Respiratory system of gastropods
Encyclopedia
The respiratory system
of gastropods 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
, supplied with oxygen by a current of water through the mantle cavity. This current is U-shaped, so that it also flushes waste products away from the anus
, which is located above the animal's head, and would otherwise cause a problem with fouling.
In the pulmonate gastropods, which are found on both land and in freshwater, the gill has been replaced by a simple lung
.
In gastropods in many ancient lineages, the gills are bipectinate, having an overall shape that is similar to a bird's feather
, with narrow filaments projecting either side of a central stalk.
Gastropods such as abalone
and keyhole limpet
s 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 shells 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 periwinkle
s, conch
es, and whelk
s. The water current is oblique, as it is in the turban shells, but many have developed a siphon 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
, 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.
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 shell
s and also in the sea hare
s, which also possess an exhalant siphon which sends fouled water away from the body.
In some nudibranch
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
that function as secondary gills. Secondary gills are also present in the unrelated genus Patella, in which they are found as folds within the mantle cavity.
Some smaller gastropods have neither true gills nor cerata. The genus Lepeta
uses the whole of the mantle cavity as a respiratory surface, while many sea butterflies
respire through their general body surface.
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.
The pulmonates have lost their gills and adapted the mantle cavity into a lung
. The lung has a single opening on the right side, called the pneumostome
, which either remains permanently open, or opens and closes as the animal breathes. The roof the lung is highly vascularised, and it is through this surface that gas exchange occurs.
The majority of pulmonates, however, are fully terrestrial. Most have the typical lung arrangement described above, but in the Athoracophoridae
, the mantle cavity is replaced by a series of blind tubules, while the Veronicellidae
respire through their skin, and have lost the lung altogether.
Some freshwater pulmonates keep a bubble of air inside the shell, which helps them to float.
Many of the very small freshwater limpets 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.
Respiratory system
The respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
of gastropods 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
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
, supplied with oxygen by a current of water through the mantle cavity. This current is U-shaped, so that it also flushes waste products away from the anus
Anus
The anus 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, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...
, which is located above the animal's head, and would otherwise cause a problem with fouling.
In the pulmonate gastropods, which are found on both land and in freshwater, the gill has been replaced by a simple lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
.
With filamentous gills
In gastropods in many ancient lineages, the gills are bipectinate, having an overall shape that is similar to a bird's feather
Feather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
, with narrow filaments projecting either side of a central stalk.
Gastropods such as abalone
Abalone
Abalone , from aulón, are small to very large-sized edible sea snails, marine gastropod molluscs in the family Haliotidae and the genus Haliotis...
and keyhole limpet
Keyhole limpet
Fissurellidae, common name the keyhole limpets and slit limpets, is a taxonomic family of limpet-like sea snails, marine gastropod molluscs in the clade Vetigastropoda.Fissurellidae is the only family in the superfamily Fissurelloidea....
s 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 shells 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 periwinkle
Periwinkle
Periwinkle may refer to:In fauna:* Periwinkle, a common name for a number of gastropod molluscs in the family Littorinidae** Common periwinkle ** Blue periwinkle...
s, conch
Conch
A conch is a common name which is applied to a number of different species of medium-sized to large sea snails or their shells, generally those which are large and have a high spire and a siphonal canal....
es, and whelk
Whelk
Whelk, also spelled welk or even "wilks", is a common name used to mean one or more kinds of sea snail. The species, genera and families referred to using this common name vary a great deal from one geographic area to another...
s. The water current is oblique, as it is in the turban shells, but many have developed a siphon formed from the rolled-up margin of the mantle
Mantle (mollusc)
The mantle 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 flaps well beyond the visceral mass itself.In many, but by no means all, species of molluscs, the epidermis of the mantle secretes...
. 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
Ampullariidae, common name the apple snails, is a family of large freshwater snails, aquatic gastropod mollusks with a gill and an operculum...
, 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.
Other gill arrangements
Torsion (gastropod)
Torsion is an anatomical event which takes place during the very early part of the life of snails and slugs of all kinds. In other words, torsion is a gastropod synapomorphy which occurs in all gastropods during larval development. Torsion is the rotation of the visceral mass, mantle and shell 180˚...
, 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 shell
Cephalaspidea
The suborder Cephalaspidea, also known as the headshield slugs and bubble snails, is a clade of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia....
s and also in the sea hare
Sea hare
The clade Aplysiomorpha, commonly known as Sea hares or Sea Bags , are medium-sized to very large Opisthobranchia with a soft internal shell made of protein...
s, which also possess an exhalant siphon which sends fouled water away from the body.
In some nudibranch
Nudibranch
A nudibranch is a member of what is now a taxonomic clade, and what was previously a suborder, of soft-bodied, marine gastropod mollusks which shed their shell after their larval stage. They are noted for their often extraordinary colors and striking forms...
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
Cerata
Cerata are anatomical structures found in nudibranch sea slugs, marine opisthobranch gastropod mollusks.They are dorsal and lateral outgrowths on the upper surfaces of the body....
that function as secondary gills. Secondary gills are also present in the unrelated genus Patella, in which they are found as folds within the mantle cavity.
Some smaller gastropods have neither true gills nor cerata. The genus Lepeta
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 antarctica Smith, 1907* Lepeta caeca...
uses the whole of the mantle cavity as a respiratory surface, while many sea butterflies
Sea butterfly
Sea butterflies, also known as Thecosomata or flapping snails, are a taxonomic suborder of small pelagic swimming sea snails. These are holoplanktonic opisthobranch gastropod mollusks in the informal group Opisthobranchia. They include some of the world's most abundant gastropod species.This group...
respire through their general body surface.
Terrestrial gastropods
Although not true pulmonates, some operculate land snails, such as the CyclophoridaeCyclophoridae
Cyclophoridae is a taxonomic family of small to large tropical land snails with an operculum, terrestrial gastropod mollusks in the informal group Architaenioglossa belonging to the clade Caenogastropoda .- Taxonomy :This family consists of the following subfamilies according to the taxonomy of...
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
Operculum (gastropod)
The operculum, meaning little lid, is a corneous or calcareous anatomical structure which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails...
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.
Terestrial pulmonates
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
. The lung has a single opening on the right side, called the pneumostome
Pneumostome
The pneumostome is a feature of the external body anatomy of an air-breathing land slug or land snail. It is a part of the respiratory system of gastropods....
, which either remains permanently open, or opens and closes as the animal breathes. The roof the lung is highly vascularised, and it is through this surface that gas exchange occurs.
The majority of pulmonates, however, are fully terrestrial. Most have the typical lung arrangement described above, but in the Athoracophoridae
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...
, the mantle cavity is replaced by a series of blind tubules, while the Veronicellidae
Veronicellidae
The Veronicellidae, common name the leatherleaf slugs, are a terrestrial family of pulmonate slugs.This family has no subfamilies ....
respire through their skin, and have lost the lung altogether.
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 limpets 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.