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spiracle
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spiracle Illustration showing different animals and their respiratory organs: a spider with book lungs, a chicken with lungs, a sponge with labeled inflow and outflow pores, a fish with gills, and a caterpillar with spiracles.
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book lung
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spiracle
spiracle Larval form of the Indian moon moth (Actias selene) with some spiracles identified.

spiracle

anatomy
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History

spiracle, in arthropods, the small external opening of a trachea (respiratory tube) or a book lung (breathing organ with thin folds of membrane resembling book leaves). Spiracles are usually found on certain thoracic and abdominal segments. In elasmobranch and ganoid fishes a pair of spiracles, derived from the gills, is used as a water passageway during respiration. The nasal opening of whales and other cetaceans is called a spiracle, as is the respiratory opening behind the eyes of rays and skates. In tadpoles the spiracle is the excurrent opening from the gill chamber.

This article was most recently revised and updated by Amy Tikkanen.