Gastropods (), commonly known as slugs and snails, belong to a large

taxonomic 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme of classes (a taxonomy) and the allocation ...

class of

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s within the phylum

Mollusca Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

called Gastropoda (). This class comprises

snail A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...

s and

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

s from saltwater, freshwater, and from the land. There are many thousands of species of

sea snail Sea snails are slow-moving marine (ocean), marine gastropod Mollusca, molluscs, usually with visible external shells, such as whelk or abalone. They share the Taxonomic classification, taxonomic class Gastropoda with slugs, which are distinguishe ...

s and

slugs Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a sma ...

, as well as

freshwater snail Freshwater snails are gastropod mollusks that live in fresh water. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs t ...

s, freshwater

limpet Limpets are a group of aquatic snails with a conical gastropod shell, shell shape (patelliform) and a strong, muscular foot. This general category of conical shell is known as "patelliform" (dish-shaped). Existing within the class Gastropoda, ...

land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial molluscs, terrestrial gastropod mollusks that have gastropod shell, shel ...

s and

s. 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 the

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s in overall number. The fossil history of this class goes back to the

Late Cambrian The Furongian is the fourth and final Epoch (geology), epoch and Series (stratigraphy), series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocia ...

. , 721

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

of gastropods are known, of which 245 are

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

and appear only in the

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

record, while 476 are currently

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

with With or WITH may refer to: * With, a preposition in English * Carl Johannes With (1877–1923), Danish doctor and arachnologist * With (character), a character in ''D. N. Angel'' * ''With'' (novel), a novel by Donald Harrington * ''With'' (album ...

or without 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 Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

in the

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

, with 65,000 to 80,000 living snail and slug

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. The

anatomy Anatomy () is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old scien ...

, behavior, feeding, and reproductive adaptations of gastropods vary significantly from one

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

or group to another, so stating many generalities for all gastropods is difficult. The class Gastropoda has an extraordinary diversification of

habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...

s. Representatives live in gardens, woodland, deserts, and on mountains; in small ditches, great rivers, and lakes; in

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

mudflat Mudflats or mud flats, also known as tidal flats or, in Ireland, slob or slobs, are coastal wetlands that form in intertidal areas where sediments have been deposited by tides or rivers. A global analysis published in 2019 suggested that tidal ...

s, the rocky

intertidal The intertidal zone or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various sp ...

, the sandy subtidal, the

abyssal The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. The word ''abyss'' comes from the Greek word (), meaning "bottomless". At depths of , this zone remains in perpetual darkness. It covers 83% of the total area o ...

depths of the oceans, including the

hydrothermal vent Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hot ...

s, and numerous other ecological niches, including

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

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 external

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

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 Abalone ( or ; via Spanish , from Rumsen language, Rumsen ''aulón'') is a common name for any small to very large marine life, marine gastropod mollusc in the family (biology), family Haliotidae, which once contained six genera but now cont ...

conch Conch ( , , ) is a common name of a number of different medium-to-large-sized sea snails. Conch shells typically have a high Spire (mollusc), spire and a noticeable siphonal canal (in other words, the shell comes to a noticeable point on both ...

es, periwinkles,

whelk Whelks are any of several carnivorous sea snail species with a swirling, tapered shell. Many are eaten by humans, such as the common whelk of the North Atlantic. Most whelks belong to the family Buccinidae and are known as "true whelks." Othe ...

s, and numerous other sea snails that produce

seashell A seashell or sea shell, also known simply as a shell, is a hard, protective outer layer usually created by an animal or organism that lives in the sea. Most seashells are made by Mollusca, mollusks, such as snails, clams, and oysters ...

s that are coiled in the adult stage—though in some, the coiling may not be very visible, for example in

cowries Cowrie or cowry () is the common name for a group of small to large sea snails in the family Cypraeidae. Cowrie shells have held cultural, economic, and ornamental significance in various cultures. The cowrie was the shell most widely used wo ...

. In a number of

of species, such as all the various

s, the shell is coiled only in the

larval A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

stage, and is a simple conical structure after that.

Etymology

In the scientific literature, gastropods were described as "gasteropodes" by in 1795. The word ''gastropod'' comes from Greek ( 'stomach') and ( 'foot'), a reference to the fact that the animal's "foot" is positioned below its guts. The earlier name "univalve" means one

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...

(or shell), in contrast to

bivalve Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class (biology), class of aquatic animal, aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed b ...

s, such as clams, which have two valves or shells.

Diversity

At all

levels, gastropods are second only to insects in terms of their

diversity Diversity, diversify, or diverse may refer to: Business *Diversity (business), the inclusion of people of different identities (ethnicity, gender, age) in the workforce *Diversity marketing, marketing communication targeting diverse customers * ...

. Gastropods have the greatest numbers of named

mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...

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).Chapman, A.D. (2009)
Numbers of Living Species in Australia and the World, 2nd edition
. Australian Biological Resources Study, Canberra. Accessed 12 January 2010. (printed); (online). 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 Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

gastropods. Many deep-sea species remain to be discovered, as only 0.0001% of the deep-sea floor has been studied biologically."gastropod"
. (2010). In Encyclopædia Britannica. Retrieved March 05, 2010, from Encyclopædia Britannica Online. The total number of living species of freshwater snails is about 4,000. Recently

species of gastropods (extinct since 1500) number 444, 18 species are now

extinct in the wild A species that is extinct in the wild (EW) is one that has been categorized by the International Union for Conservation of Nature as only consisting of living members kept in captivity or as a naturalized population outside its historic range ...

(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, the

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margi ...

and the

continental rise The continental rise is a low-relief zone of accumulated sediments that lies between the continental slope and the abyssal plain. It is a major part of the continental margin, covering around 10% of the ocean floor. Formation This geologic s ...

are home to the highest diversity, while the continental shelf and abyssal depths have a low diversity of marine gastropods.

Habitat

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 a marine environment. Gastropods have a worldwide distribution, from the near

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

and

Antarctic The Antarctic (, ; commonly ) is the polar regions of Earth, polar region of Earth that surrounds the South Pole, lying within the Antarctic Circle. It is antipodes, diametrically opposite of the Arctic region around the North Pole. The Antar ...

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 Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...

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 protein

conchiolin Conchiolins (sometimes referred to as conchins) are complex proteins which are secreted by a mollusc's outer epithelium (the mantle). These proteins are part of a matrix of organic macromolecules, mainly proteins and polysaccharides, that ass ...

. Snails such as ''

Sphincterochila boissieri ''Sphincterochila'' is a genus of air-breathing land snails, terrestrial pulmonate gastropod molluscs in the family Sphincterochilidae.MolluscaBase eds. (2020). MolluscaBase. Sphincterochila Ancey, 1887. Accessed through: World Register of Mari ...

'' and ''

Xerocrassa seetzeni ''Xerocrassa seetzeni'' is a species of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Geomitridae.MolluscaBase eds. (2022). MolluscaBase. Xerocrassa seetzeni (L. Pfeiffer, 1847). Accessed through: World Regist ...

'' have adapted to desert conditions. Other snails have adapted to an existence in ditches, near deepwater

hydrothermal vents Hydrothermal vents are fissures on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hots ...

, in

oceanic trench Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...

es 10,000 meters (6 miles) below the surface, the pounding surf of

rocky shore A rocky shore is an intertidal area of seacoasts where solid rock predominates. Rocky shores are biologically rich environments, and are a useful "natural laboratory" for studying intertidal ecology and other biological processes. Due to th ...

cave Caves or caverns are natural voids under the Earth's Planetary surface, surface. Caves often form by the weathering of rock and often extend deep underground. Exogene caves are smaller openings that extend a relatively short distance undergrou ...

s, and many other diverse areas. Gastropods can be accidentally transferred from one habitat to another by other animals, e.g. by

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

Anatomy

Snails are distinguished by an anatomical process known as

torsion Torsion may refer to: Science * Torsion (mechanics), the twisting of an object due to an applied torque * Torsion of spacetime, the field used in Einstein–Cartan theory and ** Alternatives to general relativity * Torsion angle, in chemistry Bio ...

, where the visceral mass of the animal rotates 180° to one side during development, such that the

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

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 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, the olfactory organs, the foot slime-gland,

nephridia The nephridium (: nephridia) is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys (which originated from the chordate nephridia). Nephridia remove metabolic wastes from an animal's body. Nephridia co ...

, 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 A sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting ...

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 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 A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...

with two or four sensory

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s 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 a

protoconch A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called " ...

Shell

Most shelled gastropods have a one piece

(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 The apex is the highest point of something. The word may also refer to: Arts and media Fictional entities * Apex (comics) A-Bomb Abomination Absorbing Man Abraxas Abyss Abyss is the name of two characters appearing in Ameri ...

pointing upward). Numerous species have an operculum, 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.

Body wall

Some

sea slugs Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails (marine gastropod mollusks) that, over evolutionary t ...

are very brightly colored. This serves either as a warning, when they are

poisonous A poison is any chemical substance that is harmful or lethal to living organisms. The term is used in a wide range of scientific fields and industries, where it is often specifically defined. It may also be applied colloquially or figurati ...

or contain

stinging cell A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

s, or to

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

them on the brightly colored

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds, ...

sponge Sponges or sea sponges are primarily marine invertebrates of the animal phylum Porifera (; meaning 'pore bearer'), a basal clade and a sister taxon of the diploblasts. They are sessile filter feeders that are bound to the seabed, and a ...

s, and seaweeds on which many of the species are found. Lateral outgrowths on the body of

nudibranch Nudibranchs () are a group of soft-bodied marine gastropod molluscs, belonging to the order Nudibranchia, that shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have b ...

s are called

cerata :''The tortrix moth genus ''Cerata'' is considered a junior synonym of ''Cydia (genus), Cydia. Cerata, singular ceras, are anatomical structures found externally in nudibranch sea slugs, especially in aeolid nudibranchs, marine animal, marine opi ...

. These contain an outpocketing of

digestive gland The hepatopancreas, digestive gland or midgut gland is an organ of the digestive tract of arthropods and molluscs. It provides the functions which in mammals are provided separately by the liver and pancreas, including the production of digestive ...

s called the

diverticula In medicine or biology, a diverticulum is an outpouching of a hollow (or a fluid-filled) structure in the body. Depending upon which layers of the structure are involved, diverticula are described as being either true or false. In medicine, t ...

Sensory organs and nervous system

The

sensory organs A sense is a biological system used by an organism for sensation, the process of gathering information about the surroundings through the detection of stimuli. Although, in some cultures, five human senses were traditionally identified as s ...

of gastropods include olfactory organs, eyes,

statocyst The statocyst is a balance sensory receptor present in some aquatic invertebrates, including bivalves, cnidarians, ctenophorans, echinoderms, cephalopods, crustaceans, and gastropods, A similar structure is also found in '' Xenoturbella''. T ...

s and

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are located on sensory neurons that convert mechanical pressure into action potential, electrical signals tha ...

s. Gastropods have no hearing.Chase R.: ''Sensory Organs and the Nervous System''. in Barker G. M. (ed.): ''The biology of terrestrial molluscs''. CABI Publishing, Oxon, UK, 2001, . 1-146, cited pages: 179–211. In terrestrial gastropods (land snails and slugs), the olfactory organs, located on the tips of the four

s, are the most important sensory organ. The chemosensory organs of

opisthobranch Opisthobranchs () is a now informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopistho ...

marine gastropods are called

rhinophore A rhinophore is one of a pair of Chemoreceptor, chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, Marine (ocean), marine gastropod opisthobranch mollusks suc ...

s. 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 A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...

that only distinguish light and dark, to more complex pit eyes, and even to lens eyes. In land snails and slugs, vision is not the most important sense, because they are mainly

nocturnal Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite. Nocturnal creatur ...

animals. The nervous system of gastropods includes the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

and the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

. The central nervous system consists of

ganglia A ganglion (: ganglia) is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there a ...

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.

Digestive system

The

radula The radula (; : radulae or radulas) is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters ...

of a gastropod is usually adapted to the food that a species eats. The simplest gastropods are the

s and

, herbivores that use their hard

to rasp at

seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), '' Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...

s on rocks. Many marine gastropods are burrowers, and have a

siphon A siphon (; also spelled syphon) is any of a wide variety of devices that involve the flow of liquids through tubes. In a narrower sense, the word refers particularly to a tube in an inverted "U" shape, which causes a liquid to flow upward, abo ...

that extends out from the Mantle (mollusc), 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 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.

Respiratory system

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 Pulmonata, pulmonate family, 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,

s. Some nudibranchs have smooth or warty backs with no visible gill mechanism, such that respiration may likely take place directly through the skin.

Circulatory system

Gastropods have Circulatory system#Open circulatory system, open circulatory system and the transport fluid is hemolymph. Hemocyanin is present in the hemolymph as the respiratory pigment.

Excretory system

The primary organs of excretion in gastropods are nephridium, 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 the body cavity, and digestive glands opening into the stomach.

Reproductive system

Mating of gastropods#Courtship, Courtship is a part of mating of gastropods, 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

s, there are separate sexes (dioecious/Gonochorism, gonochoric); most land gastropods, however, are hermaphrodites.

Life cycle

Mating of gastropods#Courtship, Courtship 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: * Egg laying and the eggs of gastropods * The embryonic development of gastropods * The larvae or larval stadium: some gastropods may be trochophore and/or veliger * Estivation and hibernation (each of these are present in some gastropods only) * The growth of gastropods * Courtship and mating in gastropods: fertilization is internal or external according to the species. External fertilization is common in marine gastropods.

Feeding behavior

file:Pomacea maculata.jpg, An apple snail, ''Pomacea maculata'', floating and eating a piece of carrot 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 a few ciliary feeders, in which the

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 th
Archaeogastropoda
maintain horizontal rows of slender marginal teeth. In some species that have evolved into endoparasites, such as the Eulimidae, eulimid ''Thyonicola dogieli, Thyonicola doglieli'', many of 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.

Terrestrial gastropods

Studies based on direct observations, fecal and Gastrointestinal tract, gut analyses, as well as food-choice experiments, have revealed that snails and slugs consume a wide variety of food resources. Their diet spans from living plants at various developmental stages such as pollen, 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 as herbivores, omnivores, carnivores, and detritivores. However, the majority are microbivores, primarily consuming microbes associated with decaying organic material. Despite their ecological importance, there is a notable lack of research exploring the specific roles that terrestrial gastropods play within soil food webs.

Fungivory

Many terrestrial gastropod mollusks are known to consume fungi, a behavior observed in various species of snails and slugs across distinct families. Notable examples of fungivore slugs include members of the family Philomycidae, which feed on slime molds (myxomycetes), and the Ariolimacidae, which primarily consume mushrooms (basidiomycetes). Snail families that contain fungivore species include Clausiliidae, Macrocyclidae, and Polygyridae. Mushroom-producing fungi used as a food source by snails and slugs include species from several genera. Some examples are milk-caps (''Lactarius'' spp.), the oyster mushroom (''Pleurotus ostreatus''), and the Boletus, penny bun. Additionally, slugs feed on fungi from other genera, such as ''Agaricus'', ''Pleurocybella'', and ''Russula''. Snails have also been reported to feed on Boletus, penny buns as well as ''Coprinellus'', ''Aleurodiscus'', ''Armillaria'', ''Grifola '', ''Marasmiellus'', ''Mycena'', ''Pholiota'', and ''Ramaria''. As for slime molds, commonly consumed species include ''Stemonitis axifera'' and ''Symphytocarpus flaccidus''. 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. 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. Moreover, by consuming fungi, snails and slugs can also indirectly help in their Biological dispersal, dispersal by carrying along some of their spores or the fungi themselves.

Genetics

Gastropods exhibit an important degree of variation in mitochondrial gene organization when compared to other animals. Main events of Mutation, gene rearrangement occurred at 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 Chromosomal inversion, inversion, and Chromosomal translocation, translocations of the tRNAs D and N). Within Heterobranchia, gene order seems relatively conserved, and gene rearrangements are mostly related with Transposon, transposition of tRNA genes.

Geological history and evolution

The first gastropods were exclusively marine, with the earliest known representatives appearing in the

(e.g., ''Chippewaella'', ''Strepsodiscus''). However, their only definitive gastropod feature is a coiled shell, which raises the possibility that they may belong to the stem lineage of gastropods, or might not be gastropods at all. Early Cambrian species such as ''Helcionella'', ''Barskovia'', and ''Scenella'' are no longer considered gastropods, and the small coiled ''Aldanella'' from the same period is probably not even a mollusk. It is not until the Ordovician that true crown-group gastropods appear. By this time, gastropods had diversified into a variety of forms and inhabited a range of aquatic environments. Fossil gastropods from the early Paleozoic are often poorly preserved, making identification difficult. However, the Silurian genus ''Poleumita'' contains at least 15 identified species. Overall, gastropods were less common in the Paleozoic than bivalves. Most Paleozoic gastropods belong to primitive groups, some of which still exist today. By the Carboniferous 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 the Mesozoic era that the ancestors of many extant gastropods evolved. One of the earliest known terrestrial gastropods is ''Anthracopupa'' (or ''Maturipupa''), found in the Carboniferous Coal Measures of Europe. However, land snails and their relatives were rare before the Cretaceous period. 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 the Purbeck Marble of the Jurassic and the Sussex Marble of the early Cretaceous, both from southern England. These limestones contain abundant remains of the pond snail ''Viviparus''. 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. 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 these trace fossils are of debatable origin, some of them do resemble the trails made by living gastropods today. Gastropod fossils may sometimes be confused with ammonites or other shelled cephalopods. An example of this is ''Bellerophon (genus), Bellerophon'' from the limestones of the Carboniferous period in Europe, the shell of which is planispirally coiled and can be mistaken for the shell of a cephalopod. Gastropods also provide important evidence of faunal changes during the Pleistocene epoch, reflecting the impacts of advancing and retreating ice sheets. Cretaceous_Gastropod_Fossils_Lebanon

Phylogeny

A cladogram showing the phylogenic relationships of Gastropoda with example species: Neomphaliones and Lower Heterobranchia are not included in the above cladogram.

Taxonomy

Current classification

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. * Gastropoda ** Adenogonogastropoda (Angiogastropoda) *** Apogastropoda **** Caenogastropoda **** Heterobranchia *** Neritimorpha ** Patellogastropoda ** Vetigastropoda (including Neomphaliones) Turritellatricarinata

History

Since Charles Darwin, Darwin, biological taxonomy has attempted to reflect the phylogeny of organisms, i.e., the tree 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: * Opisthobranchia (gills to the right and behind the heart). * Gymnomorpha (no shell) * Prosobranchia (gills in front of the heart). * Pulmonata (with a lung instead of gills) The Taxonomy (biology), taxonomy of the Gastropoda is still under revision, and more and more of the old taxonomy is being abandoned, as the results of DNA 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 strictly monophyletic groups (only one lineage of gastropods in each group). Integrating new findings into a working Taxonomy (biology), taxonomy 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. 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 2004, Brian Simison and David R. Lindberg showed possible Paraphyly, diphyletic origins of the Gastropoda based on mitochondrial gene order and amino acid sequence analyses of complete genes. In 2005, Philippe Bouchet and Jean-Pierre Rocroi made sweeping changes in the systematics, resulting in the Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), Bouchet & Rocroi taxonomy, which is a step closer to the evolutionary history of the

.Bouchet 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. . 397 pp
vliz.be
The Bouchet & Rocroi classification system is based partly on the older systems of classification, and partly on new cladistic research. In the past, the taxonomy of gastropods was largely based on phenetic morphological characters of the taxa. The recent advances are more based on molecular characters from DNA and RNA 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.Philippe Bouchet, Jean-Pierre Rocroi, Bernhard Hausdorf, Andrzej Kaim, Yasunori Kano, Alexander Nützel, Pavel Parkhaev, Michael Schrödl and Ellen E. Strong. 2017.
Revised Classification, Nomenclator and Typification of Gastropod and Monoplacophoran Families
''. Malacologia, 61(1-2): 1-526. In the Taxonomy of the Gastropoda (Bouchet et al., 2017), Bouchet et al. taxonomy, the authors used unranked

s for taxa above the rank of superfamily (replacing the ranks suborder, order, superorder and subclass), while using the traditional Linnaean taxonomy, Linnaean approach for all taxa below the rank of superfamily. Whenever monophyly 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. Fixed ranks like family, genus, and species however remain useful for practical classification and remain used in the World 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.

Ecology and conservation

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.

Predators

Gastropods are prey to a wide range of organisms depending on the environment. In marine habitats, gastropods are preyed upon by fish, marine birds, marine mammals, crustaceans, and other mollusks such as cephalopods. In terrestrial environments, gastropod predators include

s, arachnids (spiders, harvestmen),

s, and mammals, among others.

Gallery

File:Caucasotachea atrolabiata.jpg, ''Caucasotachea atrolabiata'' (Heterobranchia) File:Cypraea Tigris.jpg, alt=Cypraea_Tigris, ''Cypraea tigris'' (Caenogastropoda) File:Mauritia mauritiana,.jpg, ''Mauritia mauritiana'' (Caenogastropoda) File:Amblychilepas compressa 001.jpg, alt=Amblychilepas_compressa_001, ''Amblychilepas compressa'' (Vetigastropoda) File:Conus rosiae 002.jpg, alt=, ''Conus rosiae'' (Caenogastropoda) File:Marisa cornuarietis ,.jpg, ''Marisa cornuarietis'' (Caenogastropoda) File:Pomacea canaliculata.jpg, ''Pomacea canaliculata'' (Caenogastropoda) File:Helicella macedonica.jpg, ''Helicella macedonica'' (Heterobranchia) File:Geophorus romblonensis.jpg, ''Geophorus romblonensis'' (Neritimorpha) File:Architectonica perspectiva S4-01.jpg, ''Architectonica perspectiva'' (Heterobranchia) File:Cypraea onyx S2-21 37mm.jpg, ''Erronea onyx'' (Caenogastropoda) File:Lyncina lynx S2-22 46mm.jpg, ''Lyncina lynx'' (Caenogastropoda) File:Helicostyla roissyana S5-01 Mehestan Natural History Collection, Iran 2025, 3.6mm.jpg, ''Helicostyla roissyana'' (Heterobranchia) File:Helicostyla rufogaster S2-22 Mehestan Natural History Collection, Iran 2025, 46mm.jpg, ''Helicostyla rufogaster'' (Heterobranchia) File:Achatina zebra S6 01 Mehestan Natural History Collection, Iran 2025, 73mm.jpg, ''Cochlitoma zebra'' (Heterobranchia)

References

Sources

* This article incorporates CC-BY 2.0, CC-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 (identifier), doi:10.1186/1471-2148-9-210. PMC (identifier), PMC 2741453. PMID (identifier), 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. * 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. * Parkinson, B., Hemmen, J. & Groh, K. (1987): ''Tropical Landshells of the World.'' 279 S., Verlag Christa Hemmen. Wiesbaden. * 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.

External links

Gastropod reproductive behavior

* – Article about Social learning (social pedagogy), social learning also in gastropods.
Gastropod photo gallery
mostly fossils, a few modern shells
A video of a crawling Garden Snail
(''Cornu aspersum''), YouTube
Grove, S.J. (2018). A Guide to the Seashells and other Marine Molluscs of Tasmania: Molluscs of Tasmania with images
{{Authority control Gastropods, Mollusc classes Asymmetry Articles containing video clips Extant Cambrian first appearances Taxa named by Georges Cuvier