spiracle

n. air hole, opening which allows the passage of air; (Zoology) respiratory aperture (as in whales, sharks, spiders, etc.)

Spiracles are small openings on the surface of some animals that usually lead to respiratory systems.In elasmobranchs (sharks and rays), a spiracle is found behind each eye, and is often used to pump water through the gills while the animal is at rest (Fouts, 2003). A spiracle is also found in primitive bony fishes as the bichir.
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Noun
1. a breathing orifice
(hypernym) orifice, opening, porta
(hyponym) blowhole

(n.)
The nostril, or one of the nostrils, of whales, porpoises, and allied animals.
  

(n.)
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.
  

(n.)
Any small aperture or vent for air or other fluid.
  

(n.)
A tubular orifice communicating with the gill cavity of certain ganoid and all elasmobranch fishes. It is the modified first gill cleft.
  

Synonyms and related words:
air duct, air hole, air passage, air shaft, air tube, airway, armhole, avenue, blowhole, breathing hole, bullet-hole, bunghole, channel, chute, cringle, deadeye, debouch, door, egress, emunctory, escape, estuary, exhaust, exit, eye, eyelet, floodgate, flume, gasket, grommet, guide, keyhole, knothole, loop, loophole, louver, louverwork, manhole, mousehole, naris, nostril, opening, out, outcome, outfall, outgate, outgo, outlet, peephole, pigeonhole, pinhole, placket, placket hole, pore, port, porthole, punch-hole, sally port, shaft, sluice, spilehole, spout, tap, touchhole, transom, vent, ventage, venthole, ventiduct, ventilating shaft, ventilator, vomitory, way out, weir, wind tunnel