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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 ...
of
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
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. 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
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 ...
in 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 ...
, 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 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 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 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, whelks, 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. In a number of
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 species, such as all the various
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, 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
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. ...
levels, gastropods are second only to the insects in terms of their diversity. 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
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 ...
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 and the continental rise 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'' 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 shores,
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 ...
s.


Anatomy

Snails are distinguished by an anatomical process known as torsion, 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 ...
s, nephridia, 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 ''gaster'', stomach, 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 (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 orifice, which lies on the same side of the body as the anus.


Shell

Most shelled gastropods have a one piece shell (with exceptional bivalved gastropods), typically coiled or spiraled, at least in the larval stage. This coiled shell usually opens on the right-hand side (as viewed with the shell apex pointing upward). Numerous species have an operculum, which in many species acts as a trapdoor to close the shell. This 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 or contain stinging cells, 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,
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 nudibranchs are called cerata. These contain an outpocketing of digestive gland called the diverticula.


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, statocysts 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
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, 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 rhinophores. The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles. However, "eyes" in gastropods range from simple ocelli that only distinguish light and dark, to more complex pit eyes, and even to lens eyes. In land snails and slugs, vision 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
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
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 ...
s, herbivores that use their hard
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 ...
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 A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
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, 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, nudibranchs. Some nudibranchs have smooth or warty backs with no visible gill mechanism, such that respiration may likely take place directly through the skin.


Circulatory system

Gastropods have
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
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 ...
as the respiratory pigment.


Excretory system

The primary organs of excretion in gastropods are nephridia, 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 ...
or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in the body cavity, and digestive glands opening into the stomach.


Reproductive system

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 behavior in some gastropods, including some of the Helicidae. 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 darts. In many marine gastropods other than the
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 ...
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); 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 ...
s.


Life cycle

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 the behavior of mating gastropods with some
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 ...
families of land snails creating and utilizing love darts, 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 An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...
of gastropods * The larvae or larval stadium: some gastropods may be trochophore and/or veliger *
Estivation Aestivation ( la, aestas (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 ...
and
hibernation Hibernation is a state of minimal activity and metabolic depression undergone by some animal species. Hibernation is a seasonal heterothermy characterized by low body-temperature, slow breathing and heart-rate, and low metabolic rate. It most ...
(each of these are present in some gastropods only) * The growth of gastropods * Courtship and mating in gastropods:
fertilization Fertilisation or fertilization (see spelling differences), also known as generative fertilisation, syngamy and impregnation, is the fusion of gametes to give rise to a new individual organism or offspring and initiate its development. Proce ...
is internal or external according to the species. External fertilization is common in marine gastropods.


Feeding behavior

A '' Pomacea maculata'' floating and eating a carrot The diet of gastropods differs according to the group considered. Marine gastropods include some that are
herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
s,
detritus In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
feeders,
predatory Predation is a biological interaction where 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 kill th ...
carnivores,
scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...
s,
parasite 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 ...
s, and also a few ciliary feeders, in which 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 ...
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 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 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 ...
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, for example:
Cone shell ''Conus'' is a genus of predatory sea snails, or cone snails, marine gastropod mollusks in the family Conidae.Bouchet, P.; Gofas, S. (2015). Conus Linnaeus, 1758. In: MolluscaBase (2015). Accessed through: World Register of Marine Species at ...
s, ''
Testacella ''Testacella'' is genus of small to medium-large, predatory, air-breathing, land slugs. MolluscaBase eds. (2022). MolluscaBase. Testacella Lamarck, 1801. Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia ...
'', ''
Daudebardia ''Daudebardia'' are small air-breathing land snails or semi-slugs, terrestrial pulmonate gastropods in the family Oxychilidae Oxychilidae is a taxonomic family of air-breathing land snails, terrestrial pulmonate gastropod mollusks in t ...
'',
Turrid Turrid, plural turrids, is a common name for a very large group of predatory sea snails, marine gastropod mollusks which until recently were all classified in the family Turridae. However, recently the family was discovered to be polyphyletic ...
s,
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 Trigonochlamydidae. The species was first recognised from various sites in Wales and w ...
and others.


Genetics

Gastropods exhibit an important degree of variation in mitochondrial gene organization when compared to other animals. Main events of
gene rearrangement V(D)J recombination 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 of antibodies/immunoglobulins and T cell rece ...
occurred at the origin of Patellogastropoda and Heterobranchia, whereas fewer changes occurred between the ancestors of Vetigastropoda (only
tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino ac ...
s D, C and N) and
Caenogastropoda Caenogastropoda is a taxonomic clade, 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 clade is the most diverse and ecologically successfu ...
(a large single
inversion Inversion or inversions may refer to: Arts * , a French gay magazine (1924/1925) * ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas * Inversion (music), a term with various meanings in music theory and musical set theory * ...
, 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 representatives of the group appearing in 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, ...
(''
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 gastropod. Morphology ''C. patellitheca'' is known from broad, low, cap-sha ...
'', '' 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 The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
organisms like ''
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 ''Barskovia'' is a torted conical shell known from earliest Cambrian small skeletal fossils, interpreted as a helcionelloid. References {{Taxonbar, from=Q21351640 Helcionelloida ...
'' 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, althou ...
'' are no longer considered gastropods, and the tiny coiled ''
Aldanella ''Aldanella'' is an extinct paleozoic mollusc that was assigned to the Gastropod stem group but may also belong to a paraphyletic "Monoplacophora Monoplacophora , meaning "bearing one plate", is a polyphyletic superclass of molluscs with a ...
'' of earliest
Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...
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,
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 ...
gastropods from the rocks of the early
Palaeozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and '' ...
era are too poorly preserved for accurate identification. Still, the
Silurian The Silurian ( ) is a geologic period and system spanning 24.6 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 shortest period of the Paleozo ...
genus ''
Poleumita ''Poleumita'' is an extinct genus of medium-sized sea snails, 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 ...
'' contains fifteen identified species. Fossil gastropods were less common during the
Palaeozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and '' ...
era than
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. Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive. By the
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
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 The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
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 Measure In lithostratigraphy, the coal measures are the coal-bearing part of the Upper Carboniferous System. In the United Kingdom, the Coal Measures Group consists of the Upper Coal Measures Formation, the Middle Coal Measures Formation and the Lower Coal ...
s of the
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
period in Europe, but relatives of the modern land snails are rare before the
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
period, when the familiar '' Helix'' first appeared. In rocks of the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
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 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 Strat ...
" 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 Mya. The J ...
period 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 rela ...
" of the early Cretaceous period, which both occur in southern England, are
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
s containing the tightly packed remains of the pond snail ''
Viviparus ''Viviparus'', common name the river snails, is a genus of large, freshwater snails with an operculum, aquatic gastropod mollusks.Bouchet, P. (2014). Viviparus Montfort, 1810. Accessed through: World Register of Marine Species at http://www ...
''. Rocks of the
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
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
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. 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
ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...
s or other shelled
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
s. An example of this is ''
Bellerophon Bellerophon (; Ancient Greek: Βελλεροφῶν) or Bellerophontes (), born as Hipponous, was a hero of Greek mythology. He was "the greatest hero and slayer of monsters, alongside Cadmus and Perseus, before the days of Heracles", and his ...
'' from the limestones of the
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
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 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 in Antarctica and Greenland; during the Last Glacial Period at La ...
during the
Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...
epoch.


Cladogram

A cladogram showing the phylogenic relationships of Gastropoda with example species:
Cocculiniformia The Cocculinoidea is a superfamily of deepwater limpets (marine gastropods), the only superfamily in the order Cocculinida , one of the main orders of gastropods according to the taxonomy as set up by ( Bouchet & Rocroi, 2005). The clade Coccil ...
, Neomphalina and Lower Heterobranchia are not included in the above cladogram.


Taxonomy

Since Darwin, biological taxonomy has attempted to reflect the
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...
of organisms, i.e., the
tree of life The tree of life is a fundamental archetype in many of the world's mythological, religious, and philosophical traditions. It is closely related to the concept of the sacred tree.Giovino, Mariana (2007). ''The Assyrian Sacred Tree: A History ...
. 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 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 ...
(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. Th ...
(no shell) *
Prosobranchia Prosobranchia was a large taxonomic 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 polyphyletic (consisting of more than one lineage of descent). Gene ...
(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 includ ...
(with a lung instead of gills) The
taxonomy 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. ...
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 In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...
groups (only one lineage of gastropods in each group). Integrating new findings into a working
taxonomy 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. ...
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 com ...
, 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. 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 Biological 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: cladograms, phylogenetic tre ...
, resulting in a taxonomy that is a step closer to the evolutionary history of 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 ...
. 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 Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
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
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, ...
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 cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic grou ...
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 David R. Lindberg (1948, U.S.A.) is an American malacologist and professor of integrative biology at the University of California, Berkeley. He is also the Curator for the University of California Museum of Paleontology and co-editor of the journ ...
showed possible
diphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In c ...
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 use ...
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 also in gastropods.
Gastropod photo gallery
mostly fossils, a few modern shells
A video of a crawling Garden Snail
('' Cornu aspersum''),
YouTube YouTube is a global online video platform, online video sharing and social media, social media platform headquartered in San Bruno, California. It was launched on February 14, 2005, by Steve Chen, Chad Hurley, and Jawed Karim. It is owned by ...

Grove, S.J. (2018). A Guide to the Seashells and other Marine Molluscs of Tasmania: Molluscs of Tasmania with images
{{Authority control Mollusc classes Asymmetry Articles containing video clips Extant Cambrian first appearances Taxa named by Georges Cuvier