Dart formation in Helix aspersa (Mollusca, Gastropoda)

The structure of pristine preserved shells of Mesozoic ammonoids was examined in order to identify whether there are homologous or homoplasic traits in the internal structure of the shell wall that can be used for phylogeny and taxonomy, particularly in regard to episodic growth interruptions and the dorsal shell wall. Different sculptural elements that are usually associated with an interruption in shell growth, like varices, constrictions, flares, parabolae and radial lirae, were analysed to determine whether these have a general ground plan in internal structure or not. Varices and constrictions shows no interruptions in shell growth but have characteristic internal thickenings formed by the nacreous layer. Owing to the general structural conformity of varices and constrictions in the shells of Jurassic and Cretaceous taxa, they are probably homologous traits. Flares, parabolae and radial lirae are characterized by an interruption in growth, they mark the succession of two different shell generations. Parabolae and flares mark an interruption of shell growth caused by the formation of a frill-like, outwardly bent temporary aperture (but differ in their general shape). The outer prismatic layer, the nacreous layer and an apertural prismatic coating (i.e. indicates a mantle cover) build their aperture. Radial lirae are formed by imbrication of two successive sigmoid shell lamellae, formed either by the organic periostracum or the outer prismatic layer. Each lira has a characteristic adorally-projecting, scythe-like appendage arising from its crest. Owing to the general structural and morphological conformity of flares and parabolae it is likely that both represent different expressions of a homologous structure. Morphological transitions imply that parabolae and radial lirae are probably homologous as well. Mesozoic Ammonoidea had different types of the dorsal shell wall. The vast majority of planispirally taxa forms a prismatic reduced dorsal shell wall, consisting of an outer organic component (e.g. wrinkle layer) and the subsequent formed dorsal inner prismatic layer. The latter is only secreted in the rear of the living chamber. Reduced dorsal shell wall construction of Ammonoidea is generally homologous and exists in the early ontogenetic stages of all taxa. Rather few ammonoid taxa reinforce the dorsal shell wall. Some planispirally taxa form a nacreous reduced dorsal shell wall in the rear part of the living chamber, which is reinforced by secondary pair of nacreous and inner prismatic layers. Heteromorph taxa and some planispirally taxa secreted a complete dorsal shell wall at the aperture, i.e. the ventral, lateral and dorsal shell wall form a continum aperturally and adapically. The dorsal shell layers are identical with the ventral shell wall. The broad phylogenetic distribution of dorsally secreted nacre indicates a plesiomorphic relic trait of the orthocone ammonoid ancestors.

During the courtship of Helix aspersa, the snails push calcareous darts into one another. To examine the importance f this unusual action for the normal expression of their sexual behaviour, one group of Helix aspersa was prevented from exchanging darts by surgically removing their dart sacs. Another group of Helix aspersa had their digitiform glands surgically removed. These glands secrete a mucus that coats the dart. Glandless snails were capable of exchanging darts, but the darts lacked their normal mucus coating. Both dartless and glandless pairs required more courtship time to reach copulation than did sham‐operated controls. Therefore, it appears that it is the mucus from the digitiform gland, not the mechanical action of the dart, which affects courtship duration.Injections of gland homogenate decreased the courtship duration of sexually receptive, dartless, and glandless snails. Gland homogenate also increased the size of the recipient's genital eversion, and retarded locomotion. The mucus was only effective if it entered the circulatory system of a sexually receptive snail at a specific stage of genital eversion.The active agent in the digitiform gland mucus fulfills the requirements for the substance to be classified as a pheromone. It enters the circulatory system of the conspecific via inoculation by the dart.

Mussel Mytilus galloprovincialis (Lamarck, 1819) is widespread in the north-western part of the Black Sea, it is the active filter feeders sea water, is an important component of various zoocenoses. Mollusk is the object of fisheries and mariculture. Three phenotypes of mussel are separated on features of distribution of a violet pigment in outer prismatic shell layer: Fa – in a prismatic layer of purple pigment absent; Fb – pigment paints the whole of prismatic layer; Fc – pigment is localized in the form of radial strips alternating with unpigmented zones. The first two forms are interpreted homozygotes, last – heterozygotes.The purpose of the work is to study the distribution of mussels different phenotypic groups on the depths of the Odessa coast.The material for the work were the mussels collected in may 2012 at two stations – on the beach Langeron (depth 3,5 m) and in the area of hydrobiological station of Odessa National Mechnikov University (at a depth of 1 m breakwater; 6 m – fouling stones). Samples were collected with the frame area of 0,01 m2. Total collected and analyzed 459 exemplars of mussels, which were divided into the size groups with an interval of 10 mm.Index deficiency of heterozygotes (D) was calculated according to the equation:D = (Hо– Hс)/Нс ,Hо – the number of heterozygotes observed in the population; Hс – the number of heterozygotes expected by Hardy-Weinberg equation. A positive value means a deficit of heterozygotes D and negative – of their surplus.At a depth of 3,5 m represented only mussels of three size groups. About 52% of the total numbers of mollusks are size class of 20-29 mm, for other two classes remaining accounted to 24%.Among the small mollusks provided only at a depth of 6 m, the dominant were mussels of phenotype Fb (60%); half mussel of phenotype Fa (30%) and 10% – mussels of phenotype Fc. In large size class at a depth of 1 m dominated mussels of phenotype Fb – up to 100%.Mussels of phenotype Fa represent a smaller part of mollusks in almost all researched depths (1, 3,5, and 6 m), respectively, 23, 18 and 25% of the total number.At a depth of 1 m the number of mussels of phenotypes Fb and Fc is almost the same – 40 and 37%. At a depth of 3,5 m the number of these mussels of phenotypes differ slightly – 35 and 47%. Mussels of phenotype Fb, on the contrary, is dominated at a depth of 6 m, they accounted for more than half of the total number of animals – 55%. Analysis of the conformity of actual frequencies of phenotypes with theoretical data calculated by the relation of the Hardy-Weinberg equilibrium using the criterion c2 showed that at depths of 1 and 3,5 m obtained facts were not statistically significant.At a depth of 1,0 and 3,5 m observed a deficit of heterozygotes, and at the 6-meter depth – their surplus.

An endocochliate embryo model for the Mesozoic Ammonitida is proposed based on scanning electron microscopy of the ammonitella (= embryonic shell) stage of well‐preserved Japanese Cretaceous specimens belonging to nine species of five superfamilies. As in other specimens described previously, the ammonitella wall succeeding from the initial chamber ("protoconch") in the species examined consists of the inner prismatic, middle subprismatic and outer prismatic layers, with minute tubercles resting on the outer. Developmental patterns of these structures and their comparison with primary shell formation in modern Nautilus and Spirula suggest that the outer thin prismatic layer with microtubercles was secreted by the exterior epithelium after the completion of the main ammonitella wall by the interior shell gland. Thus, the early ammonite embryo might have had an endocochliate structural plan as in coleoids, and at the time of hatching the overlying mantle epithelium had shifted anteriorly to become an ectocochliate condition.

Abstract. Marine bivalve mollusk shells can offer valuable insights into past oceanographic variability and seasonality. Given its ecological and archeological significance, Mytilus californianus (California mussel) presents the opportunity to examine seasonal and decadal changes recorded in its shell over centuries to millennia. While dark–light growth bands in M. californianus shells could be advantageous for reconstructing past environments, uncertainties remain regarding shell structure, environmental controls of dark–light-band formation, and the amount of time represented by a dark–light pair. By analyzing a suite of M. californianus shells collected in 2002, 2003, 2019, and 2020 from Bodega Bay, California, we describe the mineralogical composition; establish relationships among the growth band pattern, micro-environment, and collection season; and compare shell structure and growth band expression between the archival (2002–2003) and modern (2019–2020) shells. We identified three mineralogical layers in M. californianus: an outer prismatic calcite layer, a middle aragonite layer, and a secondary inner prismatic calcite layer, which makes M. californianus the only Mytilus species to precipitate a secondary calcite layer. Within the inner calcite layer, light bands are strongly correlated with winter collection months and could be used to reconstruct periods with moderate, stable temperatures and minimal upwelling. Additionally, modern shells have significantly thinner inner calcite layers and more poorly expressed growth bands than the archival shells, although we also show that growth band contrast is strongly influenced by the micro-environment. Mytilus californianus from northern California is calcifying differently, and apparently more slowly, than it was 20 years ago.

Environmental control of strontium and magnesium in Mytilus

The shell microstructure of 30 species belonging to 14 genera and nine families of protobranchs were newly described using scanning electron microscopy. As a result, 13 microstructures were recognized. The shell microstructural composition of protobranchia is conservative at a superfamily level among the Recent species, whereas this trend is not necessarily apply to that of fossil protobranchs. Greater diversity of the shell microstructure was revealed in protobranchs than previously known. (1) Nuculoidea commonly have outer prismatic and middle/inner nacreous structures. The outer prismatic layer is newly classified into five types in Nuculidae. In particular, the irregular fibrous prismatic structure was first observed in Nuculoidea. The interspecific variability of outer prismatic layers seems to provide crucial criteria for phylogenetic grouping in this superfamily. (2) Nuculanoidea have non-nacreous structures including the homogeneous, fibrous prismatic and fine complex crossed lamellar str...

In nature, shells exhibit remarkable high toughness and impact resistance to the external load despite their brittle main constituent and simple hierarchical structure. In this work, the structure of the mussel shell Hyriopsis cumingii is analyzed by scanning electron microscope and atomic force microscope, and the macro/micro compression and impact tests are performed. Results show that the shell has a three-layer structure: an outer cuticle layer, a prismatic layer, and a nacreous layer. The stiffer and load-dependent prismatic layer is conducive to improve the impact resistance of shell structure. Fracture morphology after failure proves that cracks are transgranularly propagated inside the prism and aragonite platelet, and the crack deflection and platelet pullout can effectively lock the stress, thereby eventually improving the impact-resistance and toughness of the shell.

Limpets of the family Nacellidae construct their shells with an outer prismatic layer, underlain by an acicular-foliated layer, and occasionally an internal crossed-lamellar layer. The outer layer consists of prisms oriented approximately perpendicular to the shell growth surface. At the transition to the acicular-foliated layer, these prisms subdivide into segments that become incorporated into the underlying folia. The folia are extensive, radially oriented, and further subdivided into transverse acicles, hence the term "acicular-foliated". Crystallographically, the outer prisms are remarkable in having their c-axes oriented at a high angle to their elongation and aligned toward the shell margin, with one a-axis typically perpendicular to the growth surface. The prisms exhibit a high degree of co-orientation, with textures ranging from diffuse to well-organized sheet textures. When considering rhombohedral face orientations, the texture may appear either single- or double-crystal-like. This crystallographic arrangement is inherited by the acicular-foliated layer, where the texture invariably becomes stronger. Such an unusual orientation likely results from oriented nucleation on an organic template, possibly the mantle surface, combined with crystal competition in the direction toward the shell margin. From both morphological and crystallographic perspectives, the prismatic-acicular-foliated microstructural complex of nacellids is unparalleled among molluscs.

polymorphs, calcite, aragonite, and vaterite, of which the former two are most commonly observed as biological polymorphs in marine mollusks. The pearl oyster P. fucata can generate these two polymorphs in vivo; calcite crystals in the outer prismatic layer and aragonite crystals in the inner nacreous layer of the shell, under the same physical conditions. These phenomena are a key to solving the enigma of bio-mineralization. The early research on shells of mollusks was mainly carried out by electron-microscopic observation [2–6]. Shells are mainly composed of two distinct layers. The outer prismatic layer shows the honeycomb-like network structure of a polygonal prism. The inner nacreous layer shows a cemented brick or veneer-like multilayer structure. Figure 1 shows a schematic representation of the inner nacreous layer. In this case, part of the brick corresponds to the aragonite crystal and part of the cement corresponds to the organic matrix. The organic matrix was first discovered in 1855 by Fremy [7], and is designated as “conchiolin”. Biochemical research on the organic matrix has recently developed, and now it has become clear that the organic matrix is mainly composed of proteins. Some parts of the organic matrix are soluble in water containing EDTA, and are called the water-soluble organic matrix (WSM). Most parts of the organic matrix are insoluble in water and are called the water-insoluble organic matrix (WISM). The group of Morse and colleagues [8–12] and that of Weiner and colleagues [13– 17] reported that shell proteins existing in the WSM mainly controlled the polymorphs of calcium carbonate crystals. In contrast, the early work of Watabe and Wilbur [18] and Wilbur and Watabe [19] and more recent reports by Wheeler [20] and by Samata et al. [21] showed that WISM proteins were mainly involved in polymorphic control. At present, it is difficult to determine which view is correct, because the groups with opposing views used different materials. The groups of Morse and colleagues [8–12] and Weiner and colleagues

The shell wall in ammonoids contains a pore-canal network similar to that detected recently in the shell wall of the Ordovician nautiloid Orthoceras. In the Jurassic monomorphic ammonoids Quenstedtoceras, Cosmoceras, Lissoceras and the Cretaceous heteromorphic ammonoid Ptychoceras investigated in this study vertical canals arranged in parallel rows, are partially preserved, although no horizontal canals are preserved as in Orthoceras. In Quenstedtoceras and Ptychoceras the vertical canals extend not only through the inner prismatic layer, as in Orthoceras, but also through the nacreous layer. Therefore both layers were secreted on the body-shell attachment band behind the apertural margin. In the juvenile shells, only the very thin outer prismatic layer formed the apertural margin. As in Orthoceras, the canals had walls of calcified organic fibres that were partially or entirely dissolved during diagenesis. The pore-canal network in the shell wall of Quenstedtoceras and Ptychoceras contributed to achieving neutral buoyancy. As indicated by the high numbers of mini-pores in the connecting rings, the siphuncle was employed for adjusting buoyancy during vertical migrations. The “wrinkles”, “furrows”, “pits”, “dots”, “ridges”, “Ritzsteifen” and “Runselschicht” in the “wrinkle layer”, previously described in the ammonoid shell walls, are remnants of the pore-canal network.

The arrangement of sedimentation patterns in titration rows of various haemagglutinins is reported and titres read as clumping and as sedimentation patterns compared. Five main types of sedimentation patterns are described. In some systems negative and pseudo-negative patterns correspond to strong clumping but positive disc patterns can be present in the absence of clumping. Chromic chloride can be used as coupling reagent for passive haemagglutination tests with conjugated dinitrophenyl and polyalanin haptens. Extracts from the albumin glands of Helix aspersa contain anti-A-like haemagglutinin and contents from eggs of S. trutta an anti-B-like substance.

Comprehensive biochemistry. Volume 11: Water-soluble vitamins, hormones, and antibiotics: Edited by Marcel Florkin and Elmer H. Stotz. Elsevier, Amsterdam (1963). xvi + 237 pp. $11.50

Brain areas with normatively greater cerebral perfusion in early life may be more susceptible to beta amyloid deposition in late life

In this work, a kind of compact, dual-band and dual-polarized stacked patch antenna with an extremely simple structure is proposed for mm-wave communications. Two patch layers are engaged for the patch antenna, which corresponds to the low 28-GHz band and the high 39-GHz band radiations, respectively. The given antenna is capacitively coupled fed through the coaxial cables. The overall dimension of the proposed antenna which operates over the two mm-wave frequency bands from 26.4 to 29.7 GHz and from 36.5 to 44.7 GHz is only 4 mm × 4 mm × 1.12 mm.