A new subspecies of Ruthenica filograna(Pulmonata: Clausiliidae) from Croatia

A new subspecies of land snails of the clausiliid genus Ruthenica has been found on the territory of Republic of Croatia. Illustrated description is presented. New subspecies differs from others in shell shape, semi-apostrophic aperture and sculpture pattern.

Methodology for calculating rope drums for stability

. The problems of the stability of rope drums are quite urgent. The rope drum is in most cases a thin-walled shell, which, under the influence of external pressure from the rope, can lead to loss of stability. The stability issues of the drum shell, which is loaded with rope turns, are very important, because the safety and reliability of the rope hoist is directly related to them The studies carried out made it possible to obtain a new method for calculating the stability of cylindrical shells, which takes into account not only the length of the shell, but also the rigidity of the connection with the head. In addition, a calculation formula was obtained to determine the critical pressure of the oval shell, which gives a fairly good agreement with the experiments of American scientists. The work also considered the effect of the difference in wall thickness on the critical load of the drum. The studies carried out made it possible to conclude that the parameters of the rope drums make it possible to completely eliminate the need to install rings and stiffeners. Also as a result of research it was found that the shell of the crane drum under the influence of a radial load cannot lose stability. Studies have shown that in all cases the stability margin of the rope drum shell is greater than the strength margin. In this case, the load created by the rope wound on the drum is considered, with the ratios of the radius of the drum and the rope typical for crane construction. In addition, a coefficient was established that takes into account the elasticity of the shell-head joint. The studies carried out have shown that such initial deviations of the drum shell shape as ovality do not give a significant increase in the critical load. The results obtained are quite important, since they allow reducing the metal consumption of the rope drum shell and at the same time ensuring its reliable operation. A decrease in metal consumption is achieved by reducing the thickness of the shell and the absence of the need to install rings and stiffeners. This will lead to a decrease in metal consumption and energy consumption of the crane itself, and also simplifies the technology of manufacturing a rope drum.

Intra-Specific Variability in Whorl Growth-Rate among Land Gastropods with Conispirally-Coiled Shells

For most conispirally-coiled Gastropods with determinate growth, the geometry of spirally-winding whorls is usually constrained by a strong negative correlation between whorl growth rate and the number of whorls reached at adulthood, as originally reported by the late S.J. Gould. Yet, beyond the tight control of shell-shape at the species level – resulting from this constraint – what about the amplitude of the intra-specific variability of whorl growth-rate, partly contributing to the variability of the overall shell-size at the species level? I address the issue by designing and implementing a new, indirect method for routinely evaluating whorl growth-rate, thereby aiming at considerably saving measurement time, and making it possible to easily achieve repeated measurements across samples large enough to reach statistical significance. This approach was applied to a series of eight common land snail species. The amplitude of intra-specific variability in whorl growth, evaluated this way, proves: (i) being markedly different among the eight investigated species (by a factor that can exceed 2x); (ii) being, yet, high enough, in all cases, to require compensating variations in the adult number of whorls, so as to limit the resulting consequences on the amplitude of the intra-specific variability of adult shell-size. Despite those marked differences in the amplitudes of intra-specific variability of whorl growth-rate among species, no significant relationship was observed between intraspecific variability of whorl growth rate and species-specific shell-shape types (discoidal/globular/elongate) and only weak positive relationship was observed with species-specific typical shell sizes. However, a rather strong positive correlation was found, as expected, between the degree of intra-specific variability of the whorl growth-rate and the degree of intra-specific variability of the number of whorls reached at adulthood (with the yet unexplained exception of one among the eight investigated species).

Journeys Through Shape and Time: Palaeobiology of Cenozoic New Zealand Spissatella and Eucrassatella (Bivalvia, Crassatellidae)

<p>A novel, highly-integrated approach combining morphometric, stratocladistic and sclerochronological methods has been applied to two genera of New Zealand Cenozoic crassatellid bivalve (Family Crassatellidae): Spissatella Finlay, 1926 and Eucrassatella Iredale, 1924. This study builds on previous work on Spissatella that demonstrated their amenability to shape analysis and provided a foundation for evolutionary studies of the group. The taxonomy of these crassatellids has been in need of revision; a number of changes to generic placement having been proposed in recent publications without redescription. These bivalves are character-depauperate and known only from fossil material within New Zealand, making them challenging subjects for the phylogenetic analysis that would, ideally, inform taxonomic revision. Geometric morphometric methods have been used to characterise the morphological variation of the study group in terms of shape. Landmarks/semilandmarks that capture internal hard-part morphology and external shell shape, have been compared with internal landmarks only, outline shape semilandmarks only, and outline shape Fourier transform methods, and are shown to best combine comprehensive coverage of total shell form with high correct reassignment of individuals to taxa in multidimensional morphospace. Procrustes-superimposed landmark/semilandmark configurations have been ordinated using Principal Components Analysis (PCA), and PCA plots have been used to compare the shape variation of each species. The independance in morphospace of Spissatella n. sp. C from S. trailli and S. clifdenensis has been established. Covariation of internal morphology and shell-shape has been interpreted as supporting the interdependance of shell and body/mantle proposed by Stasek (1963). PCA scores have been combined with traditional morphological characters and stratigraphic data to produce a phylogenetic tree using stratocladistics, a form of parsimony-based analysis which seeks to minimise combined morphological and stratigraphic debt. This technique also assesses the placement of taxa in ancestral positions on internal nodes of the tree. Combining discretised morphometric data with stratigraphic and morphological data in a single analysis has been shown to produce a more resolved tree than analyses based only on continuous morphometric data. The new analyses demonstrate paraphyly of both Eucrassatella and Spissatella as previously recognised. A taxonomic revision of the studied taxa has been undertaken, incorporating information from both morphometric and phylogenetic studies. Spissatella subobesa and S. maudensis are referred to Eucrassatella. Spissatella discrepans is synonymised with S. acculta. Triplicitella n. gen. and S.maxwelli n. sp. are described. Oxygen isotope analysis has been employed to show that shell-banding in these species is, on average, likely to have been laid down annually. Using this information, the longitudinal dataset of outlines from Crampton & Maxwell (2000) has been recalibrated to use chronological age rather than size to compare shape across taxa, and investigate heterochrony in twelve pairs of species representing either ancestor-descendant, sister-group or lineage-segment relationships. All of the heterochronic processes sensu Gould (1977), namely progenesis, neoteny, acceleration and hypermorphosis, as well as proportioned dwarfism and proportioned gigantism, are identified as having affected evolution within this clade.</p>

Journeys Through Shape and Time: Palaeobiology of Cenozoic New Zealand Spissatella and Eucrassatella (Bivalvia, Crassatellidae)

<p>A novel, highly-integrated approach combining morphometric, stratocladistic and sclerochronological methods has been applied to two genera of New Zealand Cenozoic crassatellid bivalve (Family Crassatellidae): Spissatella Finlay, 1926 and Eucrassatella Iredale, 1924. This study builds on previous work on Spissatella that demonstrated their amenability to shape analysis and provided a foundation for evolutionary studies of the group. The taxonomy of these crassatellids has been in need of revision; a number of changes to generic placement having been proposed in recent publications without redescription. These bivalves are character-depauperate and known only from fossil material within New Zealand, making them challenging subjects for the phylogenetic analysis that would, ideally, inform taxonomic revision. Geometric morphometric methods have been used to characterise the morphological variation of the study group in terms of shape. Landmarks/semilandmarks that capture internal hard-part morphology and external shell shape, have been compared with internal landmarks only, outline shape semilandmarks only, and outline shape Fourier transform methods, and are shown to best combine comprehensive coverage of total shell form with high correct reassignment of individuals to taxa in multidimensional morphospace. Procrustes-superimposed landmark/semilandmark configurations have been ordinated using Principal Components Analysis (PCA), and PCA plots have been used to compare the shape variation of each species. The independance in morphospace of Spissatella n. sp. C from S. trailli and S. clifdenensis has been established. Covariation of internal morphology and shell-shape has been interpreted as supporting the interdependance of shell and body/mantle proposed by Stasek (1963). PCA scores have been combined with traditional morphological characters and stratigraphic data to produce a phylogenetic tree using stratocladistics, a form of parsimony-based analysis which seeks to minimise combined morphological and stratigraphic debt. This technique also assesses the placement of taxa in ancestral positions on internal nodes of the tree. Combining discretised morphometric data with stratigraphic and morphological data in a single analysis has been shown to produce a more resolved tree than analyses based only on continuous morphometric data. The new analyses demonstrate paraphyly of both Eucrassatella and Spissatella as previously recognised. A taxonomic revision of the studied taxa has been undertaken, incorporating information from both morphometric and phylogenetic studies. Spissatella subobesa and S. maudensis are referred to Eucrassatella. Spissatella discrepans is synonymised with S. acculta. Triplicitella n. gen. and S.maxwelli n. sp. are described. Oxygen isotope analysis has been employed to show that shell-banding in these species is, on average, likely to have been laid down annually. Using this information, the longitudinal dataset of outlines from Crampton & Maxwell (2000) has been recalibrated to use chronological age rather than size to compare shape across taxa, and investigate heterochrony in twelve pairs of species representing either ancestor-descendant, sister-group or lineage-segment relationships. All of the heterochronic processes sensu Gould (1977), namely progenesis, neoteny, acceleration and hypermorphosis, as well as proportioned dwarfism and proportioned gigantism, are identified as having affected evolution within this clade.</p>

Shell shape, morphometrics and relative growth of four sympatric limpet species from the Algarve coast (southern Portugal)

This study analysed and compared the shell shape, morphometrics and relative growth of four sympatric limpet species (Patella depressa, Patella ulyssiponensis, Patella vulgata and Siphonaria pectinata) collected at Praia da Luz in Lagos (Algarve coast – southern Portugal). Morphometric relationships were established through regression analysis between linear (shell length, width and height), ponderal (total weight), area (shell base and surface areas) and volume variables (shell internal and total volumes). Relative growth (isometry vs allometry) was analysed to assess variation in the growth rate of morphometric variables throughout the species ontogeny. In addition, morphometric indices (ellipticity, conicity, density, surface area and volumetry) were calculated to further characterize shell shape. Overall, 1482 individuals with broad size and weight ranges were analysed (P. depressa = 354; P. ulyssiponensis = 306; P. vulgata = 408; S. pectinata = 414). All regressions were highly significant (P < 0.001) and the morphometric variables were strongly correlated (r = 0.761 to 0.994). Among 28 morphometric relationships, there were 14 isometries, 13 positive allometries and only one negative allometry. The morphometric indices revealed clear morphological differences between species and were mostly size-dependent, reflecting gradual changes in shell shape during growth. The main results are compared with a compilation of analogous data reported for these limpet species throughout their distributional range. Overall, the general trends in relative growth are discussed in terms of the species life habits, main traits and functional morphology.

Ontogeny in the steinmanellines (Bivalvia: Trigoniida): an intra- and interspecific appraisal using the Early Cretaceous faunas from the Neuquén Basin as a case study

Despite the paleontological relevance and paleobiological interest of trigoniid bivalves, our knowledge of their ontogeny—an aspect of crucial evolutionary importance—remains limited. Here, we assess the intra- and interspecific ontogenetic variations exhibited by the genus Steinmanella Crickmay (Myophorellidae: Steinmanellinae) during the early Valanginian–late Hauterivian of Argentina and explore some of their implications. The (ontogenetic) allometric trajectories of seven species recognized for this interval were estimated from longitudinal data using 3D geometric morphometrics, segmented regressions, and model selection tools, and then compared using trajectory analysis and allometric spaces. Our results show that within-species shell shape variation describes biphasic ontogenetic trajectories, decoupled from ontogenetic changes shown by sculpture, with a gradual decay in magnitude as ontogeny progresses. The modes of change characterizing each phase (crescentic growth and anteroposterior elongation, respectively) are conserved across species, thus representing a feature of Steinmanella ontogeny; its evolutionary origin is inferred to be a consequence of the rate modification and allometric repatterning of the ancestral ontogeny. Among species, trajectories are more variable during early ontogenetic stages, becoming increasingly conservative at later stages. Trajectories’ general orientation allows recognition of two stratigraphically consecutive groups of species, hinting at a potentially higher genus-level diversity in the studied interval. In terms of functional morphology, juveniles had a morphology more suited for active burrowing than adults, whose features are associated with a sedentary lifestyle. The characteristic disparity of trigoniids could be related to the existence of an ontogenetic period of greater shell malleability betrayed by the presence of crescentic shape change.

Shell shape as an indicator of phenotypic stocks of Tehuelche scallop (Aequipecten tehuelchus) in Northern Patagonia, Argentina

Tehuelche scallop, Aequipecten tehuelchus, is a commercially exploited species in Northern Patagonia, Argentina. Without genetic differentiation at the species level, A. tehuelchus presents three morphotypes: tehuelchus, madrynensis, and a non-common variant felipponei. The main goal of this study was to analyze the shell shape variation of Tehuelche scallop to differentiate and identify the phenotypic stocks. The shape differences between and within the two main morphotypes (tehuelchus and madrynensis) were assessed using geometric morphometrics in nine localities. The shell shape presented variability at geographic scale, with the morphologic traits that maximized the differentiation among localities between the tehuelchus and madrynensis morphotypes. Scallops from madrynensis morphotype presented higher and circular shell discs with smaller auricles than those from tehuelchus morphotype. Morphometric differentiation was also detected among localities of each morphotype, wherein most of the variability was related to the disc circularity and the symmetry of the auricles. The presence of morphologic variation in San Matias and San Josi gulfs, wherein a single genetic pool is shared, evidenced the plastic nature of the species. Given the distribution of this resource in distinct provincial jurisdictions, the differentiation of phenotypic stocks has relevance in the context of fishery management, especially if zoning and rotational strategies are implemented.

Shell morphometric ratios as a tool for taxonomic determination in gastropods: a case study in Nerita (Gastropoda, Neritidae)

In the study, we compare the shell shape morphometrics in four species of neritid gastropods (Nerita fulgurans, Nerita tessellata, Nerita peloronta and Nerita versicolor), collected in Accra Beach (Barbados Island). We tested the hypothesis that the morphometric ratios can be used as a tool in the taxonomic determination among these four species of neritids. For this we determine the morphometric ratios from the external (length, height, width) and internal (shell aperture length, shell aperture width) measures. A principal component analysis (PCA) was used to determine which ratios were significant, and subsequently the proposed hypothesis was tested using the Kruskal–Wallis test. The morphometric ratios AW/H and AL/L were decisive in distinguishing the four species of neritids studied. In this study, the hypothesis of the efficacy of the use of shell morphometric ratios as an instrument in taxonomic studies was corroborated for the four species. Due to its low cost, this methodology can be applied in the recognition of species that have lost their external characteristics such as operculum, spire or colour and also in the identification of fossil specimens.

Accurate Results for Free Vibration of Doubly Curved Shallow Shells of Rectangular Planform (Part.1)

A method is presented for determining the free vibration frequencies of doubly curved, isotropic shallow shells under general edge conditions and is used to obtain accurate natural frequencies for wide range of geometric parameters. Based on the shallow shell theory applicable to thin thickness shells, a method of Ritz is extended to derive a frequency equation wherein the displacement functions are modified to accommodate arbitrary sets of edge conditions for both in-plane and out-of-plane motions. In numerical computation, convergence is tested against series terms and comparison study is made with existing results by other authors. Twenty one sets of frequency parameters are tabulated for a wide range of shell shape and curvature ratio to serve as data for future comparison and practical design purpose.