Pneumostome
Encyclopedia
Slug
Slug is a common name that is normally applied to any gastropod mollusc that lacks a shell, has a very reduced shell, or has a small internal shell...
or 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...
. It is a part of the respiratory system of gastropods
Respiratory system of gastropods
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...
.
It is an opening in the right side 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...
of a Pulmonata
Pulmonata
The Pulmonata, or "pulmonates", are 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...
or subcladed Stylommatophora or snail. Air enters through the pneumostome into the animal's single 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...
, the air-filled mantle cavity.
The pneumostome is often much easier to see in slugs than in snails, because of the absence of a shell
Gastropod shell
The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...
. The pneumostome is usually very clearly visible on the right side of the animal when the pneumostome is wide open. However, the position of the pneumostome is often not at all easy to discern when the pneumostome is closed.
The pneumostome opens and closes in a cyclical manner. The frequency of pneumostome closing and opening is typically less than 0.5 closures per minute in fully hydrated slugs and snails. The rate of closures per minute increases the more dehydrated the slug is.