I noticed that there appeared to be some type of sensor or moveable flap above and to the rear of the eye. It was only about 1/8th of an inch/square.
Consulting my ID books I learned that this is called a Spiracle. It's present in some sharks and Rays/Skates.
As we know some sharks must be in constant motion in order to move water through the gills to oxygenate the shark's blood. Some sharks don't have to keep moving. This much I knew but I didn't know why some didn't have to keep moving. Some have a Spiracle and some don't (there may be other reasons as well).
When the Dogfish decides to quit moving and rest the Spiracles open and force water through the gills.
So through my curiousity I learned what that flap that I observed was and also learned something that I hadn't expected...why sharks that are able to remain at rest are able to remain at rest.
Hopefully, someone else will find this interesting
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