Gills and Spiracles
In common with the bony fishes, sharks and rays have gills to extract oxygen from the water in which they live. Most shark species have five pairs of gill openings, but there are several that have six or seven pairs of gill openings. Rays have either five or six pairs, located on the underside of the body.
The rays and many of the bottom-dwelling sharks have spiracles behind the eyes. Spiracles are holes that allow the rays and sharks to take in water for breathing while they rest on the sea floor. Fast-swimming sharks lack spiracles and depend on water entering the mouth and passing through the gill openings to breathe, so they must swim continuously to breathe.
Fins and Movement
Generally, sharks and rays have three types of unpaired fins (dorsal, anal and caudal) and two types of paired fins (pectoral and pelvic). However, some groups do not have all of these features, or the features have been modified (over millions of years) to form long tails or flattened body discs. Body shape and locomotion vary between different animals in the group.
Gummy shark (Mustelus antarcticus).
Note: spiracle behind the eye
(© Ken Hoppen, firstname.lastname@example.org)