How do slugs breathe?

On Saturday i went to a cookout at a friends house. While there we found a slug and started studying it. Owel saw this hole in the side of the slug that was opening and closing. Is this how slugs breathe? Lets find out...

The pneumostome is a feature (the respiratory opening) of the external body anatomy of an air-breathing land slug or land snail. This feature is usually clearly visible on the right side of the animal when the pneumostome is open, but may not be easy to see when it is closed.
This is an opening in the right side of the mantle of a Pulmonata ordered or subclassed slug (suborder Stylommatophora) or snail, through which its single lung is filled with air.
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.