Everything about Spiracles totally explained
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
chirrups.
Spiracles in insects
Insects and some more advanced
spiders have spiracles on their
exoskeletons to allow air to enter the
trachea (Solomon et al., 2002). However, the two groups differ in how the tracheae function: in insects, the tracheal tubes primarily deliver
oxygen directly to the animals'
tissues. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle. In order to open, the muscle relaxes. The closer muscle is controlled by the
central nervous system but can also react to localized chemical stimuli. Several aquatic insects have similar or alternative closing methods to prevent water from entering the trachea. In spiders, however, the oxygen diffuses into the
hemolymph (Foelix, 1996). A similar diffusion effect also occurs in some insect caterpillars. In these groups the respiration is more reminiscent of
lungs. In spiders and other arachnids they've structures called
book lungs.
Further Information
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