A snail is, in loose terms, a shelled gastropod. The name is most applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name snail is used for most of the members of the molluscan class Gastropoda that have a coiled shell, large enough for the animal to retract into; when the word "snail" is used in this most general sense, it includes not just land snails but numerous species of sea snails and freshwater snails. Gastropods that lack a shell, or have only an internal shell, are called slugs, land snails that have only a small shell are called semi-slugs. Snails have considerable human relevance, including as food items, as pests, as vectors of disease, their shells are used as decorative objects and are incorporated into jewelry; the snail has had some cultural significance, has been used as a metaphor. Snails that respire using a lung belong to the group Pulmonata; as traditionally defined, the Pulmonata were found to be polyphyletic in a molecular study per Jörger et al. dating from 2010.
But snails with gills form a polyphyletic group. Both snails that have lungs and snails that have gills have diversified so over geological time that a few species with gills can be found on land and numerous species with lungs can be found in freshwater. A few marine species have lungs. Snails can be found in a wide range of environments, including ditches and the abyssal depths of the sea. Although land snails may be more familiar to laymen, marine snails constitute the majority of snail species, have much greater diversity and a greater biomass. Numerous kinds of snail can be found in fresh water. Most snails have thousands of microscopic tooth-like structures located on a banded ribbon-like tongue called a radula; the radula works like a file. Many snails are herbivorous, eating plants or rasping algae from surfaces with their radulae, though a few land species and many marine species are omnivores or predatory carnivores. Snails cannot absorb colored pigments when eating paper or cardboard so their feces are colored.
Several species of the genus Achatina and related genera are known as giant African land snails. The largest living species of sea snail is Syrinx aruanus; the snail Lymnaea makes decisions by using only two types of neuron: one deciding whether the snail is hungry, the other deciding whether there is food in the vicinity. The largest known land gastropod is the African giant snail Achatina achatina, the largest recorded specimen of which measured 39.3 centimetres from snout to tail when extended, with a shell length of 27.3 cm in December 1978. It weighed 900 g. Named Gee Geronimo, this snail was owned by Christopher Hudson of Hove, East Sussex, UK, was collected in Sierra Leone in June 1976. Gastropods that lack a conspicuous shell are called slugs rather than snails; some species of slug have a red shell, some have only an internal vestige that serves as a calcium repository, others have no shell at all. Other than that there is little morphological difference between slugs and snails. There are however important differences in habitats and behavior.
A shell-less animal is much more maneuverable and compressible, so quite large land slugs can take advantage of habitats or retreats with little space, retreats that would be inaccessible to a similar-sized snail. Slugs squeeze themselves into confined spaces such as under loose bark on trees or under stone slabs, logs or wooden boards lying on the ground. In such retreats they are in less danger from either predators or desiccation, those are suitable places for laying their eggs. Slugs as a group are far from monophyletic; the reduction or loss of the shell has evolved many times independently within several different lineages of gastropods. The various taxa of land and sea gastropods with slug morphology occur within numerous higher taxonomic groups of shelled species. Land snails are known as an agricultural and garden pest but some species are an edible delicacy and household pets. There are a variety of snail-control measures that gardeners and farmers use in an attempt to reduce damage to valuable plants.
Traditional pesticides are still used, as are many less toxic control options such as concentrated garlic or wormwood solutions. Copper metal is a snail repellent, thus a copper band around the trunk of a tree will prevent snails from climbing up and reaching the foliage and fruit. Placing crushed egg shells on the soil around garden plants can deter snails from coming to the plants; the decollate snail will capture and eat garden snails, because of this it has sometimes been introduced as a biological pest control agent. However, this is not without problems, as the decollate snail is just as to attack and devour other gastropods that may represent a valuable part of the native fauna of the region. In French cuisine, edible snails are served for instance in Escargot à la Bourguignonne; the practice of rearing snails for food is known as heliciculture. For purposes of cultivation, the snails are kept in a
Seven Sisters, Sussex
The Seven Sisters is a series of chalk cliffs by the English Channel. They form part of the South Downs in East Sussex, between the towns of Seaford and Eastbourne in southern England, they are within the South Downs National Park, bounded by the coast, the Cuckmere and the A259 road. They are the remnants of dry valleys in the chalk South Downs, which are being eroded by the sea. From west to east, the sequence starts just east of Cuckmere Haven; the cliff peaks and the dips between them are individually named. Listed below, the peaks are in italics. There are seven hills, with an eighth one being created by the erosion of the sea. Haven Brow Short Bottom Short Brow Limekiln Bottom Rough Brow Rough Bottom Brass Point Gap Bottom Flagstaff Point Flagstaff Bottom Flat Hill Flathill Bottom Baily's Hill Michel Dean Went Hill Brow. Just east of the last peak is Birling Gap. Beyond, on the top of the next hill, is Belle Tout lighthouse and beyond that Beachy Head. A lighthouse in the sea marks the latter headland.
The South Downs Way runs along the edge of the cliffs, taking a undulating course. Many landmarks around the area are named after the cliffs, including the Seven Sisters Sheep Centre; the Seven Sisters cliffs are used in filmmaking and television production as a stand-in for the more famous White Cliffs of Dover, since they are free of anachronistic modern development and are allowed to erode naturally. As a result, the Seven Sisters and Beachy Head remain a bright white colour, whereas the White Cliffs of Dover are protected due to the important port and are therefore covered in vegetation and are greening as a result, they are featured at the beginning of the film Robin Hood: Prince of Thieves, at the end of the film Atonement where Robbie and Cecilia always wanted to live. Much of the 2015 feature film Mr. Holmes was filmed around the Seven Sisters. An east-facing photo of the Seven Sisters is included as one of the default landscape wallpapers packaged with Microsoft Windows 7. Seven Sisters Country Park
Russia the Russian Federation, is a transcontinental country in Eastern Europe and North Asia. At 17,125,200 square kilometres, Russia is by far or by a considerable margin the largest country in the world by area, covering more than one-eighth of the Earth's inhabited land area, the ninth most populous, with about 146.77 million people as of 2019, including Crimea. About 77 % of the population live in the European part of the country. Russia's capital, Moscow, is one of the largest cities in the world and the second largest city in Europe. Extending across the entirety of Northern Asia and much of Eastern Europe, Russia spans eleven time zones and incorporates a wide range of environments and landforms. From northwest to southeast, Russia shares land borders with Norway, Estonia, Latvia and Poland, Ukraine, Azerbaijan, China and North Korea, it shares maritime borders with Japan by the Sea of Okhotsk and the U. S. state of Alaska across the Bering Strait. However, Russia recognises two more countries that border it, Abkhazia and South Ossetia, both of which are internationally recognized as parts of Georgia.
The East Slavs emerged as a recognizable group in Europe between the 3rd and 8th centuries AD. Founded and ruled by a Varangian warrior elite and their descendants, the medieval state of Rus arose in the 9th century. In 988 it adopted Orthodox Christianity from the Byzantine Empire, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Rus' disintegrated into a number of smaller states; the Grand Duchy of Moscow reunified the surrounding Russian principalities and achieved independence from the Golden Horde. By the 18th century, the nation had expanded through conquest and exploration to become the Russian Empire, the third largest empire in history, stretching from Poland on the west to Alaska on the east. Following the Russian Revolution, the Russian Soviet Federative Socialist Republic became the largest and leading constituent of the Union of Soviet Socialist Republics, the world's first constitutionally socialist state; the Soviet Union played a decisive role in the Allied victory in World War II, emerged as a recognized superpower and rival to the United States during the Cold War.
The Soviet era saw some of the most significant technological achievements of the 20th century, including the world's first human-made satellite and the launching of the first humans in space. By the end of 1990, the Soviet Union had the world's second largest economy, largest standing military in the world and the largest stockpile of weapons of mass destruction. Following the dissolution of the Soviet Union in 1991, twelve independent republics emerged from the USSR: Russia, Belarus, Uzbekistan, Azerbaijan, Kyrgyzstan, Tajikistan and the Baltic states regained independence: Estonia, Lithuania, it is governed as a federal semi-presidential republic. Russia's economy ranks as the twelfth largest by nominal GDP and sixth largest by purchasing power parity in 2018. Russia's extensive mineral and energy resources are the largest such reserves in the world, making it one of the leading producers of oil and natural gas globally; the country is one of the five recognized nuclear weapons states and possesses the largest stockpile of weapons of mass destruction.
Russia is a great power as well as a regional power and has been characterised as a potential superpower. It is a permanent member of the United Nations Security Council and an active global partner of ASEAN, as well as a member of the Shanghai Cooperation Organisation, the G20, the Council of Europe, the Asia-Pacific Economic Cooperation, the Organization for Security and Co-operation in Europe, the World Trade Organization, as well as being the leading member of the Commonwealth of Independent States, the Collective Security Treaty Organization and one of the five members of the Eurasian Economic Union, along with Armenia, Belarus and Kyrgyzstan; the name Russia is derived from Rus', a medieval state populated by the East Slavs. However, this proper name became more prominent in the history, the country was called by its inhabitants "Русская Земля", which can be translated as "Russian Land" or "Land of Rus'". In order to distinguish this state from other states derived from it, it is denoted as Kievan Rus' by modern historiography.
The name Rus itself comes from the early medieval Rus' people, Swedish merchants and warriors who relocated from across the Baltic Sea and founded a state centered on Novgorod that became Kievan Rus. An old Latin version of the name Rus' was Ruthenia applied to the western and southern regions of Rus' that were adjacent to Catholic Europe; the current name of the country, Россия, comes from the Byzantine Greek designation of the Rus', Ρωσσία Rossía—spelled Ρωσία in Modern Greek. The standard way to refer to citizens of Russia is rossiyane in Russian. There are two Russian words which are commonly
Soil is a mixture of organic matter, gases and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: as a medium for plant growth as a means of water storage and purification as a modifier of Earth's atmosphere as a habitat for organismsAll of these functions, in their turn, modify the soil; the pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, the biosphere. The term pedolith, used to refer to the soil, translates to ground stone in the sense "fundamental stone". Soil consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, soil scientists can envisage soils as a three-state system of solids and gases. Soil is a product of several factors: the influence of climate, relief and the soil's parent materials interacting over time, it continually undergoes development by way of numerous physical and biological processes, which include weathering with associated erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Soil science has two basic branches of study: pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well. Soil is commonly referred to as earth or dirt. Soil is a major component of the Earth's ecosystem; the world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution.
With respect to Earth's carbon cycle, soil is an important carbon reservoir, it is one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback; this prediction has, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species microbial and in the main still unexplored. Soil has a mean prokaryotic density of 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater.
Organic carbon held in soil is returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter. Since plant roots need oxygen, ventilation is an important characteristic of soil; this ventilation can be accomplished via networks of interconnected soil pores, which absorb and hold rainwater making it available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can remove impurities, kill disease agents, degrade contaminants, this latter property being called natural attenuation. Soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, water, temperature moderation and protection from toxins. Soils provide available nutrients to plants and animals by converting dead organic matter into various nutrient forms.
A typical soil is about 50% solids, 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant, while the percent soil water and gas content is considered variable whereby a rise in one is balanced by a reduction in the other; the pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, density, consistency, temperature and reactivity; the horizons differ in thickness and gene
A love dart is a sharp, calcareous or chitinous dart which some hermaphroditic land snails and slugs create. Love darts stored internally in a dart sac. Love darts are made in sexually mature animals only, are used as part of the sequence of events during courtship, before actual mating takes place. Darts are quite large compared to the size of the animal: in the case of the semi-slug genus Parmarion, the length of a dart can be up to one fifth that of the semi-slug's foot; the process of using love darts in snails is a form of sexual selection. Prior to copulation, each of the two snails attempts to "shoot" one darts into the other snail. There is no organ to receive the dart; the dart does not fly through the air to reach its target however. The love dart is not a penial stylet; the exchange of sperm between both of the two land snails is a separate part of the mating progression. Recent research shows that use of the dart can favor the reproductive outcome for the snail, able to lodge a dart in its partner.
This is because mucus on the dart introduces a hormone-like substance that allows far more of its sperm to survive. Love darts known as shooting darts, or just as darts, are shaped in many distinctive ways which vary between species. What all the shapes of love darts have in common is their harpoon-like or needle-like ability to pierce. Mating begins with a courting ritual. For example, in land snails of the genus Helix, including the escargot Helix pomatia, the common garden snail Helix aspersa, copulation is preceded by an elaborate tactile courtship; the two snails circle around each other for up to six hours, touching with their tentacles, biting lips and the area of the genital pore, which shows some preliminary signs of the eversion of the penis. As the snails approach mating, hydraulic pressure builds up in the blood sinus surrounding the organ housing the dart; each snail manoeuvres to get its genital pore in the best position, close to the other snail's body. When the body of one snail touches the other snail's genital pore, it triggers the firing of the dart.
The darting can sometimes be so forceful. It can happen that a dart will pierce the body or head and protrude on the other side. After both snails have fired their darts, the snails exchange sperm. A snail does not have a dart to fire the first time it mates, because the first mating is necessary to trigger the process of dart formation. Once a snail has mated, it fires a dart before some, but not subsequent matings. A snail mates without having a dart to use, because it takes time to create a replacement dart. In the case of the garden snail Cornu aspersum, it takes a week for a new dart to form; the dart is shot with some variation in force, with considerable inaccuracy, such that one-third of the darts that are fired in Cornu aspersum either fail to penetrate the skin, or miss the target altogether. Snails have only simple visual systems and cannot see well enough to use vision to help aim the darts. Although the existence and use of love darts in snails has been known for at least several centuries, until the actual function of love darts was not properly understood.
It was long assumed that the darts had some sort of "stimulating" function, served to make copulation more likely. It was suggested that darts might be a "gift" of calcium; these theories have proved to be incorrect. A closer look into the behavior of Cornu aspersum, shows that it is not the mechanical action of the dart that increases paternity in sperm donors but instead the mucus that coats the dart; the mucus carries an allohormone, transferred into the recipient snail’s hemolymph when the dart is stabbed. This allohormone reconfigures the female component of the reproductive system in the receiving individual: the bursa copulax is closed off, the copulatory canal is opened; this reconfiguration allows more sperm to access the sperm storage area and fertilize eggs, rather than being digested. This increases the shooter’s paternity; the love dart known as a "gypsobelum", is made of calcium carbonate, secreted by a specialized organ within the reproductive system of several families of air-breathing snails and slugs in terrestrial pulmonate gastropod mollusks within the clade Stylommatophora.
Darts can range in size from about 30 millimetres long in the larger snail species, down to about 1 millimetre in the smallest snails that have darts. Most darts are less than 5 millimetres long, but they are substantial compared with the size of the animal. There is the cross section of the love dart; the morphology of the dart is species-specific. For example, individual snails of the two rather similar helicid species Cepaea hortensis and Cepaea nemoralis can sometimes only be distinguished by examining the shape of the love dart and the vaginal mucus glands Note: The taxonomic placement of all the families mentioned in this article