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 edge. Sometimes the shell has a

siphonal canal The siphonal canal is an anatomical feature of the shells of certain groups of sea snails within the clade Neogastropoda. Some sea marine gastropods have a soft tubular anterior extension of the mantle called a siphon through which water i ...

to accommodate this structure. A siphon enables the animal to draw water into their

mantle cavity The mantle (also known by the Latin word pallium meaning mantle, robe or cloak, adjective pallial) is a significant part of the anatomy of molluscs: it is the dorsal body wall which covers the visceral mass and usually protrudes in the form of ...

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 A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

, but many freshwater species, and the majority of terrestrial species, have a pallial

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

. The respiratory protein in almost all gastropods is

hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2 ...

, but one freshwater

pulmonate Pulmonata or pulmonates is an informal group (previously an order, and before that, a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group inclu ...

family, the

Planorbidae Planorbidae, common name the ramshorn snails or ram's horn snails, is a family (biology), family of air-breathing freshwater snails, Aquatic animal, aquatic pulmonate gastropod Mollusca, molluscs. Unlike most molluscs, the blood of ram's horn sn ...

, have

hemoglobin Hemoglobin (haemoglobin, Hb or Hgb) is a protein containing iron that facilitates the transportation of oxygen in red blood cells. Almost all vertebrates contain hemoglobin, with the sole exception of the fish family Channichthyidae. 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

wart Warts are non-cancerous viral growths usually occurring on the hands and feet but which can also affect other locations, such as the genitals or face. One or many warts may appear. They are distinguished from cancerous tumors as they are caus ...

y backs with no visible gill mechanism, such that respiration may likely take place directly through the skin.

Circulatory system

Gastropods have

open circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart a ...

and the transport fluid is

hemolymph Hemolymph, or haemolymph, is a fluid, similar to the blood in invertebrates, that circulates in the inside of the arthropod's body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which hemolymph c ...

Hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2 ...

is present in the

as the respiratory pigment.

Excretory system

The primary organs of excretion in gastropods are

, which produce either

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the Chemical formula, formula C5H4N4O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the meta ...

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 The stomach is a muscular, hollow organ in the upper gastrointestinal tract of Human, humans and many other animals, including several invertebrates. The Ancient Greek name for the stomach is ''gaster'' which is used as ''gastric'' in medical t ...

Reproductive system

Courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage or committed romantic, ''de facto'' relationship. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marri ...

is a part of

mating In biology, mating is the pairing of either opposite-sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. '' Copulation'' is the union of the sex organs of two sexually repr ...

behavior in some gastropods, including some of the

Helicidae Helicidae is a large, diverse family of western Palaearctic, medium to large-sized, air-breathing land snails, sometimes called the "typical snails." It includes some of the largest European land snails, several species are common in anthropoge ...

. Again, in some land snails, an unusual feature of the

reproductive system of gastropods The reproductive system of gastropods (slugs and snails) varies greatly from one group to another within this very large and diverse taxonomic class of animals. Their reproduction, reproductive strategies also vary greatly. In many marine (ocean ...

is the presence and utilization of

love dart A love dart (also known as a gypsobelum, shooting darts, or just as darts) is a sharp, calcium carbonate, calcareous or chitinous Dart (missile), dart which some hermaphroditic land snails and slugs create. Love darts are both formed and stor ...

s. In many marine gastropods other than the

s, there are separate sexes (

dioecious Dioecy ( ; ; adj. dioecious, ) is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproduction is ...

gonochoric In biology, gonochorism is a sexual system where there are two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric. Gonochorism contrast ...

); most land gastropods, however, are

hermaphrodite A hermaphrodite () 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 ...

Life cycle

is a part of the behavior of

gastropods with some

families of land snails creating and utilizing

s, the throwing of which have been identified as a form of

sexual selection Sexual selection is a mechanism of evolution in which members of one sex mate choice, choose mates of the other sex to mating, mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ...

. The main aspects of the life cycle of gastropods include: * Egg laying and the eggs of gastropods * The

embryonic development In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermat ...

of gastropods * The larvae or larval stadium: some gastropods may be

trochophore A trochophore () is a type of free-swimming planktonic marine larva with several bands of cilia. By moving their cilia rapidly, they make a water eddy to control their movement, and to bring their food closer in order to capture it more easily. ...

and/or

veliger A veliger is the planktonic larva of many kinds of sea snails and freshwater snails, as well as most bivalve molluscs (clams) and tusk shells. Description The veliger is the characteristic larva of the gastropod, bivalve and scaphopod taxono ...

Estivation Aestivation ( (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a lowered me ...

and

hibernation Hibernation is a state of minimal activity and metabolic reduction entered by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It is mos ...

(each of these are present in some gastropods only) * The growth of gastropods * Courtship and mating in gastropods:

fertilization Fertilisation or fertilization (see American and British English spelling differences#-ise, -ize (-isation, -ization), spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give ...

is internal or external according to the species. External fertilization is common in marine gastropods.

Feeding behavior

An apple snail, ''Pomacea maculata'', floating and eating a piece of carrot">Pomacea_maculata.html" ;"title="apple snail, ''Pomacea maculata">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 eulimid '' Thyonicola doglieli'', many of the standard gastropod features are strongly reduced or absent. A few

sea slug Sea slug is a common name for some Marine biology, marine invertebrates with varying levels of resemblance to terrestrial Slug, slugs. Most creatures known as sea slugs are gastropods, i.e. they are Sea snail, sea snails (marine gastropod moll ...

s 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 shell ''Conus'' is a genus of venomous and predatory cone snails.Bouchet, P.; Gofas, S. (2015). Conus Linnaeus, 1758. In: MolluscaBase (2015). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&i ...

s, '' Testacella'', ''

Daudebardia ''Daudebardia'' are small air-breathing land snails or semi-slugs, terrestrial pulmonate gastropods in the family Oxychilidae, the glass snails. Species Species within the genus ''Daudebardia'' include: ** ''Daudebardia brevipes'' (Draparnaud ...

'',

turrid Turrid, plural turrids, is a common name for a very large group of predatory sea snails, Marine (ocean), marine gastropod mollusks which until recently were all classified in the family Turridae. However, recently the family was discovered to be ...

ghost slug ''Selenochlamys ysbryda'', the ghost slug, is a species of predatory air-breathing land slug. It is a shell-less pulmonate gastropod mollusc in the family Oxychilidae, although when first described it was assumed to be in the Trigonochlamydid ...

s and others.

Terrestrial gastropods

Studies based on direct observations,

fecal Feces (also known as faeces or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the large intestine. Feces contain a relatively small amount of ...

and 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 Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...

, seeds,

seedling A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...

s, and wood, to decaying plant material like leaf litter. Additionally, they feed on fungi,

lichens A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

, soil, and even other animals, both living and dead, including their feces. Given this diverse diet, terrestrial gastropods can be classified as

herbivores A herbivore is an animal anatomically and physiologically evolved to feed on plants, especially upon vascular tissues such as foliage, fruits or seeds, as the main component of its diet. These more broadly also encompass animals that eat ...

omnivores An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

carnivores A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose nutrition and energy requirements are met by consumption of animal tissues (mainly mu ...

, and

detritivores Detritivores (also known as detrivores, detritophages, detritus feeders or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

. However, the majority are

microbivores Microbivory (adj. microbivorous, microbivore) is a feeding behavior consisting of eating microbes (especially bacteria) practiced by animals of the mesofauna, microfauna and meiofauna. Microbivorous animals include some soil nematodes, springta ...

, primarily consuming

microbe A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

s associated with decaying organic material. Despite their

ecological Ecology () is the natural science of the relationships among living organisms and their environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere levels. Ecology overlaps with the closely re ...

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 Fungivory or mycophagy is the process of organisms consuming fungi. Many different organisms have been recorded to gain their energy from consuming fungi, including birds, mammals, insects, plants, amoebas, gastropods, nematodes, bacteria and othe ...

slugs include members of the family

Philomycidae Philomycidae are a family of air-breathing land slugs (snails without shells or with only shell remnants). They are terrestrial molluscs, terrestrial pulmonate gastropod mollusks in the superfamily Arionoidea (according to the Taxonomy of the G ...

, which feed on

slime molds Slime mold or slime mould is an informal name given to a polyphyly, polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myx ...

(myxomycetes), and the

Ariolimacidae Ariolimacidae is a family (biology), family of air-breathing land slugs, terrestrial molluscs, terrestrial pulmonate gastropod mollusks in the superfamily Arionoidea (according to the Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), taxonomy ...

, which primarily consume mushrooms (

basidiomycetes Basidiomycota () is one of two large division (mycology), divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. Mor ...

). Snail families that contain fungivore species include

Clausiliidae Clausiliidae, also known by the common name door snails, is a Taxonomy (biology), taxonomic family (biology), family of small, very elongate, mostly Gastropod shell#Chirality in gastropods, left-handed, air-breathing land snails, sinistral terre ...

Macrocyclidae Macrocyclidae is a family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in the superfamily Acavoidea The Acavoidea are a taxonomic superfamily of air-breathing land snails and slugs, terrestrial pulmonate gastropod ...

, and

Polygyridae Polygyridae is a family (biology), family of air-breathing land snails, terrestrial molluscs, terrestrial pulmonate gastropod mollusks in the superfamily Helicoidea.MolluscaBase eds. (2021). MolluscaBase. Polygyridae Pilsbry, 1895. Accessed thro ...

. Mushroom-producing fungi used as a food source by snails and slugs include species from several genera. Some examples are

milk-cap Milk-cap (also milk cap, milkcap, or milky) is a common name that refers to mushroom-forming fungi of the genera ''Lactarius'', '' Lactifluus'', and '' Multifurca'', all in the family Russulaceae. The common and eponymous feature of their fruit ...

s (''

Lactarius ''Lactarius'' is a genus of mushroom-producing, ectomycorrhizal fungi, containing several Edible mushroom, edible species. The species of the genus, common name, commonly known as milk-caps, are characterized by the milky fluid ("latex") they ex ...

'' spp.), the

oyster mushroom ''Pleurotus'' is a genus of Gill (mushroom), gilled mushrooms which includes one of the most widely eaten mushrooms, ''Pleurotus ostreatus, P. ostreatus''. Species of ''Pleurotus'' may be called oyster, abalone, or tree mushrooms, and are ...

(''Pleurotus ostreatus''), and the penny bun. Additionally, slugs feed on fungi from other genera, such as ''

Agaricus ''Agaricus'' is a genus of mushroom-forming fungi containing both edible and poisonous species, with over 400 members worldwide and possibly again as many disputed or newly discovered species. The genus includes the common ("button") mushroom ...

'', ''

Pleurocybella ''Pleurocybella'' is a genus of fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushroom ...

'', and ''

Russula ''Russula'' is a very large genus composed of around 750 worldwide species of fungi. The genus was described by Christian Hendrik Persoon in 1796. The mushrooms are fairly large, and brightly colored – making them one of the most recognizable ...

''. Snails have also been reported to feed on penny buns as well as ''

Coprinellus ''Coprinellus'' is a genus of mushroom-forming fungi in the family Psathyrellaceae. The genus was circumscribed by the Finnish mycologist Petter Adolf Karsten in 1879. Most ''Coprinellus'' species were transferred from the once large genus '' Co ...

'', ''

Aleurodiscus ''Aleurodiscus'' is a genus of corticioid fungi in the family Stereaceae The Stereaceae are a family of corticioid fungi in the Russulales order. Species in the family have a widespread distribution, are lignicolous or terrestrial (in leaf l ...

'', ''

Armillaria ''Armillaria'' is a genus of fungi that includes the '' A. mellea'' species ('honey fungus') that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as ''A. mellea''. ''Armillaria'' sp. are long-live ...

'', '' Grifola '', ''

Marasmiellus ''Marasmiellus'' is a genus of fungi in the family (biology), family Omphalotaceae. The widespread genus, circumscription (taxonomy), circumscribed by American mycologist William Murrill in 1915, contains over 250 species. The name comes from the ...

'', ''

Mycena ''Mycena'' is a genus of about 500 species of fungi. Rarely more than a few centimeters in width, the mushrooms are characterized by a small conical or bell-shaped cap and a thin fragile stem. Most are grey or brown, but a few species have brigh ...

'', ''

Pholiota ''Pholiota'' is a genus of small to medium-sized, fleshy mushrooms in the family Strophariaceae. They are saprobes that typically live on wood. The genus has a widespread distribution, especially in temperate regions, and contains about 150 spe ...

'', and ''

Ramaria The genus ''Ramaria'' comprises approximately 200 species of coral fungi. Several, such as '' Ramaria flava'', are edible and picked in Europe, though they are easily confused with several mildly poisonous species capable of causing nausea, vom ...

''. As for slime molds, commonly consumed species include ''

Stemonitis axifera ''Stemonitis axifera'' is a species of slime mold. It fruits in clusters on dead wood, and has distinctive tall reddish-brown sporangia, supported on slender stalks. Taxonomy The species was first described as ''Trichia axifera'' by Jean Baptist ...

'' 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 dispersal by carrying along some of their

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s or the fungi themselves.

Genetics

Gastropods exhibit an important degree of variation in

mitochondrial gene Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the DNA contained in ...

organization when compared to other animals. Main events of

gene rearrangement V(D)J recombination (variable–diversity–joining rearrangement) is the mechanism of somatic recombination that occurs only in developing lymphocytes during the early stages of T and B cell maturation. It results in the highly diverse repertoire ...

occurred at the origin of

Patellogastropoda The Patellogastropoda, common name true limpets and historically called the Docoglossa, are members of a major phylogenetic group of marine (ocean), marine gastropods, treated by experts either as a clade or as a taxonomic Order (biology), order. ...

and

Heterobranchia Heterobranchia, the heterobranchs (meaning "different gill"), is a taxonomic clade of snails and slugs, which includes marine, aquatic, and terrestrial gastropod molluscs. Heterobranchia is one of the main clades of gastropods. Currently Het ...

, whereas fewer changes occurred between the ancestors of

Vetigastropoda Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically the Vetigastropoda are sometimes treated as an order, although they are treated as an unranked clade in Bouch ...

(only

tRNA Transfer ribonucleic acid (tRNA), formerly referred to as soluble ribonucleic acid (sRNA), is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes). In a cell, it provides the physical link between the gene ...

s D, C and N) and

Caenogastropoda Caenogastropoda is a taxonomic subclass of molluscs in the class Gastropoda. It is a large diverse group which are mostly sea snails and other marine gastropod mollusks, but also includes some freshwater snails and some land snails. The subcla ...

(a large single

inversion Inversion or inversions may refer to: Arts * ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas * Inversion (music), a term with various meanings in music theory and musical set theory * ''Inversions'' (novel) by Iain M. Bank ...

, 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.

Geological history and evolution

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

(e.g., ''

Chippewaella ''Chippewaella patellitheca'' is a stem-gastropod mollusc from Furongian-aged strata of Late Cambrian Wisconsin. According to Peter J. Wagner, it is the most Basal (phylogenetics), basal gastropod. Morphology ''C. patellitheca'' is known from b ...

'', '' 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 ''Helcionella'' is a genus of helcionellid, a fossil marine invertebrate animal that is considered to be a mollusk and may possibly be a gastropod. The shells of these animals are about a centimetre in size. The tip of the shell extends beyond ...

'', '' Barskovia'', and ''

Scenella ''Scenella'' is an extinct genus of fossil invertebrate animal which is generally considered to be a mollusc; at various times it has been suggested that this genus belongs with the gastropods, the monoplacophorans, or the helcionellids, althoug ...

'' are no longer considered gastropods, and the small coiled ''

Aldanella ''Aldanella'' is an extinct Paleozoic animal that was assigned to the Gastropod stem group but may also belong to a paraphyletic "Monoplacophora" or Annelida The annelids (), also known as the segmented worms, are animals that comprise the ...

'' from the same period is probably not even a mollusk. It is not until the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

that true

crown-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

gastropods appear. By this time, gastropods had diversified into a variety of forms and inhabited a range of

aquatic environment An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environm ...

s. Fossil gastropods from the early

Paleozoic The Paleozoic ( , , ; or Palaeozoic) Era is the first of three Era (geology), geological eras of the Phanerozoic Eon. Beginning 538.8 million years ago (Ma), it succeeds the Neoproterozoic (the last era of the Proterozoic Eon) and ends 251.9 Ma a ...

are often poorly preserved, making identification difficult. However, the

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

genus ''

Poleumita ''Poleumita'' is an extinct genus of medium-sized sea snails, fossil marine gastropods in the family Euomphalidae. This genus is known from the Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the ...

'' contains at least 15 identified species. Overall, gastropods were less common in the

than

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

. Most Paleozoic gastropods belong to primitive groups, some of which still exist today. By the

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

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 The Mesozoic Era is the Era (geology), era of Earth's Geologic time scale, geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceous Period (geology), Periods. It is characterized by the dominance of archosaurian r ...

era that the ancestors of many extant gastropods evolved. One of the earliest known terrestrial gastropods is '' Anthracopupa'' (or '' Maturipupa''), found in the

Coal Measures of Europe. However, land snails and their relatives were rare before the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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 Purbeck Marble is a fossiliferous limestone found in the Isle of Purbeck, a peninsula in south-east Dorset, England. It is a variety of Purbeck stone that has been quarried since at least Roman times as a decorative building stone. Geology S ...

of the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

and the

Sussex Marble Sussex Marble is a fossiliferous freshwater limestone material which is prevalent in the Weald Clay of parts of Kent, East Sussex and West Sussex in southeast England. It is also called Petworth Marble, Bethersden Marble or Laughton Stone in relat ...

of the early Cretaceous, both from

southern England Southern England, also known as the South of England or the South, is a sub-national part of England. Officially, it is made up of the southern, south-western and part of the eastern parts of England, consisting of the statistical regions of ...

. These limestones contain abundant remains of the pond snail ''

Viviparus ''Viviparus'', commonly known as the river snails, is a genus of large, freshwater snails with an operculum, aquatic gastropod molluscs.Bouchet, P. (2014). Viviparus Montfort, 1810. Accessed through: World Register of Marine Species at http:/ ...

''.

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

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 fossil A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

s are of debatable origin, some of them do resemble the trails made by living gastropods today. Gastropod fossils may sometimes be confused with

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

s or other shelled

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s. An example of this is ''

Bellerophon Bellerophon or Bellerophontes (; ; lit. "slayer of Belleros") or Hipponous (; lit. "horse-knower"), was a divine Corinthian hero of Greek mythology, the son of Poseidon and Eurynome, and the foster son of Glaukos. He was "the greatest her ...

'' from the limestones of the

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 The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

epoch, reflecting the impacts of advancing and retreating

ice sheets In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are the Antarctic ice sheet and the Greenland ice sheet. Ice sheets ...

Phylogeny

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

showing the phylogenic relationships of Gastropoda with example species: Neomphaliones and

Lower Heterobranchia Lower Heterobranchia, also known as the Allogastropoda, is a group of rather specialized, highly evolved sea slugs and sea snails, marine (ocean), marine gastropod mollusc, mollusks within the Subclass (biology), subclass Heterobranchia.WoRMS (20 ...

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 ****

****

***

Neritimorpha Neritimorpha is a clade of gastropod molluscs that contains around 2,000 extant species of sea snails, limpets, freshwater snails, land snails and slugs. This clade used to be known as the superorder Neritopsina. Etymology The clade’s name, N ...

(including Neomphaliones) Turritellatricarinata

History

Since Darwin, biological taxonomy has attempted to reflect the

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

of organisms, i.e., the

tree of life The tree of life is a fundamental archetype in many of the world's mythology, mythological, religion, religious, and philosophy, philosophical traditions. It is closely related to the concept of the sacred tree.Giovino, Mariana (2007). ''The ...

. 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 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. Euopisth ...

(gills to the right and behind the heart). *

Gymnomorpha The Systellommatophora (synonym Gymnomorpha) is a clade of primitive, air-breathing slugs, according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005). They are marine and terrestrial pulmonate gastropods within the Heterobranchia. T ...

(no shell) *

Prosobranchia Prosobranchia was a large Taxonomy (biology), taxonomic Class (biology), subclass of sea snails, land snails and freshwater snails. This taxon of gastropods dates back to the 1920s. It has however been proven to be polyphyly, polyphyletic (consis ...

(gills in front of the heart). *

Pulmonata Pulmonata or pulmonates is an informal group (previously an order, and before that, a subclass) of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includes ...

(with a lung instead of gills) The

taxonomy image:Hierarchical clustering diagram.png, 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 o ...

of the Gastropoda is still under revision, and more and more of the old taxonomy is being abandoned, as the results of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

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 In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

groups (only one lineage of gastropods in each group). Integrating new findings into a working

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 Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

, 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

diphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In cont ...

origins of the Gastropoda based on

mitochondrial A mitochondrion () is an organelle found in the cells of most eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is used ...

gene order and

amino acid sequence Protein primary structure is the linear sequence of amino acids in a peptide or protein. By convention, the primary structure of a protein is reported starting from the amino-terminal (N) end to the carboxyl-terminal (C) end. Protein biosynthe ...

analyses of complete genes. In 2005,

Philippe Bouchet Philippe Bouchet (born 1953) is a French biologist whose primary scientific fields of study are malacology (the study of molluscs) and taxonomy. He works at the Muséum National d'Histoire Naturelle in Paris. He is also a Commissioner of the In ...

and Jean-Pierre Rocroi made sweeping changes in the

systematics Systematics is the study of the diversification of living forms, both past and present, and the relationships among living things through time. Relationships are visualized as evolutionary trees (synonyms: phylogenetic trees, phylogenies). Phy ...

, resulting in the 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 Cladistics ( ; from Ancient Greek 'branch') is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is ...

research. In the past, the taxonomy of gastropods was largely based on

phenetic In biology, phenetics (; ), also known as taximetrics, is an attempt to classify organisms based on overall similarity, usually with respect to Morphology (biology), morphology or other observable traits, regardless of their phylogeny or evoluti ...

morphological characters of the taxa. The recent advances are more based on molecular characters from

and

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

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 ''Malacologia'' is a peer-reviewed scientific journal in the field of malacology, the study of mollusks. The journal publishes articles in the fields of molluscan systematics, ecology, population ecology, genetics, molecular genetics, evolution, an ...

, 61(1-2): 1-526. In the 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 approach for all taxa below the rank of superfamily. Whenever

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

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 The World Register of Marine Species (WoRMS) is a taxonomic database that aims to provide an authoritative and comprehensive catalogue and list of names of marine organisms. Content The content of the registry is edited and maintained by scien ...

(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 Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not ki ...

to a wide range of organisms depending on the environment. In marine habitats, gastropods are preyed upon by

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

marine birds Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same envi ...

marine mammal Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...

s, crustaceans, and other mollusks such as

s. In terrestrial environments, gastropod predators include

s, arachnids (spiders, harvestmen),

s, and mammals, among others.

Gallery

File:Caucasotachea atrolabiata.jpg, ''Caucasotachea atrolabiata'' (

) File:Cypraea Tigris.jpg, alt=Cypraea_Tigris, ''Cypraea tigris'' (

) File:Mauritia mauritiana,.jpg, ''Mauritia mauritiana'' (

) File:Amblychilepas compressa 001.jpg, alt=Amblychilepas_compressa_001, ''Amblychilepas compressa'' (

) File:Conus rosiae 002.jpg, alt=, ''Conus rosiae'' (

) File:Marisa cornuarietis ,.jpg, ''Marisa cornuarietis'' (

) File:Pomacea canaliculata.jpg, ''Pomacea canaliculata'' (

) File:Helicella macedonica.jpg, ''Helicella macedonica'' (

) File:Geophorus romblonensis.jpg, ''Geophorus romblonensis'' (

) File:Architectonica perspectiva S4-01.jpg, ''Architectonica perspectiva'' (

) File:Cypraea onyx S2-21 37mm.jpg, ''Erronea onyx'' (

) File:Lyncina lynx S2-22 46mm.jpg, ''Lyncina lynx'' (

) File:Helicostyla roissyana S5-01 Mehestan Natural History Collection, Iran 2025, 3.6mm.jpg, ''Helicostyla roissyana'' (

) File:Helicostyla rufogaster S2-22 Mehestan Natural History Collection, Iran 2025, 46mm.jpg, ''Helicostyla rufogaster'' (

) File:Achatina zebra S6 01 Mehestan Natural History Collection, Iran 2025, 73mm.jpg, ''Cochlitoma zebra'' (

)

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