Optical Sensitivity of Camera-Like Eyes to White Light

Gastropod mollusks are convenient model organisms for studying the functioning of the visual system. The purpose of this work is to estimate the value of the optical sensitivity to white light for the camera-like eyes of gastropod mollusks and humans and analyze its effect on the spatial resolving power in two regions of the retina: in the center—for single photoreceptors of the first/second type in a mollusk and single cones in humans—and in the periphery—for single photoreceptors of the first/second type in a mollusk, as well as for single rods/cones and their groups, subject to spatial summation in humans. The methods of histology, light and transmission electron microscopy, morphometry, calculations and methods of statistical analysis are used in the work. In a mollusk, with a fixed pupil area, the value of the optical sensitivity of the eye to white light in the center of the retina for single photoreceptors of the first/second type is 0.5/0.006 μm2·sr and in the periphery of the retina, 0.9/0.009 μm2·sr. In humans, at the minimum and maximum pupil area, respectively, the value of the optical sensitivity of the eye to white light in the center of the retina (foveola) for single cones varies from 0.00053 to 0.028 μm2·sr, and in the periphery of the retina (far periphery) for single rods from 0.011 to 0.575 μm2·sr, for single cones from 0.025 to 1.319 μm2·sr, for the groups of rods from 3859 to 204,094 μm2·sr and for the groups of cones from 2.5 to 131 μm2·sr. The value of the optical sensitivity of the eyes to white light for single photoreceptors of the first/second type in both regions of the retina in a mollusk, as well as for single cones in the center and groups of rods/cones in the periphery of the retina in humans, corresponds to the ambient light conditions during periods of activity and does not affect the spatial resolving power.

Variability in macrozoobenthic assemblages along a gradient of environmental conditions in the stream water of karst caves (Lower Shakuranskaya Cave, western Caucasus)

The fauna of the stream water in the Lower Shakuranskaya Cave in central Abkhazia, western Caucasus, was studied. This cave has a large inlet and an extended entrance ecotone area of approximately 60 m, which makes it a convenient area for studying macrozoobenthic assemblages across a gradient of environmental factors. The cave has 13 species of stygobionts, 10 species of stygophiles and 18 species of stygoxenes. The number of species and the abundance and biomass of stygobionts per station were the highest near the boundary of the photic zone, at a distance of 50–60 m from the entrance to the cave, and gradually decreased toward both the remote parts of the cavity and the cave exit. The most abundant stygobionts were gastropod mollusks of the Hydrobiidae family, and Xiphocaridinella shrimp comprised the main part of the biomass. It has been shown that the main environmental factors determining the distribution of macrozoobenthos are luminosity and distance from the entrance to a cave. According to the differences in their reactions to these environmental factors, several groups of species were identified. In addition, three main assemblages of macrozoobenthic species were described: (1) an assemblage of epigean species near the cave entrance area; (2) stygobionts in remote parts of the cave outside the photic zone; and (3) a mixed assemblage in the cave ecotone, where a faint light penetrates. The specific details related to the faunal structure in the ecotone of the cave are discussed, as well as active and passive methods by which stygoxenes invade underground cavities.

An approach using ddRADseq and machine learning for understanding speciation in Antarctic Antarctophilinidae gastropods

Sampling impediments and paucity of suitable material for molecular analyses have precluded the study of speciation and radiation of deep-sea species in Antarctica. We analyzed barcodes together with genome-wide single nucleotide polymorphisms obtained from double digestion restriction site-associated DNA sequencing (ddRADseq) for species in the family Antarctophilinidae. We also reevaluated the fossil record associated with this taxon to provide further insights into the origin of the group. Novel approaches to identify distinctive genetic lineages, including unsupervised machine learning variational autoencoder plots, were used to establish species hypothesis frameworks. In this sense, three undescribed species and a complex of cryptic species were identified, suggesting allopatric speciation connected to geographic or bathymetric isolation. We further observed that the shallow waters around the Scotia Arc and on the continental shelf in the Weddell Sea present high endemism and diversity. In contrast, likely due to the glacial pressure during the Cenozoic, a deep-sea group with fewer species emerged expanding over great areas in the South-Atlantic Antarctic Ridge. Our study agrees on how diachronic paleoclimatic and current environmental factors shaped Antarctic communities both at the shallow and deep-sea levels, promoting Antarctica as the center of origin for numerous taxa such as gastropod mollusks.

Vitreous body of the camera-like eyes of terrestrial gastropod mollusks (Heterobranchia, Stylommatophora)

Using the methods of light and electron microscopy, the morphological properties were studied, and the evolutionary changes in the vitreous body of the camera-like eyes of some species of terrestrial gastropod pulmonate molluscs were traced. It was demonstrated that all the considered properties of the vitreous body of molluscs are typical for terrestrial pulmonates. In the course of evolution, as a result of the land development by mollusks, the properties of their vitreous body have hardly changed.

Mollusks of the family Valvatidae Gray, 1840 (Gastropoda, Heterobranchia) of the Taz River basin (Western Siberia)

The fauna of the rivers of the north of Western Siberia that do not belong to the Ob’ River basin is of particular interest from the point of view of zoogeography and understanding of the processes of formation of the freshwater malacofauna. Starting in the taiga zone, these rivers flow north and cannot serve as a way of interzonal dispersal of species from lower latitudes. However, information about the fresh-water malacofauna of these river basins is poorly presented in the scientific literature, some of the published species findings are doubtful or erroneous. The gastropod mollusks of the family Valvatidae of the Taz river basin (Western Siberia) are considered. The basin is located closer to the Yenisei than to the Ob’ River basin. The study was based on original authors’ material represented by both qualitative and quantitative samples. It has been found that eight species of mollusks of the genus Valvata occurs in the water reservoirs and streams of the Taz basin, an annotated list of species is presented, and a brief zoogeographic characteristic is given. Three species (Valvata helicoidea, V. sorensis and V. korotnevi) are for the first time recorded from the basin, one of them (V. korotnevi) is for the first time recorded from the Western Siberia waterbodies.

New data on Roxania Leach, 1847 (Gastropoda: Heterobranchia) from the Sea of Marmara based on materials of the Russian expedition in 1894

Heterobranch specimens of the genus Roxania collected during the Russian expedition (1894) aboard the Turkish steamship Selânik to the Sea of Marmara are found in the collection of the Zoological Institute of the Russian Academy of Sciences (Saint Petersburg). One of the aims of the expedition was investigation of the fauna of the Sea of Marmara including its deepest zone to compare with the Black Sea. In 1896 A.A. Ostroumoff published a report on the expedition. Heterobranch mollusks of the genus Roxania are represented in our material by two lots from the first voyage of the expedition to the archipelago of the Prince Islands. The specimens were identified by K.O. Milaschewitsch as Roxania utriculus (Brocchi, 1814) and “Cryptaxis imperforatus n. sp.”, but a description of the last taxon has not been published. In this study, the specimens labeled by Milachewitch as Cryptaxis imperforatus n. sp. were identified as belonging to Roxania monterosatoi Dautzenberg et H. Fischer, 1896. The species is recorded for the Sea of Marmara for the first time; the description and illustrations of the species are presented. Most species of gastropod mollusks collected during the expedition including all samples of Roxania were represented by empty shells. Taxonomical value of the columella morphology in Roxania species is discussed. Based on this character the species of the genus can be divided into two groups: R. utriculus species group (mouth channeled) and R. monterosatoi species group (mouth without a channel). Morphological and molecular phylogenetic investigations are needed to clarify the status of these two groups.

Gastropod Learning and Memory (Aplysia, Hermissenda, Lymnaea, and Others)

Euopisthobranchia (Aplysia), Nudipleura (Tritonia, Hermissenda, Pleurobranchaea), and Panpulmonata (Lymnaea, Helix, Limax) gastropod mollusks exhibit a variety of reflex, rhythmic, and motivated behaviors that can be modified by elementary forms of learning and memory. The relative simplicity of their nervous systems and behavioral repertoires has allowed the uncovering of processes of neuronal and synaptic plasticity underlying non-associative learning, such as habituation, sensitization, and different forms of associative learning, such as classical and operant conditioning. Decades of work on these simpler and accessible animal systems have almost uniquely yielded an understanding into the mechanistic basis of learning and memory spanning behavior, neuronal circuitry, and molecules. Given the conservative nature of evolutionary processes, the mechanisms deciphered have also provided valuable insights into the neural basis of learning and memory in other metazoans, including higher vertebrates.

First epidemiological survey of Angiostrongylus vasorum in domestic dogs from Spain

Background: Angiostrongylus vasorum is the causative agent of canine angiostrongylosis, a disease that mainly affects domestic dogs and others wild carnivores. In Europe, the number of infected animals is increasing, being mainly located in central and southern countries. In Spain, several studies have reported high prevalences of A. vasorum in wild animals. However, there are no studies that address the current situation and distribution of the disease in domestic dogs in the country. Therefore, the objective of the present study was to evaluate the prevalence of A. vasorum in different areas of Spain. Methods: Between November 2018 and October 2019, blood was sampled from a total of 2024 domestic dogs from 6 eco-epidemiological zones of Spain with climates that favour the presence of competent gastropod mollusks, and tested for the presence of A. vasorum circulating antigens using Angio Detect TM . All included dogs lived outdoors or had regular access to areas with vegetation. Results: The prevalence of canine angiostrongylosis in the studied areas of Spain was 1.73%. No differences were found between males and females. By age, significant higher prevalances were found in dogs younger than 4 years. By eco-epidemiological areas, the highest prevalences were obtained in the north (2.74%) and northwest (1.86%) of Spain, and the lowest was described in the western area (0.93%). Conclusions: The prevalence obtained can be considered high and demonstrates the presence of canine angiostrongylosis in Spain, in those areas where infected wild animals have been described and where climatic conditions are favourable for the establishment of the disease. Prophylactic measures should be prescribed for dogs at risk of infection and veterinarians should be aware of the importance of this disease.