The class Gastropoda is a diverse and highly successful class of mollusks within the phylum Mollusca. It contains a vast total of named species, second only to theinsects in overall number. The fossil history of this class goes back to theLate Cambrian. As of 2017[update], 721families of gastropods are known, of which 245 areextinct and appear only in thefossil record, while 476 are currentlyextantwith or without a fossil record.[6]
Gastropoda (previously known asunivalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversifiedclass in thephylum, with 65,000 to 80,000[3][4] living snail and slugspecies. Theanatomy, behavior, feeding, and reproductive adaptations of gastropods vary significantly from oneclade or group to another, so stating many generalities for all gastropods is difficult.
The class Gastropoda has an extraordinary diversification ofhabitats. Representatives live in gardens, woodland, deserts, and on mountains; in small ditches, great rivers, and lakes; inestuaries,mudflats, the rockyintertidal, the sandy subtidal, theabyssal depths of the oceans, including thehydrothermal vents, and numerous other ecological niches, includingparasitic ones.
Although 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 externalshell 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 asabalone,conches,periwinkles,whelks, and numerous other sea snails that produceseashells that are coiled in the adult stage—though in some, the coiling may not be very visible, for example incowries. In a number offamilies of species, such as all the variouslimpets, the shell is coiled only in thelarval stage, and is a simple conical structure after that.
In the scientific literature, gastropods were described as "gasteropodes" byGeorges Cuvier in 1795.[2] The wordgastropod comes from Greekγαστήρ (gastḗr 'stomach') andπούς (poús 'foot'), a reference to the fact that the animal's "foot" is positioned below its guts.[7]
The earlier name "univalve" means onevalve (or shell), in contrast tobivalves, such as clams, which have two valves or shells.
At alltaxonomic levels, gastropods are second only to insects in terms of theirdiversity.[8]
Gastropods have the greatest numbers of namedmollusk species. However, estimates of 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).[9] But an estimate of the total number of Mollusca, including undescribed species, is about 240,000 species.[10] The estimate of 85,000 mollusks includes 24,000 described species of terrestrial gastropods.[9]
Different estimates for aquatic gastropods (based on different sources) give about 30,000 species of marine gastropods, and about 5,000 species of freshwater andbrackish gastropods. Many deep-sea species remain to be discovered, as only 0.0001% of the deep-sea floor has been studied biologically.[11][12] The total number of living species of freshwater snails is about 4,000.[13]
Recentlyextinct species of gastropods (extinct since 1500) number 444, 18 species are nowextinct in the wild (but still exist in captivity), and 69 species are "possibly extinct".[14]
The number of prehistoric (fossil) species of gastropods is at least 15,000 species.[15]
In marine habitats, thecontinental slope and thecontinental rise are home to the highest diversity, while the continental shelf and abyssal depths have a low diversity of marine gastropods.[16]
Gastropods are found in a wide range of aquatic and terrestrial habitats, from deep ocean trenches to deserts.[citation needed]
Some of the more familiar and better-known gastropods areterrestrial gastropods (the land snails and slugs). Some live in fresh water, but most named species of gastropods live in a marine environment.[citation needed]
Gastropods have a worldwide distribution, from the nearArctic andAntarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized nearly every available medium.[citation needed]
In habitats where not enoughcalcium 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 the proteinconchiolin.[citation needed]
The anatomy of a common air-breathing land snail: much of this anatomy does not apply to gastropods in otherclades or groups.
Snails are distinguished by an anatomical process known astorsion, where the visceral mass of the animal rotates 180° to one side during development, such that theanus 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 theopisthobranch gastropods are secondarily untorted to various degrees.[19][20]
Torsion occurs in two stages. The first, mechanistic stage is muscular, and the second ismutagenetic. 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. Thegill-combs, theolfactory organs, thefoot slime-gland,nephridia, and theauricle of the heart are single or at least are more developed on one side of the body than the other. Furthermore, there is only onegenital orifice, which lies on the same side of the body as the anus.[21] 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 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.[citation needed]
Gastropods typically have a well-definedhead with two or four sensorytentacles 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 a gastropod is called aprotoconch.[citation needed]
Most shelled gastropods have a one pieceshell (with exceptionalbivalved 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 shellapex pointing upward). Numerous species have anoperculum, which in many species acts as a trapdoor to close the shell. This 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.[22]
The upper pair oftentacles on the head ofHelix pomatia have eye spots, but the main sensory organs of the snail are sensory receptors forolfaction, situated in theepithelium of the tentacles.
In terrestrial gastropods (land snails and slugs), the olfactory organs, located on the tips of the fourtentacles, are the most important sensory organ.[23] The chemosensory organs ofopisthobranch marine gastropods are calledrhinophores.
The majority of gastropods have simple visual organs, eye spots either at the tip orbase of the tentacles. However, "eyes" in gastropods range from simpleocelli that only distinguish light and dark, to more complexpit eyes, and even tolens eyes.[24] In land snails and slugs, vision is not the most important sense, because they are mainlynocturnal animals.[23]
The nervous system of gastropods includes theperipheral nervous system and thecentral nervous system. The central nervous system consists ofganglia 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.[23]
Theradula of a gastropod is usually adapted to the food that a species eats. The simplest gastropods are thelimpets andabalone, herbivores that use their hardradula to rasp atseaweeds on rocks.[citation needed]
Many marine gastropods are burrowers, and have asiphon that extends out from themantle edge. Sometimes the shell has asiphonal canal to accommodate this structure. A siphon enables the animal to draw water into theirmantle cavity and over 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.[citation needed]
Almost all marine gastropods breathe with agill, but many freshwater species, and the majority of terrestrial species, have a palliallung. The respiratory protein in almost all gastropods ishemocyanin, but one freshwaterpulmonate family, thePlanorbidae, havehemoglobin as the respiratory protein.[citation needed]
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 orwarty backs with no visible gill mechanism, such that respiration may likely take place directly through the skin.
The primary organs of excretion in gastropods arenephridia, which produce eitherammonia oruric 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 the body cavity, and digestive glands opening into thestomach.[citation needed]
Courtship and mating in gastropods:fertilization is internal or external according to the species. External fertilization is common in marine gastropods.
The diet of gastropods differs according to the group considered. Marine gastropods include some that areherbivores,detritus feeders,predatorycarnivores,scavengers,parasites, and also a few ciliary feeders, in which theradula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit, fungi, and decomposing animals while marine species can scrape algae off the rocks on the seafloor. Certain species such as theArchaeogastropoda maintain horizontal rows of slender marginal teeth. In some species that have evolved into endoparasites, such as theeulimidThyonicola doglieli, many of the standard gastropod features are strongly reduced or absent.[citation needed]
A fewsea 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.
Studies based on direct observations,fecal andgut analyses, as well as food-choice experiments, have revealed that snails and slugs consume a wide variety of food resources.[26] Their diet spans from living plants at various developmental stages such aspollen, seeds,seedlings, and wood, to decaying plant material like leaf litter. Additionally, they feed on fungi,lichens,algae, soil, and even other animals, both living and dead, including their feces. Given this diverse diet, terrestrial gastropods can be classified asherbivores,omnivores,carnivores, anddetritivores.[26] However, the majority aremicrobivores, primarily consumingmicrobes associated with decaying organic material.[27] Despite theirecological importance, there is a notable lack of research exploring the specific roles that terrestrial gastropods play within soil food webs.[26]
Feeding behaviors in slugs exhibit considerable variation. Some species display selectivity, consuming specific parts or developmental stages of fungi. For instance, certain slugs may target fungi only at particular stages of maturity, such as immature fruiting bodies or spore-producing structures.[29] Conversely, other species show little to no selectivity, consuming entire mushrooms regardless of developmental stage. This variability stresses the diverse dietary adaptations among slug species and their ecological roles in fungal consumption.[29] Moreover, by consuming fungi, snails and slugs can also indirectly help in theirdispersal by carrying along some of theirspores[29][34] or the fungi themselves.[35]
The first gastropods were exclusively marine, with the earliest known representatives appearing in theLate Cambrian (e.g.,Chippewaella,Strepsodiscus).[37] However, their only definitive gastropod feature is acoiled shell, which raises the possibility that they may belong to the stem lineage of gastropods, or might not be gastropods at all.[38] Early Cambrian species such asHelcionella,Barskovia, andScenella are no longer considered gastropods, and the small coiledAldanella from the same period is probably not even a mollusk.[citation needed]
It is not until theOrdovician that truecrown-group gastropods appear.[39] By this time, gastropods had diversified into a variety of forms and inhabited a range ofaquatic environments. Fossil gastropods from the earlyPaleozoic are often poorly preserved, making identification difficult. However, theSilurian genusPoleumita contains at least 15 identified species. Overall, gastropods were less common in thePaleozoic thanbivalves.[39]
Most Paleozoic gastropods belong to primitive groups, some of which still exist today. By theCarboniferous period, many gastropod shell shapes found in fossils resemble those of modern species, though most of these early forms are not directly related to living gastropods. It was during theMesozoic era that the ancestors of many extant gastropods evolved.[39] One of the earliest known terrestrial gastropods isAnthracopupa (orMaturipupa), found in theCarboniferousCoal Measures of Europe.[40] However, land snails and their relatives were rare before theCretaceous period.[39]
In Mesozoic rocks, gastropods become more common in the fossil record, with well-preserved shells. Fossils are found in ancient beds from both freshwater and marine environments. Notable examples include thePurbeck Marble of theJurassic and theSussex Marble of the early Cretaceous, both fromsouthern England. These limestones contain abundant remains of the pond snailViviparus.[39]Cenozoic rocks yield vast numbers of gastropod fossils, many of which are closely related to modern species. The diversity of gastropods increased significantly at the start of this era, alongside that of bivalves.[39]
Certain trail-like markings preserved in ancient sedimentary rocks are thought to have been made by gastropods crawling over the soft mud and sand. Although thesetrace fossils are of debatable origin, some of them do resemble the trails made by living gastropods today.[39]
Gastropod fossils may sometimes be confused withammonites or other shelledcephalopods. An example of this isBellerophon from the limestones of theCarboniferous period in Europe, the shell of which is planispirally coiled and can be mistaken for the shell of a cephalopod.[citation needed]
Gastropods also provide important evidence of faunal changes during thePleistocene epoch, reflecting the impacts of advancing and retreatingice sheets.[citation needed]
The present backbone classification of gastropods relies on the results of phylogenomic analyses. Consensus has not been reached yet considering the relationships at the very base of the gastropod tree of life, but otherwise the major groups are known with confidence.[42][43][44]
A group of fossil shells ofTurritella cingulifera from thePliocene ofCyprusFive views of a shell of aFulguropsis speciesMicrophoto (35x) of Gastropoda sp. from Holocene sediments of Amuq Plain SSE Turkey
SinceDarwin, biological taxonomy has attempted to reflect thephylogeny of organisms, i.e., thetree of life. The classifications used in taxonomy attempt to represent the precise interrelatedness of the various taxa. However, the taxonomy of the Gastropoda is constantly being revised and so the versions shown in various texts can differ in major ways.
In the older classification of the gastropods, there were four subclasses:[45]
Thetaxonomy of the Gastropoda is still under revision, and more and more of the old taxonomy is being abandoned, as the results ofDNA studies slowly become clearer. Nevertheless, a few of the older terms such as "opisthobranch" and "prosobranch" are still sometimes used in a descriptive way.
New insights based on DNA sequencing of gastropods have produced some revolutionary new taxonomic insights. In the case of the Gastropoda, the taxonomy is now gradually being rewritten to embody strictlymonophyletic groups (only one lineage of gastropods in each group). Integrating new findings into a workingtaxonomy remain challenging. Consistent ranks within the taxonomy at the level of subclass, superorder, order, and suborder have already been abandoned as unworkable. Ongoing revisions of the higher taxonomic levels are expected in the near future.[when?]
Convergent evolution, which appears to exist at especially high frequency in gastropods, may account for the observed differences between the older phylogenies, which were based on morphological data, and more recent gene-sequencing studies.
In 2005,Philippe Bouchet andJean-Pierre Rocroi made sweeping changes in thesystematics, resulting in theBouchet & Rocroi taxonomy, which is a step closer to the evolutionary history of thephylum.[3][47] The Bouchet & Rocroi classification system is based partly on the older systems of classification, and partly on newcladistic research. In the past, the taxonomy of gastropods was largely based onphenetic morphological characters of the taxa. The recent advances are more based on molecular characters fromDNA[48] andRNA research. This has made the taxonomical ranks and their hierarchy controversial.
In 2017, Bouchet, Rocroi, and other collaborators published a significantly updated version of the 2005 taxonomy.[49] In theBouchet et al. taxonomy, the authors used unrankedclades for taxa above the rank of superfamily (replacing the ranks suborder, order, superorder and subclass), while using the traditionalLinnaean approach for all taxa below the rank of superfamily. Whenevermonophyly has not been tested, or is known to be paraphyletic or polyphyletic, the term "group" or "informal group" has been used. The classification of families into subfamilies is often not well resolved.[citation needed]
Fixed ranks like family, genus, and species however remain useful for practical classification and remain used in theWorld Register of Marine Species (WoRMS). Also many researchers continue to use traditional ranks because they are entrenched in the literature and familiar to specialists and non-specialists alike.
Many gastropod species face threats from habitat destruction, pollution, and climate change. Some species are endangered or have become extinct due to these factors. Conservation efforts often focus on protecting their habitats, especially in freshwater and terrestrial ecosystems.
^Aktipis, S.W.; Giribet, G.; Lindberg, D.R.; W.F., Ponder (2008). "Gastropoda". In Ponder, W.; Lindberg, D.R. (eds.).Phylogeny and evolution of the Mollusca. University of California Press. pp. 201–238.ISBN978-0-520-25092-5.
^abcBouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005.Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany.ISBN3-925919-72-4. 397 pp.vliz.beArchived 2020-07-14 at theWayback Machine
^abSolem, A.G."Gastropod".Encyclopaedia Britannica. Encyclopaedia Britannica Inc. Archived fromthe original on 8 March 2016. Retrieved6 March 2017.
^abBieler R, Bouchet P, Gofas S, Marshall B, Rosenberg G, La Perna R, Neubauer TA, Sartori AF, Schneider S, Vos C, ter Poorten JJ, Taylor J, Dijkstra H, Finn J, Bank R, Neubert E, Moretzsohn F, Faber M, Houart R, Picton B, Garcia-Alvarez O, eds. (2020)."Gastropoda".MolluscaBase.World Register of Marine Species. Retrieved2020-09-29.
^Strong, Ellen E.; Schrödl, Michael; Parkhaev, Pavel; Nützel, Alexander; Kano, Yasunori; Kaim, Andrzej; Hausdorf, Bernhard; Rocroi, Jean-Pierre; Bouchet, Philippe (December 31, 2017). "Revised Classification, Nomenclator and Typification of Gastropod and Monoplacophoran Families".Malacologia.61 (1–2):1–526.doi:10.4002/040.061.0201.S2CID91051256.
^"Gastropod".Online Etymology Dictionary.Archived from the original on 6 October 2018. Retrieved3 September 2019.
^McArthur, A.G.; M.G. Harasewych (2003). "Molecular systematics of the major lineages of the Gastropoda.". In C. Lydeard; D.R. Lindberg (eds.).Molecular Systematics and Phylogeography of Mollusks. Washington: Smithsonian Books. pp. 140–160.
^Appeltans W., Bouchet P., Boxshall G.A., Fauchald K., Gordon D.P., Hoeksema B.W., Poore G.C.B., van Soest R.W.M., Stöhr S., Walter T.C., Costello M.J. (eds) (2011). World Register of Marine Species. Accessed atmarinespecies.orgArchived 2015-10-03 atarchive.today on 2011-03-07.
^"gastropod"Archived 2008-10-13 at theWayback Machine. (2010). In Encyclopædia Britannica. Retrieved March 05, 2010, from Encyclopædia Britannica Online.
^(in Spanish) Nájera J. M. (1996). "Moluscos del suelo como plagas agrícolas y cuarentenarias".X Congreso Nacional Agronómico / II Congreso de Suelos 1996 51-56.PDFArchived 2011-07-21 at theWayback Machine
^Kay, A.; Wells, F. E.; Poder, W. F. (1998). "Class Gastropoda". In Beesley, P. L.; Ross, G. J. B.; Wells, A. (eds.).Mollusca: The Southern Synthesis. Fauna of Australia. CSIRO Publishing. pp. 565–604.ISBN978-0-643-05756-2.
^Brusca, R. C.; Brusca, G. J. (2003). "Phylum Mollusca".Invertebrates. Sinauer Associates, Inc. pp. 701–769.ISBN978-0-87893-097-5.
^abcdeChase R.:Sensory Organs and the Nervous System. in Barker G. M. (ed.):The biology of terrestrial molluscs. CABI Publishing, Oxon, UK, 2001,ISBN0-85199-318-4. 1-146, cited pages: 179–211.
^Götting, Klaus-Jürgen (1994). "Schnecken". In Becker, U.; Ganter, S.; Just, C.; Sauermost, R. (eds.).Lexikon der Biologie. Heidelberg: Spektrum Akademischer Verlag.ISBN978-3-86025-156-0.
^Welter-Schultes, F. W. (2012).European non-marine molluscs: a guide for species identification = Bestimmungsbuch für europäische Land- und Süsswassermollusken (1. ed.). Göttingen: Planet Poster Ed.ISBN978-3-933922-75-5.
^abBarahona-Segovia, Rodrigo M.; Gallardo-Pillancari, Esteban; Orrego, Gabriel; Osorio, Felipe (2024). "Mycophagy and feeding on other native land snails by the black snail Macrocyclis peruvianus (Gastropoda, Macrocyclidae)".Austral Ecology.49 (2).Bibcode:2024AusEc..49E3491B.doi:10.1111/aec.13491.
^Wolf, F. T.; Wolf, F. A. (1939). "The snailPolygyra thyroidus as a mycophagist".Bulletin of the Torrey Botanical Club.66 (1):1–5.doi:10.2307/2481011.JSTOR2481011.
^Lilleskov, E. A.; Bruns, T. D. (2005). "Spore dispersal of a resupinate ectomycorrhizal fungus, Tomentella sublilacina, via soil food webs".Mycologia.97 (4):762–769.doi:10.3852/mycologia.97.4.762.PMID16457345.
^Vašutová, Martina; Mleczko, Piotr; López-García, Alvaro; Maček, Irena; Boros, Gergely; Ševčík, Jan; Fujii, Saori; Hackenberger, Davorka; Tuf, Ivan H.; Hornung, Elisabeth; Páll-Gergely, Barna; Kjøller, Rasmus (2019). "Taxi drivers: the role of animals in transporting mycorrhizal fungi".Mycorrhiza.29 (5):413–434.Bibcode:2019Mycor..29..413V.doi:10.1007/s00572-019-00906-1.PMID31292712.
^Yochelson, Ellis L.; Nuelle, Laurence M. (1985). "Strepsodiscus (Gastropoda) in the Late Cambrian of Missouri".Journal of Paleontology.59 (3):733–740.JSTOR1304993.
^Budd, G. E., and S. Jensen. 2000: A critical reappraisal of the fossil record of the bilaterian phyla. Biological Reviews 75:253–295.
^Poppe G.T. & Tagaro S.P. 2006. The new classification of Gastropods according to Bouchet & Rocroi, 2005. Visaya, février 2006: 10 pp.journal-malaco.frArchived 2007-09-27 at theWayback Machine
This article incorporatesCC-BY-2.0 text from the following source: Cunha, R. L.; Grande, C.; Zardoya, R. (2009). "Neogastropod phylogenetic relationships based on entire mitochondrial genomes".BMC Evolutionary Biology.9: 210.doi:10.1186/1471-2148-9-210.PMC 2741453.PMID 19698157.
Abbott, R. T. (1989):Compendium of Landshells. A color guide to more than 2,000 of the World's Terrestrial Shells. 240 S., American Malacologists. Melbourne, Fl, Burlington, Ma.ISBN0-915826-23-2
Abbott, R. T. & Dance, S. P. (1998):Compendium of Seashells. A full-color guide to more than 4,200 of the world's marine shells. 413 S., Odyssey Publishing. El Cajon, Calif.ISBN0-9661720-0-0
Parkinson, B., Hemmen, J. & Groh, K. (1987):Tropical Landshells of the World. 279 S., Verlag Christa Hemmen. Wiesbaden.ISBN3-925919-00-7
Ponder, W. F. & Lindberg, D. R. (1997):Towards a phylogeny of gastropod molluscs: an analysis using morphological characters.Zoological Journal of the Linnean Society,119 83–265.
Robin, A. (2008):Encyclopedia of Marine Gastropods. 480 S., Verlag ConchBooks. Hackenheim.ISBN978-3-939767-09-1
.jpg)
.jpg)
_(2999358117).jpg)
_(4309322782).jpg)
_(3063441884).jpg)
_(3000195752).jpg)
_(4947706383).jpg)
.jpg)
_(4631972937).jpg)
