A lateral line is present on either side of a shark, consisting of a row of small, mucus-filled pores that can sense the presence of other animals via pressure changes. There is no lung or swim bladder is present. Instead, buoyancy is assisted by oil in the large liver. A cloaca is a common opening for the digestive, urinary, and reproductive tracts. Between the external and internal gill slits are the gill chambers.
Gill arches are cartilage supports underlying the gills.
Blood in the capillaries flows countercurrent to the outflow of water. Gill rakers on the internal side of the gill help to direct food away from the gills and into the esophagus and the digestive tract. During copulation, a clasper is inserted in the the female cloaca and sperm runs along a groove on the clasper to fertilize. Sharks have 5-7 lateral gill slits on either side, with a rounded spiracle , or modified first gill slit close behind the eye. In rays, the gill slits are ventral and the spiracle is correspondingly larger.