Noun
The nostril, or one of the nostrils, of whales, porpoises, and allied animals.
One of the external openings communicating with the air tubes or tracheae of insects, myriapods, and arachnids. They are variable in number, and are usually situated on the sides of the thorax and abdomen, a pair to a segment. These openings are usually elliptical, and capable of being closed. See Illust. under Coleoptera.
A tubular orifice communicating with the gill cavity of certain ganoid and all elasmobranch fishes. It is the modified first gill cleft.
Source: Webster's dictionaryA modified slit called a spiracle lies just behind the eye, which assists the shark with taking in water during respiration and plays a major role in bottom–dwelling sharks. Source: Internet
Chimaeras differ from other cartilagenous fish, having lost both the spiracle and the fifth gill slit. Source: Internet
In slow-moving or bottom-dwelling species, especially among skates and rays, the spiracle may be enlarged, and the fish breathes by sucking water through this opening, instead of through the mouth. Source: Internet
The pleura are usually small or hidden in some species, with each pleuron having a single spiracle. Source: Internet
A spiracular chamber is present, but the spiracle is closed and never opens during development. Source: Internet