In the thresher shark , the upper lobe can be almost as long as its body. They are important for stability as the shark swims. In male sharks, the paired pelvic fins have rod-like extension on the inner edge. These extension are used as claspers during internal fertilization. These are the slit-like openings behind a shark's head.
Most sharks have five pairs of gill slits, but some have six or seven pairs.
As a shark breathes, oxygen-rich water enters its mouth. The now oxygen-depleted water exits through the gill slits. Most sharks have 5 to 15 rows of teeth in each jaw. When a tooth falls out, there's already a tooth waiting to replace it. The new tooth moves forward as though on a conveyor belt.