The

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

s varies greatly in form. These variations were once used as a basis for dividing the group into subclasses. The majority of marine gastropods breathe through a single

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 ...

, supplied with oxygen by a current of water through the

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 ...

. This current is U-shaped, so that it also flushes waste products away from 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 ...

, which is located above the animal's head, and would otherwise cause a problem with fouling. In the

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 ...

gastropods, which are found on both land and in freshwater, the gill has been replaced by a simple

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 ...

With gills

With filamentous gills

In gastropods in many ancient lineages, the

gills 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 ...

are bipectinate, having an overall shape that is similar to a bird's

feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premier ...

, with narrow filaments projecting either side of a central stalk. Gastropods 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 ...

and keyhole limpets have two gills, which is believed to be the arrangement in the earliest fossil gastropods. The water current to supply these gills is evacuated through a slit or notch in the upper surface of the shell, below which the anus opens. In most other gastropods, the right gill has been lost. In groups such as the

turban shell Turbinidae, the turban snails, are a family of small to large marine gastropod molluscs in the superfamily Trochoidea.Bouchet, P. (2014). Turbinidae Rafinesque, 1815. Accessed through: World Register of Marine Species at http://www.marinespecie ...

s the gill still retains its primitive bipectinate form, and in these animals, the water current is oblique, entering the mantle cavity on the left side of the head, flowing over the gill, and then being flushed out on the right side. The anus is also on the right side of the body, so that waste matter is efficiently carried away. Bipectinate gills have to be supported by membranes, and these can become fouled with debris and sediment, restricting such gastropods to relatively clean-water environments, such as water flowing over solid rock. In living gastropods, a unipectinate arrangement is more common, allowing species to invade muddy or sandy environments. This type of gill is firmly anchored to the mantle wall along its length, with a single row of filaments projecting down into the water stream. Unipectinate gills are found in a wide range of snails, including marine, freshwater, and even terrestrial forms. Examples include periwinkles,

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, and

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. The water current is oblique, as it is in the turban shells, but many have developed 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 ...

formed from the rolled-up margin of the mantle. The siphon sucks in water to the mantle cavity, and may be long enough to extend through the substrate in burrowing species. In one amphibious group, the

Ampullariidae Ampullariidae, commonly known as the apple snails, is a family of large freshwater snails, aquatic gastropod mollusks with a gill and an operculum. These snails simultaneously have a gill and a lung as functional respiratory structures, wh ...

, the mantle cavity is divided into two, with a unipectinate gill on one side, and a lung on the other, so that these snails can respire using air or water. Melanoides tuberculatus

Other gill arrangements

In many gastropods, the filamentous gill has been replaced by a "plicate", or folded, structure. Many of these gastropods have also undergone detorsion, such that the mantle cavity and gill have shifted round to the right side of the body. This type of arrangement is found in the bubble shells and also in the

sea hare The clade Anaspidea, commonly known as sea hares (''Aplysia'' species and related genera), are medium-sized to very large opisthobranch gastropod molluscs with a soft internal shell made of protein. These are marine gastropod molluscs in the s ...

s, which also possess an exhalant siphon which sends fouled water away from the body. In some

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, the mantle cavity and the original gill have disappeared altogether. Instead, the upper surface of the body has numerous club-shaped or branched projections 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 ...

that function as secondary gills. Secondary gills are also present in the unrelated genus ''

Patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as m ...

'', in which they are found as folds within the mantle cavity. Some smaller gastropods have neither true gills nor cerata. The genus ''

Lepeta ''Lepeta'' is a genus of sea snails, the true limpets, marine gastropod mollusks in the family Lepetidae. Species Species within the genus ''Lepeta'' include: * ''Lepeta caeca'' (Müller O.F., 1776) * '' Lepeta depressa'' Hedley, 1916 ;Species b ...

'' uses the whole of the mantle cavity as a respiratory surface, while many

sea butterflies Sea butterflies, scientific name Thecosomata (thecosomes, "case / shell-body"), are a taxonomic suborder of small pelagic swimming sea snails. They are holoplanktonic opisthobranch gastropod mollusks. Most Thecosomata have some form of calcified ...

respire through their general body surface.

Terrestrial gastropods

Although not true pulmonates, some operculate land snails, such as the

Cyclophoridae Cyclophoridae is a taxonomic family of small to large tropical land snails with an operculum, terrestrial gastropod mollusks in the order Architaenioglossa belonging to the subclass Caenogastropoda (according to the taxonomy of the Gastropo ...

have also lost their gills, and developed a vascularised lung from the mantle cavity. These groups lack a pneumostome, having a much larger opening to the cavity. Since this opening is usually closed by the operculum when the animal retreats into its shell, there is often a separate breathing tube or a notch in the shell to allow air in and out.

Terrestrial pulmonates

The

s have lost their gills and adapted the

into a pallial

. The lung has a single opening on the right side, called the

pneumostome The pneumostome or breathing pore is a respiratory opening of the external body anatomy of an air-breathing land slug or land snail. It is a part of the respiratory system of gastropods. It is an opening in the right side of the mantle of a ...

, which either remains permanently open, or opens and closes as the animal breathes. The roof of the lung is highly vascularised, and it is through this surface that gas exchange occurs. The majority of pulmonates are fully terrestrial. Most have the typical lung arrangement described above, but in the

Athoracophoridae Athoracophoridae, common name the leaf-veined slugs, are a family of air-breathing land slugs, terrestrial pulmonate gastropod mollusks in the infraorder Stylommatophora, the stalk-eyed snails and slugs. Many of the species have an attractive p ...

, the mantle cavity is replaced by a series of blind tubules, while the

Veronicellidae The Veronicellidae, also known by their common name the leatherleaf slugs, are a family of pulmonate terrestrial slugs. The herbivorous molluscs occur mainly in the tropical and subtropical areas of America, Asia and Africa. They act as intermed ...

respire through their skin, and have lost the lung altogether.

Freshwater snails

For freshwater snails with gills see above.

Freshwater pulmonates

Despite the presence of a lung, many pulmonates spend much of their lives underwater. Some of these possess secondary gills within the mantle cavity, while others must regularly return to the surface to breathe air, keeping their pneumostome closed while they are submerged. Some freshwater pulmonates keep a bubble of air inside the shell, which helps them to float. Many of the very small 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 which live in cold water have lost the ability to breathe air, and instead flood their mantle cavity with water. Oxygen diffuses from the water to the snail's body directly.Dillon R. T. (2006). ''Chapter 21. Freshwater Gastropoda''. pages 251-259. In: Sturm C. F., Pearce T. A. & Valdés A. (eds.) (2006). ''The Mollusks: A Guide to Their Study, Collection, and Preservation''. American Malacological Society, 445 pp. .

References

{{DEFAULTSORT:Respiratory System Of Gastropods Gastropod anatomy Invertebrate respiratory system