Subject: spiracles and nares of dogfish sharks

Martine Berube (martine@sbs.bangor.ac.uk)
Wed, 24 Mar 1999 13:41:39 GMT

At 02.39 PM 23-03-1999 -0500, you wrote:
>What system is the spiracle a part of? Also are nares cemo receptors or
>electromagnetic in function? Thank you!

You certainly had me taking my old textbooks out!

The spiracles are actually reduced, modified gills, therefore are part of
the respiratory system.  Most fish respire by taking in water through the
mouth and sending it through the pharynx to the gills.  However, when a
spiracle is present like in the dogfish shark, water enters through it also.
Spiracles provide oxygenated blood directly to the eye and brain through a
separate blood vessel which is reduced or absent in active, fast-swimming
sharks.


Regarding the nares function, I would say chemo receptors (be careful, I am
not totally sure here). This is base on the fact that we know that sharks
have an acute sense of smell. They are well-known for their ability to
detect a concentration as low as one part per billion of some chemicals,
such as certain amino acids. 
Martine Berube
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