The pneumostome or breathing pore is a respiratory opening of the external body anatomy of a

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 inclu ...

land

slug Slug, or land slug, is a common name for any apparently shell-less Terrestrial mollusc, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...

land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial molluscs, terrestrial gastropod mollusks that have gastropod shell, shel ...

. It is a part of the respiratory system of gastropods. It is an opening in the right side of the mantle of a stylommatophoran snail or slug. Air enters through the pneumostome into the animal's single

lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...

, the air-filled mantle cavity. Inside the mantle cavity the animal has a highly

vascular Vascular can refer to: * blood vessels, the vascular system in animals * vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue ...

ized area of tissue that functions as a lung. The pneumostome is often much easier to see in slugs than in snails, because of the absence of a

shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...

which can often block the view of this area. In a land slug, when the pneumostome is wide open, it is usually very clearly visible on the right side of the animal. However, the position of the pneumostome is often not at all easy to discern when this orifice is completely 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.

Position of pneumostome as a diagnostic feature

The images in the gallery below show the position of the pneumostome in three different families of slugs: Image:Black slug.jpg, Arionidae ('' Arion ater''), the pneumostome is just anterior to the midpoint of the mantle Image:Bielzia coerulans-1.jpg, Limacidae ('' Bielzia coerulans''), the pneumostome is just posterior to the midpoint of the mantle Image:Tandonia budapestensis 2.jpg, Milacidae ('' Tandonia budapestensis''), the pneumostome is just posterior to the midpoint of the mantle

References

External links

Short clip of ''Ariolimax columbianus'' displaying its pneumostome
YouTube, Feb 17, 2008 Gastropod anatomy Invertebrate respiratory system Articles containing video clips {{respiratory-stub