Epiphragm
Encyclopedia
An epiphragm is a temporary structure which can be created by many species of shelled, air-breathing land snail
Land snail
A land snail is any of the many species of snail that live on land, as opposed to those that live in salt water and fresh water. Land snails are terrestrial gastropod mollusks that have shells, It is not always an easy matter to say which species are terrestrial, because some are more or less...

s, terrestrial
Terrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 pulmonate gastropod mollusks. It can also be created by freshwater snail
Freshwater snail
A freshwater snail is one kind of freshwater mollusc, the other kind being freshwater clams and mussels, i.e. freshwater bivalves. Specifically a freshwater snail is a gastropod that lives in a watery non-marine habitat. The majority of freshwater gastropods have a shell, with very few exceptions....

s when temporary pools dry up.

In most species the epiphragm is made of dried mucus
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...

 and although it is elastic, it is fairly easily torn when forcibly removing a snail from its substrate. In a few species the epiphragm is thick and quite rigid, being reinforced with calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

. This kind of epiphragm is very strong and may be difficult to break.

Function

The epiphragm is created to seal the aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....

 of the shell against desiccation
Desiccation
Desiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately sealed container.-Science:...

. It is used when the snail is inactive. Most land snails are only active when the humidity is high such as after rain and at night, and become inactive during dry weather.

The main feature of the epiphragm is to reduce water loss through the aperture
Aperture
In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture of an optical system is the opening that determines the cone angle of a bundle of rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are,...

 during inactivity. .

An 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...

 is a somewhat similar but permanent anatomical feature that is found in other clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

s of gastropods. The operculum serves some of the same functions as an epiphragm.

Sometimes it protects the snail against predation. It protects certain species of snail if they are eaten by birds (such as Japanese White-eye
Japanese White-eye
The Japanese White-eye , also known as the mejiro , is a small passerine bird in the white-eye family. The specific epithet is occasionally written japonica, but this is incorrect due to the gender of the genus. Its native range includes much of east Asia, including Japan, China, Vietnam, Taiwan,...

). The snail can remain alive as it passes through the digestive tract because it is sealed off from the digestive processes. Snails may also benefit from being moved to new locations.

Mucus epiphragm

In most species of air-breathing land snail, the epiphragm is a simple membrane composed of layers of dried mucus. This is created routinely at the start of a period of inactivity during times of decreased humidity. The epiphragm of Helix aspersa
Helix aspersa
Helix aspersa, known by the common name garden snail, is a species of land snail, a pulmonate gastropod that is one of the best-known of all terrestrial molluscs. The species has been placed in the genus Helix, in all sources between 1774 and 1988 and in most sources until recently...

is secreted from 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...

 collar of the snail by intense muscular activity.

This simple mucus epiphragm covers the entire aperture of the snail, being attached at the rim of the aperture, and depending on the habits of the species of snail, is very often also glued to a solid substrate
Substrate (biology)
In biology a substrate is the surface a plant or animal lives upon and grows on. A substrate can include biotic or abiotic materials and animals. For example, encrusting algae that lives on a rock can be substrate for another animal that lives on top of the algae. See also substrate .-External...

, such as a rock surface, a wall, a tree branch or the stem of a plant, reducing water loss from the soft tissues of the snail's body. A mucus epiphragm is usually transparent or translucent, and is fairly elastic.

Calcareous epiphragm

A few species, including Helix pomatia
Helix pomatia
Helix pomatia, common names the Burgundy snail, Roman snail, edible snail or escargot, is a species of large, edible, air-breathing land snail, a terrestrial pulmonate gastropod mollusk in the family Helicidae...

create a normal mucus epiphragm for short periods of rest, but can also create a different, specialized solid hard epiphragm, prior to annual hibernation. This kind of epiphragm is a solid structure with a good deal of calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

 in it. This specialized epiphragm is much more efficient at conserving water loss than a thin mucus epiphragm would be.

This very sturdy flat calcareous
Calcareous
Calcareous is an adjective meaning mostly or partly composed of calcium carbonate, in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines.-In zoology:...

structure has a small perforation to allow for oxygen exchange. Helix pomatia snails hibernate for many months buried in the soil, and a strong solid epiphragm protects them not only from desiccation, but also against attacks by soil-dwelling predators such as carnivorous beetle larvae.
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