In elasmobranchs (sharks, skates, and rays), a spiracle is found behind each Eye, and is used to Pump water through the gills while the animal is at rest (Fouts, 2003).
In insects and some more advanced spiders, spiracles allow air to enter Trachea (Solomon et.al., 2002). However, unlike insects, tracheal tubes in spiders do not deliver Oxygen to the animals tissues (Foelix, 1996). Instead the oxygen diffuses into the Hemolymph (Foelix, 1996).