million cases annually. These plus-strand RNA viruses have T=3 icosahedral protein capsids with 90 pronounced protruding (P) domain dimers to which antibodies and cellular receptors bind. In the case of mouse norovirus (MNV), bile salts have been shown to enhance receptor (CD300lf) binding to the P domain. We previously demonstrated that the P domains of several genotypes are markedly flexible and ‘float’ over the shell, but the role of this flexibility was unclear. Recently, we demonstrated that bile causes a 90° rotation and collapse of the P domain on to the shell surface. Since bile binds distal to the P/shell interface, it was not at all clear how it could cause such dramatic changes. Here we present the near-atomic resolution cryo-EM structure of the protruding MNV complexed with a neutralizing Fab. Combined with previous results, we show here that bile salts cause allosteric conformational changes in the P domain that block antibody recognition to the top of the P domain. In addition, bile also causes a major rearrangement of the P domain dimers that are likely responsible for the bile-induced collapse of the P domain onto the shell. In the contracted shell conformation, antibodies to the P1 and shell domains are not expected to bind. Therefore, at the site of infection in the gut, the host’s own bile allows the virus to escape antibody-mediated neutralization while enhancing cell attachment. Importance: The major feature of the Calicivirus capsids are the 90 protruding domains (P domains) that are the site of cell receptor(s) attachment and antibody epitopes. We previously demonstrated that these P domains are highly mobile and that bile causes these ‘floating’ P domains in mouse norovirus (MNV) to contract onto the shell surface. Here, we present the near atomic cryo-EM structure of the isolated MNV P domain complexed with a neutralizing Fab fragment. Together, the data shows that bile causes two sets of changes. First, bile causes allosteric conformational changes in the epitopes at the top of the P domain that block antibody binding. Second, bile causes the P domain dimer subunits to rotate relative to each other, causing contraction of the P domain that buries epitopes at the base of the P and shell domains. Collectively, MNV uses the host’s own metabolites to enhance cell receptor binding while simultaneously blocking antibody recognition.

Nitrogen isotope sclerochronology - insights into coastal environmental conditions and Pinna nobilis ecology

<p><em>Pinna nobilis</em> is a large bivalve endemic to the Mediterranean Sea that lives in shallow coastal areas. Due to its size and relatively fast shell growth rates, it is an interesting taxon for high resolution geochemical and sclerochronological research. Subsequently to previous analyses of δ<sup>18</sup>O and δ<sup>13</sup>C in <em>P. nobilis</em> shells, here, we investigate nitrogen isotopes in the carbonate-bound organic matrix (δ<sup>15</sup>N<sub>CBOM</sub>) of this species. Our objectives were to test if <em>P. nobilis</em> shells (i) can be used as an indicator of the isotopic baseline of the system, and (ii) is a good candidate for obtaining high-resolution temporal data on environmental δ<sup>15</sup>N variability. Due to the multiple mass mortality events of <em>P. nobilis</em> spreading throughout the Mediterranean, including the Adriatic Sea, we also tested if (iii) <em>P. nobilis</em> geochemistry changes as a response to diseases.</p><p>Shells were opportunistically collected by skin diving from 4 shallow coastal localities in the eastern Adriatic, as a part of a project on mortality monitoring. Specimens from Lim channel (October 2019), Kaštela Bay (January 2020) and Mali Ston Bay (November 2019) were collected alive, while in Pag Bay, shells of three recently dead specimens were collected in September 2020. Tissue and epibionts were removed and shells carefully cleaned and air-dried. Shell powder was collected by milling sample swaths by hand using a DREMEL Fortiflex drill equipped with a 300 μm tungsten carbide drill bit. For δ<sup>15</sup>N<sub>CBOM</sub> analysis, three shells from each locality were processed and three replicas were collected from each of these shells by milling shallow lines parallel to the growth axis from the internal shell surface. In addition, high-resolution δ<sup>15</sup>N<sub>CBOM</sub> data were obtained for one shell from Kaštela by milling lines (N=40) perpendicular to the major growth axis from the external shell surface. From this shell we also collected shell powder for δ<sup>18</sup>O<sub>shell</sub> and δ<sup>13</sup>C<sub>shell</sub> analysis to enable placing δ<sup>15</sup>N<sub>CBOM</sub> into temporal context. Isotope samples were analyzed Union College on an elemental analyzer - isotope ratio mass spectrometer.</p><p>Results indicate significant differences in δ<sup>15</sup>N<sub>CBOM</sub> between sampling localities, with lowest values recorded for shells from Pag Bay (3.73±0.36‰), and highest for shells sampled in Lim channel (7.04±0.63‰). High-resolution δ<sup>15</sup>N<sub>CBOM</sub> data obtained from the shell collected from Kaštela Bay corresponded to a time interval from spring 2018 to spring 2019. These data showed relatively small variations (5.02±0.33‰). However, δ<sup>15</sup>N<sub>CBOM</sub> values increased to 8.65±1.61‰ closest to the shell margin, and were coupled with a decrease in δ<sup>13</sup>C<sub>shell</sub> values, indicating that this animal was experiencing stressful conditions several months prior to its death. According to our findings, δ<sup>15</sup>N<sub>CBOM</sub> values serve as an indicator of the isotopic baseline of the ecosystem as well as a potential powerful tool to study bivalve physiology.</p><p>Research was the supported by the Croatian Science Foundation, research project BivACME.</p>