spir·a·cle 
(spĭrə-kəl, spīrə-)
(spĭrə-kəl, spīrə-)n.
1. Zoology A respiratory aperture, especially:
a. Any of several tracheal openings in the exoskeleton of an insect, spider, or other terrestrial arthropod.
b. A small respiratory opening behind the eye of most sharks and rays and certain other fishes.
c. The blowhole of a cetacean.
2. An aperture or opening through which air is admitted and expelled.
[Middle English, from Latin spīrāculum, from spīrāre, to breathe.]
spi·racu·lar (spī-răkyə-lər, spĭ-) adj.