Nictitating Systematists Taxonomy

Gill Slit - A vertical opening located behind the eyes on sharks, and along the belly in rays. The gill slits are openings that allow water to flow out from the gill cavities. Sharks and rays are unique among living fishes in possessing five to seven gill slits, rather than the more common fish condition of having only a single gill opening. Some species of sharks, notably bamboo and nurse sharks, have a “shared” slit for the fourth and fifth gills. If examined closely, however, the septum (=fleshy divider) between gill slits can be observed.