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

taxonomic Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...

class Class 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 differentl ...

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s within the

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

Mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

called Gastropoda (). This class comprises

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

s and

slug 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 smal ...

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

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

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 smal ...

, as well as

freshwater snail Freshwater snails are gastropod mollusks which 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 ...

s, freshwater

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

s, and

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 gastropod mollusks that have shells (those without shells are known as ...

s and

s. The class Gastropoda contains a vast total of named species, second only to the

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

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

Late Cambrian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...

. , 721

families Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Ideall ...

of gastropods are known, of which 245 are

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed 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 preserved ...

record, while 476 are currently

extant Extant 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 * Extant taxon, a taxon which is not extinct, ...

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

in the

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

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. The

anatomy Anatomy () is the branch of biology concerned with the study of the 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 science, having its ...

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

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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

habitat In ecology, the term habitat summarises the array of resources, physical and 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 ...

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 environment ...

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 fl ...

s, the rocky

intertidal The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of Marine habitat, habitats with var ...

, the sandy subtidal, the

abyssal The abyssal zone or abyssopelagic zone is a layer of the pelagic zone of the ocean. "Abyss" derives from the Greek word , meaning bottomless. At depths of , this zone remains in perpetual darkness. It covers 83% of the total area of the ocean an ...

depths of the oceans, including the

hydrothermal vent A hydrothermal vent is a fissure 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 hotspot ...

s, and numerous other ecological niches, including

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

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 ** Thin-shell structure Science Biology * Seashell, a hard ou ...

big enough that the soft parts can withdraw completely into it. Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as slugs; those with a shell into which they can partly but not completely withdraw are termed semislugs. The marine shelled species of gastropods include species such as

abalone Abalone ( or ; via Spanish , from Rumsen ''aulón'') is a common name for any of a group of small to very large marine gastropod molluscs in the family (biology), family Haliotidae. Other common name In biology, a common name of a taxon o ...

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

es, periwinkles,

whelk Whelk (also known as scungilli) is a common name applied to various kinds of sea snail. Although a number of whelks are relatively large and are in the family Buccinidae (the true whelks), the word ''whelk'' is also applied to some other marine ...

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. The shell is part of the body of the animal. Empty seashells are often found washe ...

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, marine gastropod mollusks in the family Cypraeidae, the cowries. The term ''porcelain'' derives from the old Italian term for the cowrie shell (''porcellana'') du ...

. In a number of

of species, such as all the various

s, the shell is coiled only in the

larval A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The l ...

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 slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...

(or shell), in contrast to

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

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

Diversity

At all

levels, gastropods are second only to the 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

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

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 molluscs 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 known only by living members kept in captivity or as a naturalized population outside its historic range due ...

(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 margin ...

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 str ...

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

Habitat

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 ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...

and

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized nearly every available medium. In habitats where not enough calcium carbonate is available to build a really solid shell, such as on some acidic soils on land, various species of slugs occur, and also some snails with thin, translucent shells, mostly or entirely composed of 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 assem ...

. Snails such as ''

Sphincterochila boissieri ''Sphincterochila zonata zonata'' is a subspecies of air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Sphincterochilidae. MolluscaBase eds. (2022). MolluscaBase. Sphincterochila zonata zonata (Bourguignat, 1853). ...

'' and ''

Xerocrassa seetzeni ''Xerocrassa seetzeni'' is a species of air-breathing land snail, a terrestrial animal, terrestrial pulmonate gastropod mollusk in the family Geomitridae. MolluscaBase eds. (2022). MolluscaBase. Xerocrassa seetzeni (L. Pfeiffer, 1847). Accessed t ...

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

hydrothermal vents A hydrothermal vent is a fissure 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 hotspot ...

, 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 their ...

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

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 Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

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 Bi ...

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

anus The anus (Latin, 'ring' or 'circle') is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, the residual semi-solid waste that remains after food digestion, which, d ...

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 an asymmetrical growth, with the majority occurring on the left side. This leads to the loss of right-paired appendages (e.g., ctenidia (comb-like respiratory apparatus),

gonad A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sper ...

nephridia The nephridium (plural ''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. Neph ...

, etc.). 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. However, this "rotation hypothesis" is being challenged by the "asymmetry hypothesis" in which the gastropod mantle cavity originated from one side only of a bilateral set of mantle cavities. 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 animals may ...

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, which gives them their name (

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''gaster'',

stomach The stomach is a muscular, hollow organ in the gastrointestinal tract of humans and many other animals, including several invertebrates. The stomach has a dilated structure and functions as a vital organ in the digestive system. The stomach i ...

, and ''pous'',

foot The foot ( : feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is a separate organ at the terminal part of the leg made ...

). 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 ...

. The principal characteristic of the Gastropoda is the asymmetry of their principal organs. The essential feature of this asymmetry is that the anus generally lies to one side of the median plane.; The ctenidium (gill-combs), the

osphradium The osphradium is a pigmented chemosensory epithelium patch in the mantle cavity present in six of the eight extant classes of molluscs (it is absent in the scaphopoda and monoplacophora; among cephalopoda, only the nautilus has what appears to be ...

(olfactory organs), the

hypobranchial gland The hypobranchial gland is a glandular structure which is part of the anatomy of many mollusks, including several different families of gastropods, and also many protobranch bivalves. This gland produces mucus as well as biologically active comp ...

(or pallial mucous gland), 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 (or reproductive organ) is any part of an animal or plant that is involved in sexual reproduction. The reproductive organs together constitute the reproductive system. In animals, the testis in the male, and the ovary in the female, a ...

orifice, which lies on the same side of the body as the anus.

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 teenaged super villainess in the Marvel Universe * Ape-X, a super-intelligent ape in the Squadron Supreme universe *Apex ...

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 tim ...

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

poisonous Poison is a chemical substance that has a detrimental effect to life. 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 figuratively, with a broa ...

or contain

stinging cell A cnidocyte (also known as a cnidoblast or nematocyte) is an explosive cell containing one large secretory organelle called a cnidocyst (also known as a cnida () or nematocyst) that can deliver a sting to other organisms. The presence of this ce ...

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 ...

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, the members of the phylum Porifera (; meaning 'pore bearer'), are a basal animal clade as a sister of the diploblasts. They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through t ...

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 which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to matc ...

s are called

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

. These contain an outpocketing of digestive gland 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 world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...

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, and crustaceans. A similar structure is also found in ''Xenoturbella''. The statocyst cons ...

s and

mechanoreceptor A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, ...

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 now an 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 ...

marine gastropods are called

rhinophore A rhinophore is one of a pair of chemosensory club-shaped, rod-shaped or ear-like structures which are the most prominent part of the external head anatomy in sea slugs, marine gastropod opisthobranch mollusks such as the nudibranchs, sea har ...

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 (sometimes called a pigment pit) refers to a form of eye or an optical arrangement composed of a single lens and without an elaborate retina such as occurs in most vertebrates. In this sense "simple eye" is distinct from a multi-l ...

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 an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnal meaning the opposite. Nocturnal creatures generally have highly developed sens ...

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 bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain ...

and the

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

. The central nervous system consist of

ganglia A ganglion 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 are both sympatheti ...

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 (, ; plural radulae or radulas) is an anatomical structure used by molluscs 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 ...

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

s and

s, 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 (from grc, σίφων, síphōn, "pipe, tube", also spelled nonetymologically 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 a ...

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 is ...

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 respiratory organ that many 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 respiration on land provided they are ...

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

lung The lungs are the primary organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of t ...

. 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 includ ...

family, the

Planorbidae Planorbidae, common name the ramshorn snails or ram's horn snails, is a family of air-breathing freshwater snails, aquatic pulmonate gastropod molluscs. Unlike most molluscs, the blood of ram's horn snails contains iron-based hemoglobin ins ...

, have

hemoglobin Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyte ...

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 typically small, rough, hard growths that are similar in color to the rest of the skin. They typically do not result in other symptoms, except when on the bottom of the feet, where they may be painful. While they usually occur on the ...

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 The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...

and the transport fluid is

hemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which ...

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 compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

uric acid Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen, and hydrogen with the 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 metabolic breakdown of ...

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

Reproductive system

Courtship Courtship is the period wherein some couples get to know each other prior to a possible marriage. Courtship traditionally may begin after a betrothal and may conclude with the celebration of marriage. A courtship may be an informal and private m ...

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 reproduc ...

behavior in some gastropods, including some of the

Helicidae Helicidae is a large, diverse family of small to large, air-breathing land snails, sometimes called the "typical snails." A number of species in this family are valued as food items, including ''Cornu aspersum'' (formerly ''Helix aspersa'') the b ...

. 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 reproductive strategies also vary greatly, see Mating of gastropods. In many ...

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, calcareous or chitinous dart which some hermaphroditic land snails and slugs create. Love darts are both formed and stored internally in a dart sac. These ...

s. In many marine gastropods other than the

s, there are separate sexes (

dioecious Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

gonochoric In biology, gonochorism is a sexual system where there are only 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 c ...

); most land gastropods, however, are

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

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 mode of natural selection in which members of one biological 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 t ...

. 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, A ''Pomacea maculata'' floating and eating a 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 and decomposing animals while marine species can scrape algae off the rocks on the seafloor. Certain species such as th
Archaeogastropda
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, for example: Cone shells, ''Testacella'', ''Daudebardia'', Turrids, Ghost slug and others.

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 representatives of the group appearing in the

(''Chippewaella'', ''Strepsodiscus''), though their only gastropod character is a coiled shell, so they could lie in the stem lineage, if they are gastropods at all. Earliest Cambrian organisms like ''Helcionella'', ''Barskovia'' and ''Scenella'' are no longer considered gastropods, and the tiny coiled ''Aldanella'' of earliest Cambrian time is probably not even a mollusk. As such, it's not until the Ordovician that the first crown-group members arise. By the Ordovician period the gastropods were a varied group present in a range of aquatic habitats. Commonly,

gastropods from the rocks of the early Palaeozoic era are too poorly preserved for accurate identification. Still, the Silurian genus ''Poleumita'' contains fifteen identified species. Fossil gastropods were less common during the Palaeozoic era than

s. Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive. By the Carboniferous period many of the shapes seen in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms. It was during the Mesozoic era that the ancestors of many of the living gastropods evolved. One of the earliest known terrestrial (land-dwelling) gastropods is ''Anthracopupa'' (=''Maturipupa''), which is found in the Coal Measures of the Carboniferous period in Europe, but relatives of the modern land snails are rare before the Cretaceous period, when the familiar ''Helix (gastropod), Helix'' first appeared. In rocks of the Mesozoic era, gastropods are slightly more common as fossils; their shells are often well preserved. Their fossils occur in ancient beds deposited in both freshwater and marine environments. The "Purbeck Marble" of the Jurassic period and the "Sussex Marble" of the early Cretaceous period, which both occur in southern England, are limestones containing the tightly packed remains of the pond snail ''Viviparus''. Rocks of the Cenozoic era yield very large numbers of gastropod fossils, many of these fossils being closely related to modern living forms. The diversity of the gastropods increased markedly at the beginning of this era, along with that of the

s. 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 are one of the groups that record the changes in fauna caused by the advance and retreat of the Ice sheet, Ice Sheets during the Pleistocene epoch.

Cladogram

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

Taxonomy

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. Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005), Bouchet & Rocroi (2005)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
/ref> made sweeping changes in the systematics, resulting in a taxonomy that is a step closer to the evolutionary history of the

. 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. The debate about these issues is not likely to end soon. In the Bouchet, Rocroi ''et al.'' taxonomy, the authors have 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, and should be regarded as the best possible hypothesis. 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 the 2017 issue of the ''Malacologia'' journal (available online from 4 January 2018), a significantly updated version of the 2005 "Bouchet & Rocroi" taxonomy was published in the paper "Revised Classification, Nomenclator and Typification of Gastropod and Monoplacophoran Families".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.

References

This article incorporates CC-BY-2.0 text from the reference. * 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

* - An 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