pneumostome

The pneumostome is the external respiratory opening of the mantle cavity in terrestrial pulmonate gastropods, such as land snails and slugs. The opening is typically located on the edge of the mantle on one side of the body and ranges from circular to oval in shape. It leads into the mantle cavity, which contains the lung tissue used for gas exchange.

The pneumostome is bordered by a flexible rim and can be opened or closed by muscular action. This regulation allows the animal to balance respiration with water conservation; opening wider supports greater oxygen uptake when active or in humid conditions, while closing helps minimize water loss during dry periods.

Functionally, respiration in terrestrial pulmonates occurs primarily through the lung via air entering the pneumostome into the pulmonary sac. The size and visibility of the opening can vary among species and even with activity, humidity, and temperature. The pneumostome’s morphology and position provide a useful morphological character for identifying and differentiating species within this group.

Etymology and context: The term pneumostome derives from Greek pneuma meaning air and stoma meaning mouth or opening. The pneumostome represents a key adaptation enabling terrestrial life for snails and slugs, marking a primary interface between the animal and the terrestrial environment for gas exchange.