spiracle

A spiracle is a small external opening that forms part of an animal’s respiratory system. The term comes from Latin spiraculum, meaning a little breath. Spiracles are found in a variety of aquatic and terrestrial animals and can serve different respiratory functions depending on the group.

In arthropods, especially insects, spiracles are external openings that connect to the tracheal system. Most species have a series of paired spiracles on the thorax and abdomen. They regulate gas exchange and water loss by opening and closing, with air passing through tracheae and tracheoles directly to tissues. Some aquatic or semi-aquatic species have adaptations that modify spiracle function for different environments.

In cartilaginous fishes such as sharks and rays, the spiracle is an opening located behind the eye that leads to the pharynx and gill slits. It provides a route for water to reach the gills, which is useful when the animal is feeding or stationary with the mouth closed. The size and presence of spiracles vary among species; in some, they are prominent, while in others they are reduced or absent.

Beyond these senses, spiracle is primarily a descriptive term for respiratory openings in certain invertebrates and vertebrates. Its usage emphasizes the external pores through which air or water enters a body’s respiratory pathways.