86-520: A snail is a shelled gastropod . The name is most often applied to land snails , terrestrial pulmonate gastropod molluscs . However, the common name snail is also used for most of the members of the molluscan class Gastropoda that have a coiled shell that is large enough for the animal to retract completely into. When the word "snail" is used in this most general sense, it includes not just land snails but also numerous species of sea snails and freshwater snails . Gastropods that naturally lack
172-681: A figure of speech in reference to slow-moving things. 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 also form a polyphyletic group; in other words, snails with lungs and snails with gills form a number of taxonomic groups that are not necessarily more closely related to each other than they are related to some other groups. Both snails that have lungs and snails that have gills have diversified so widely over geological time that
258-531: A warning , when they are poisonous or contain stinging cells , or to camouflage them on the brightly colored hydroids , sponges , and seaweeds on which many of the species are found. Lateral outgrowths on the body of nudibranchs are called cerata . These contain an outpocketing of digestive glands called the diverticula . The sensory organs of gastropods include olfactory organs , eyes, statocysts and mechanoreceptors . Gastropods have no hearing. In terrestrial gastropods (land snails and slugs),
344-418: A conspicuous shell are commonly called slugs rather than snails. Some species of slug have a maroon-brown shell, some have only an internal vestige that serves mainly as a calcium lactate repository, and others have some to 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
430-405: A dry, finely ground, and scratchy substance such as diatomaceous earth can also deter snails. The decollate snail ( Rumina decollata ) will capture and eat garden snails, and 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 likely to attack and devour other gastropods that may represent
516-487: A few ciliary feeders, in which the radula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit and decomposing animals while marine species can scrape algae off the rocks on the seafloor. Certain species such as the Archaeogastropda maintain horizontal rows of slender marginal teeth. In some species that have evolved into endoparasites, such as the eulimid Thyonicola doglieli , many of
602-421: A few species with gills can be found on land and numerous species with lungs can be found in freshwater. Even a few marine species have lungs. Snails can be found in a very wide range of environments, including ditches , deserts , and the abyssal depths of the sea. Although land snails may be more familiar to laymen, marine snails constitute the majority of snail species, and have much greater diversity and
688-441: A fossil record. Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum , with 65,000 to 80,000 living snail and slug species . The anatomy , behavior, feeding, and reproductive adaptations of gastropods vary significantly from one clade or group to another, so stating many generalities for all gastropods
774-400: A gastropod is called a protoconch . Most shelled gastropods have a one piece shell (with exceptional bivalved gastropods ), typically coiled or spiraled, at least in the larval stage. This coiled shell usually opens on the right-hand side (as viewed with the shell apex pointing upward). Numerous species have an operculum , which in many species acts as a trapdoor to close the shell. This
860-446: A gastropod is usually adapted to the food that a species eats. The simplest gastropods are the limpets and abalones , herbivores that use their hard radula to rasp at seaweeds on rocks. Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw water into their mantle cavity and over
946-580: A greater biomass . Numerous kinds of snail can also 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, ripping food into small pieces. 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 also colored. Several species of
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#17327730368491032-671: A group are far from monophyletic ; scientifically speaking "slug" is a term of convenience with little taxonomic significance. The reduction or loss of the shell has evolved many times independently within several very different lineages of gastropods. The various taxa of land and sea gastropods with slug morphology occur within numerous higher taxonomic groups of shelled species; such independent slug taxa are not in general closely related to one another. Land snails are known as an agricultural and garden pest but some species are an edible delicacy and occasionally household pets . In addition, their mucus can also be used for skin care products. There
1118-399: A large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ( / ɡ æ s ˈ t r ɒ p ə d ə / ). This class comprises snails and slugs from saltwater, freshwater, and from the land. There are many thousands of species of sea snails and slugs , as well as freshwater snails , freshwater limpets , land snails and slugs . The class Gastropoda
1204-491: A marine environment. Gastropods have a worldwide distribution, from the near Arctic and Antarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized nearly every available medium. In habitats where not enough calcium carbonate is available to build a really solid shell, such as on some acidic soils on land, various species of slugs occur, and also some snails with thin, translucent shells, mostly or entirely composed of
1290-413: A penis. A female spotted hyena's apparent penis is in fact an enlarged clitoris, which contains an external birth canal. It can be difficult to determine the sex of spotted hyenas until sexual maturity , when they may become pregnant. When a female spotted hyena gives birth, she passes the cub through the cervix internally, but then passes it out through the elongated clitoris. The term hermaphrodite
1376-402: A reference to the fact that the animal's "foot" is positioned below its guts. The earlier name "univalve" means one valve (or shell), in contrast to bivalves , such as clams, which have two valves or shells. At all taxonomic levels, gastropods are second only to insects in terms of their diversity . Gastropods have the greatest numbers of named mollusk species. However, estimates of
1462-472: A sequential hermaphrodite is also stipulated to only change sex once. ) This contrasts with simultaneous hermaphrodites, in which an individual possesses fully functional male and female genitalia. Sequential hermaphroditism is common in fish (particularly teleost fish) and many gastropods (such as the common slipper shell ). Sequential hermaphroditism can best be understood in terms of behavioral ecology and evolutionary life history theory , as described in
1548-496: A shell, or have only an internal shell, are mostly called slugs , and land snails that have only a very small shell (that they cannot retract into) are often called semi-slugs . Snails have considerable human relevance, including as food items, as pests, and as vectors of disease, and their shells are used as decorative objects and are incorporated into jewelry. The snail has also had some cultural significance, tending to be associated with lethargy. The snail has also been used as
1634-628: A valuable part of the native fauna of the region. Certain varieties of snails, notably the family Muricidae , produce a secretion that is a color-fast natural dye . The ancient Tyrian purple was made in this way as were other purple and blue dyes. The extreme expense of extracting this secretion is sufficient quantities limited its use to the very wealthy. It is such dyes as these that led to certain shades of purple and blue being associated with royalty and wealth. Throughout history, snails have been kept as pets. There are many famous snails such as Lefty (Born Jeremy) and within fiction, Gary and Brian
1720-471: Is a diverse and highly successful class of mollusks within the phylum Mollusca. It contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian . As of 2017 , 721 families of gastropods are known, of which 245 are extinct and appear only in the fossil record, while 476 are currently extant with or without
1806-472: Is a part of the behavior of mating gastropods with some pulmonate families of land snails creating and utilizing love darts , the throwing of which have been identified as a form of sexual selection . The main aspects of the life cycle of gastropods include: The diet of gastropods differs according to the group considered. Marine gastropods include some that are herbivores , detritus feeders, predatory carnivores , scavengers , parasites , and also
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#17327730368491892-429: Is 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 also a snail repellent, and thus a copper band around the trunk of a tree will prevent snails from climbing up and reaching the foliage and fruit. A layer of
1978-810: Is both male and female. And an hermaphrodite (which is also called Androgynus ) shall be heire, either as male or female, according to that kind of sexe which doth prevaile." During the Victorian era , medical authors attempted to ascertain whether or not humans could be hermaphrodites, adopting a precise biological definition to the term. From that period until the early 21st century, individuals with ovotesticular syndrome were termed true hermaphrodites if their gonadal tissue contained both testicular and ovarian tissue, and pseudohermaphrodites if their external appearance ( phenotype ) differed from sex expected from internal gonads. This language has fallen out of favor due to misconceptions and stigma associated with
2064-434: Is common in bryophytes and some vascular plants. Historically, the term hermaphrodite was used in law to refer to people whose sex was in doubt. The 12th-century Decretum Gratiani states that "Whether an hermaphrodite may witness a testament, depends on which sex prevails" ("Hermafroditus an ad testamentum adhiberi possit, qualitas sexus incalescentis ostendit."). Alexander ab Alexandro (1461–1523) stated, using
2150-422: Is difficult. The class Gastropoda has an extraordinary diversification of habitats . Representatives live in gardens, woodland, deserts, and on mountains; in small ditches, great rivers, and lakes; in estuaries , mudflats , the rocky intertidal , the sandy subtidal, the abyssal depths of the oceans, including the hydrothermal vents , and numerous other ecological niches, including parasitic ones. Although
2236-493: Is much more maneuverable and compressible, so even quite large land slugs can take advantage of habitats or retreats with very 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 often suitable places for laying their eggs. Slugs as
2322-433: Is muscular, and the second is mutagenetic . The effects of torsion are primarily physiological. The organism develops by asymmetrical growth, with the majority of growth occurring on the left side. This leads to the loss of right-side anatomy that in most bilaterians is a duplicate of the left side anatomy. The essential feature of this asymmetry is that the anus generally lies to one side of the median plane. The gill-combs ,
2408-470: Is not the most important sense, because they are mainly nocturnal animals. The nervous system of gastropods includes the peripheral nervous system and the central nervous system . The central nervous system consists of ganglia connected by nerve cells. It includes paired ganglia: the cerebral ganglia, pedal ganglia, osphradial ganglia, pleural ganglia, parietal ganglia and the visceral ganglia. There are sometimes also buccal ganglia. The radula of
2494-422: Is not to be confused with ovotesticular syndrome in mammals, which is a separate and unrelated phenomenon. While people with the condition were previously called " true hermaphrodites" in medical literature, this usage is now considered to be outdated as of 2006 and misleading, as people with ovotesticular syndrome do not have functional sets of both male and female organs. The term hermaphrodite derives from
2580-640: Is probably not even a mollusk. As such, it's not until the Ordovician that the first crown-group members arise. By the Ordovician period the gastropods were a varied group present in a range of aquatic habitats. Commonly, fossil gastropods from the rocks of the early Palaeozoic era are too poorly preserved for accurate identification. Still, the Silurian genus Poleumita contains fifteen identified species. Fossil gastropods were less common during
2666-649: Is similar to that of plants, suggesting that similar pressures are operating to direct the evolution of selfing in animals and plants. A rough estimate of the number of hermaphroditic animal species is 65,000, about 5% of all animal species, or 33% excluding insects. Insects are almost exclusively gonochoric, and no definitive cases of hermaphroditism have been demonstrated in this group. There are no known hermaphroditic species among mammals or birds . About 94% of flowering plant species are either hermaphroditic (all flowers produce both male and female gametes) or monoecious , where both male and female flowers occur on
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2752-544: Is used in botany to describe, for example, a perfect flower that has both staminate (male, pollen-producing) and carpellate (female, ovule-producing) parts. The overwhelming majority of flowering plant species are hermaphroditic. Flowering plant species with separate, imperfect, male and female flowers on the same individual are called monoecious . Monoecy only occurs in about 7% of flowering plant species. Monoecious plants are often referred to as hermaphroditic because they produce both male and female gametes. However,
2838-460: Is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined. Some gastropods have adult shells which are bottom heavy due to the presence of a thick, often broad, convex ventral callus deposit on the inner lip and adapical to the aperture which may be important for gravitational stability. Some sea slugs are very brightly colored. This serves either as
2924-471: The Aztec moon god Tecciztecatl bore a snail shell on his back. This symbolised rebirth; the snail's penchant for appearing and disappearing was analogised with the moon . Keong Emas ( Javanese and Indonesian for Golden Snail ) is a popular Javanese folklore about a princess magically transformed and contained in a golden snail shell. The folklore is a part of popular Javanese Panji cycle telling
3010-487: The Caenogastropoda families like Ampullariidae , have both a gill and a lung. Shell : Snail shells are mainly composed of a mixture of proteins called conchin , and calcium carbonate . Conchin is the main component in the outer layer of the shell, known as the periostracum . The inner layers of the shell are composed of a network of calcium carbonate, conchin, and different mineral salts. The mantle produces
3096-514: The Latin : hermaphroditus , from Ancient Greek : ἑρμαφρόδιτος , romanized : hermaphroditos , which derives from Hermaphroditus (Ἑρμαφρόδιτος), the son of Hermes and Aphrodite in Greek mythology . According to Ovid , he fused with the nymph Salmacis resulting in one individual possessing physical traits of male and female sexes. According to the earlier Diodorus Siculus , he
3182-648: The Palaeozoic era than bivalves . Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive. By the Carboniferous period many of the shapes seen in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms. It was during the Mesozoic era that
3268-479: The Planorbidae , have hemoglobin as the respiratory protein. In one large group of sea slugs, the gills are arranged as a rosette of feathery plumes on their backs, which gives rise to their other name, nudibranchs . Some nudibranchs have smooth or warty backs with no visible gill mechanism, such that respiration may likely take place directly through the skin. Gastropods have open circulatory system and
3354-474: The continental slope and the continental rise are home to the highest diversity, while the continental shelf and abyssal depths have a low diversity of marine gastropods. Gastropods are found in a wide range of aquatic and terrestrial habitats, from deep ocean trenches to deserts. Some of the more familiar and better-known gastropods are terrestrial gastropods (the land snails and slugs). Some live in fresh water, but most named species of gastropods live in
3440-446: The olfactory organs , the foot slime-gland , nephridia , and the auricle of the heart are single or at least are more developed on one side of the body than the other. Furthermore, there is only one genital orifice, which lies on the same side of the body as the anus. Furthermore, the anus becomes redirected to the same space as the head. This is speculated to have some evolutionary function, as prior to torsion, when retracting into
3526-581: The sexual differentiation stage; however, this is now known to be incorrect, as humans are simply undifferentiated before this stage and possess a paramesonephric duct , a mesonephric duct , and a genital tubercle . The evolution of anisogamy may have contributed to the evolution of simultaneous hermaphroditism and sequential hermaphroditism, it remains unclear if the evolution of anisogamy first led to hermaphroditism or gonochorism . A 2023 study argued that hermaphroditism can evolve directly from mating types under certain circumstances, such as if
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3612-476: The adult stage—though in some, the coiling may not be very visible, for example in cowries . In a number of families of species, such as all the various limpets , the shell is coiled only in the larval stage, and is a simple conical structure after that. In the scientific literature, gastropods were described as "gasteropodes" by Georges Cuvier in 1795. The word gastropod comes from Greek γαστήρ ( gastḗr 'stomach') and πούς ( poús 'foot'),
3698-574: The adults take several years to change from female to male, the broodstock are extremely valuable individuals. Simultaneous hermaphrodites (or homogamous hermaphrodites) are individuals in which both male and female sexual organs are present and functional at the same time. Self-fertilization often occurs. When spotted hyenas were first scientifically observed by explorers, they were thought to be hermaphrodites. Early observations of wild spotted hyenas led researchers to believe that all spotted hyenas, male or female, were born with what looked to be
3784-520: The ancestors of many of the living gastropods evolved. Hermaphrodite A hermaphrodite ( / h ər ˈ m æ f r ə ˌ d aɪ t / ) is a sexually reproducing organism that produces both male and female gametes . Animal species in which individuals are either male or female are gonochoric , which is the opposite of hermaphroditic. The individuals of many taxonomic groups of animals , primarily invertebrates, are hermaphrodites, capable of producing viable gametes of both sexes . In
3870-540: The body cavity, and digestive glands opening into the stomach . Courtship is a part of mating behavior in some gastropods, including some of the Helicidae . Again, in some land snails, an unusual feature of the reproductive system of gastropods is the presence and utilization of love darts . In many marine gastropods other than the opisthobranchs , there are separate sexes ( dioecious / gonochoric ); most land gastropods, however, are hermaphrodites . Courtship
3956-585: The country are Helix lucorum and Helix pomatia . Snails and slug species that are not normally eaten in certain areas have occasionally been used as famine food in historical times. A history of Scotland written in the 1800s recounts a description of various snails and their use as food items in times of plague. Snails can also be associated with parasitic diseases such as schistosomiasis , angiostrongyliasis , fasciolopsiasis , opisthorchiasis , fascioliasis , paragonimiasis and clonorchiasis , which can be transmitted to humans. Because of its slowness,
4042-423: The deep-sea floor has been studied biologically. The total number of living species of freshwater snails is about 4,000. Recently extinct species of gastropods (extinct since 1500) number 444, 18 species are now extinct in the wild (but still exist in captivity), and 69 species are "possibly extinct". The number of prehistoric (fossil) species of gastropods is at least 15,000 species. In marine habitats,
4128-612: The dry wood/straw. The snails are then prepared for cooking. Their texture when cooked is slightly chewy and tender. As well as being eaten as gourmet food, several species of land snails provide an easily harvested source of protein to many people in poor communities around the world. Many land snails are valuable because they can feed on a wide range of agricultural wastes, such as shed leaves in banana plantations . In some countries, giant African land snails are produced commercially for food. Land snails, freshwater snails and sea snails are all eaten in many countries. In certain parts of
4214-425: The earliest representatives of the group appearing in the Late Cambrian ( Chippewaella , Strepsodiscus ), though their only gastropod character is a coiled shell, so they could lie in the stem lineage, if they are gastropods at all. Earliest Cambrian organisms like Helcionella , Barskovia and Scenella are no longer considered gastropods, and the tiny coiled Aldanella of earliest Cambrian time
4300-405: The effects of pheromones on growth rate. Radula : The radula is an anatomical structure used by most species of Mollusca for feeding. Gastropods are morphologically highly variable and have diverse feeding strategies. Snails can be herbivores , detritivores, scavengers , parasites , ciliary feeders, or have highly specialized predation . Nearly all snails utilize a feeding apparatus including
4386-439: The fertilization is well organized and the average size of groups is small. Simultaneous hermaphroditism that exclusively reproduces through self-fertilization has evolved many times in plants and animals, but it might not last long evolutionarily. Joan Roughgarden and Priya Iyer argued that the last common ancestor for animals was hermaphroditic and that transitions from hermaphroditism to gonochorism were more numerous than
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#17327730368494472-405: The foot, the mantle , and the radula . Foot : The foot is a muscular organ used by Gastropods for locomotion . Gastropods' stomachs are located within their foot. Both land and sea snails travel by contracting foot muscles to deform the mucus layer beneath it into different wave-like patterns. Mantle : The mantle is the organ that produces shells for most species of mollusca. In snails,
4558-409: The form of small adults. The only additional development they will undergo is to consume calcium to strengthen their shell. Snails can be male, female, hermaphroditic , or parthenogenetic so there are many different systems of sexual determination. Snails have complex organ systems and anatomies that differ greatly from most animals . Snails and most other Mollusca share three anatomical features;
4644-424: The genus Achatina and related genera are known as giant African land snails; some grow to 15 in (38 cm) from snout to tail, and weigh 1 kg (2 lb). The largest living species of sea snail is Syrinx aruanus ; its shell can measure up to 90 cm (35 in) in length, and the whole animal with the shell can weigh up to 18 kg (40 lb). The smallest land snail, Angustopila psammion ,
4730-411: The gill. They use the siphon primarily to "taste" the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers. Almost all marine gastropods breathe with a gill , but many freshwater species, and the majority of terrestrial species, have a pallial lung . The respiratory protein in almost all gastropods is hemocyanin , but one freshwater pulmonate family,
4816-423: The great majority of tunicates , mollusks , and earthworms , hermaphroditism is a normal condition, enabling a form of sexual reproduction in which either partner can act as the female or male. Hermaphroditism is also found in some fish species , but is rare in other vertebrate groups. Most hermaphroditic species exhibit some degree of self-fertilization. The distribution of self-fertilization rates among animals
4902-431: The growth of ovarian tissues ). Thus, testicular and ovarian tissues will both be present in the same individual. Of all total recorded cases of ovotesticular DSD, in only 8% percent of all cases was SRY present, leaving the rest of cases that could be explained to other or less common causes, with the vast majority simply being currently unexplainable. Fetuses were previously thought to be phenotypically female before
4988-553: The individual flowers are not hermaphroditic if they only produce gametes of one sex. 65% of gymnosperm species are dioecious, but conifers are almost all monoecious. Some plants can change their sex throughout their lifetime, a phenomenon called sequential hermaphroditism . In andromonoecious species, the plants produce perfect (hermaphrodite) flowers and separate fertile male flowers that are sterile as female. Andromonoecy occurs in about 4000 species of flowering plants (2% of flowering plants). In gynomonoecious species,
5074-400: The mantle secretes the shell along the snail shell opening, continuously growing and producing the shell for the entirety of the snail’s life. The mantle creates a compartment known as the mantle cavity and is used by many mollusca as the surface where gas exchange occurs. Snails that use the mantle cavity as a lung are known as Pulmonate snails. Other snails may only have a gill . Snails in
5160-572: The name "snail" can be, and often is, applied to all the members of this class, commonly this word means only those species with an external shell big enough that the soft parts can withdraw completely into it. Slugs are gastropods that have no shell or a very small, internal shell; semislugs are gastropods that have a shell that they can partially retreat into but not entirely. The marine shelled species of gastropods include species such as abalone , conches , periwinkles , whelks , and numerous other sea snails that produce seashells that are coiled in
5246-486: The olfactory organs, located on the tips of the four tentacles , are the most important sensory organ. The chemosensory organs of opisthobranch marine gastropods are called rhinophores . The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles. However, "eyes" in gastropods range from simple ocelli that only distinguish light and dark, to more complex pit eyes , and even to lens eyes . In land snails and slugs, vision
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#17327730368495332-421: The oral structures of one or more jaws and the radula. The radula comprises a chitinous ribbon with teeth arranged in transverse and longitudinal rows. The radula continually renews itself during the entire lifespan of a mollusk. The teeth and membrane are continuously synthesized in the radular sac and then shifted forward towards the working zone of the radula. The teeth harden and mineralize during their travel to
5418-509: The origin of Patellogastropoda and Heterobranchia , whereas fewer changes occurred between the ancestors of Vetigastropoda (only tRNAs D, C and N) and Caenogastropoda (a large single inversion , and translocations of the tRNAs D and N). Within Heterobranchia, gene order seems relatively conserved, and gene rearrangements are mostly related with transposition of tRNA genes. The first gastropods were exclusively marine, with
5504-519: The plants produce hermaphrodite flowers and separate male-sterile pistillate flowers. One example is the meadow saxifrage, Saxifraga granulata . Charles Darwin gave several other examples in his 1877 book "The Different Forms of Flowers on Plants of the Same Species". About 57% of moss species and 68% of liverworts are unisexual , meaning that their gametophytes produce either male or female gametes, but not both. Sequential hermaphroditism
5590-555: The protein conchiolin . Snails such as Sphincterochila boissieri and Xerocrassa seetzeni have adapted to desert conditions. Other snails have adapted to an existence in ditches, near deepwater hydrothermal vents , in oceanic trenches 10,000 meters (6 miles) below the surface, the pounding surf of rocky shores , caves , and many other diverse areas. Gastropods can be accidentally transferred from one habitat to another by other animals, e.g. by birds . Snails are distinguished by an anatomical process known as torsion , where
5676-474: The result of an atypical set of sex chromosomes. One common cause of variations in sex characteristics traits is the crossing over of the testis-determining factor (SRY) from the Y chromosome to the X chromosome during meiosis . The SRY is then activated in only certain areas, causing development of testes in some areas by beginning a series of events starting with the upregulation of the transcription factor (SOX9), and in other areas not being active (causing
5762-487: The reverse. Other scientists have criticized this argument; saying it’s based on paraphyletic Spiralia , assignments of sexual modes for the phylum level than the species level, and methods exclusively based on maximum parsimony . Hermaphroditism is polyphyletic in invertebrates where it evolved from gonochorism and gonochorism is also ancestral to hermaphroditic fishes. According to Nelson Çabej simultaneous hermaphroditism in animals most likely evolved due to
5848-442: The same plant. There are also mixed breeding systems , in both plants and animals, where hermaphrodite individuals coexist with males (called androdioecy ) or with females (called gynodioecy ), or all three exist in the same species (called trioecy ). Sometimes, both male and hermaphrodite flowers occur on the same plant ( andromonoecy ) or both female and hermaphrodite flowers occur on the same plant ( gynomonoecy ). Hermaphrodism
5934-459: The shell through addition around a central axis called the columella , causing a spiraling pattern. The spiraling patterns on a snail’s shell are known as coils or whorls . Whorl size generally increases as the snail ages. Size differences in shell size are believed to be mainly influenced by genetic and environmental components. Moister conditions often correlate with larger snails. In larger populations, adult snails attain smaller shell sizes due to
6020-419: The shell, first the posterior end would get pulled in, and then the anterior. Now, the front can be retracted more easily, perhaps suggesting a defensive purpose. Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot. The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of
6106-568: The size-advantage mode first proposed by Michael T. Ghiselin which states that if an individual of a certain sex could significantly increase its reproductive success after reaching a certain size, it would be to their advantage to switch to that sex. Sequential hermaphrodites can be divided into three broad categories: Dichogamy can have both conservation-related implications for humans, as mentioned above, as well as economic implications. For instance, groupers are favoured fish for eating in many Asian countries and are often aquacultured . Since
6192-502: The snail . 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 dark place in a wired cage with dry straw or dry wood. Coppiced wine-grape vines are often used for this purpose. During the rainy period, the snails come out of hibernation and release most of their mucus onto
6278-408: The snail has traditionally been seen as a symbol of laziness. In Christian culture, it has been used as a symbol of the deadly sin of sloth . In Mayan mythology , the snail is associated with sexual desire, being personified by the god Uayeb . Snails were widely noted and used in divination . The Greek poet Hesiod wrote that snails signified the time to harvest by climbing the stalks, while
6364-593: The standard gastropod features are strongly reduced or absent. A few sea slugs are herbivores and some are carnivores. The carnivorous habit is due to specialisation. Many gastropods have distinct dietary preferences and regularly occur in close association with their food species. Some predatory carnivorous gastropods include: cone shells , Testacella , Daudebardia , turrids , ghost slugs and others. Gastropods exhibit an important degree of variation in mitochondrial gene organization when compared to other animals. Main events of gene rearrangement occurred at
6450-572: The stories about the prince Panji Asmoro Bangun (also known as Raden Inu Kertapati) and his consort, princess Dewi Sekartaji (also known as Dewi Chandra Kirana). In contemporary speech, the expression "a snail's pace" is often used to describe a slow, inefficient process. The phrase " snail mail " is used to mean regular postal service delivery of paper messages as opposed to the delivery of email , which can be virtually instantaneous. Gastropod Gastropods ( / ˈ ɡ æ s t r ə p ɒ d z / ), commonly known as slugs and snails , belong to
6536-648: The term hermaphrodite, that the people who bore the sexes of both man and woman were regarded by the Athenians and the Romans as monsters, and thrown into the sea at Athens and into the Tiber at Rome. Similarly, the 17th-century English jurist and judge Edward Coke (Lord Coke), wrote in his Institutes of the Lawes of England on laws of succession stating, "Every heire is either a male, a female, or an hermaphrodite, that
6622-505: The terminology " disorders of sex development " (also known as variations in sex characteristics .) This is particularly significant because of the relationship between medical terminology and medical intervention. Intersex civil society organizations , and many human rights institutions, have criticized medical interventions designed to make bodies more typically male or female. In some cases, variations in sex characteristics are caused by unusual levels of sex hormones, which may be
6708-399: The terms, and also a shift to nomenclature based on genetics. The term "intersex" described a wide variety of combinations of what are ambiguous biological characteristics. Intersex biology may include, for example, ambiguous-looking external genitalia, karyotypes that include mixed XX and XY chromosome pairs (46XX/46XY, 46XX/47XXY or 45X/XY mosaic ). Clinically, medicine currently uses
6794-715: The total number of gastropod species vary widely, depending on cited sources. The number of gastropod species can be ascertained from estimates of the number of described species of Mollusca with accepted names: about 85,000 (minimum 50,000, maximum 120,000). But an estimate of the total number of Mollusca, including undescribed species, is about 240,000 species. The estimate of 85,000 mollusks includes 24,000 described species of terrestrial gastropods. Different estimates for aquatic gastropods (based on different sources) give about 30,000 species of marine gastropods, and about 5,000 species of freshwater and brackish gastropods. Many deep-sea species remain to be discovered, as only 0.0001% of
6880-437: The transport fluid is hemolymph . Hemocyanin is present in the hemolymph as the respiratory pigment. The primary organs of excretion in gastropods are nephridia , which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in
6966-406: The visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head. This process is unrelated to the coiling of the shell, which is a separate phenomenon. Torsion is present in all gastropods, but the opisthobranch gastropods are secondarily untorted to various degrees. Torsion occurs in two stages. The first, mechanistic stage
7052-555: The working zone. The presence of the radula is common throughout most snail species, but often differs in many characteristics, like the shape, size, and number of odontoblasts that form a tooth. Snails' eating habits vary widely, with some being generalists and some being specialist feeders. Snails feed at night. They feed primarily on decaying organic matter. Their diet also includes fungi, lichens, green foliage, worms, centipedes, insects, animal feces, carrion, and other slugs. Some snails feed on other snails too. Gastropods that lack
7138-597: The world snails are fried. For example, in Indonesia , they are fried as satay , a dish known as sate kakul . The eggs of certain snail species are eaten in a fashion similar to the way caviar is eaten. In Bulgaria , snails are traditionally cooked in an oven with rice or fried in a pan with vegetable oil and red paprika powder. Before they are used for those dishes, however, they are thoroughly boiled in hot water (for up to 90 minutes) and manually extracted from their shells. The two species most commonly used for food in
7224-513: Was born with a physical body combining male and female sexes. The word hermaphrodite entered the English lexicon as early as the late fourteenth century. Sequential hermaphrodites ( dichogamy ) occur in species in which the individual first develops as one sex, but can later change into the opposite sex. (Definitions differ on whether sequential hermaphroditism encompasses serial hermaphroditism; for authors who exclude serial hermaphroditism,
7310-510: Was discovered in 2022 and measures 0.6 mm in diameter. The largest known land gastropod is the African giant snail Achatina achatina , the largest recorded specimen of which measured 39.3 centimetres (15.5 in) from snout to tail when fully extended, with a shell length of 27.3 cm (10.7 in) in December 1978. It weighed exactly 900 g (about 2 lb). Named Gee Geronimo, this snail
7396-584: Was owned by Christopher Hudson (1955–79) of Hove, East Sussex, UK, and was collected in Sierra Leone in June 1976. Snails are protostomes . That means during development, in the gastrulation phase, the blastopore forms the mouth first. Cleavage in snails is spiral holoblastic patterning. In spiral holoblastic cleavage, the cleavage plane rotates each division and the cell divisions are complete. Snails do not undergo metamorphosis after hatching. Snails hatch in
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