Respiratory system of gastropods

Last updated September 16, 2022

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.

With gills

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

Gastropods such as abalone 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 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 periwinkles, conches, and whelks. 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.

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 hares, which also possess an exhalant siphon which sends fouled water away from the body.

In some nudibranchs, 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.

Terrestrial gastropods

Although not true pulmonates, some operculate land snails, such as the Cyclophoridae 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 pulmonates have lost their gills^[1] and adapted the mantle cavity into a pallial 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 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, the mantle cavity is replaced by a series of blind tubules, while the Veronicellidae 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.^[1]

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.^[1] Oxygen diffuses from the water to the snail's body directly.^[1]

Related Research Articles

The gastropods, commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda.

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, which are separated by a division of the mantle cavity. This adaptation allows these animals to be amphibious. Species in this family are considered gonochoristic, meaning that each individual organism is either male or female.

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 that over evolutionary time have either completely lost their shells, or have seemingly lost their shells due to having a greatly reduced or internal shell. The name "sea slug" is most often applied to nudibranchs, as well as to a paraphyletic set of other marine gastropods without obvious shells.

Neogastropoda is an order of sea snails, both freshwater and marine gastropod molluscs.

Heterobranchia, the heterobranchs, is a taxonomic clade of snails and slugs, which includes marine, aquatic and terrestrial gastropod mollusks.

Pulmonata, or "pulmonates", is an informal group of snails and slugs characterized by the ability to breathe air, by virtue of having a pallial lung instead of a gill, or gills. The group includes many land and freshwater families, and several marine families.

A siphon is an anatomical structure which is part of the body of aquatic molluscs in three classes: Gastropoda, Bivalvia and Cephalopoda.

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.

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 independently from different ancestral gastropods. This general category of conical shell is known as "patelliform" (dish-shaped). All members of the large and ancient marine clade Patellogastropoda are limpets. Within that clade, the members of the Patellidae family in particular are often referred to as "true limpets".

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.

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˚ with respect to the head and foot of the gastropod. This rotation brings the mantle cavity and the anus to an anterior position above the head.

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 drawn into the mantle cavity and over the gill and which serves as a chemoreceptor to locate food. In certain groups of carnivorous snails, where the siphon is particularly long, the structure of the shell has been modified in order to house and protect the soft structure of the siphon. Thus the siphonal canal is a semi-tubular extension of the aperture of the shell through which the siphon is extended when the animal is active.

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 estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.

A siphonal notch is a feature of the shell anatomy in some sea snails, marine gastropod mollusks.

Siphonarioidea is a taxonomic superfamily of air-breathing sea snails or false limpets, marine gastropod mollusks in the clade Panpulmonata.

The excretory system of gastropods removes nitrogenous waste and maintains the internal water balance of these creatures, commonly referred to as snails and slugs. The primary organ of excretion is a nephridium.

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 to major rivers. The great majority of freshwater gastropods have a shell, with very few exceptions. Some groups of snails that live in freshwater respire using gills, whereas other groups need to reach the surface to breathe air. In addition, some are amphibious and have both gills and a lung. Most feed on algae, but many are detritivores and some are filter feeders.

Pseudonebularia dovpeledi is a species of sea snail, a marine gastropod mollusk in the family Mitridae, the miters or miter snails.

A ctenidium is a respiratory organ or gill which is found in many molluscs. This structure exists in bivalves, cephalopods, Polyplacophorans (chitons), and in aquatic gastropods such as freshwater snails and marine snails. Some aquatic gastropods possess one ctenidium known as monopectinate and others have a pair of ctenidia known as bipectinate.

This outline is provided as an overview of, and organized list of articles relevant to, the subject of gastropods :

References

1 2 3 4 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. ISBN 978-1-58112-930-4.

Barnes, Robert D. (1982). Invertebrate Zoology. Philadelphia, PA: Holt-Saunders International. pp. 328–341. ISBN 0-03-056747-5.

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.

[Dillon_2006-1] 1 2 3 4 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. ISBN 978-1-58112-930-4.

[1]

v t e Gastropod anatomy
Shell	Aperture Apex Body whorl Callus Columella Lip Lira Nacre Periostracum Peristome Planispiral Plait Protoconch Sculpture Selenizone Siphonal canal Siphonal notch Spire Stromboid notch Suture Umbilicus Valve Varix Whorl
Other hard parts	Clausilium Love dart Operculum Pearl Radula
External soft parts	Caryophyllidia Caudal mucous pit Cerata Cnidosac Mantle Mentum Notum Parapodium Pneumostome Rhinophore Semper's organ Siphon Suprapedal gland
Internal soft parts	Circulatory system of gastropods Crop Ctenidium Digestive system of gastropods Diverticula Excretory system of gastropods Gastric shield Hancock's organ Hepatopancreas Hypobranchial gland Nephridium Nervous system of gastropods Nidamental gland Odontophore Oesophageal pouch Osphradium Reproductive system of gastropods Respiratory system of gastropods Sensory organs of gastropods
Other	Epiphragm Pseudofeces Torsion Circumesophageal nerve ring Trochophore Tyrian purple Veliger