|spiracle (ˈspaɪərəkəl, ˈspaɪrə-)|
|1.||any of several paired apertures in the cuticle of an insect, by which air enters and leaves the trachea|
|2.||a small paired rudimentary gill slit just behind the head in skates, rays, and related fishes|
|3.||any similar respiratory aperture, such as the blowhole in whales|
|4.||geology a protrusion of sediment into a lava flow, formed by the explosive transition of water into steam|
|[C14 (originally: breath): from Latin spīrāculum vent, from spīrāre to breathe]|
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
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